THE UPSIDE DOWNBack to the Future
John Mitchinson explores why we are hardwired to remember the past, with memories that are made in the moment
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Whatever your relationship to the idea of monarchy, recent weeks have been notable for the intensity of the memories they have summoned up. Remembering what you were doing – or who you were – in 1977 or 2002 was at least as important for most of us as watching any of the formal Platinum Jubilee celebrations.
But what is happening inside your brain may surprise you.
In the Pixar movie Inside Out, the main character Riley’s memories are coloured orbs, temporarily stored on shelves in Head Quarters before being shipped to Long Term Memory at night. Most of us, if pressed, would still describe memory as a process of filing and retrieving events from the past, which are stored somewhere in our brain. But we are beginning to understand that memory doesn’t quite work like that.
The key players are a matching pair of slender structures buried deep inside each of our cerebral hemispheres we call the hippocampus, so named from their resemblance to seahorses (hippos, meaning ‘horse’ in Greek, and kampos meaning ‘sea monster’).
It turns out a single memory isn’t a single thing. It can combine sight, sound and smell, with all these elements being held in different parts of the cortex until they are reformulated by the hippocampus into a memory. Memories are made, not retrieved.
This is the idea that animates one of the most thoughtful of recent books on the subject, Pieces of Light, by the British developmental psychologist Charles Fernyhough: “When you have a memory, you don’t retrieve something that already exists, fully formed – you create something new. Memory is about the present as much as it is about the past. A memory is made in the moment, and collapses back into its constituent elements as soon as it is no longer required. Remembering happens in the present tense. It requires the precise coordination of a suite of cognitive processes, shared among many other mental functions and distributed across different regions of the brain.”
This leads us to perhaps the most important question of all: why do we need to remember things at all? The answer, paradoxically, seems to lie in neither the past nor the present, but the future.
Being able to summon up scenes from the past feels like a definitively human activity. The sharing of memories within families and friendship groups helps us lay down the strong neural pathways that allow us to retrieve them more easily. The ability to use this personal database of experience to imagine and shape the future might be the real evolutionary bonus of human memory.
There is empirical evidence for this too. MRI scans show that the underlying brain patterns generated remembering the past and imagining the future are practically identical.
To test this in more detail, an experiment was set by the neuroscience team at the Wellcome Trust Centre for Neuroimaging at University College London led by Eleanor Maguire and Demis Hassabis in 2007. Their thesis was that, if amnesiac patients found it difficult to form autobiographical memories, they might also find it difficult to imagine future experiences.
The experiment involved asking five severely amnesiac patients to imagine and describe 10 new experiences using location prompts such as a tropical sandy beach or a museum full of ancient artefacts. In comparison to the non-amnesiac controls, four of the five patients performed significantly less well. Crucially, their descriptions lacked spatial complexity, sensory detail or meaningful emotional content. They had no problem placing themselves in the scenarios suggested – they just couldn’t make a persuasive or coherent story out of it once they were there. Of particular significance was that all five had severely impaired hippocampi.
As well as logging and encoding memories, the Wellcome research suggested the hippocampus also plays a key role in what the research team called ‘scene construction’. Memory and imagination both require a stage on which to perform. As Eleanor Maguire put it, the hippocampus is “providing the spatial backdrop or context into which the details of our experiences are bound”. Given the hippocampus’ other important function is to help us navigate through space, this seems like more than a neat coincidence.
When we remember a scene from our past, we reconstruct it spatially using our hippocampus and fill it with representations from other parts of our brain to produce the memory. We do exactly the same thing when we imagine our future, only this time we use the constructed scene to help us plan our actions.
The more we study them, the more we find that the key processes of the brain, like memory, are active on many different levels, running to different time scales, in order to optimise flexibility. This is a key evolutionary adaptation. The faster our brains can learn and adapt, the better our chances of survival.