is mental time travel possible

Mental time travel is a great decision-making tool — this is how to use it

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When the future seems largely unpredictable, is there anything you can do to prepare for it?

“Yes!” says futurist and game designer Jane McGonigal . All you need to do is to tap into your imagination and envision all your potential futures — using what she calls “futures thinking.” 

“Futures thinking isn’t a superpower, and you don’t have to fix everything or save everyone,” McGonigal writes in her new book called Imaginable . “But futures thinking is an incredibly useful, practical tool to prepare your mind to adapt faster to new challenges, build hope and resilience, reduce anxiety and depression, and inspire you to take actions today that set yourself up for future happiness and success.”

Her book draws on the latest research in psychology and neuroscience to show you how to train your mind to think the unthinkable. In this excerpt, you’ll get a taste of how you can start thinking like a futurist — and create a better future for yourself. 

For the next 30 seconds, I want you to imagine yourself waking up tomorrow morning. Try to picture it in your mind or describe it to yourself as clearly as possible. 

These questions may help make your imagined scene clearer. What room or space are you in? What wakes you up — an alarm, the sunlight, someone nudging you or calling you? Is it light out or still dark? Is there anyone with you? What are you wearing? What kind of mood are you in? And what’s the very first thing you do now that you’re awake?

Keep imagining your tomorrow morning until you have a clear answer to all of these questions.

This quick mental time trip you just took is an example of a highly imaginable future — it was likely quite easy for you to envision, with plenty of vivid details.

Now let’s try something more challenging. For the next 30 seconds, I want you to imagine yourself waking up one year from today. 

Again, try to envision this as clearly as possible. Feel free to change as many or as few details as you want from the first scene you imagined. Are you somewhere different? Are you physically changed? What’s your mood? Do you have a different morning habit? What might that new habit be?

Keep imagining your morning one year from now until you have answers to all of these questions — even the harder ones. Notice how easily and automatically ideas came to you, or how hard you had to work to come up with details.

If you’re having difficulty imagining life 10 years from now, write down a description of what you imagine. It can be easier to think about the future with words rather than with mental images.

Now let’s try one more act of imagination. This time, I want you to imagine yourself waking up 10 years from today.

Take as long as you need to come up with a vivid and plausible image — of yourself, of the space that you’re in, and who might be with you. Where are you? What’s around you? What do you see, hear, smell, and feel? What’s the first thing on your mind when you wake up? What do you have planned for the day? How are you physically different?

Try not to make this future scene a total fantasy; stay grounded in what you feel is genuinely realistic and possible for you. If you’re having difficulty, write down a description of what you imagine. Sometimes, it’s easier to think about the future with words rather than with mental images.

You’ll probably find that 10 years is a trickier challenge compared with one year. Why? You’ve never been 10 years older than you are now, so your brain doesn’t know what to expect. Plus, there’s so much opportunity for things to change in a decade — your body, relationships, life circumstances, physical environment.

Your brain intuitively grasps this unknowability, so instead of confidently projecting one possibility, it opens up a blank space for you to consider multiple possibilities. You have to start making intentional choices about what you want to imagine in your future — you have to fill in the blanks.

“Episodic future thinking” or EFT is often described as “mental time travel” — your brain is working to help you see and feel the future as clearly and vividly as if you were already there.

Filling in the blanks takes considerable effort. But that’s precisely why this kind of imagination is so powerful. Instead of simply remembering what it knows, your brain has to invent a new possibility. It draws on past experiences, current hopes and fears, and your intuitions about what might possibly change in 10 years.

Then, after you’ve made this new memory, something amazing happens: What was previously unimaginable to your brain is now imaginable. You can revisit this new memory whenever you want and examine how it makes you feel. Does it spark positive or negative emotions? These pre-feelings can help you decide: Should you change what you’re doing today to make this future more or less likely? And because you invented this memory, you can change it whenever you want.

Scientists call this form of imagination “episodic future thinking,” or EFT. EFT is often described as a kind of “mental time travel” because your brain is working to help you see and feel the future as clearly and vividly as if you were already there.

EFT isn’t an escape from reality. It’s a way of playing with reality, to discover risks and opportunities you might not have considered. EFT is not a daydream in which you fantasize about waking up in a world where your problems are magically solved. It is a way of connecting who you are today with what you might really feel and do in the future.

An important element of imagination training is to fill your brain with what I call “clues to the future,” concrete examples of new ideas that might shape how your future turns out.

Because EFT allows us to pre-feel different possible futures, it’s a powerful decision-making, planning and motivational tool. It helps us decide: Is this a world I want to wake up in? What do I need to do to be ready for it? Should I change what I’m doing today to make this future more or less likely?

According to fMRI studies, EFT involves heightened activity and increased connectivity between 11 distinct brain regions. Compare this to remembering a past event, which activates 6 of the 11 regions of the brain.

There are three major kinds of sense making that happen when you engage in mental time travel to your future. First, your brain has to do what cognitive scientists call “scene construction” — mentally building the future world. Think of this as crafting the stage set, cast and props for a theatrical play.

During EFT, your brain goes on a hunt for realistic details and plausible ideas. To do this, it activates the hippocampus , the seat of memory and learning, and digs through your memories, plus any other facts and ideas you’ve stored away. Depending on what kind of future you’re imagining, the hippocampus identifies the most relevant stuff and retrieves and recombines it into a new scene.

Whatever you see in your future will always come from information your brain has already perceived and processed. Ideally, as you get better at imagining the unimaginable, you’ll incorporate not just obvious ideas and events but also surprising things that could be important in your future.

Another important part of imagination training is to try out new behaviors that could prove useful in the future. I call these micro-actions — taking no more than five minutes to do something today you’ve never done before.

That’s why an important element of imagination training is to fill your brain with what I call “clues to the future,” concrete examples of new ideas that might shape how your future turns out. When you have a hippocampus full of clues, your brain will have better data to draw on, and the scenes you construct will be way more interesting.

After scene construction, your brain starts to do what cognitive scientists call “opportunity detection.” Here, you look for ways to fulfill your needs and achieve your goals. For example: If you predict you will be hungry when you wake up in 10 years, what will future you eat? If you imagine yourself lonely when you wake up, who will future you try to connect with? Opportunity detection is like an actor showing up for rehearsal and asking, “What’s my motivation?” In other words: What do you want in this scene?

To figure this out, your brain fires up the ventromedial prefrontal cortex (vmPFC), a region that’s heavily used whenever you set goals and track your progress. Like the hippocampus, the vmPFC can suggest any goals you’ve had or previously considered. One of the most interesting things about EFT is that the motivations that pop into your mind first are likely to be closely linked to your deepest values and most essential needs, like always learning something new, helping others, pushing yourself to do brave things, taking care of your family, being creative, or  putting new ideas or art into the world.

But you still have to figure out the best way for future you to achieve these future goals. So then the putamen , also part of the motivation and reward system, kicks in. The putamen helps keep track of which specific actions and behaviors typically lead to positive results for you. It’s the part of your brain that knows things like “I feel better when I get some fresh air”; “I make my mom happy when I text her back right away”; “If I’m having a bad day, cooking helps”; or “If I don’t stand up for myself in the moment, I’ll beat myself up about it later.”

There are real benefits to intentionally and carefully imagining futures that frighten you. This can help you do the important work of getting ready for anything — even things you’d rather not experience.

The putamen is like a reality check on your future imagination. Since the putamen is trained on real experiences, the future actions it suggests will be heavily influenced by strategies that worked for you in the past. That’s why another important part of imagination training is to try out new behaviors that could prove useful in the future. I call these micro-actions — taking no more than five minutes to do something today you’ve never done before. When you experiment with micro-actions, you expand what your putamen considers realistic behavior.

Finally, as your brain works to transport you to the future, feelings will kick in. The insula and amygdala , emotion centers in the brain, fire up to give you a preview of how you might feel in the future — excited, disappointed, hopeful, afraid, proud, jealous, joyful, sad, curious, bored, embarrassed, relieved, loved, lonely, awed, confused, stressed out, free or more. These emotions give you important information and help you decide: Is this a future I want to wake up in? Should I take actions today to make this future more or less likely?

Crucially, these are real feelings. Studies show that the emotions you experience during EFT can be just as psychologically powerful as emotions experienced in the present. This is one reason why many of us prefer to imagine best-case-scenario futures and avoid imagining the futures that scare us.

But there are real benefits to intentionally and carefully imagining futures that frighten you. This can help you do the important work of getting ready for anything — even things you’d rather not think about, let alone actually experience, someday.

Excerpted from the new book Imaginable: How to See the Future Coming and Feel Ready for Anything Even Things That Seem Impossible Today by Jane McGonigal. Copyright © 2022 by Jane McGonigal. Used by permission of Spiegel & Grau LLC, New York. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.

Watch her TED Talk here:

About the author

Jane McGonigal is a future forecaster and world-renowned designer of alternate reality games designed to improve real lives and solve real problems. She is the Director of Games Research & Development at the Institute for the Future and currently teaches the course “How to Think Like a Futurist” at Stanford University, as well as serving as the lead instructor for the Institute for the Future’s series on the Coursera platform. She is The New York Times bestselling author of the books "Reality Is Broken" and "SuperBetter" and the new book "Unimaginable." Her innovative games and ideas have been recognized by the World Economic Forum, Harvard Business Review, Fast Company, MIT Technology Review, O Magazine and the New York Times, among others.

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The Science of Mental Time Travel and Why Our Ability to Imagine the Future Is Essential to Our Humanity

By maria popova.

Lewis Carroll’s Alice in Wonderland remains one of my all-time favorite books , largely because Carroll taps his training as a logician to imbue the whimsical story with an allegorical dimension that blends the poetic with the philosophical. To wit: The Red Queen remembers the future instead of the past — an absurd proposition so long as we think of time as linear and memory as beholden to the past, and yet a prescient one given how quantum physics (coincidentally, a perfect allegorical exploration of Wonderland ) conceives of time and what modern cognitive science tells us about how elastic our experience of time is . As it turns out, the Red Queen is far more representative of how human memory actually works than we dare believe.

“To be human,” writes Dan Falk in In Search of Time: The History, Physics, and Philosophy of Time ( public library ), “is to be aware of the passage of time; no concept lies closer to the core of our consciousness” — something evidenced by our millennia-old quest to map this invisible dimension . One of the most remarkable and evolutionarily essential elements of experiencing time through human consciousness is something psychologists and cognitive scientists call mental time travel — a potent bi-directional projection that combines episodic memory , which allows us to draw on our autobiographical experience and call up events, experiences, and emotions that occurred in the past, with the ability to imagine and anticipate future events. Falk puts it unambiguously:

Without it, there would be no planning, no building, no culture; without an imagined picture of the future, our civilization would not exist.

As it turns out, episodic memory — a term coined in the early 1970s by Canadian neuroscientist Endel Tulving, author of the seminal book Elements of Episodic Memory — is central to our capacity for mental time travel and, according to many scientists, fairly unique to humans. Unlike other facets of memory, such as the acquisition of new skills, which are rooted in the here-and-now, Falk points out that episodic memory allows us “to peer back across time, using our imagination to revisit just about any event that we choose.” This mental reliving of the past may be the root of some distinct human maladies — take the wistful reminiscence over a lost love, for instance — but it is also central to our evolutionary survival, allowing us to anticipate future outcomes based on past ones and thus to plan better and be more prepared for what tomorrow may bring. (The dark side of this evolutionarily beneficial faculty is that our over-planning often ends up shortchanging our happiness .)

And yet the benefits outweigh the costs, in evolutionary terms. Falk explains:

The capacity for mental time travel gave our ancestors an invaluable edge in the struggle for survival. They believe there is a profound link between remembering the past and imagining the future. The very act of remembering, they argue, gives one the “raw material” needed to construct plausible scenarios of future events and act accordingly. Mental time travel “provides increased behavioral flexibility to act in the present to increase future survival chances.” If this argument is correct, then mental time travel into the past — remembering — “is subsidiary to our ability to imagine future scenarios.” Tulving agrees: “What is the benefit of knowing what has happened in the past? Why do you care? The importance is that you’ve learned a lesson,” he says. “Perhaps the evolutionary advantage has to do with the future rather than the past.” Modern neuroscience appears to confirm that line of reasoning: as far as your brain is concerned, the act of remembering is indeed very similar to the act of imagining the future.

Though we might not be able to “remember” the future, as the Red Queen does, we do envision it in ways strikingly similar to how we picture events from the past — Falk notes that fMRI studies indicate we use similar regions in the brain’s frontal and temporal lobes when thinking about events in either direction of time. What’s more, psychologists have found that much like it’s harder for us to remember an event in the distant past than a recent one, it’s harder for us to imagine an event in the distant future than one expected to take place soon. This hints at the massively misguided way in which we think of and evaluate memory, which we falsely depict as a recording device , versus foresight. Falk writes:

When we imagine the future, we know what we picture is really just an educated guess; we may be right in the broad brushstrokes, but we are almost certainly wrong in the details. We hold memory to a higher standard. We feel — most of the time — that our memories are more than guesses, that they reflect what really happened. When confronted with a conflicting account of how last week’s party unfolded, we cling to our beliefs: He must be mistaken; I know what I saw.

Falk cites the Harvard psychologist Daniel Schacter:

[The brain is] a fundamentally prospective organ that is designed to use information from the past and the present to generate predictions about the future. Memory can be thought of as a tool used by the prospective brain to generate simulations of possible future events… We tend to think of memory as having primarily to do with the past… And maybe one reason we have it is so that we can have a warm feeling when we reminisce, and so on. But I think the thing that has been neglected is its role in allowing us to predict and simulate the future.

In order to mentally time-travel into the future, the brain has to accomplish a couple of things at once — we activate our “semantic memory,” which encompasses our basic knowledge of facts about the world and thus helps paint a backdrop for the imagined scene, and we call on our episodic memory, which pulls on our autobiographical library of remembered experiences to fill in specific details for this general scene. Curiously, episodic memory tends to be rather flawed but, according to two scientists Falk quotes, that’s okay since its core purpose is to provide “a more general toolbox that allowed us to escape from the present and develop foresight, and perhaps create a sense of personal identity.”

To be sure, just like elsewhere in cognitive science , human exceptionalism may be misplaced here — scientists have found that other species are also capable of varying degrees of mental time travel. Falk cites one of the most intriguing experiments, involving scrub jays. He writes:

Psychologist Nicola Clayton and her colleagues housed the birds on alternate days in two different compartments — one in which the jays always received “breakfast,” and one in which they did not. Then the birds were unexpectedly given extra food in the evening, at a location where they could access either compartment. The jays promptly cached their surplus — and they preferentially cached it in the “no breakfast” compartment. Because the birds were not hungry at the time of the caching, the researchers claim that the birds truly anticipated the hunger they would experience the next morning.

Still, the fact that humans are capable of remarkably elaborate and detailed mental time travel reveals something unique about our evolution and the development of such hallmarks of humanity as language and theory of mind. Falk writes:

In all likelihood, the capacity for mental time travel did not develop in isolation but rather alongside other crucial cognitive abilities. “To entertain a future event one needs some kind of imagination,” [the prominent psychologists Thomas] Suddendorf and [Michael] Corballis write, “some kind of representational space in our mind for the imaginary performance.” Language could also play an important role. Our language skills embrace mental time travel by the use of tenses and recursive thinking; when we say “A year from now, he will have retired,” we’re imagining a future time in which some event — which has not yet happened — will lie in the past… Mental time travel may have been “a pre-requisite to the evolution of language itself.” If mental time travel is indeed unique to humans, it may help us understand why complex language is also, apparently, unique.

In fact, the development of mental time travel may even be how the concept of time itself came into existence — according to Suddendorf and Corballis, our species emerged victorious in “an extraordinary evolutionary arms race” largely due to our growing capacity for foresight and sophisticated language, which not only gave us culture and “coordinated aggression” but also, for the first time in evolutionary history, enabled us to understand the concepts of “past” and “future.” The mental reconstruction of what has been and the imagining of what could be, they argue, created the concept of time and enabled us to understand the continuity between the past and the future. Falk, once again, puts it succinctly:

Mental time travel may indeed be the cognitive rudder that allows our brains to navigate the river of time.

In Search of Time is a fantastic read in its entirety, covering such facets of life’s most intricate dimension as how the calendar was born, why illusion and reality aren’t always so discernible from one another, and what the ultimate fate of the universe might be. Complement it with these seven excellent books on time and a fascinating read on how our memory works .

— Published July 1, 2014 — https://www.themarginalian.org/2014/07/01/mental-time-travel-dan-falk/ —

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The Complex Role of Mental Time Travel in Depressive and Anxiety Disorders: An Ensemble Perspective

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The original contributions presented in the study are included in the article/supplementary material. Further inquiries can be directed to the corresponding author.

The ensemble hypothesis proposes that uniquely human cognitive abilities depend on more than just language. Besides overt language, inner speech, and causal interpretations, executive attention, mental time travel, and theory of mind abilities are essential parts that combine additively and even multiplicatively. In this review, we consider the implications of the ensemble hypothesis for the psychopathologies of anxiety and depression. Generalized anxiety disorder (GAD) and major depressive disorder (MDD) are two of the most common mental disorders worldwide. The mechanisms that differentiate them are difficult to identify, however. Mental time travel has been implicated in models of depressive and anxiety disorders, but here we argue that at least two other ensemble components, namely, interpreter biases and executive attention, must also be considered. Depressive and anxiety disorders have both been found to show impairments in all three of these components, but the precise relationships seem to distinguish the two kinds of disorders. In reviewing the literature, we develop models for depression and anxiety that take into account an ensemble of mental components that are unique for each disorder. We specify how the relations among mental time travel, interpreter biases, and executive attentional control differ in depression and anxiety. We conclude by considering the implications of these models for treating and conceptualizing anxiety and depression.

Introduction

Depressive and anxiety disorders are two major categories of psychopathology, yet they have proven difficult to differentiate in some respects. As will be documented below, both are characterized by dysfunctional executive attention and pessimistic attributional styles, with a high degree of comorbidity. Here we build on the premise of Roepke and Seligman (2016) that the core problem in depression is a difficulty in mental time travel, specifically, an inability to envision positive events in the future. We consider the role of mental time travel in differentiating the two disorders and conclude that this component of human cognition is by itself insufficient. Mental time travel, we suggest, is moderated by problems with executive attention and an interpretive component responsible for causal attributions and inner speech.

In an important paper, Roepke and Seligman (2016) argued that prospection, or the mental representation of future events, plays a major role in depression. Human episodic memory enables mental time travel, that is to say, the ability both to recall past autobiographical events and to imagine possible future events ( Tulving, 2002 ). Roepke and Seligman suggested that the negative beliefs about the future and feelings of hopelessness that characterize depressive disorders ( Beck, 1974 ) can be directly linked to faulty prospection, an inability to envision possible futures and poor evaluation of possible futures. In their view, “.faulty prospection is the core causal process of much depression” (p. 24). A similar proposal was advanced by Miloyan et al. (2014) to account for depression; they also extended the analysis by suggesting that a different form of faulty prospection, centered on worry rather than pessimism and hopelessness, lay at the core of anxiety disorders.

We agree that problems with mental time travel are central to psychopathology, but we question whether this component can be isolated from other cognitive components to ascertain its relative contribution. Instead, we argue that other fundamental components of human cognition are concurrently at work in both depressive and anxiety disorders. In our view, it is important to consider how other components impair or even enhance the functioning of mental time travel. To develop this perspective, we draw on the ensemble hypothesis, which holds that human cognition depends on five core systems or components that interact in non-additive ways ( Kellogg, 2013 ; Kellogg and Evans, 2019 ). Mental time travel is necessary but not sufficient for explaining either the remarkable competencies of human cognition or its breakdowns in disorders such as anxiety and depression. An advanced executive form of working memory, a theory of mind augmenting social cognition, language, the ability to interpret information using inner speech, and causal inference are necessary, as well as an episodic memory capable of mental time travel. Kellogg (2013) introduced the ensemble hypothesis in the context of understanding the exceptional cognitive abilities in the evolution of our species, Homo sapiens . The book provides the reasons for considering the five components and their interactions in normally developing and functioning human beings. Kellogg and Evans (2019) offered further evidence in support of the hypothesis from behavioral studies, lesion studies, and studies involving neuro-atypical populations.

The key claim of the ensemble hypothesis is that two or more mental capacities can interact in a multiplicative fashion to yield competencies in a well-functioning human being that exceed their simple additive effects. For example, delay of gratification is a phenomenon that entails an ability both to prospectively consider the future and to exercise cognitive control using executive attention. In typically developing children, growth in the capacity of executive attention for self-regulation boosts the ability to delay rewards in anticipation of a larger future reward ( Mischel et al., 1989 ). Similarly, planning in problem solving requires future thinking and a normally functioning system of executive attention. Frontal lobe injuries that damage networks of executive attention often impair planning ( Kellogg and Evans, 2019 ). In normally functioning adults, retrospective memory for a list of words presented in a laboratory task requires an intact hippocampus and medial temporal lobe, but it is also boosted by maintenance and elaborative rehearsal strategies that depend on executive attention. Failing to deploy attentional resources to an encoding strategy impairs the recall of a list of words presented in a laboratory task in individuals with depression ( Hertel and Rude, 1991 ). As will be considered in detail later, the normal functioning of mental time travel can be altered by depression because of its effects, in part, on executive attention.

The purpose of the present paper is to consider the implications of the ensemble hypothesis for two broad categories of psychopathology: depression and anxiety. We suggest that much of the phenomenology and symptoms that underlie depressive and anxiety disorders can best be understood as an interaction of components of the hypothesized ensemble. We wish to extend the insights provided by Miloyan et al. (2014) and Roepke and Seligman (2016) by demonstrating how the interpreter and executive attention influence mental time travel. As will be seen, language is considered in the form of inner speech, but the broader concept of language as interpersonal communication falls outside the scope of the current paper. Similarly, as will be addressed in the limitation section of our paper, an extensive literature on theory of mind and social cognition in depression ultimately needs to be accounted for. Even so, our focus on the interpreter, executive attention, and mental time travel documents the importance of the interactions posited by the ensemble hypothesis.

To illustrate, consider the case of depression (see Figure 1 ), as exemplified by major depressive disorder (MDD). As will be discussed in detail later, the interpreter shown in Figure 1 refers to the inner voice and causal inference capacity of the left hemisphere of the human brain that enables attributions about the self and other people ( Gazzaniga, 2000 ; Kellogg, 2013 ). In depression, the interpreter is biased to assign blame to the self for negative experiences. This pessimistic and personally negative explanatory style ( Petersen and Seligman, 1984 ) causes the depressed individual to focus attention on negative past events and have difficulty envisioning anything positive about the future. Further, there is evidence that depression is associated with a concurrent deficit in executive attention ( Ólafsson et al., 2011 ), causing impaired cognitive control over mental time travel resulting in persistent negative rumination. Thus, the influence of both a bias in interpretation and a deficit in executive attention, we propose, could underlie faulty prospection in depressed individuals. The interactive model of Figure 1 differs from the position of Roepke and Seligman (2016) with respect to effective approaches to treatment for depression. They advocate for treatments targeting mental time travel, specifically, the core problem with prospection. Alternately, we contend that efforts to improve executive attention and to correct the pessimistic explanatory style of the interpreter ought not be neglected, because they can alter the functioning of mental time travel.

Model of major depressive disorder.

The plan of the paper is, first, to introduce several components of the ensemble hypothesis that are central to our analysis of depressive and anxiety disorders. Second, we consider evidence on the role of mental time travel in depressive and anxiety disorders. Third, we discuss literature regarding the pessimistic explanatory style in depression and suggest that anxious individuals are characterized by a related but distinct dysfunctional style of explaining events as threatening to the self. The emphasis on loss in depression and threats in anxiety can influence the functioning of mental time travel, we propose. Fourth, we document that both kinds of disorders are associated with impairments in executive attention that may compound problems with mental time travel. Fifth, we discuss how the symptoms of depression versus anxiety can best be understood by considering mental time travel, the interpreter, and executive attention as an integrated ensemble. We conclude by considering the implications of the ensemble perspective regarding effective therapies for depressive and anxiety disorders.

Mental Time Travel, the Interpreter, and Executive Attention

Mental time travel is the unusual form of human episodic memory that allows the mind to recollect the specific time and place of a past event in one’s personal history ( Tulving, 2002 ; Suddendorf and Corballis, 2007 ). It is conceived as mental time travel because the same neural systems are involved in imagining future events as well as recollecting past events. The brain systems involved in mental time travel include the hippocampus and medial temporal lobe structures as well as the default mode network activated in resting state conditions when no external task is presented ( Buckner et al., 2008 ). The ability to construct spatially coherent scenes in which an event takes place is essential in both recollecting the past and imagining the future. It has been suggested that scene construction is a core function of the hippocampus ( Clark and Maguire, 2016 ).

A uniquely human mental ability appears to be the interpretive capacity of the left hemisphere ( Gazzaniga, 2000 ). Over the course of human evolution, our oral language capacity became internalized as inner speech, mediated by language networks in the left hemisphere. Vygotsky (1962) emphasized that speech begins in early childhood as a means for communication, but as speech is internalized, it also becomes a means for planning and problem solving. Self-directed inner speech, then, has long been recognized as an important vehicle for thinking and appraising situations and events. The interpreter constructs a personal narrative that explains why we feel and behave as we do. Inner speech is combined with a specialization of the left hemisphere for a specific kind of thinking. The left hemisphere is not only specialized for the use of language, including self-directed language of inner speech, but it is also specialized for forming hypotheses ( Wolford et al., 2000 ) and making inferences about causal relationships ( Roser et al., 2005 ). Similarly, the ability to reason deductively is known to be impaired in patients with left frontal lesions but not right frontal lesions ( Reverberi et al., 2010 ).

In clinical psychology, the interpreter is important in understanding the role of inner speech and causal inference in how people respond to stressful life events. How an individual cognitively appraises stressors can either attenuate or exacerbate the strain that they cause. This role for causal attributions has long been recognized in understanding depressive and anxiety disorders. For example, Petersen and Seligman (1984) highlighted that depression is characterized by a personalized and pessimistic explanatory style. The individual attributes personal, pervasive, and permanent causes to negative personal experiences, committing what social psychologists call the fundamental attribution error. The role played by the interpreter in explaining why things happen and what significance events have for the self is central to both depression and anxiety, as will be detailed later in the paper.

The executive attention component of working memory enables the coordination and regulation of representations held in verbal, visual, and spatial stores of short-term memory. Working memory, planning, cognitive control, self-regulation, and response inhibition have all been referred to as executive functions that have traditionally been viewed as dependent on the frontal lobe ( Alvarez and Emory, 2006 ; Posner and Rothbart, 2007 ; Diamond, 2013 ; Ajilchi and Nejati, 2017 ). A more complex understanding has emerged in the literature with two distinct brain networks involved in executive attention; these include but are not limited to regions in the frontal lobe ( Posner and Peterson, 1990 ; Petersen and Posner, 2012 ).

By studying a battery of executive functioning tasks, Miyake et al. (2000) identified three correlated but distinctive processes underlying performance. Updating the contents of working memory, shifting goals as required in multitasking, and inhibiting irrelevant information are considered three essential and irreducible functions of executive attention. A widely used test of individual differences in working memory capacity, called the Operation Span (OSPAN) test, indicates that the ability to inhibit irrelevant information is especially important and shows a strong correlation with general fluid intelligence or the ability to solve novel problems ( Engle et al., 1999 ).

Mental time travel, the interpreter, and executive attention are three fundamental components of human cognition. Kellogg (2013) proposed that these components, together with theory of mind and language, comprise an ensemble that renders human cognition unique and qualitatively different from non-human cognition. Importantly, his hypothesis suggests that it is the interaction of these components that yields the unique properties of human cognition. If that is so, then it stands to reason that common forms of psychopathology should reveal such interactions, too. In persons experiencing anxiety or depression, a deficit in one component can cascade to degrade the functioning of another component, despite that the latter component is not necessarily dysfunctional.

Mental Time Travel Impairments

Roepke and Seligman (2016) reviewed a variety of evidence that faulty prospection lies at the heart of depression. First, persons experiencing depression can envision negative future scenarios more readily, compared to non-depressed persons ( MacLeod and Byrne, 1996 ). This characteristic is also shared with those experiencing anxiety, indicating it is not a unique dysfunction of mental time travel associated with depression. Miloyan et al. (2014) suggested that anxious as well as depressed individuals anticipate negative future events but that each disorder shows a unique profile of faulty prospection. Individuals with anxiety anticipate more negative experiences, but not fewer positive experiences, relative to control participants without a history of psychiatric diagnosis, according to some studies ( MacLeod and Byrne, 1996 ; MacLeod et al., 1997b ). Depression, on the other hand, is associated with a failure to anticipate positive future events ( Miranda and Mennin, 2006 ; Pomerantz and Rose, 2014 ). When depressed psychiatric outpatients were asked to describe a distressing personal problem and to imagine and rate the likelihood of both the worst and best possible outcomes, they rated the worst outcome as being more likely and the best outcome as being less likely, relative to generalized anxiety disorder (GAD) and control groups ( Beck et al., 2006 ).

Thus, it is possible that a faulty form of prospection found in depression results in a diminished ability to envision positive future events ( MacLeod and Salaminiou, 2001 ). However, both this finding and the finding that individuals with depression envision more negative future events than do controls can also be linked to a pessimistic explanatory style. MacLeod et al. (1997a) found that both depressed and anxious patients not only judged future negative events to be more likely, relative to controls; they also provided more supportive as opposed to contradictory reasons for their occurrence. As MacLeod et al. (p. 22) concluded, “…mood-disturbed subjects were pessimistic about what would happen to them in the future, and this was supported by their causal thinking about those events.” Thus, the pessimistic explanatory style of the interpreter rather than a malfunction in mental time travel per se could explain the findings. They could also be linked to the deficits in executive attention that are associated with depression ( Ólafsson et al., 2011 ). As will be argued in later sections of the paper, problems with mental time travel may arise because of the moderating influences of the interpreter and executive attention.

An important exception regarding memory impairment in depression is the tendency to focus and elaborate upon sad events ( Williams et al., 1997 ). A case can be made for mood congruent memory in depression ( Mineka and Nugent, 1995 ). For example, in a study by Derry and Kuiper (1981) , a list of depression-related adjectives (e.g., bleak, dismal, helpless) and non-depression-related adjectives (e.g., amiable, curious, loyal) were presented in an incidental learning task. The nature of the orienting task was manipulated, with one way being whether the adjective applied to the self. On a subsequent recall test, this self-reference orienting task resulted in a greater proportion of depressed-content words recalled (41%) than non-depressed content (16%) for depressed patients. Strikingly, this pattern was completely reversed for normal controls, who recalled more non-depressed content (43%) compared with depressed content (8%). Even a group of psychiatric controls showed a reversal with more non-depressed content (36%) relative to depressed content (18%). None of these effects were observed for structural (small letters?) and semantic (means the same?) orienting tasks, indicating that they are contingent on judging the word as relevant to the self.

Similarly, in another study, after being shown a list of words including pleasant, unpleasant, and neutral words, individuals with depression recalled more unpleasant words compared with pleasant words ( McDowall, 1984 ). A non-depressed control group as well as another control group made up of psychiatric patients with a diagnosis other than depression did not show this bias toward improved memory for unpleasant words. The depressed patients’ free recall of unpleasant words was at the same level as that for the two control groups, whereas they showed a memory impairment for pleasant words. This indicates that the mood congruent benefit of remembering unpleasant words can offset the usual memory impairment found in depression.

Clark and Teasdale (1982) found that autobiographical experiences also reveal mood congruency even within the same group of individuals with depression. The investigators compared the recall of personal memories at two different times of day to capitalize on diurnal variations in mood among psychiatric patients experiencing depression. The percentage of unhappy memories (52.3%) was reliably greater when the individual reported being more depressed compared with less depressed (36.7%). Happy memories (37.7 versus 51.1%) showed exactly the reverse pattern.

The above studies show that depression can bias retrospection in the direction of remembering sad events more readily than happy events. Would such findings also hold for prospection? MacLeod et al. (1997b) measured the recall of past experiences and the anticipation of future experiences in anxious, depressed, and control individuals. The study prompted the participants to remember or anticipate either positive experiences or negative experiences. This prompt variable allowed the comparison of the number of positive events versus negative events produced under conditions of both retrospection and prospection. Their findings showed no difference between the retrospection and prospection conditions for either disorder. Of importance, individuals with depression produced fewer events compared with controls—both positive and negative—both in recalling their past and in anticipating their future.

An analogous outcome has been found in laboratory studies of the retrospective recall of word lists versus prospective memory for future actions. Hertel and Rude (1991) found poorer free recall of a list of words presented earlier for currently depressed patients compared with recovered patients and control individuals with no history of depression in a retrospective task. Rude et al. (1999) similarly reported that depressed individuals perform poorly on a prospective memory task requiring the ability to self-initiate an action in the future. Their difficulties with “remembering to remember” to act in the future were parallel to impairments found in retrospective tasks, according to the authors. Of course, these tasks are different from the autobiographical reports examined by MacLeod et al., but the conclusions reached are consistent. MacLeod et al. (1997a) also found that anxious individuals did not differ from controls either in remembering or in anticipating positive events. However, they generated more negative events compared with controls regardless of whether they were engaged in retrospection or prospection. Their findings thus confirm that anxiety is primarily a disorder of worrying about negative outcomes ( Barlow, 1988 ). Whereas MacLeod et al.’s control participants both recalled and anticipated about 44% more positive life events than negative ones, the anxious participants only recalled 15% more positive events. Compared to participants with depression, the participants with anxiety recalled and anticipated about 67% more negative events.

Finally, MacLeod et al. expected that individuals with depression would show a mood congruent effect by remembering or anticipating more negative events compared with positive events. In contrast to prior studies reviewed earlier, this outcome did not occur. Rather, negative events were remembered by patients with depression at about the same rate as found in the controls. This rate was equivalent to the number of positive events remembered by those with depression, who were 75% less likely to remember positive events than were patients with anxiety and controls. This is reminiscent of the findings with the free recall of word lists reported by McDowall (1984) . Unpleasant words were remembered as well by patients with depression as by controls, but recall for pleasant words showed a marked impairment.

The above findings on memory could depend on the severity of the depressive disorder. It is important to note in that regard that MacLeod et al. (1997b) examined patients who met the diagnostic criteria for panic disorder and MDD. Similarly, the studies by Derry and Kuiper (1981) , Clark and Teasdale (1982) , McDowall (1984) , Hertel and Rude (1991) , and Rude et al. (1999) examined psychiatric inpatients or patients with depression in the community with screening done to insure they met the diagnostic criterion for depression. By contrast, in a non-clinical student population, neither trait anxiety nor trait depression was associated with difficulties in a measure of prospective memory ( Arnold et al., 2014 ). Thus, the severity of the disorder probably plays a role in the effects of depression and anxiety on mental time travel.

In contrast to the picture for clinical depression, the findings on retrospective memory for anxiety disorders are mixed. MacLeod and McLaughlin (1995) found that individuals currently receiving treatment for GAD performed worse than those in a control group on an explicit recognition test for words presented in a laboratory setting. By contrast, on explicit memory tests of cued recall ( Mathews et al., 1989 ) and free recall ( Becker et al., 1999 ), anxious individuals performed at the same level as control participants. For threatening words included among the lists presented in the laboratory, GAD patients showed no advantage in recall or recognition, but they did show superior performance on various implicit memory tests compared with controls ( Mathews et al., 1989 ; MacLeod and McLaughlin, 1995 ). A similar heightened explicit memory for threatening words was found by Becker et al. (1999) for individuals diagnosed with panic disorder but not with social phobia or GAD. In a review of the literature on memory and anxiety disorders, Mineka and Nugent (1995) concluded that the evidence for an explicit memory bias for threatening events is weak, difficult to replicate, and unconvincing, at least with respect to persons experiencing GAD.

We conclude from this sample of findings in the literature that while depression impairs mental time travel ability, it does not seem to be a selective difficulty with prospection. Judging from the findings of MacLeod et al. (1997a) , at least for positive events, anxious individuals do not appear to show any impairment in mental time travel, either in its prospective or in its retrospective form. In fact, they appear to recollect past negative events and envision future negative events more often than is found in both non-anxious controls and depressed patients. However, other studies indicate that such memory bias for threatening events is tenuous at best in anxiety. Patients with depression, on the other hand, forget positive events more readily than is found in non-depressed controls. A central question is what accounts for these differences in the functioning of the mental time travel component. We propose that considering the role played by the interpreter and executive attention helps to understand the pattern of results found for mental time travel.

Interpreter Biases

As noted earlier, the interpreter in individuals with depression employs a pessimistic explanatory style ( Petersen and Seligman, 1984 ). An inability to envision a positive future and a facility with envisioning a negative future could be understood as a dysfunction of the explanatory style found in individuals with depression rather than a fault with mental time travel per se ( MacLeod et al., 1997a ). A negative style of explaining why things happen as they do is a prime reason for feelings of hopelessness in depressed people ( Alloy et al., 1988 ). Individuals with depression tend to attribute the reasons for events in life to internalized causes about the self that are stable over time and that are global or pervasive in multiple situations. Another compounding factor is a negative attributional style that attributes negative events to uncontrollable causes ( Sanjuán and Magallares, 2009 ). As a consequence, persons with depression might be able to recollect or imagine an event that most people would regard as positive (e.g., getting a job promotion) but then interpret it as negative. Individuals with depression might appraise the promotion as full of pitfalls—more responsibility, longer working hours, and greater stress. Remembering or anticipating a job promotion may not be the problem but, rather, its pessimistic interpretation.

The interpreter, therefore, has a prominent, if not central, role in depression. Indeed, Beck (1974) designed cognitive behavioral therapy (CBT) to confront and modify a depressed person’s inner speech of hopelessness and self-deprecation. By altering the person’s cognitive appraisals of situations and causal explanations of events, mood improves as a result. Beck’s concept of the cognitive triad included a negative view of the self, negative interpretations of ongoing experiences, and a negative view of the future. Although the latter could be caused by faulty prospection, the first two stem from the distorted explanations of the interpreter.

Comparisons of the interpretative style of depressed versus anxious individuals have yielded conflicting results, however. For example, Heimberg et al. (1989) , by contrast, found that the attributional style found in the learned helplessness of individuals with depression was also characteristic of multiple anxiety disorders, such as social phobia, agoraphobia, and panic disorder. In their study, the two disorders differed only in that depression produced global and unstable attributions regarding the causes of positive events, whereas anxiety was associated with the same kind of attributions for negative events. Still other findings indicate that attributing internal, stable, and global causes to negative events is in fact found in currently depressed individuals, but especially in those with comorbid anxiety ( Fresco et al., 2006 ). Similarly, Luten et al. (1997) concluded that a pessimistic attributional style is not specific to depression but, rather, is correlated with high levels of negative affect as is also found in in persons with anxiety disorders. Ahrens and Haaga (1993) even reported that a negative event attributional style was only found with anxiety disorders rather than with depression.

Thus, it seems that pessimistic forms of causal inference about life’s events are a non-specific risk factor for anxiety and depression. This commonality with respect to the dysfunction of the interpreter is a likely reason why depressive and anxiety disorders share a high degree of comorbidity ( Gotlib, 1984 ; Kessler et al., 2007 ; Grisanzio et al., 2018 ).

Despite their similarities and high rates of comorbidity, there may be some unique aspects to the interpreter’s dysfunction in anxiety disorders, however. Riskind and Williams (2005) identified a looming cognitive style in which individuals overestimate the progression of a potential threat in terms of both spatial and temporal dimensions. Individuals with a high score on their looming cognitive scale misinterpret potential threats as catastrophic threats. A study by Reardon and Williams (2007) showed that this looming cognitive style is uniquely associated with anxiety disorders. A pessimistic cognitive style contributed to both anxiety disorders and depressive disorders, but individuals predisposed to anxiety disorders also were prone to a looming cognitive style that magnifies potential threats. Anxiety disorders also feature highly persistent negative self-talk. The excessive worry that characterizes anxiety is largely verbal in nature ( Borkovec et al., 1998 ). Instead of imagining a threat in a visual–spatial context, anxious individuals talk to themselves about it. Finally, it has long been recognized that the causal inferences made in depression are associated with personal failures and self-deprecation ( Beck, 1974 ). This contrasts with worries about uncertainties and potential dangers in the case of anxiety disorders ( Beck et al., 1987 ; Clark et al., 1990 ).

As shown in Figure 2 , the anxious interpreter views events as threatening to the self rather than as a negative reflection of the self as in depression ( Figure 1 ). Kendall and Ingram (1989) differentiated the two disorders precisely in terms of their characteristic attributions. The interpretations of the depressive person often are “self-referent, definitive, past-oriented cognitions of sadness, failure, degradation, and loss,” in contrast to the “future oriented ‘questioning’ cognitions” found in anxiety disorders ( Kendall and Ingram, 1989 ; p. 36).

Model of generalized anxiety disorder.

In our view, the interpreter biases play a role in the problems observed in mental time travel with depressed and anxious individuals ( Eysenck et al., 2006 ). For depression ( Figure 1 ), the pessimism of the interpreter causes individuals with depression to remember and ruminate about negative life experiences that reinforce feelings of loss and self-blame. Perhaps the difficulty with imagining a positive future is a direct consequence of depressed individuals focusing on negative past events. Roepke and Seligman (2016 , p. 27), in fact, suggest the possibility that persons experiencing depression “struggle to recall a good past,” with few positive memories ( Williams and Scott, 1988 ).

For GAD ( Figure 2 ), the interpreter is biased to detect threats to the self. This might cause one to recall, see, and foresee dangers rather than losses. Instead of mental time travel being impaired relative to control individuals who are neither depressed nor anxious, there is, if anything, an excessive prospection and retrospection of negative events. This outcome can be seen in the study by MacLeod et al. (1997b) , who reported that anxious individuals both retrospectively and prospectively generated more negative events than did controls and even individuals with depression. Similarly, when asked to recall recent life events, 77% of anxious participants remembered danger events compared to 44% of depressed participants ( Finlay-Jones and Brown, 1981 ). Loss events, on the other hand, were more frequently remembered by participants with depression (65%) compared with anxiety (15%). Comparable findings for autobiographical recall have been reported by Witheridge et al. (2010) .

Thus, in our view, the interpreter plays a key role in the functioning of the mental time travel component. The content of the events that are remembered in depression is more likely to deal with loss rather than danger. This, we suggest, occurs because of the bias of the interpreter on mental time travel. In anxiety disorders, retrospection is not impaired; if anything, there is excessive rather than impaired prospection and retrospection about threatening events. In addition to mental time travel being moderated by the interpreter, we further consider in the next section the possible influence of executive attention.

Executive Attention Deficits in Depression and Anxiety

A number of studies have shown that anxiety and depression are associated with impaired performance on a variety of neuropsychological tests that measure for executive control functions ( Reinholdt-Dunne et al., 2013 ; Devito et al., 2018 ). This supports the notion that both disorders are associated with impairments in executive attentional control. In this article, we refer to executive attention as executive attentional control and attentional control, interchangeably. In accordance with Stefanopoulou et al. (2014 , p. 330), attentional control can be defined as “the ability to sustain focus on tasks in the face of competing activities or to shift attention from one task to another.” However, depression and anxiety do not show the same pattern of executive attention deficits.

The Attentional Control Scale (ACS) is a self-reported attention control measure that is comprised of two components: focusing and shifting ( Reinholdt-Dunne et al., 2013 ). Ólafsson et al. (2011 , p.77) define attentional focusing as “the capacity to intentionally hold the attentional focus on desired channels and thereby resist unintentional shifting to irrelevant or distracting channels” and define attentional shifting as “the capacity to intentionally shift the attentional focus to desired channels, thereby avoiding unintentional focusing on particular channels.” Because it has been noted that those with anxiety show attentional impairment in relation to shifting and focusing ( Devito et al., 2018 ), the ACS has been used to compare the relationship between attentional focusing, attentional shifting, and levels of anxiety and depression in adults. Ólafsson et al. (2011) found that when controlled for depression, the focusing ACS subscale significantly predicted anxiety ratings, whereas when anxiety ratings were controlled for, the shifting subscale significantly predicted depression ratings. Reinholdt-Dunne et al. (2013) supported these findings when they found ACS focusing to be associated with lower anxiety and ACS shifting to be associated with fewer depression symptoms. These findings support the claim that anxiety is more associated with attentional focusing and depression is more associated with attentional shifting.

Shi et al. (2019) performed a meta-analysis to investigate the size and nature of attentional control deficits in participants with anxiety versus non-anxious participants. They found that anxiety-producing deficits were supported in processing efficiency, rather than effectiveness, on a variety of behavioral tasks. However, they also found that when looking at task switching studies alone, both efficiency and effectiveness produced anxiety-related deficits in attentional control. Their results also showed that studies requiring participants to operate under high cognitive load conditions showed greater anxiety-related attentional control deficits compared to studies where participants were under normal cognitive load conditions ( Shi et al., 2019 ).

Although attentional control deficits have been related to anxiety disorders, these deficits are prominently seen in individuals diagnosed with GAD, characterized by uncontrollable worry. This uncontrollable worry has been connected to deficits of the central executive function of working memory, which includes attentional control as a key component of working memory ( Stefanopoulou et al., 2014 ). Uncontrollable worrying can be attention-demanding and, consequently, consumes voluntary attentional resources required ( Eysenck et al., 2007 ). This links uncontrollable worry to impairments in attentional control.

Stefanopoulou et al. (2014) used the key-pressing task to assess the extent to which attentional resources were depleted by worry in individuals with GAD. Stefanopoulou et al. (2014) found that GAD individuals were less random on the key-pressing task while worrying compared to when thinking of a positive topic, indicating that fewer residual attentional control resources were available during the worrying process. However, the performance of the healthy participants did not differ between conditions. GAD participants also reported having more negative thoughts and anxiety during this task compared to healthy participants. This same study also used the N-back task, which “varies in difficulty and is sensitive to subtle difference in ability to handle increasing demands on attentional control” ( Stefanopoulou et al., 2014 , p. 330). During this task, GAD participants exhibited longer reaction times compared to healthy participants for the higher load conditions. These results together indicate a greater difficulty in sustaining focus in conditions requiring a higher degree of attentional control, suggesting that poor attentional control may partially explain the excessive worry seen in individuals with GAD.

Further, there appears to be a bidirectional relationship between attentional control and anxiety ( Devito et al., 2018 ). Impairments in attentional control may increase one’s risk for developing anxiety, and anxiety symptoms may prevent executive components of attention from being recruited. We indicate this bidirectional relationship between the interpreter and executive attention in Figure 2 . The pessimistic explanatory style and negative self-talk of the interpreter consume limited attentional resources. The resulting deficit in executive attention weakens the ability to inhibit the dysfunctional thinking of the interpreter in anxiety disorders.

Whether a similar bidirectional relationship occurs in depression is unclear. An argument against this takes into account the speech and inner speech of depressed versus anxious individuals based on the symptoms outlined in the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition ( DSM-V ). The hallmark of GAD is excessive worry in the form of inner speech. By contrast, in MDD, fatigue and tiredness occur on nearly a daily basis, and this can be accompanied by slowed speech, long pauses before responding, and a decrease in the amount and variety of speech content ( American Psychiatric Association, 2013 , p. 132). These suggest that inner speech in MDD is more likely to be inhibited or overly regulated rather than exaggerated, as is apparent in GAD. Moreover, in a review of the literature on inner speech, Alderson-Day and Fernyhough (2015) noted that the evidence for inner speech playing a central role in anxiety disorders is stronger and more specific than it is with depression. The verbalized worry of anxiety is, in their words (p. 948), “…repetitive thinking that is.negative, uncontrollable, and aimed at some ill-defined problem solving, such as a problem with a clear solution.” We propose that the bidirectional links between executive attention and the interpreter produce worry in GAD that is indeed out of control (see Figure 2 ). A positive feedback loop ensues in which worry depletes attention, which in turn worsens worry. In depression, the negative impact of depleting attention does not appear to feed back on the interpreter. Instead, we suggest, it feeds forward to impact mental time travel. Specifically, the deficit in executive attention found in depression results in a loss of control in mental time travel (see Figure 1 ). The arrows shown in Figures 1 , ​ ,2 2 are intended to reflect the major pathways of influence from one component to another. From the perspective of the ensemble hypothesis, all possible links among components are potentially relevant, including bidirectional relationships. In a normally developed and well-functioning adult human being, each of these components influences the others. Our aim in these figures is to take a minimalist approach by highlighting only strong interactions that differ from normal under a diagnosis of psychopathology. The purpose is to differentiate as clearly as possible how MDD and GAD differ from each other. For example, we intentionally omit an influence of executive attention on mental time travel in GAD. Although it is known that the availability of executive attention affects the functioning of mental time travel even in healthy individuals, we only indicate interactions that are unique to GAD or MDD.

Memory Impairment From an Ensemble Perspective

As shown in Figure 1 , we suggest that both retrospection and prospection will be impaired as a result of a deficit in executive attention ( Hertel and Rude, 1991 ; Rude et al., 1999 ). Evidence for a causal role played by attention comes from an intervention designed by Hertel and Rude (1991) to remediate the attentional deficits. Hertel and Rude studied three groups of individuals who were currently depressed, recovered from depression, or without a history of depression in an incidental learning and memory task. The participants’ ability to recall a list of target words that they had viewed in the first phase of the experiment was markedly impaired in the individuals with depression compared with recovered and healthy controls. But this outcome only occurred when their attention to the words during learning was unconstrained by the demands of the task. For half of the participants, the investigators required the participants to repeat the target words aloud on each trial, as a means of focusing their attention. Strikingly, this manipulation eliminated the memory impairment of the depressed patients entirely. This result suggests that retrospection per se is not necessarily deficient in depression, but a memory deficit can be observed as a result of the influence of executive attention not being appropriately allocated to the task at hand.

A comparable finding was reported by McDowall (1984) . On a free recall test, inpatients with depression performed markedly worse than did a control group consisting of non-depressed psychiatric inpatients in remembering pleasant words. However, when given an orienting task of rating each word for pleasantness as was shown during the study phase, patients with depression showed no difference in recall between pleasant and unpleasant words and performed no worse than did the psychiatric control group doing the same task. Their mean recall of 5.6 words out of 12 was only slightly less than was found for a non-psychiatric control group (6.8 words), again with no difference between pleasant versus unpleasant words. As with the word repetition technique used by Hertel and Rude (1991) , the orienting task directed attention to the words in a way that eliminated most, if not all, of the memory impairment for individuals with depression.

Ruminating on negative life experiences is part and parcel of the sense of loss, hopelessness, and self-deprecation frequently seen in persons experiencing depression. In our view, these phenomena are the direct result of the interpreter bias found in depression. It is the influence of the interpreter with mental time travel that contributes to the inability of individuals with depression to think about positive life experiences, whether they lie in the past, the present, or the future. Further, the persistence and intrusiveness of negative memories in depression could reflect an inability to inhibit them because of executive attention deficits (see Figure 1 ). Poor cognitive control may combine with the loss bias of the interpreter to produce the profile of memory problems found in depression.

As shown in Figure 2 , for GAD, the mental time travel system is biased to focus on the uncertainties and threats of life experiences. Instead of loss and self-blame, the content of memories predominately concerns threats to the self in anxiety disorders to the extent that they are biased at all. This can account for why negative events are, at times, better remembered or anticipated by anxious individuals (e.g., MacLeod et al., 1997b ). However, in contrast to the memory bias effects for losses observed in depression, similar effects for threatening events in anxiety disorders are harder to detect reliably ( Mineka and Nugent, 1995 ). They might be found in panic disorder but not GAD ( Becker et al., 1999 ). Or they can be observed with implicit memory tests but not explicit tests of recall or recognition ( Mathews et al., 1989 ; MacLeod and McLaughlin, 1995 ). They might also be observed when people are asked to recall autobiographical events of personal relevance ( Finlay-Jones and Brown, 1981 ; Witheridge et al., 2010 ) but not when they are asked to remember word lists that contain some threatening versus neutral words ( Levy and Mineka, 1998 ).

We suggest that the mixed picture for memory bias in anxiety disorders occurs because executive attention deficits do not generally disrupt mental time travel in persons experiencing GAD, which is not the case for MDD (see Figure 2 ). The deficit in executive attention causes a loss of control with the interpreter but not with mental time travel. Without both a loss of cognitive control and a threat bias from the interpreter, the mental time travel system functions relatively normally in GAD. That implicit tests of memory reveal bias effects for negative information implies that a threat bias from the interpreter is at work. But for the declarative memory system of episodic memory to show such effects, it requires both the threat bias and a loss of cognitive control over mental time travel. Perhaps only in severe cases of anxiety disorders, such as panic disorder, does the loss of cognitive control from deficits in executive attention spill over to affect mental time travel, much as it does in depression. This could account for the results of Becker et al. (1999) for panic disorder in contrast with other forms of anxiety disorder. It is worth noting that MacLeod et al. (1997b) studied anxious participants who all met the criteria for panic disorder. Thus, the characteristics of their sample might have explained why they observed a bias for negative events when so many other studies have been unable to do so, as they noted in their discussion section.

In summary, accounting for the consistent memory bias for losses or a lack of positive memories in MDD seems to depend on distorting inputs from both executive attention and the interpreter (see Figure 1 ). For persons experiencing GAD without panic disorder, the input from executive attention is weak or non-existent. Without this concomitant symptomatology, the bias of the interpreter for threatening events does not distort either retrospective or prospective memory, although it shows up on implicit, non-declarative forms of memory.

Limitations, Implications, and Future Directions

As noted previously, our explication of the complex role of mental time travel in explaining the phenomenology and research findings related to MDD and GAD has focused on interrelationships between three of the five components of the ensemble hypothesis. In focusing on these three constructs, we acknowledge the limited attention we have given to the importance of the two remaining ensemble components—overt use of language and social cognition—in accounting for differences and similarities in MDD and GAD. Reviewing the broader concept of language as interpersonal communication falls outside the scope of the current paper. Similarly, the extensive literature on theory of mind and social cognition in disorders such as MDD and GAD merits careful consideration that is not undertaken by our current analysis. Research indicates that theory of mind, a specialized aspect of social cognition ( Frith and Frith, 2007 ), plays a complex role in presentations of depression and anxiety where aspects of social cognition are prominent ( Bora and Berk, 2016 ; Washburn et al., 2016 ). Examples would include depression in the context of discordant relationships or bereavement, and social anxiety disorder. Exploring the interrelationships between social cognition and other components of the ensemble hypothesis is a fruitful direction for further theorizing and research.

Also, our paper is limited in scope, in that we focused on accounting for differences between disorders such as MDD and GAD, rather than examining similarities in their phenomenology and accounting for the high comorbidity of these conditions. We believe that further analysis of the interrelationships among the ensemble of mental components in MDD and GAD may help account for the comorbidity of these two disorders. For example, the high incidence of comorbidity might be accounted for by the reciprocal relations between the cognitive ensemble components and symptoms that constitute pathways that connect the disorders ( Borsboom and Cramer, 2013 ). It is worth noting the strong similarities of MDD and GAD as portrayed in Figures 1 , ​ ,2. 2 . Both disorders involve several components of the ensemble hypothesis, including executive attention and the interpreter, in addition to mental time travel. The specific characteristics of memory functioning seem to depend on these interrelated cognitive components of the ensemble perspective. Thus, future theorizing and research should explore the interrelated components of the ensemble hypothesis as they relate to comorbid presentations of MDD and GAD.

Regarding one final limitation of our paper, we acknowledge that the ensemble component of “mental time travel” as it pertains to episodic foresight involves multiple constructs, each with substantive theoretical and empirical literatures that lie beyond the scope of our paper. Examples would include the role of mental time travel in future decision making involving delayed rewards ( Boyer, 2008 ) and the literature on “affective forecasting” ( Wilson and Gilbert, 2005 ) as it relates to the ensemble components in persons experiencing depression or anxiety. Once again, future theorizing and research should explore the interrelationships of such constructs with the ensemble components as they pertain to the etiology and phenomenology of MDD and GAD.

In review, we believe that similarities and differences between MDD and GAD are best conceptualized by considering an ensemble of mental components. Although mental time travel plays a role in both disorders, this component is influenced by the interpreter that assigns causal attributions to events and a dysfunction in executive attention.

If depression is primarily a problem with faulty prospection, then it is reasonable to target future thinking as perhaps the most effective form of treatment. Roepke and Seligman (2016) reviewed four variations of CBT that emphasize positive expectancies, hopeful thinking, a focus on future-oriented solutions to problems, and goal setting and planning. Initial results with each of these approaches have been positive and are worthy of additional study in randomized trials. Further, Roepke and Seligman (2016) suggest several new future-oriented interventions that might be considered (e.g., using visual imagery to imagine a route to future success).

While new approaches certainly merit exploration, we note that the premise underlying these—namely, that faulty prospection is the core causal process in depression—is open to debate. We believe that the effects of the interpreter and executive attention, in conjunction with mental time travel, should be considered to better understand both MDD ( Figure 1 ) and GAD ( Figure 2 ). From this ensemble perspective, therapies should target all three components rather than focusing only on mental time travel.

For example, mindfulness-based therapies including short-term meditation explicitly address deficits in executive attention. A short-term program (5 days of training for 20 min per day) has been shown to improve attention and self-regulation in a sample of healthy young adults ( Tang et al., 2007 ). Such mindfulness-based interventions have been shown to minimize relapse and offer promise in the treatment of acute symptoms of depression and anxiety, although more research is needed to clearly establish their clinical efficacy ( Edenfield and Saeed, 2012 ). In a different approach, training attention using computer-based tasks has been found beneficial in treating generalized social anxiety disorder ( Schmidt et al., 2009 ). If anxiety disorders as well as depression primarily are influenced by the mental time travel component ( Miloyan et al., 2014 ), then it is difficult to explain why treatments targeting the executive attention deficit would be effective. Yet, it is known that executive functioning matters. Although neurocognitive abilities can improve with CBT treatment for anxiety and depression, individuals with poor attentional control show decreased benefit from such treatment compared to those with adequate executive skills ( Devito et al., 2018 ).

Many techniques in traditional CBT build on the premise of altering the pessimistic explanatory styles employed by depressive and anxious individuals. These techniques are based on the premise that the symptoms and dysfunctional behaviors of these disorders are mediated by cognitive factors. The therapeutic goal, then, is to restructure the dysfunctional thinking and beliefs underlying the disorder. Cognitive distortions must be identified and refuted in restructuring the functions of the interpreter. The evidence supporting CBT as an effective treatment of both anxiety and depression is solid ( Butler et al., 2006 ). As Roepke and Seligman (2016) pointed out, CBT interventions already include a number of techniques that improve future thinking. Even so, the aim of CBT is to alter thinking patterns in general, including past and present thinking as well as future thinking. It is not clear that new approaches that emphasize future-oriented thinking only would be, or even should be, superior to standard CBT.

In terms of future directions, transdiagnostic psychotherapies for depression and anxiety ( Clark, 2009 ) could potentially be understood within and informed by the aspects of the ensemble hypothesis. The ensemble models shown in Figures 1 , ​ ,2 2 suggest that a unified approach to CBT plus mindfulness/attention training might well be plausible for treating both depressive and anxiety disorders. Finally, in recent years, network approaches to psychopathology have emphasized the interplay of symptoms across a variety of traditionally defined, yet comorbid, disorders ( Borsboom and Cramer, 2013 ). The psychopathology network approach contends that such emotional disorders arise from interactions among symptoms, as well as their reciprocally reinforcing relationships ( Borsboom, 2017 ). It may be possible to conceptualize these networks of psychopathology within the context of the ensemble hypothesis of human cognition considered here.

Data Availability Statement

Author contributions.

RK developed the concept of the paper. RK and CC wrote the first draft. JG contributed with advice and revisions to subsequent drafts. All authors reviewed the final manuscript.

Conflict of Interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Funding. The funds required for open access fees required to publish this article were provided through Faculty Development accounts available to the first and third authors from the Department of Psychology at Saint Louis University.

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December 20, 2014

How Virtual Time Travel Affects Our Feelings about the Past and Future

"Too late" might be the two most tragic words in English, but what if you could rewind the clock? What if the past was not immutable? Would we regret past bad decisions more or less?

By Susana Martinez-Conde

This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American

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“Too late” might be the two most tragic words in English, but what if you could rewind the clock? The possibility of changing the past has captivated the imaginations of writers and filmmakers, like in Stephen King’s recent novel “ 11/22/63 ”, about a time traveler who tries to prevent Kennedy’s assassination, or the movie “ Looper ”, in which criminal organizations send their enemies back in time to be killed by paid assassins there. Most physicists agree that time travel is not possible in our universe, but our brains beg to differ. We constantly engage in mental time travel, revisiting our past experiences and decisions to ponder different outcomes. Alas, the actual past is immutable, and we must sooner or later disengage our imagination to confront reality and deal with our past choices. Plus any associated regret. But what if the past was not immutable? Would we regret past bad decisions more or less? Since our brains create our experience of reality, what if we could make our brains believe that the past is pliable? How would such an illusion affect the way that we would feel then about our past choices, and the moral decisions that we may face in the future?

Mel Slater and his colleagues at the University of Barcelona recently published a study that used immersive virtual reality to induce the illusion of realistic time travel in experimental participants, who traveled back in time to try to prevent a mass murder. The researchers also explored the moral dilemmas the subjects faced when given the opportunity to change the past.

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Before the experiment started, the scientists asked all subjects to secretly rate three past decisions that they regretted, on a scale of one to a hundred, with one hundred representing their greatest regret. The researchers kept the information in sealed envelopes, which they returned each subject for reevaluation at the end of his or her virtual reality performance.

The virtual reality scenario consisted of an art gallery with two levels: ground and upper. The participant played the role of an elevator operator that allowed visitors (computer-generated avatars) to access the two levels. The operator sat in a booth with the elevator’s controls on a panel, and could not only see the entire gallery from his or her station—including the elevator, which was an open platform that ascended or descended with a push-button command—but the operator could also see himself or herself in a mirror throughout the action. Besides the up and down button, the operator could set off an alarm that made a loud sound and froze the elevator in place—this becomes important as the story unfolds.

The operator’s job started off as tedious. Six visitors ramble into the gallery, poking around and looking at art, with five of them eventually deciding to browse the upper floor (the participant used the elevator controls to give them access). One visitor stays on the ground level. After the seventh guest arrives, all hell breaks loose. It turns out he’s a cold-blooded murderer (though the participant could not know this until the shooting begins). When the soon-to-be-bad guy asks to go to the upper level, the unwary participant grants him access as usual. But when he arrives at the upper floor the he whips out a gun and proceeds to execute the five people on the upper floor from the elevator platform. Chaos ensues. The visitors scream in fear and pain—Oh! The Humanity!—and they collapse in bloody heaps. Some visitors crouch on the floor hoping to remain unnoticed, but to no avail. A woman in a pink t-shirt stumbles over the bannister after being shot, and lands broken-bodied on the ground floor. It’s gruesome and horrifying!

As the nightmare develops, the participants’ mat realize that their hands are not tied… they have the power to choose one of three options. They can leave the elevator on the upper floor where the gunman may continue to kill until all five people are dead. They can send the elevator down, where there is only one visitor (which, if the participant reacts quickly enough, will result in a smaller death tally). Or they can activate the alarm to freeze the elevator in place (not useful since the gunman is already shooting).

The lurid scenario is a variation of the classic moral dilemma known as the “trolley problem”: an out of control trolley on a railway track will kill five workers, unless an operator diverts it to a different track, where it will kill a single worker. Asked what they would do in the operators’ place, most people choose to divert the trolley, sacrificing one person to save five. So it would seem that the majority of us would provide a rational solution to the trolley problem: the greatest benefit to the greatest number. Except that in another version of the trolley problem, the out-of-control trolley will kill five people unless a large man is pushed onto the track to stop the vehicle. In that case, only a minority of people choose to kill one man to save five. Diverting a train that kills a person is one thing, but to actually kill somebody directly with your own hands is something else. It may be irrational, but it makes a difference to most of us.

Back in the virtual reality scenario, the vast majority of participants chose to press the alarm once the shooting starts, rather than to immediately divert the murderer to the lower floor that has just one visitor. This was surprising as it seemed to contradict the trolley experiment findings. The alarm serves no purpose and affects the ongoing murder not at all. Whereas most people choose to divert the trolley to sacrifice one instead of five, here the participant usually chooses to allow the larger group to die in lieu of prompt action. The researchers reasoned that, unlike a scenario with only two possible solutions, if people have a third choice in which they don’t have to kill anybody, they will select that action most of the time, even if it results in a greater number of deaths overall. Again, it’s irrational, but it makes a difference to our brains.

At this point in the experiment, all participants had equivalent grisly experiences, but then they were split into two groups to relive their experiences in different ways. They were assigned to either a “Repetition” condition or a “Time Travel” condition. In the Repetition condition, participants simply played again and encountered the same exact sequence of choices as in the original scenario, though this time they had the benefit of past experience. In the Time Travel condition things got really interesting: subjects played again, but this time they saw their past selves carry out their own actions from the last session, and they now they had the option of interacting with the elevator buttons as the action played out again: they could now affect the past.

As a participant replaying the previous events, in either the Time Travel or the Repetition condition, you can achieve one of two solutions to thwart the gunman and prevent any deaths. First, once the gunman is in the elevator you can press the alarm while he was on his way up to the second floor, which freezes the elevator and traps the gunman before he can kill anybody. Second, you can keep all seven visitors downstairs and trap the gunman upstairs. Several subjects were able to implement the first solution, but nobody figured out the second option. One third possibility was to keep the gunman downstairs, but in that case the visitor programmed to remain on the ground floor would always die.

Each subject got to play three times: first the original condition, which was identical for each group, and then they either played two Time Travel sessions or two Repetition sessions. For the subjects assigned to the Time Travel group, the third time around depended on the actions they performed the second time. That is, every time history changed, the oldest mission was obliterated and the newest past mission became the frame of reference.

After the subjects completed all the virtual reality simulations, they were given questionnaires that evaluated the effectiveness of the illusions of body ownership, agency and presence in the virtual reality environment. These were fundamental to determine whether the virtual reality experience felt real to the subjects. Other questionnaires measured the strength of the time travel illusion other aspects of the participants’ experience, like how guilty they felt about harm to the victims. The subjects also had to think again about the personal regrettable decisions that they had scored before the experiment began, and they re-rated how much they regretted them. The researchers recorded the first and second scores, though they never knew the nature of the private regrets.

One point of all this was to find out if the Time Travel condition would produce a stronger time travel illusion than the Repetition condition—remember, both conditions involve reliving the past. The answer was that the time travel illusion was equally effective in either the Repetition or Time Travel conditions. Subjects who participated in the Time Travel condition had the strongest illusion of traveling to the past, but only when they also experienced a strong sense of ownership of their virtual body. The subset of subjects who experienced the time travel illusion also had stronger feelings of guilt about their involvement in the virtual scenario than those participants for whom the illusion of time travel was less potent. This makes intuitive sense: the guilt-ridden participants may have felt more guilt because they also felt that the people in the museum were more real, and were actually hurt. If so, the harm the victims suffered was, at least partly, a consequence of the participants’ actions (or non-actions, or mistakes). The guilty feelings were attenuated for the participants who reported that they had tried their best.

But the experimenters went further to ask a truly interesting question: Does the experience of illusory time travel affect people’s attitudes about moral dilemmas and their own private “bad decisions” in their personal life histories? The researchers’ thinking was that the brain cannot effectively distinguish between reality and virtual reality, and so it cannot fundamentally differentiate actual time travel from illusory time travel. If so, the virtual time travelers would implicitly learn that the past is not immutable. How would such (mis)perception affect their moral decisions?

Interestingly, the participants who experienced the time travel illusion most effectively felt less regret about previous poor decisions in their pasts, compared to how they felt before experiencing virtual time travel. The researchers conclusion about this is that, now that the subjects had been able to alter the past—despite the fact that it was all an illusion—their brains reacted to real biographical events as though they too may be mutable. An unconscious illusion of hope!

Finally, the subjects read several descriptions of moral dilemma scenarios (including three scenarios based on the classic trolley problem), and responded with a yes/no answer:

(a) Boxcar 5—the boxcar by default will kill 5, throwing the switch will divert the boxcar to kill 1 instead. Question: would you throw the switch?

(b) Boxcar 1—the boxcar by default will kill 1, throwing the switch will divert the boxcar to kill 5 instead. Question: Would you throw the switch?

(c) Boxcar footbridge—the boxcar by default will kill 5. If a man with a heavy backpack is pushed onto the track from a footbridge where he and the observer are standing then the 5 will be saved but the man will be killed. Question: would you push the man off the footbridge onto the track?

Subjects who experienced the time travel illusion responded in more rational fashion to these dilemmas: they were more likely to opt to save the greater number of lives at the cost of sacrificing individuals. The investigators speculate that the illusion of time travel may have increased the subjects’ thinking about the future consequences of their actions, which would be greater for five deaths than for one death.

Among the many fascinating implications of this study, perhaps the most captivating has to do with the potential therapeutic advantages of virtual time travel. Some cognitive behavioral therapy techniques already use mental time travel to treat PTSD, incorporating an alternative appraisal of the traumatic experience into the patience’s memory of the event. Virtual time travel may offer a more compelling illusion that the past is mutable, and help to soften the impact of traumatic memories.

Physics tells us that our universe’s past will never change. But our conscious experience is a neural simulation of the universe that our brains create. Our neural circuitry creates a virtual reality of its own, which is the only reality that we have ever known. So there, in our consciousness, anything goes, and illusory time travel in virtual reality may be a suitable foil for an immutable past.

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Mental Time Travel? A Neurocognitive Model of Event Simulation

• Published: 30 April 2020
• Volume 11 , pages 233–259, ( 2020 )

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• Donna Rose Addis 1 , 2 , 3  

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Mental time travel (MTT) is defined as projecting the self into the past and the future. Despite growing evidence of the similarities of remembering past and imagining future events, dominant theories conceive of these as distinct capacities. I propose that memory and imagination are fundamentally the same process – constructive episodic simulation – and demonstrate that the ‘simulation system’ meets the three criteria of a neurocognitive system. Irrespective of whether one is remembering or imagining, the simulation system: (1) acts on the same information, drawing on elements of experience ranging from fine-grained perceptual details to coarser-grained conceptual information and schemas about the world; (2) is governed by the same rules of operation, including associative processes that facilitate construction of a schematic scaffold, the event representation itself, and the dynamic interplay between the two (cf. predictive coding); and (3) is subserved by the same brain system. I also propose that by forming associations between schemas, the simulation system constructs multi-dimensional cognitive spaces, within which any given simulation is mapped by the hippocampus. Finally, I suggest that simulation is a general capacity that underpins other domains of cognition, such as the perception of ongoing experience. This proposal has some important implications for the construct of ‘MTT’, suggesting that ‘time’ and ‘travel’ may not be defining, or even essential, features. Rather, it is the ‘mental’ rendering of experience that is the most fundamental function of this domain-general simulation system enabling humans to re-experience the past, pre-experience the future, and also comprehend the complexities of the present.

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Acknowledgements

I gratefully acknowledge the editors of this Special Issue who also organized the Otago Mental Time Travel Symposium that served as inspiration for the paper, and the comments of anonymous reviewers. This work was supported thanks to funding from the Canada 150 Research Chairs Program.

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Addis, D.R. Mental Time Travel? A Neurocognitive Model of Event Simulation. Rev.Phil.Psych. 11 , 233–259 (2020). https://doi.org/10.1007/s13164-020-00470-0

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The passage of time is all in your mind. 

Human brains independently measure episodic movement — that’s a trippy finding reported by French and Dutch researchers in a new study published Monday in the Journal of Neuroscience . 

Our brains possess “an internal or inherent flow of time, that was not driven by something going on in the external world,” neuroscientist and lead study author Leila Reddy told Vice of her team’s findings, which she referred to as evidence of the human mind’s “mental time travel” ability.

To get evidence of this hard-to-conceptualize concept, Reddy and her team studied the brains of epileptics who already needed invasive electrode implants in their brains independent of the research. 

“These patients have severe, drug-resistant epilepsy and are awaiting surgery,” Reddy told Vice of the study participants. “Part of the pre-surgical procedure involves implanting electrodes in the brain to monitor seizure activity. Once the electrodes are inserted in the brain, we ask the patients if they are willing to participate in short experiments for us, and we can record from single neurons to test different hypotheses.” 

Researchers found the participants’ brains’ “time cells” fired at specific moments, including moments when there weren’t external stimuli, suggesting they were responding to an internal sense of sequencing. 

“I think a big question here is to ultimately understand how memories are encoded,” Reddy told Vice. “Episodic memory, in particular, is the memory of what happened, when, and where. Time cells could provide the scaffolding for representing the ‘when.’ Emerging evidence suggests that the same hippocampal neurons might also encode the ‘where’ and the ‘what,’ providing a broader framework for encoding memories.”

Moving forward, to better understand how humans process time, she believes researchers will need to look even closer at the mechanisms by which the brain encodes both time’s passage and memories. 

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Physicist explains why time travel isn’t possible

(Credit: Georgi Kostadinov/Flickr )

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A simple question from his wife—Does physics really allow people to travel back in time?—propelled physicist Richard Muller on a quest to resolve a fundamental problem that had puzzled him throughout his career: Why does the arrow of time flow inexorably toward the future, constantly creating new “nows?”

“The future does not yet exist … it is being created.”

That quest resulted in a new book called NOW: The Physics of Time (W. W. Norton, 2016), which delves into the history of philosophers’ and scientists’ concepts of time, uncovers a tendency physicists have to be vague about time’s passage, demolishes the popular explanation for the arrow of time,“ and proposes a totally new theory.

His idea: Time is expanding because space is expanding.

“The new physics principle is that space and time are linked; when you create new space, you will create new time,” says Muller, a professor emeritus of the University of California, Berkeley.

In commenting on the theory and Muller’s new book, astrophysicist Neil deGrasse Tyson, host of the 2014 TV miniseries Cosmos: A Spacetime Odyssey , writes, “Maybe it’s right. Maybe it’s wrong. But along the way he’s given you a master class in what time is and how and why we perceive it the way we do.”

How our brains create ‘mental time travel’

“Time has been a stumbling block to our understanding of the universe,” adds Muller. “Over my career, I’ve seen a lot of nonsense published about time, and I started thinking about it and realized I had a lot to say from having taught the subject over many decades, having thought about it, having been annoyed by it, having some really interesting ways of presenting it, and some whole new ideas that have never appeared in the literature.”

The origin of ‘now’

Ever since the Big Bang explosively set off the expansion of the universe 13.8 billion years ago, the cosmos has been growing, something physicists can measure as the Hubble expansion. They don’t think of it as stars flying away from one another, however, but as stars embedded in space and space continually expanding.

Muller takes his lead from Albert Einstein, who built his theory of general relativity—the theory that explains everything from black holes to cosmic evolution—on the idea of a four-dimensional spacetime. Space is not the only thing expanding, Muller says; spacetime is expanding. And we are surfing the crest of that wave, what we call “now.”

How far into the future are you still yourself?

“Every moment, the universe gets a little bigger, and there is a little more time, and it is this leading edge of time that we refer to as now,” he writes. “The future does not yet exist … it is being created. Now is at the boundary, the shock front, the new time that is coming from nothing, the leading edge of time.”

Because the future doesn’t yet exist, we can’t travel into the future, he asserts. He argues, too, that going back in time is equally improbable, since to reverse time you would have to decrease, at least locally, the amount of space in the universe. That does happen, such as when a star explodes or a black hole evaporates. But these reduce time so infinitesimally that the effect would be hidden in the quantum uncertainty of measurement—an instance of what physicists call cosmic censorship.

“The only example I could come up with is black hole evaporation, and in that case it turns out to be censored. So I couldn’t come up with any way to reverse time, and my basic conclusion is that time travel is not possible,” he says.

Merging black holes

Muller’s theory explaining the flow of time led to a collaboration with Caltech theoretician Shaun Maguire and a paper posted online in June that explains the theory in more detail—using mathematics—and proposes a way to test it using LIGO, an experiment that detects gravitational waves created by merging black holes.

“The idea of studying time itself did not exist prior to Einstein. Einstein gave physics the gift of time.”

If Muller and Maguire are right, then when two black holes merge and create new space, they should also create new time, which would delay the gravitational wave signal LIGO observes from Earth.

“The coalescing of two black holes creates millions of cubic miles of new space, which means a one-time creation of new time,” Muller says. The black hole merger first reported by LIGO in February 2016 involved two black holes weighing about 29 and 36 times the mass of the sun, producing a final black hole weighing about 62 solar masses. The new space created in the merger would produce about 1 millisecond of new time, which is near the detection level of LIGO. A similar event at one-third the distance would allow LIGO to detect the newly created time.

‘I expect controversy!’

Whether or not the theory pans out, Muller’s book makes a good case.

“[Muller] forges a new path. I expect controversy!” writes UC Berkeley Nobel laureate Saul Perlmutter, who garnered the 2011 Nobel Prize in Physics for discovering the accelerating expansion of the universe. Muller initiated the project that led to that discovery, which involved measuring the distances and velocities of supernovae. The implication of that discovery is that the progression of time is also accelerating, driven by dark energy.

For the book project, Muller explored previous explanations for the arrow of time and discovered that many philosophers and scientists have been flummoxed by the fact that we are always living in the “now:” from Aristotle and Augustine to Paul Dirac—the discoverer of antimatter, which can be thought of as normal matter moving backward in time—and Albert Einstein. While philosophers were not afraid to express an opinion, most physicists basically ignored the issue.

“No physics theories have the flow of time built into them in any way. Time was just the platform on which you did your calculations—there was no ‘now’ mentioned, no flow of time,” Muller says. “The idea of studying time itself did not exist prior to Einstein. Einstein gave physics the gift of time.”

Team detects ripples in spacetime, just as Einstein predicted

Einstein, however, was unable to explain the flow of time into the future instead of into the past, despite the fact that the theories of physics work equally well going forward or backward in time. And although he could calculate different rates of time, depending on velocity and gravity, he had no idea why time flowed at all. The dominant idea today for the direction of time came from Arthur Eddington, who helped validate Einstein’s general theory of relativity. Eddington put forward the idea that time flows in the direction of increasing disorder in the universe, or entropy. Because the Second Law of Thermodynamics asserts that entropy can never decrease, time always increases.

Was Stephen Hawking wrong?

This idea has been the go-to explanation since. Even Stephen Hawking, in his book A Brief History of Time , doesn’t address the issue of the flow of time, other than to say that it’s “self-evident” that increasing time comes from increasing entropy.

“I don’t see any way that it affects our everyday lives. But it is fascinating.”

Muller argues, however, that it is not self-evident: it is just wrong. Life and everything we do on Earth, whether building houses or making teacups, involves decreasing the local entropy, even though the total entropy of the universe increases. “We are constantly discarding excess entropy like garbage, throwing it off to infinity in the form of heat radiation,” Muller says. “The entropy of the universe does indeed go up, but the local entropy, the entropy of the Earth and life and civilization, is constantly decreasing.

“During my first big experiment, the measurement of the cosmic microwave radiation, I realized there is 10 million times more entropy in that radiation than there is in all of the mass of the universe, and it’s not changing with time. Yet time is progressing,” he says. “The idea that the arrow of time is set by entropy does not make any predictions, it is simply a statement of a correlation. And to claim it is causation makes no sense.”

In his book, Muller explains the various paradoxes that arise from the way the theories of relativity and quantum mechanics treat time, including the Schrodinger’s cat conundrum and spooky action at a distance that quantum entanglement allows. Neither of these theories addresses the flow of time, however. Theories about wormholes that can transport you across the universe or back in time are speculative and, in many cases, wrong.

The discussion eventually leads Muller to explore deep questions about the ability of the past to predict the future and what that says about the existence of free will.

Muller admits that his new theory about time may have observable effects only in the cosmic realm, such as our interpretation of the red shift—the stretching of light waves caused by the expansion of space—which would have to be modified to reflect the simultaneous expansion of time. The two effects may not be distinguishable throughout most of the universe’s history, but the creation of time might be discernible during the rapid cosmic inflation that took place just after the Big Bang, when space and time expanded much, much faster than today.

He is optimistic that in the next few years LIGO will verify or falsify his theory.

“I think my theory is going to have an impact on calculations of the very early universe,” Muller says. “I don’t see any way that it affects our everyday lives. But it is fascinating.”

Source: UC Berkeley

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ORIGINAL RESEARCH article

A neuroeconomic theory of mental time travel.

• 1 Department of Economics, University of Southern California, Los Angeles, CA, United States
• 2 CEPR, London, United Kingdom

We propose a theoretical model that places attention at the center of mental time travel (MTT) ability. This theory predicts that attention promotes a memory-based process that encodes memories of unexpected events, facilitates accurate recollection of information of such events during MTT, and optimizes subsequent decision-making. This process coexists with a habitual process that governs all other events and treats them equally. Our theory demonstrates that the memory-based process is useful when the environment features novel experiences that are likely to be relevant in future decision-making, hence worth remembering accurately. By contrast, the habitual process is optimal in environments that either do not change significantly, or have a small chance of being repeated in the future. This may explain why the ability to mentally travel in time has developed differently in humans than in other species. Implications are discussed in the context of decision-making.

1. Introduction

According to the classic Tulving theory ( Tulving, 1985a ), memory has the distinctive mission of permitting humans to mentally travel backwards and forwards in time. Mental time travel (MTT) allows us to recall past events to avoid dangers and choose the best future courses of action. Central to MTT is episodic memory, which processes memories of personal events and experiences and makes it possible to use past experiences to simulate future events or alternative pasts. Episodic memory summarizes sensory, perceptual, and emotional information and features a visual representation component. It is part of the declarative memory system, which encodes precise information that can be verbalized, but also easily forgotten ( Squire, 2004 ; Poldrack and Foerde, 2008 ) 1 . The relationship between episodic memory components and MTT has been widely documented. From a developmental perspective, MTT develops as soon as children understand the concept of “yesterday” and “tomorrow,” and in conjunction with the development of episodic memory ( Suddendorf and Busby, 2005 ; Hayne and Imuta, 2011 ). The MTT ability is also less developed in subjects with a poor visual imaginary or those who tend to suppress emotions ( D'Argembeau and Van der Linden, 2006 ).

The neural correlates of episodic memory are well-understood. Episodic memory involves the medial temporal lobe (MTL), which hosts the hippocampus. Dysfunction of the latter (amnesia) has been associated with either no memory of personal events or a difficulty in forming new memories about personal events further associated with no ability to project oneself in the future ( Tulving, 1985b ; Klein et al., 2002 ; Hassabis et al., 2007 ). The MTL is also implicated in episodic future thinking –or the construct of future possible scenarii– and episodic counterfactual thinking –or the simulation of alternative pasts– ( Schacter et al., 2015 ). Interestingly, episodic memory has been shown to interact with working memory ( Balconi, 2013 ). In particular, increased activation of the dorsolateral prefrontal cortex (dlPFC) during the formation of episodic memories results in their enhancement. Working memory also plays a role in the episodic buffer, which allows the use of old memories to form new ones. The dlPFC has been shown to have a causal role in episodic memory formation and to be responsible for suppressing memories through suppressing hippocampal processing ( Benoit et al., 2014 ). These findings taken together indicate that a neural circuit involving hippocampal regions and working memory regions are at the core of episodic memory. As such, we conjecture that an interplay between these structures affects the selection of memories worth being recalled in the future.

MTT is often believed to be uniquely human and to have been shaped through evolution ( Suddendorf et al., 2009 ). However, episodic memory capacity depends on a fundamental neural circuit that is similar across mammalian and avian species, which suggests a shared underlying neural ancestry rather than a specific human evolutionary trajectory ( Allen and Fortin, 2013 ). It is therefore still unclear to which extent this capacity supports MTT in animals ( Suddendorf and Busby, 2003 ; Suddendorf and Corballis, 2007 ). Working memory capacity is also believed to have evolved differentially across species, and humans are thought to be unique in some of the uses they make of it ( Carruthers, 2013 ). These differences in both MTT and working memory capacities between humans and non-humans may be related. Fitness depends on the environments that species encounter, and some environments require specific abilities to adapt. In theory, an environment requiring better prospective and processing capabilities may have triggered the evolution of modern human working memory and MTT abilities. Hence, the specific interplay between episodic memory and working memory might have been shaped by evolution differentially across species to adapt to different environments.

These observations taken together suggest that MTT ability is supported by episodic memory, which is involved in an interplay with the working memory system to encode memories of relevance as a function of the environment. Said differently, observations are compatible with the existence of a goal-directed (top down) memory management mechanism that allocates attentional resources to form memories with the objective of maximizing future rewards. In this article, we consider a stochastic environment that produces events relevant for decision-making. These can be memorized and later recalled to make decisions. We build a theoretical framework to identify the most efficient interplay between a system capable of forming memories at a cost (episodic memory) and a goal-directed mechanism that allocates attentional resources in order to best serve future decision-making in a given environment.

To identify such an efficient mechanism, we adopt an optimization approach. This approach is widely used in decision-making fields such as Economics, and has been applied to model behavior driven by interactions between brain systems ( Bernheim and Rangel, 2004 ; Brocas and Carrillo, 2008 , 2014 ). This approach consists of endowing brain systems (e.g., those involved in goal-directed attention) with the ability to optimize their behavior (e.g., allocate attention) conditional on the stimulus they receive (e.g., features of an event) and the goal to fulfill (e.g., the relevance of the event in future decisions) 2 . This approach captures two critical features of brain processing. First, it recognizes brain modularity and the fact that each system is handling a specific task. Second, it envisions systems as being tuned to operate efficiently to interpret the information they receive and to formulate a response.

2. Remembering the Past to Predict the Future

2.1. the basic model.

We consider a mathematical formulation of MTT, which extends and complements the simple two-memory system representation introduced by Brocas and Carrillo (2016) . We use a deliberately simplistic car-parking example to illustrate this theory. First, an event occurs. It corresponds to the location in the parking lot where the individual (from now on “he") has parked in the morning. We denote this event by x . The event can be conceptualized as a draw from the random variable X which, in our example, is simply the distribution of parking spots that the person has been using in the past. We assume that X follows a normal distribution:

This means that the person usually parks around the spot θ. The parameter p , the precision (or inverse of the variance) of the random variable X , captures how much the draw varies from day-to-day. In our example, it represents how congested the parking lot is, and therefore how likely it is to find a spot near θ. By abuse of language we will refer to θ, the average of the distribution, as a “typical” realization of the event.

The individual needs to form a memory about the event. He recruits the episodic memory for this purpose. In our example, the memory represents the individual's recollection of the spot where he parked his car in the morning. To model imperfect recollection of events, we assume that when the individual travels back in time at a later date, his memory m of the true event x is given by:

The memory is a distorted representation of the true event. The size of the distortion is inversely related to the amount of attentional resources e invested when forming the memory. More precisely, the distortion takes the form of a noise u that follows a normal distribution with mean 0 and precision e . In expectation, the memory is correct, that is, there is no systematic bias in the distortion: E ( m ) = x . Under infinite attention ( e = +∞), the individual will perfectly recall the state ( m = x with certainty), and with no attention ( e = 0), the recollection is infinitely vague. Given attentional resources are scarce, there is an opportunity cost of allocating them to this task. We assume that the cost of attention is increasing and convex, formally represented by a quadratic cost function c ( e ) = e 2 /2. Thus, the main difference relative to Brocas and Carrillo (2016) is that, in the present paper, the individual chooses between a continuum of possible levels of attention ( e ∈ [0, +∞)) rather than only two levels ( e 1 and e 2 with e 2 > e 1 > 0).

The recollected memory m is used to plan an action a . In the context of our example, the action of the individual is where to look for his car when it is time to go home. The individual obtains a payoff inversely related to the distance between the true location and the location where the individual looks. Again for simplicity, we model this payoff with a standard quadratic utility loss function:

with l > 0. According to this formulation, if the event (true location) x is recalled with exactitude ( m = x ), the individual's optimal action is:

This simply means that it is optimal to look for the car wherever it is located. Deviations from ã( x ) –looking for the car in a different spot– implies a loss (e.g., a time delay or a longer walk) which increases with the absolute distance | a − x | and the sensitivity of the individual to losses ( l ). The timeline of the decision process is summarized in Figure 1 .

Figure 1 . Timing of the decision making problem.

This individual decision problem has standard multi-stage features. It is formally solved by backward induction.

2.2. Optimal Action Given Available Memory

If a finite amount of attention e has been allocated to the task, the true location will not be recalled with exactitude. Instead an (imperfect) memory m will be retrieved. Given that memory, the action that maximizes the expected payoff is:

where F e ( x | m ) is the revised cumulative distribution function of the event x given the attention exerted ( e ), and the memory ( m ). Given a quadratic objective function, the optimal decision satisfies the first-order condition and is given by:

where E e is the expectation operator. The optimal action coincides with the expected belief about the event given the memory retrieved. The normality assumption of the variables X and u implies that:

According to (3), the memory is centered around the true event x but with a distortion that depends inversely on the attentional effort e . Once a memory is retrieved, the updated belief about the event ( X | m ) is a random variable. Its expected value is a convex combination of the prior θ and the memory m . Combining Equations (2, 3), we can rewrite the optimal action as:

Given limited attention, memories are known to be imperfect and therefore cannot be fully trusted. Hence, in our example, it is optimal for the individual to look for his car not where his memory tells him to ( m ) but, instead, somewhere between the typical location and where his memory tells him to (between θ and m ). If more attention has been dedicated to memorize the event ( e high), the memory is more reliable, so the action is closer to the memory. The action is also closer to the memory when the dispersion in choices is higher ( p low) since, in that case, the knowledge about the typical location is less valuable. This is summarized as follows (proofs of all Propositions can be found in the Supplementary Material section).

Proposition 1. Suboptimal actions are the result of imperfect memories and they are modulated by attention. Individuals can trust their memories more if they are highly attentive (e high) and if their typical behavior is less reliable (p low) .

2.3. Optimal Attention Anticipating the Future Action

We now use backward induction to determine the optimal attention e * in stage 2 given the anticipated optimal action a * to be exerted in stage 4 as determined in Equation (4) (see Figure 1 ).

After observing the event x , allocating attention e affects the distribution from which memories are drawn, which we denote by G e ( m | x ). Given a memory m , the action will subsequently be a * ( m , e ) = E e [ X | m ] . Therefore, the expected payoff of allocating attention e , net of opportunity costs, is:

It is optimal to allocate resources that achieve the highest expected payoff, namely:

which leads to the following conclusion:

Proposition 2. There exists a range of events [ x , x ] containing the typical event ( x < θ < x ) such that it is optimal not to exert any attention (e * = 0) when the realization of the event falls in that range. Some level of attention is optimal (e * > 0) when the realization falls outside that range ( x ∉ [ x , x ]). In that case, attention increases as the event moves away from the typical realization .

The idea behind this result is simple. The event is a stochastic variable centered around θ. When the current realization of the event is sufficiently close to this value (| x − θ| small), it is not worth remembering. Instead it is a better strategy to save on attentional resources, act as if the location is θ and incur a moderate loss − l ( x − θ) 2 . This case corresponds to a form of “habitual thinking,” that is a thinking process based on general prior information rather than accurate information. By contrast, when the realization is sufficiently far from it (| x − θ| large), it is worth exerting attention to remember the event with precision and avoid an action excessively far from the optimal one. In our example, if the individual has parked the car near the typical spot θ, it is worth not paying any attention and looking in that spot first, but if the individual has parked very far from it, then it is worth remembering the location with some accuracy.

Overall, when x is observed, the individual exerts an optimal level of attention e * and the average action he undertakes is given by:

The optimal solution of the problem is summarized in Figure 2 . The individual exerts more attention when the realized event is far from typical (Figure 2A ) resulting in an action that is more congruent with the event (Figure 2B ). Events that are close to typical ( x ∈ [ x , x ]) do not require any attention to be memorized and they are followed by typical actions (θ).

Figure 2 . Optimal mechanism. (A) No attention is allocated ( e * = 0) when the event is close to typical ( x close to θ) and attention increases as the event becomes more unexpected ( x far from θ). (B) In the absence of memory limitations, actions should follow the 45 degree line. Under memory limitations, actions are based on prior knowledge ( a * = θ) when no attention has been allocated ( x ∈ [ x , x ]) and it is based on the memory signal when attention has been allocated. As events are more extreme, memory signals are less distorted, and actions are closer to optimal.

2.4. Modulating Attention and Choice

Attention and actions are modulated by features of the environment. We can perform comparative statics to measure how changes in specific features of the problem affect the amount of attention exerted and the subsequent action undertaken.

2.4.1. The Effect of Stakes

Stakes are captured in our setting with the parameter l , that measures the sensitivity to losses. Not surprisingly, the optimal level of attention is increasing in the sensitivity to losses. If the individual expects to incur a large disutility of not finding his car quickly, he should allocate more attention to the formation of a reliable memory. This in turn impacts the decision. With a higher sensitivity to losses comes greater attention, and therefore more reliable memories. These memories are trusted more, which is reflected in actions closer to the memory and farther away from the typical event. We represent this effect in Figure 3 .

Figure 3 . Effect of stake. Optimal attention (A) and decisions (B) under low stakes (full line) and high stakes (dashed lines). As stakes increase, attention increases and actions are on average closer to the event. Also, the range of events for which no attention is exerted shrinks.

Note that l can equally capture the likelihood that the information contained in the event will be useful in the future. Under this interpretation, our theory predicts that it is efficient to invest more attention when this likelihood increases.

Proposition 3. As stakes increase, attention increases, making memories more precise and reliable. As a result, actions rely more heavily on the memory and less on the typical event .

2.4.2. The Effect of the Environment

We can compute the expected payoff of the individual before the realization of the event and anticipating that he will allocate an optimal amount of attention. It is given by:

In terms of our example, it represents the expected utility of the individual when he is going to work and has not yet parked his car. Interestingly, the individual is better-off when the distribution from which the event occurs is concentrated around its mean (high p ) or, in our example, when he frequently finds a parking spot close to the typical location. This means that, even though the individual optimally reacts to extreme events by exerting more attention, he still benefits when such events do not occur frequently. An environment that changes little offers a guarantee to obtain safe rewards at minimal cost.

Proposition 4. Environments in which events do not vary much (high p) are conducive of habitual thinking and yield high expected rewards .

Notice that by choosing attention over a continuum of options, we can determine the marginal effect of stakes and events on the optimal level of attention. Perhaps more importantly, this model delivers new results relative to Brocas and Carrillo (2016) . In particular, we can show that no attention is sometimes optimal and that the individual is better-off when the environment does not change significantly. These results have behavioral and neurophysiological implications that are discussed in the next section.

3. Implications of the Theory

According to our theory, decision-making that requires knowledge of previous events is optimized through an interplay between the episodic memory system (with capabilities to form memories) and the attentional system (with capabilities to enhance memories). This interplay is orchestrated by goal-directed mechanisms that select relevant memories and optimize their collection to best serve decision-making. This overall process makes it possible to recall past events with more or less accuracy, and to simulate future rewards informed by past memories. Importantly, our model also shows that memories and behavior resulting from this process are modulated by a series of parameters describing the environment in which decisions are made.

3.1. Dual Process Theories

The central result of the theoretical section is the existence of two regimes, one in which events are not memorized and decisions are based on prior information and another in which events are memorized and (imperfectly) recollected to optimize decision-making. As such, our theory provides support for the coexistence of a habitual process (which operates in the limit, when attentional resources are too difficult to be recruited or not worth the cost) and a memory-based process (which is modulated by the amount of attentional resources allocated to the task). These correspond to events that fall inside and outside the range [ x , x ], respectively (see Figure 2 ).

The habitual process is optimal when events are close to typical ( x close to θ), and when decisions are not very important ( l small). It is an efficient process associated with simple strategies that rely on prior information about the environment. However, whenever stakes increase or events are rare, the costly memory-based process should be activated to help integrate the important specific features into decisions. This theoretical finding is consistent with the existing literature. Indeed, behavioral studies have suggested that we often use heuristics that rely on limited information about past events ( Bröder and Schiffer, 2003 , 2006 ). Recent neuroimaging analyses have also shown that processing more precise information requires a memory-based process that taxes regions involved in working memory, such as dlPFC ( Khader et al., 2011 , 2016 ). Our theory rationalizes these findings and identifies the conditions under which heuristic-based decision-making (which does not require precise memory or the ability to simulate the future based on the past) is efficient and when it should be replaced by a costly memory-based process. Moreover, the theory predicts that structures involved in working memory should be recruited when events are far from typical (or unexpected), which is consistent with evidence implicating the dlPFC in these types of events ( Kapur et al., 1997 ; Fletcher et al., 2001 ).

3.2. Dysfunctions

Our theory can be extended to address the behavioral implications of dysfunctions of the two main systems involved in memory formation, namely working memory and episodic memory.

3.2.1. Working Memory Dysfunction

Critical to our results is the working memory system that makes it possible to form and recall episodic memories of relevance for decision making. In the context of our model, the disorder can be captured by rescaling the cost function. More precisely, the cost of attention can vary across individuals and be given by c ( e ) = α e 2 /2 where α represents the idiosyncratic cost of a unit of attention (in the basic model, α = 1). This modification affects the cost-benefit trade-off reported in section 2.4. Using the same methodology as in section 2, we notice that the optimal allocation of attention is decreasing in α (see the Appendix in Supplementary Material for the formal derivation). Said differently, this theory predicts that dysfunctions of the working memory system result in the allocation of fewer resources to remember events. As the cost of attention increases, the region [ x , x ] becomes larger. This, in turn, implies that the habitual process becomes more prevalent and decisions are more often based on the typical realization of events rather than on accurate information. Interestingly, working memory disorders (such as attention deficit hyperactivity disorders) have been associated with episodic memory deficits in particular in complex memory tasks ( Felton et al., 1987 ; Quinlan and Brown, 2003 ). Working memory disorders generally relate to the inability to allocate attention to the task at hand or for the duration required to complete it. Individuals act as if allocating attentional resources is extremely costly and decision-making trade-offs turn to favor limited attention. This description is consistent with the predictions of the model: when working memory becomes taxing, it is optimal to rely on habitual processes.

3.2.2. Episodic Memory Dysfunction

Mental time travel abilities have been shown to not work properly in amnesic patients, who can neither remember episodic memories nor simulate future events ( Klein et al., 2002 ). Amnesia refers to the inability to encode memories and is an extreme case of an episodic memory dysfunction. Such dysfunction can be accommodated in our model by assuming that after exerting an amount of attention e , the memory is actually encoded with probability q and it is not encoded with probability 1 − q . Our basic model would correspond to q = 1, whereas the case of an amnesic patient incapable of forming any memory would correspond to q = 0. This limited ability to form memories affects the optimal allocation of attention as well as subsequent decisions. Indeed, individuals who form memories only very rarely (low q ) should exercise less attention because the latter is likely to be wasted. Said differently, the theory predicts that dysfunctions of the episodic memory system result in allocating fewer resources to remembering events. As the probability of actually encoding memories decreases, the region [ x , x ] becomes larger. Dysfunctions of episodic memories also yield choices closer to heuristic decision-making. This, as in the case of a working memory dysfunction, translates into decisions that rely heavily on the habitual process. In the limit case in which no memory can be formed ( q = 0), the individual is not able to simulate past events to make decisions and relies exclusively on the habitual system ([ x , x ] takes the entire support).

In sum, dysfunctions of the working memory system and the episodic memory system will result in an increased difficulty to form new memories and simulate future events based on these memories. It will also imply an increased tendency to resort to the habitual memory system. Conditional on the dysfunction, this is the best response of the individual to his environment. However, from the perspective of an outside observer, behavior will appear to not reflect the true information contained in the events and to rely on inadequate heuristic rules. This prediction is consistent with the evidence reported in the case of clinical populations, in particular for patients suffering from amnesia ( Klein et al., 2002 ), stress disorders ( Brown et al., 2014 ), schizophrenia ( Aleman et al., 1999 ) and other related dysfunctions of hippocampal regions. Similar memory disorders are also observed as a consequence of normal aging ( Friedman, 2013 ) or neurodegenerative diseases such as Alzheimer's, Parkinson's and Huntington's diseases ( Panegyres, 2004 ), that gradually cause episodic memory dysfunction or executive dysfunctions that affect working memory.

3.3. Value-Based Decision-Making

Recent literature in neuroscience has dedicated much attention to value-based decision-making. These decisions involve the choice between options of different values that need to be constructed and compared. This paradigm is used to describe neural correlates of economic choices between items in situations involving time delays, uncertainty or risk. The evidence supports the existence of a common reward system ( Levy and Glimcher, 2012 ). It also shows that decisions may be modulated by activity in regions involved in working memory (such as the dlPFC) in situations requiring more detailed or higher-order information, such as food choices subject to self-control problems ( Hare et al., 2009 ). It is plausible that this activity is related to the retrieval of information encoded in the past and relevant to the current decision. Recent research focuses on the interplay between episodic memory and value based decision-making ( Weilbächer and Gluth, 2016 ), but our understanding of these relationships is still limited. Our theory provides a framework to understand how value is formed at the date of decision as a function of how prior information is encoded. We illustrate these concepts with two examples.

3.3.1. Self-Control in the Food Domain

Let us consider the standard paradigm used in the literature on value and self-control. Suppose that X represents the health characteristic of food items. The individual tries food item x and learns its health characteristic. This information may be used in a future consumption episode. Knowing the exact characteristic of the food yields optimal consumption decisions. Our model predicts that this information will not be memorized if it is close to typical. The habitual process will feed a habitual value formation and a habitual behavior, while a memory-based process will help the individual choose the behavior that best fits his needs. Furthermore, our theory also implies that the item will be treated as healthier than it really is if x < θ, and therefore is over-consumed. Similarly, the item will be treated as less healthy than it really is if x > θ, and therefore is under-consumed. Overall and as illustrated in Figure 4A , our theory argues that the efficient memory management process is at the core of biases in behavior.

Figure 4 . Value-based decisions. (A) Items that are less healthy (healthier) than typical will be imperfectly memorized when they are unexpected and not memorized if they are close to typical. In both cases, they are over-consumed (under-consumed) in future episodes. (B) Due to imperfect memory, individuals over-invest (under-invest) in lottery tickets they have purchased in the past and turned out to be less (more) profitable than typical.

These biases will be exacerbated if the individual is impulsive and heavily discounts the future ( l is small) or has a working memory deficit. Interestingly, associations between impulsivity, low discounting and disrupted episodic future thinking have been observed among both healthy and obese subjects ( Daniel et al., 2013 ; Bromberg et al., 2015 ). Our model is consistent with these findings and suggests some mechanisms. A first possible cause might be an inherent attention deficit that prevents attentional resources to be allocated to the formation of memories. The episodic memory system itself may be intact, but not triggered when necessary. This hypothesis is appealing in the case of eating behavioral disorders, since research in this area has documented disruptions of the working memory system and in particular the dlPFC ( Seymour et al., 2015 ). Another mechanism involves an impaired episodic system that does not form efficient memories and makes the allocation of attentional resources wasteful. Interestingly, eating disorders are also associated with a dysfunction of the mesolimbic regions implicated in processing rewards ( Avena and Bocarsly, 2012 ) and these regions are critical for hippocampal memory formation ( Wittmann et al., 2008 ).

3.3.2. Risk Perception

Suppose that X represents the expected return of a risky investment (e.g., a lottery ticket). In a given event, the individual purchases a ticket x and learns whether it was a good investment. This information may be used in the future to determine whether to purchase it again or not. Our model predicts that lottery tickets associated with returns close to those of typical tickets will be treated equally. In particular, within that region, lottery tickets that have smaller expected returns than typical will be purchased too often (see Figure 4B ). Individuals will behave as if they take irrational risks or overestimate their chances of winning. Again, disruptions of the attentional system will exacerbate these inefficiencies. This idea is consistent with studies showing that pathologic gamblers exhibit disruption of this system ( Fujimoto et al., 2017 ). Alternatively, dysfunction of the episodic memory, which is known to be sensitive to reward outcomes, may affect the formation of memories and result in inefficient behavior ( Mason et al., 2017 ).

These results allow us to rationalize both the observed behavior and the neural correlates of behavior that have been reported in the literature. First, the observed interactions between episodic memory regions and attention related regions are a logical response to the need of optimizing memories in order to support decision-making. Second, the behavior resulting from these interactions is efficient. Biases in behavior are the by-product of attentional limitations imposed on information processing.

3.4. Time Perception Biases

The literature on time perception has reported numerous biases on the perception of objective time ( Wearden and Lejeune, 2008 ; Grondin, 2010 ). For instance, individuals who are told in advance that they will have to make a time judgment later recall time differently than individuals who are not ( Block and Zakay, 1997 ). Time perception can also be manipulated through emotional interventions, such as emotional sounds or pictures, which are likely to disrupt the encoding of relevant time-keeping information ( Droit-Volet and Meck, 2007 ; Fayolle et al., 2015 ). Indeed, evidence suggests that emotions modulate arousal and attention causing variations in the subjective perception of time ( Coull et al., 2004 ; Droit-Volet and Gil, 2009 ).

If we reinterpret x as the time at which the subject arrived at work this morning and a as the report he makes when asked later in the day (θ being his typical arrival time), our model predicts that these reports will vary as a function of the environment. If the individual anticipates that he will need to make a time judgment later and that his accuracy is important (high l ), the level of attention exerted to memorize the true time will be high, resulting in an accurate memory and a report close to that memory. If he does not anticipate it, he will behave as if the event is not linked to a future reward (low l ). He will then exert little or no attention and, as a consequence, will report an estimate at or around his usual arrival time. This suggests that the processes involved in retrospective and prospective time paradigms differ and are bound to produce different reports, reflecting implicit manipulations of reward functions.

Along the same lines, if the individual is distracted, overloaded or subject to emotions that impact the amount of attention he can allocate to the task, his behavior can be formally modeled in a similar way to a working memory dysfunction. Our theoretical prediction is that such an individual will be more likely to resort to the habitual system, and will exhibit a less accurate perception of time. Distractions and emotional manipulations will divert attentional resources and prevent the individual from forming correct memories of time. This is again consistent with evidence of increased inaccuracy in the case of mental workload and suggests that attention is central to temporal experience ( Brown and Boltz, 2002 ).

3.5. A Theory of Evolution

If memories are relevant to future choices, then the role of memory is to reconstruct past events to optimize future decisions and collect future rewards. However, if these operations require costly attention, not all events should be memorized and reconstructed equally. Events that are close to typical should not be encoded, since the prior knowledge of the environment is sufficient to guide future decisions with reasonable precision. As events become more striking, different from usual and/or contain important information for future decision-making, it is more important to remember them with accuracy. Overall, the relevance of memories to future rewards should determine the quality of those memories. This strongly suggests that the role of memory and MTT are context dependent. From our analysis, two basic features of the environment are relevant for MTT abilities. First, MTT is necessary when the environment is changing, featuring novel episodes constantly (in our model, large shifts in x relative to θ). This suggests that we will resort to costly attention mechanisms to remember rare experiences, but not everyday casual episodes. Hence, we will display the ability to travel back in time to precisely recall these rare experiences. Second, MTT is also necessary when the environment is likely to be relevant in the future (high l ). Costly attention mechanisms will be recruited for remembering episodes that we would like to repeat in the future, but not events that have no chance of occurring again.

The results obtained with our optimization approach are consistent with evolutionary explanations of the unique time travel human ability ( Suddendorf et al., 2009 ). Given evolution selects features that allow species to adapt to their environment, different evolution patterns should emerge across species as a function of differences in their respective environments. Species that are subject to an environment where the set of events is limited can efficiently operate based on a fixed or heuristic rule, that corresponds to acting as if events were always typical. These decisions do not require goal-directed attention. In such environments, there is no specific need for remembering events, and therefore no specific role for episodic memory or an interplay between episodic memory and attentional processes. This of course does not mean that episodic memory or attention systems have not developed in such species. It simply suggests that they did not need to develop for the purpose of using past events to optimize future decision-making, or that they did not need to develop to the extent humans did.

4. Discussion

The objective of our study was to identify the most efficient interplay between a system capable of forming memories (episodic memory) and a goal-directed mechanism that allocates attentional resources in order to best serve future decision-making. We have shown that the optimal way to manage memory formation entails an attention-free habitual system that categorizes events as typical when they are close to what is expected, and a costly memory-based mechanism that optimizes the future recollection of events when they are rare or unexpected. The latter relies on an interplay between brain structures involved in attention and episodic memory regions. The habitual mechanism generates heuristic rules always resulting in the same decision, while the memory-based process allows decisions to be modulated by true events, though imperfectly. This dual system permits an alignment of future decisions with past information in the most efficient way but it results in inefficiencies that depend on the environment. Inefficiencies are larger when events are not predicted to be useful in the future or when relatively rare events are treated as typical.

The conclusion that extreme outcomes are remembered more vividly than typical outcomes (Proposition 2 and Figure 2 ) relies on the assumption that subjects consciously optimize attention when forming memories. If, in a certain situation, an absent-minded person does not allocate attention as a function of the event, the result would be the opposite, namely a more reliable memory of typical than non-typical outcomes. In our motivating example, such person would be unable to locate the car whenever he parks it in an unusual spot.

Interestingly, and as discussed in section 3, the predictions of the model rationalize existing evidence in terms of both behavior and neural correlates. This has two implications. First, our study supports the idea that the brain processes information efficiently. The existence of different channels (e.g., cognitive or habitual) giving rise to different behavior (e.g., rational or heuristic) relies on a fundamental trade-off between the costs and benefits of information processing. A costly system is triggered when it is worth engaging it. In the context of MTT, our theory suggests that MTT is an invaluable ability when the environment produces events worth remembering. Second, our theory provides a conceptual framework to understand the role of attention in the formation of episodic memories as a function of the environment in which memories are formed. This suggests that the theory can be used to formulate hypotheses in new experimental paradigms. For example, one could design simple memory paradigms that would include a preliminary description of the distribution of experimental events, and would then ask participants to memorize individual events and to later recall them. The main theoretical predictions (Propositions 1 and 2) could be tested by comparing accuracy between expected and unexpected events and by contrasting neural activity across these two types of events. Attentional manipulations could further help assess the causality between attention and accuracy. Moreover, our theory suggests that stakes play a critical role in the formation of memories (Proposition 3). We conjecture that variations in stakes should be associated with differences in neural responses in both episodic memory and working memory regions. This hypothesis could be tested by designing incentivized memory experiments and varying the magnitude of the rewards for remembering accurately. Differences in accuracy should be correlated with differences in activation within regions involved in attention. Last, by comparing the average payoffs of subjects asked to recall similar or different pieces of information over the course of an experiment and by contrasting the patterns of neural activity within attention regions, one could assess whether habitual thinking is more prevalent and results in higher payoffs in environments in which events are more recurrent (Proposition 4). More generally, the model outlined here may be the starting point for a more general, testable neuroeconomic theory of decision-making with imperfect recall.

Author Contributions

All authors listed have made a substantial, direct and intellectual contribution to the work, and approved it for publication.

This work has received the support of the National Science Foundation, SES-1425062.

Conflict of Interest Statement

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Supplementary Material

The Supplementary Material for this article can be found online at: https://www.frontiersin.org/articles/10.3389/fnins.2018.00658/full#supplementary-material

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Keywords: declarative memory, mental time travel, neuroeconomic theory, memory-based process, attention

Citation: Brocas I and Carrillo JD (2018) A Neuroeconomic Theory of Mental Time Travel. Front. Neurosci. 12:658. doi: 10.3389/fnins.2018.00658

Received: 09 January 2018; Accepted: 03 September 2018; Published: 26 September 2018.

Reviewed by:

Copyright © 2018 Brocas and Carrillo. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY) . The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

*Correspondence: Isabelle Brocas, [email protected]

Disclaimer: All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article or claim that may be made by its manufacturer is not guaranteed or endorsed by the publisher.

Strength Essence

How to Practice Time Travel Meditation (With Your Mind)

Yes, it is possible to practice time travel meditation! I’ve done it, and so can you with a light body activation, the intention to time travel through meditation, and practice.

The mind, or your consciousness, is a very powerful tool that is not stuck in linear time, as we perceive it.

The records of your Soul have been kept (and continue to be kept) in the Akashic Records, and will show you details of your future, past, past lives, and alternate timelines if you know how to access them through meditation.

Time Travel Meditation FAQ

Table of Contents

Is Time Travel Possible through Meditation?

Time travel is possible during meditation, and I myself have done it several times. I’ve traveled back in time, to the future, and also to alternate timelines.

People often wonder if meditation time travel is possible and how to time travel in meditation. They also wonder if you can do an open eye meditation time travel.

I have never done an open eye time travel meditation simply because it is harder to get into the “Meditation Zone” necessary for accessing your time travel records during meditation. I’m sure it is possible, but probably takes much more practice.

Can Bad Things Happen on Time Travel Meditation?

You may see something during your time travel meditation that scares or excites you enough to pull you out of “viewing” your past or future self.

But, the key word here is “viewing”. You are safe within your physical body in your home, or wherever you’ve chosen to do your time travel meditation.

Your consciousness will safely return to your body once you are done traveling to the past with your mind (or the future).

When you begin working with your Akashic Records and 8th Chakras, you may be fearful that you’ll see something bad, painful, or scary during your time travel meditation.

Time travel meditation IS NOT inherently evil, or bad, or will otherwise harm your physical body in any way.

I ALWAYS ask Archangel Michael to protect me while I am practicing my meditation to time travel.

How to Travel Back in Time with your Mind

Time traveling to the past with your mind can be done in a variety of ways. When I first time traveled during meditation, it was an accident.

Since then, I’ve traveled to the past, past lives, alternate timelines, and future timelines (so I could change the course of my life in the present for the better).

Here are the specific steps I’ve taken now when I wish to see the past through meditation, the future, or even past lives, and alternate timelines.

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1. Activate Your Star Tetrahedron (Merkaba)

When I began working with the Teacher’s of Light clairaudiently, they told me to help others “Activate their cars”.

When I asked what was meant by “their cars”, the answer I received was “sacred geometry”.

Sacred geometry can be activated by each individual (if they choose to do so). This is the geometry that was lost at the fall of consciousness and is not automatically turned on around those of us who have been living in a 3rd Dimensional Consciousness.

Examples of the sacred geometry that are now available to be activated by us are the Octahedron, Star Tetrahedron (Merkaba), and Metatron’s Cube.

When used, sacred geometric structures provide a “container” to house our auric fields. They provide stability, structure, and lessen the noise and energies of others bouncing off us all the time.

Sacred geometric structures are particularly important for highly sensitive people and Empaths to activate, as this will greatly reduce the pain they feel from others emotions.

I include how to activate your Star Tetrahedron in my $5 E-Book, How to Ascend to the 5th Dimension: Where ANYTHING You Want – YOU GOT IT!

And, there are also many free YouTube videos for activating it as well.

The Star Tetrahedron is also used for traveling off-world just before sleep, including how to time travel with your mind, and remote viewing (which I cover in further detail in my Mastering Astral Projection post).

2. Ask for Time Travel Meditation Guidance & Protection

When you are using the mind to travel back in time, or forwards in time, or wherever you’d like to view, please always ask for protection.

I pray to Source Consciousness and ask that Archangel Michael and my spirit guides surround me with protection and love while I practice my meditation time travel exercises.

I also surround myself with white light and Empath Protection Crystals to further cement in the protection while time traveling. (I don’t want to take any chances.)

I also pray for guides to assist me in making my time travel meditation a success. I specifically ask to “see” what I need to from the past that is holding me back in the present, or what I need to know about the future, or ask to “see” any past lives that may be holding be back.

This is called “setting an intention” and is important to set-up your time travel meditation.

This lets the Universe, your guides, your Soul, and Archangel Azrael (who assists with accessing your Akashic records to make time travel meditation possible) know what it is that you’d like to “see”, learn, or experience while you time travel through meditation.

3. Learn the Ancient Meditation for Reaching Higher States of Consciousness

After my near-death experience and being brought back to life highly Clairaudient, I began meditating to begin a very long spiritual awakening recovery process.

You can read more of my story in my E-Book: My Spiritual Awakening Recovery: How I Overcame Grief & Addiction to Spiritually Awaken & Create My Own Reality!

I did this for years before I finally asked the Teacher’s of Light for meditation tips!

Turns out, I was doing it wrong! Or maybe not wrong, per se, but I wasn’t meditating to the fullness of my ability.

The Teacher’s of Light suggested an Ancient way of meditation that many meditation gurus and Masters have practiced for centuries.

This Ancient Meditation for Reaching Higher States of Consciousness will supercharge your meditation practice, get you into the deep “Meditation Zone” sooner, and helps to fully turn off your rational mind.

Learn this advanced meditation technique, bookmark it, practice it, and use it during all your spiritual practices such as Astral Projection , Lucid Dreaming , Time Traveling Through Meditation, or any other Akashic Record reading.

3. Practice the Ancient Meditation and Your Pranayama Breathing Often

Even when I am not attempting to time travel through meditation, I practice the ancient meditation technique often.

I usually do this before bed since it helps me slow my mind and fall asleep without the use of prescription drugs (which I used to be addicted to).

This practice allows me to get into the “Meditation Zone” which I go into more in-depth in this Ultimate Beginner’s Guide to Mindfulness Meditation post.

When you get into the “Meditation Zone” or some call it “The Void”, your rational mind stops talking. You become one with your breath, and your ability to “see” Divine guidance is heightened.

Set your intention before you began your meditation time travel experience by praying for what knowledge you’d like to access during your meditation. This way, you will not have to use your rational mind once you get to the meditative zone (Which can pull you out of the experience!)

4. Spin and Activate Your 8th Chakra to Time Travel Through Meditation

To do this, simply visualize a glowing golden ball at your 8th chakra (your record-keeping chakra), roughly 12 inches above the top of your physical head.

See it begin to spin.

I like to visualize myself hitting these energy centers hard with my hand to begin them spinning.

Then say, “Spin and activate my 8th chakra”.

5. Continue Focusing on Your 8th Chakra (Your Record Keeping Chakra) During Your Time Travel Meditation

In order to “see” into other timelines, or your own past and future while meditating, it is important to access your 8th chakra (roughly 12 inches above your head).

Your 8th chakra is one of the 5th Dimensional transpersonal chakras (Located outside of your physical body). Another is the Earth Star Chakra , also nicknamed “The Billionaire Chakra”.

When working with the 8th chakra, always ask Archangel Azrael to kindly assist you in accessing the records.

You can also wear or hold Lapis Lazuli (a powerful crystal) to help you tap into the records held within your 8th chakra.

Lapis Lazuli also brings the wearer good luck, harmony, and provides a shield of protection to you while doing your time travel meditations.

Once you have located your 8th Chakra, and began it spinning and activated it – Keep your focus, or attention point upon this chakra while you meditate.

6. It is also Helpful to Open Your Third-Eye Chakra Before Your Meditation for Time Travel

Your third eye chakra being open assists your ability to psychically “see” your past, future, and past lives through meditation.

It will be much easier to “see” your Akashic Records to time travel during meditation that are held within your 8th Chakra if your third eye is strong and open.

Related Post: The Fastest Way to Open Your Third Eye

Final Thoughts on Time Travel Meditation: How to Time Travel With Your Mind

If you want to learn how to time travel through meditation, following the above steps will open the door to tap into your Akashic Records for making time travel with your mind possible.

But, it is in the prayer (setting the intention to time travel in meditation), and in the practice of your Ancient meditation technique, that will get you to your goal of time traveling while meditating.

Another helpful tip is to clean, clear, open, and activate your chakras. This unblocks your energetic centers that flow through your physical body and helps you “see”, “feel” and “know” more with your psychic abilities.

Here are some links for your chakras held within the physical body:

• Earth Star Chakra
• Root Chakra
• Sacral Chakra
• Solar Plexus Chakra
• Third-Eye Chakra

And, I write about how to access and clear your 5th Dimensional (Transpersonal) Chakras in the e-book: How to Ascend to the 5th Dimension: Where ANYTHING You Want – YOU GOT IT!

Have you ever successfully time-traveled through meditation? Have you tried these steps to make time travel to the past with your mind possible? What did you learn in your meditation time travel experience? Do you have any other time travel meditation tips, tricks, or hacks? Please like, comment, and share to social media!

As always, spread the light!

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Is Time Travel Possible?

We all travel in time! We travel one year in time between birthdays, for example. And we are all traveling in time at approximately the same speed: 1 second per second.

We typically experience time at one second per second. Credit: NASA/JPL-Caltech

NASA's space telescopes also give us a way to look back in time. Telescopes help us see stars and galaxies that are very far away . It takes a long time for the light from faraway galaxies to reach us. So, when we look into the sky with a telescope, we are seeing what those stars and galaxies looked like a very long time ago.

However, when we think of the phrase "time travel," we are usually thinking of traveling faster than 1 second per second. That kind of time travel sounds like something you'd only see in movies or science fiction books. Could it be real? Science says yes!

This image from the Hubble Space Telescope shows galaxies that are very far away as they existed a very long time ago. Credit: NASA, ESA and R. Thompson (Univ. Arizona)

How do we know that time travel is possible?

More than 100 years ago, a famous scientist named Albert Einstein came up with an idea about how time works. He called it relativity. This theory says that time and space are linked together. Einstein also said our universe has a speed limit: nothing can travel faster than the speed of light (186,000 miles per second).

Einstein's theory of relativity says that space and time are linked together. Credit: NASA/JPL-Caltech

What does this mean for time travel? Well, according to this theory, the faster you travel, the slower you experience time. Scientists have done some experiments to show that this is true.

For example, there was an experiment that used two clocks set to the exact same time. One clock stayed on Earth, while the other flew in an airplane (going in the same direction Earth rotates).

After the airplane flew around the world, scientists compared the two clocks. The clock on the fast-moving airplane was slightly behind the clock on the ground. So, the clock on the airplane was traveling slightly slower in time than 1 second per second.

Credit: NASA/JPL-Caltech

Can we use time travel in everyday life?

We can't use a time machine to travel hundreds of years into the past or future. That kind of time travel only happens in books and movies. But the math of time travel does affect the things we use every day.

For example, we use GPS satellites to help us figure out how to get to new places. (Check out our video about how GPS satellites work .) NASA scientists also use a high-accuracy version of GPS to keep track of where satellites are in space. But did you know that GPS relies on time-travel calculations to help you get around town?

GPS satellites orbit around Earth very quickly at about 8,700 miles (14,000 kilometers) per hour. This slows down GPS satellite clocks by a small fraction of a second (similar to the airplane example above).

GPS satellites orbit around Earth at about 8,700 miles (14,000 kilometers) per hour. Credit: GPS.gov

However, the satellites are also orbiting Earth about 12,550 miles (20,200 km) above the surface. This actually speeds up GPS satellite clocks by a slighter larger fraction of a second.

Here's how: Einstein's theory also says that gravity curves space and time, causing the passage of time to slow down. High up where the satellites orbit, Earth's gravity is much weaker. This causes the clocks on GPS satellites to run faster than clocks on the ground.

The combined result is that the clocks on GPS satellites experience time at a rate slightly faster than 1 second per second. Luckily, scientists can use math to correct these differences in time.

If scientists didn't correct the GPS clocks, there would be big problems. GPS satellites wouldn't be able to correctly calculate their position or yours. The errors would add up to a few miles each day, which is a big deal. GPS maps might think your home is nowhere near where it actually is!

In Summary:

Yes, time travel is indeed a real thing. But it's not quite what you've probably seen in the movies. Under certain conditions, it is possible to experience time passing at a different rate than 1 second per second. And there are important reasons why we need to understand this real-world form of time travel.

If you liked this, you may like:

Mindfulness

How time perspective affects travel, do you live in the past, present, or future.

Posted April 15, 2024 | Reviewed by Michelle Quirk

• What Is Mindfulness?
• Find a mindfulness-based counsellor
• Understanding your own time perspective can enhance your life experience.
• Our characteristic types are neither good nor bad, just different from one another.
• Children are present-oriented, while adults favor the future. Seniors tend to preserve the past.

As an enjoyable vacation winds down, some of us become impatient to get home and move on to the next thing. Maybe that’s you. But, instead, you might be someone who tries to preserve, or even expand, every remaining moment. In either case, you’ll attempt to lock these precious flashes into your memory bank with mental snapshots. But without any effort, and all too quickly, the present quickly fades into the past. How we experience time is relevant to travel. Understanding your own time perspective can enhance your experience.

Stanford University Professor Emeritus Phil Zimbardo, author of The Time Paradox , notes that we are all oriented to time in one of the following characteristic ways—past, present, or future. According to his profile, I am future-oriented. What might your style be? Let’s see.

Those of us in the future category are goal-driven, focused on the future consequences of our actions, and forward-looking in general. Then there are the present-hedonic folks, the pleasure seekers who enjoy things in real-time, with less concern about tomorrow. Folks who live in the present tend to be open to experiences they didn’t necessarily plan, and they don’t need to check it off their bucket list. If this style fits, you’re probably most content with the moment-to-moment flow of your travel.

Past-oriented people make up the remaining category. This might be you if you compare current experiences with memories of past events or situations. Past-oriented folks determine the value of travel, according to Zimbardo, by assigning a pleasure quotient to the comparison—better or worse and by how much? This style is more analytic and rational, and based less on emotional factors than is true for present-focused folks. Does this sound like you?

Our characteristic types are neither good nor bad—just different from one another. Future- and past-oriented travelers provide a logical, systematic understanding of where travel fits into human experience. These styles have great evolutionary value. Our distant ancestors, who chronicled the past and predicted the future, tended to be the shaman and storytellers of the tribe. Reviewing the past and predicting the future was critical to human survival.

Present-oriented people tend to have more fun in the moment, and every society needs this type of person to keep things from getting too serious. Savoring the present is an acquired skill and is worth the effort to cultivate! Also, by expanding the present-pleasant and then reviewing a trip in the past-positive, you can have both good feelings and pleasurable memories. Since, as Zimbardo’s research indicates, we have characteristic ways of perceiving time, maintaining a present focus may require some work—if this isn’t naturally how you see the world.

Zimbardo points to another dimension of time—one that is age-related. In general, children are present-oriented while adults favor the future. Seniors tend to preserve the past. As a future-focused senior, I'm aware of the need to put my foot on the brake and try to prolong the present—particularly the pleasing moments while vacationing. This takes some work.

Regardless of the type that best explains you, here are some strategies to expand your time orientation:

• If you’re naturally drawn to the past or future , notice these tendencies and gently nudge yourself toward the present moment. When you catch yourself reminiscing about the last time you were in Paris, as you sit at an outdoor café savoring your steaming latte and munching on a croissant, remind yourself that the people you see strolling by are there right now—not last time or next time. The weather is uniquely now, not needing a contrast with a warmer or sunnier last visit. The present can be pleasant without any backward reference—or simply less.
• Future- oriented travelers tend to spend their present moments imagining future trips, which makes sense in planning life but can steal from the here and now. Recently, on a river cruise through Austria, I was struck by how much conversation I overheard about planning the next trip. Busily sharing these thoughts with fellow travelers, these vacationers sat by a large picture window as the ship sailed into a new city—totally missing the present moment, unnoticed outside of the window.
• Again, if future is your natural mode, keep that in mind as you travel. Learn to prolong the only moment that truly exists—this one that you anticipated for months or maybe years. The first step involves gently guiding your awareness back to the present. Practicing meditation even a few minutes a day will make this process easier.

This article is based on a chapter from my book: Inward Traveler: 51 Ways to Explore the World Mindfully, 2018.

Stanford University professor emeritus, Phil Zimbardo, authored The Time Paradox, Free Press, N.Y., 2008.

Francine Toder, Ph.D. , is an emeritus faculty member of California State University, Sacramento and is a clinical psychologist retired from private practice.

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Watch CBS News

U.S. issues travel warning for Israel with Iran attack believed to be imminent and fear Gaza war could spread

By Debora Patta , Tucker Reals

Updated on: April 13, 2024 / 5:25 PM EDT / CBS News

Update: Iran launched drone attacks against Israel on Saturday. Read CBS News'  latest coverage here .

Tel Aviv  — Israel is bracing for a worst-case scenario that U.S. officials believe could materialize within just hours — the possibility of a direct attack on Israeli soil by Iran in retaliation for a strike almost two weeks ago that killed seven Iranian military officers. Iran has vowed to take revenge for Israel killing its commanders, who were hit by an April 1 strike on the Iranian embassy in Syria's capital.

Two U.S. officials told CBS News that a major Iranian attack against Israel was expected as soon as Friday, possibly to include more than 100 drones and dozens of missiles aimed at military targets inside the country. Sources have told CBS News the retaliation could include attacks carried out both by Iranian forces, and proxy groups around the region that it has been funneling additional arms to for weeks.  

The officials said it would be challenging for the Israelis to defend against an attack of that magnitude, and while they held out the possibility that the Iranians could opt for a smaller-scale attack to avoid a dramatic escalation, their retaliation was believed to be imminent. 

Asked Friday how imminent he believes an attack is, President Biden responded, "I don't want to get into secure information, but my expectation is sooner than later." The president urged Iran not to move forward, saying his message to Tehran was: "Don't."

Tehran has not indicated publicly how or when it will return fire, so it's unclear how far Iran's leaders will go. If they decide to carry out a direct attack on Israel, there's fear it could blow Israel's ongoing war against Iranian ally Hamas up into a much wider regional conflict.

With the Iranian retaliation expected at any time, the U.S. State Department on Thursday warned Americans in Israel not to travel outside major cities, which are better protected from incoming rocket fire by the country's Iron Dome missile defense system. The latest guidance noted that travel by U.S. government employees in Israel could be further restricted with little notice as things develop in the tinderbox region.

"Whoever harms us, we will harm them," Prime Minister Benjamin Netanyahu vowed Thursday as he visited troops at an Israel Defense Forces airbase. "We are prepared … both defensively and offensively."

On Saturday, all U.S. embassies in the Middle East were put on high alert and required to hold emergency action committee meetings. Diplomats in Lebanon and Israel were specifically told not to travel to certain areas within those countries.

Sima Shine, a security expert and former official with Israel's national intelligence agency Mossad, told CBS News it was a dangerous moment for the region, and the "most worried" she has been. She said anxiety over an all-out war was likely just as high "on both sides, in Israel and in Iran."

If Iran does choose to strike Israel directly, it could involve a complex missile and drone attack similar to the one Iranian forces launched against a Saudi oil facility in 2019 .

"They will try to do it on the military or some military asset," Shine predicted. "But the question will be the damage. If there would be many injured people, killed or injured … I think it has the potential for a huge escalation."

Shine stressed, however, that she still believes neither side actually wants a regional conflict.

U.S. "really trying to avoid war"

The U.S. sent a senior general to Israel this week to coordinate with the close American ally on any response it might make to an Iranian attack. Speaking Friday on "CBS Mornings," America's top military officer said, "we're really trying to avoid war."

"This is part of the dialogue that I have with my counterparts within the region, to include the Israeli chief of defense, who I talked to yesterday," said Joint Chiefs chairman Gen. Charles Q. Brown, Jr., adding that the U.S. military was "doing things not only to prevent a war, but at the same time, one of my primary things is to make sure all the forces in the region are protected."

"My role, as the chairman of the Joint Chiefs, is to plan and prepare," Brown said. "That's one thing we do very well."

Brown's Israeli counterpart, Chief of the General Staff Lt. Gen. Herzi Halevi, "completed a comprehensive situational assessment on the readiness of the IDF for all scenarios," Israel's military said Friday. 

"The IDF is very strongly prepared, both offensively and defensively, against any threat," Halevi was quoted as saying in the statement. "The IDF continues to monitor closely what is happening in Iran and different arenas, constantly preparing to deal with existing and potential threats in coordination with the United States Armed Forces." 

The IDF said the visiting U.S. general, Central Command chief Gen. Michael Erik Kurilla, was taking part in the IDF's situational assessment.

The dilemma for Iran, said Israeli expert Shine, is to figure out how to deliver its promised response to Israel's attack in Syria, but in a way that does not lead to further escalation. Likewise, Shine said Israel could choose to show restraint when it responds to whatever Iran eventually does.

If either side gets the balance wrong, the consequences for the region, and even the world, could be dire.

Weijia Jiang, David Martin, Margaret Brennan and Olivia Gazis contributed reporting.

• Middle East
• Benjamin Neta​nyahu

Debora Patta is a CBS News foreign correspondent based in Johannesburg. Since joining CBS News in 2013, she has reported on major stories across Africa, the Middle East and Europe. Edward R. Murrow and Scripps Howard awards are among the many accolades Patta has received for her work.

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