Doctor Who’s TARDIS and human memory have a lot in common: both seem small, but are able to transport you through time to many possible worlds.
We often assume that memory is primarily concerned with the past, and that we need it to create a sense of identity and our own story in life. But actually, we use memory everyday to help us evaluate our options, make choices such as which films to watch, and to think about the future. In order to do this we engage in mental time travel.
According to my nephew Miles, who’s five, the reason you need memory is:
So you can tell your mum and dad if something bad has happened to you.
And he’s really grasped the main issue here – we need memory to survive. Research shows our ability to reflect on the past allows us to make beneficial decisions and choose the best actions to take.
Read more: Comic explainer: how memory works
Back to the past
How do you choose where to buy your morning coffee? One way is to use memory to draw on individual past experiences in order to evaluate your current options and make the best choices. Should you visit the cafe that burns the milk or should you take a ten minute detour, buy your perfect flat white and risk being late for work?
When we think about specific experiences in the past, such as a holiday, there are certain moments we are more likely to remember – usually the most intense moment (the peak) and the more recent moments (the end). These characteristics bias our memories of the event and we give them more weight when evaluating the experience as a whole.
They also influence how likely we are to choose similar experiences. For example, when you think about your most recent holiday, what’s the first thing that comes to mind? Perhaps it’s a particularly enjoyable meal you had, or maybe it’s the day you got sunburnt. Given what you know now, would you choose to go on this holiday again?
Researchers asked a group of US students going on Spring Break exactly this question. They were asked to rate their enjoyment both during their trip and four weeks after they returned.
Although the ratings they made during the trip provided a more accurate reflection of their overall enjoyment, it was the evaluation they made when they returned that best predicted whether they would repeat the experience.
In addition to having a bias for remembering more recent and intense moments, certain other events are more likely to stick in memory. We encounter hundreds of places, smells, sounds, faces and objects every day, yet we can recall relatively few of these.
Read more: Where in the brain is memory stored?
Our research has shown that linking events to rewards helps us to prioritise certain events in memory. We also know that emotional and novel events are better remembered than neutral ones.
And interestingly as we get older, our memory capacity does decline, but our ability to use this important information to help us select which information to remember remains relatively intact.
Back to the future
In the same way that we draw on past experiences to evaluate our current options, we also use memory to evaluate future options and to “pre-experience” events. This gives us a way of mentally testing the water before committing to something new.
Imagine instead of offering you a cup of tea, a friend offers to make you something completely new like a raspberry-avocado-smoothie (that’s actually a thing now – but it wasn’t at the time of this research). Assuming you’ve never tried one of these, you will use your memory to imagine the consequences of the new experience.
This act of imagining new events forms associations in the same areas of the brain involved in forming and storing memories – the hippocampus and the medial prefrontal cortex.
Frozen in time
Being able to virtually travel through time makes us well adapted to our environment and helps us to plan actions such as how much food to eat.
The ability to use specific past experiences to imagine the future has been found to be impaired in several patient populations, including in people with Alzheimer’s disease and others with depression .
In a recent study we found that compared to lean individuals, people with obesity tended to disregard how long it would be until their next meal when choosing how much to eat. This lack of planning could be linked to difficulties in using memory to simulate future events.
In highlighting the importance of mental time travel, it is important not to detract from the benefits of focusing on the present moment. There is evidence that mindfulness is an effective tool for improving well-being and mental health .
So next time your mind wanders back to the past, or heads off into an alternative universe, enjoy the ride. You may just be preparing for your next action, and working out which decision is best for your survival.