Mental time travel

MEMORY, Blake wrote, enables us to “traverse times and spaces far remote”. It constitutes mental time travel, with which we can recollect, in vivid detail, events that took place many years ago. We have known, for the best part of a century, that memory is reconstructive rather than reproductive. That is, recollection involves piecing together specific details of the event, and mixing these with our own biases and beliefs. While not being completely accurate, our memories are, in most cases, reliable enough.

It is because of the reconstructive nature of memory that we are able to travel forward in time as well as back into the past. Research carried out in recent years has shown that imagining future events and recalling those that we have already experienced are dependent on the same core network of brain regions. It seems that both involve the same cognitive processes – when we look forward to something that might happen in the future, the brain generates a simulation of that event using fragments of memories of past events. 

However, the evidence for this is indirect, and it is possible that what are thought to be simulations of future events are in fact merely memories of past events being “recast” into the future. But a new study, due to be published in the September issue of the journal Neuropsychologia, now confirms that these simulations are indeed novel constructions, and also shows that remembering actual experiences and imagining possible future events depend on distinct subsystems within the common core network.

A number of studies published in the past few years have shown that remembering past events and imagining future events involve similar cognitive processes. Compelling evidence for this comes from behavioural studies of amnesics – as well as severe memory deficits, these patients also have great difficulty envisioning the future. Thus, it is suggested that fragments of past experiences provide a source of details which can be flexibly recombined to simulate future events. There is, however, no direct evidence for this; it is possible that imaging future events involves merely recasting past experiences, such that simulating the future involves retrieving a single memory of the past and projecting it forward in time, and the studies carried out to date have not yet distinguished between these possibilities.

Neuroimaging has revealed that remembering and simulating the future are now known to depend on common neural substrates; the core network activated in both cases includes the hippocampus, poserior cingulate gyrus, inferior parietal lobule, and medial frontal and lateral temporal cortices. Interestingly, activity in this network is greater during simulation of future events than during remembering. This may reflect processes that do not occur during remembering, such as the recombination of memory fragments or, if imagining the future involves merely recasting the past, the addition of a new “timestamp” to the memory of a past experience.

The new study, led by Donna Rose Addis of the University of Auckland in New Zealand, was designed to address these issues, and to investigate whether imagining the future has a neural signature that is distinct from remembering the past. 23 participants – all of them college students – were first asked to complete a spreadsheet detailing memories of nearly 200 personal events they had experienced within the past 5 years, each of which had occurred at a specific time and in a specific place. A few days later, they underwent a brain scanning session, during which they were asked to recall some of the events that had actually happened and also to imagine past and future events.

For the trials involving imagining events, the participants were presented with cues consisting of details which had been randomly extracted from different memories and then combined. Each cue consisted of details of a person, object and place taken from multiple episodes provided in the first session, and the participants were instructed to imagine these details in a single novel episode. In this way, the participants were prevented from recasting past experiences as future events; they also confirmed, in descriptions provided after the scanning sessions, that they were able to combine the separate memory elements into coherent representations of imagined future events.

As expected, the researchers found that remembering past events and simulating future ones activated overlapping regions of the core network of brain structures. But closer examination revealed that each was associated with a distinct subsystem within the network. For example, extensive regions of the medial prefrontal cortex, parietal lobe and the anterior portion of the hippocampus were activated during imaging future events, but not during retrieval of memories. On the other hand, remembering, but not imagining, led to activation of parts of the visual cortex, likely reflecting the imagery associated with memory retrieval. Furthermore, each subsystem was found to be activated over a different timescale, with the imagining subsystem becoming active earlier (at between 2-4 seconds) and peaking for longer, than the remembering subsystem.


Addis, D., et al (2009). Constructive episodic simulation of the future and the past: Distinct subsystems of a core brain network mediate imagining and remembering. Neuropsychologia 47: 2222-2238. [PDF]

Szpunar, K. K. & McDermott, K. B. (2008). Episodic future thought: Evidence from ratings of subjective experience. Conscious. Cogn. 17: 330-334. [PDF]

D’Argembeau, A. et al (2008). Neural correlates of envisioning emotional events in the near and far future. Neuroimage 40: 398-407. [PDF]

10 thoughts on “Mental time travel

  1. I wonder if you’ve ever read Jack Finney’s 1970 novel Time and Again, it is one part mental time travel, one part physical time travel. The film Somewhere in Time also uses this mental time travel trick. Supposedly, the seed of this time travel trick is based on J.B. Priestley’s popularization of J.W. Dunne’s obtuse technical writing on time.

  2. There’s an article in the current (July/August 2009) _Discover_ magazine which gets into the nature of memory storage and discusses how memories are modified each time they’re recalled. This is as disturbing as it is interesting!
    Thanks for an informative blog.

  3. This study by Addis et al. (2009) provides a neurobiological basis for the how the Bayesian model of Computational Theory of Mind (CTM) works. Most people find the Bayesian model of CTM arcane and difficulty to understand. But, I think the following real world example illustrates how the Bayesian model works:
    Imagine everyday at work you go to the cafeteria to eat lunch. The cafeteria has two identical soda machines called A and B. A and B are next to each other, both contain the same products at the same price ($1 per beverage). Depending on how you enter the cafeteria you randomly choose A or B for your purchase on a soda. One day you go to A, put in your $1 and expect to receive 1 soda. However, A delivers your soda and returns or $1! Your Bayesian brain’s expectation has been violated in a positive way and sends a signal to the dopamine reward system “This is better than I expected.” The dopamine reward system delivers a dopamine pulse that signals the Bayesian brain to update its expectation about A. The next time you go to the cafeteria your probability of choosing A is increased over B. This process of contrasting prior experience with current experience (positive, neutral or negative) is how the Bayesian brain updates its database to provide complex adaptation to changes in the environment.
    This neuroimaging study provides a window into the neurobiological mechanisms underlying the Bayesian brain.

  4. There are some forms of future anticipation that seem less connected to the past than others: for instance, the prediction of scientists and inventors, especially when those predictions are used to corroborate, or test, a new theory or product: thus, when Benjamin Franklin predicted that lightning would follow the string of a kite that was grounded, he was anticipating an event that was, presumably, significantly different from any he’d previously seen. When Einstein predicted that, during a solar eclipse, light from the sun would be bent by the gravity of the moon, the resulting confirmation had never before been seen or anticipated. A similarly new –but previously unseen– result occurred when the first atomic bomb was tested at Los Alamos. The modern computer was anticipated, but not actually remembered –as far as we can tell– by the pioneers of digital science and technology (Von Neumann, Turing, Jobs, etc.).
    All perception is “programmed,” “interpretive, or “theory-laden.” That goes for memory as well as for immediate experience. It’s even more true of anticipations and predictions, which depend as much on the subject’s beliefs and cognitive framework as they do on past experience. The future –and especially what’s new and interesting about the future– is almost never a simple repetition of the past, whether in science or in personal experience.

  5. I wonder what this result can say about people with “false memory” (confabulatory hypermnesia) that you talked about previously. If they are “remembering” activites that never happened, does their brain respond in the same way as “simulating future events” from this study, or would their brain respond as if it was retrieving a normal memory?

  6. I’m delighted to see this empirical connection proposed / implicated between ‘imagination’ and ‘intuition’ – especially as the later function was elaborated by C.Jung, and what often appeared to be ‘extra sensory perception’.
    – but also in verifying the intrinsic originality of the better science fiction. …
    and seeming to substantiate that i/i is a kind of distinguishable function in human – primate, mammalian – neurology! Bravo!
    Background: I’m a socio-cultural anthropologist with my primary interest in ‘the study of (socio-cultural) future (s)’, that is how images of the future are constructed, communicated and acted upon in diverse socio-cultural settings.
    Currently I’m teaching (3rd ed. Fall’09) an “Anthro: Intro to Futures” course to FroshMonsters, a course that culminates, Part III, in the last 5 weeks with a peer-interviewing exercise that employs Robert B. Textor’s “Ethnographic Futures Research” paradigm and with student rotation through the three roles of interviewer, interviewee and recorder; with each recorder’s document graded.)
    Findings – thus far: Their ‘futures’ have been, overwhelmingly, and frighteningly-to-me unimaginative projections of the ‘mostly sub-urban’ Phoenix/TheValley (now more extensive than LA!) neighborhoods (and world-views) that they have been reared in.
    Note: they are, concurrently, bringing their family (‘helicopter parents’) and HS networks (social networking) along onto campus with them -via cell-phone + ‘net-social networks. .. in defiance of traditional ‘University campus’ culture …
    How do these research findings help me to better intervene in this cognitive “ice-jam” ? — I’m immediately adding this ‘blog’ as an option (obligatory?) in their Unit I-II required ‘web-site review assignments’, …
    How do these ‘rough’ findings, poise me to bust this cognitive ice-jam?
    … and what are your suggestions?
    collegial thanks!
    Reed Riner

  7. From studies I remember reading human beings are distressingly bad at predicting what the future will be like. My recollection was that the study was looking at various people’s ideas of what getting a big windfall (hitting a lottery or an inheritance) would be like and following up with those who actually had a windfall.
    Most people in anticipating a windfall project a future that is much like the present or recent past, whereas the experience of having had a windfall was a dramatic change in circumstances unlike the persons life before. For example, a person who sat around drinking beer in the present would project that they would sit around more and drink more beer. That prediction would be way off of the mark.
    I think this fits in with the unimaginative projections of the previous posting. It isn’t lack of imagination but a human tendency to project the recent past into the future.

  8. Is it not possible that what you are proving here is that the memory does not actually exist as we thought previously, that remembering things in the past is the same as imagining things that will happen in the future. You are making things up as you believe them to be regardless? You have a basic idea of what to work from and you imagine the rest?

  9. Apple… shall I remind you that the article specifies that different networks within the systems are activated for past recollection and future projection?

Comments are closed.