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THE BIG IDEA: WHY AM I SO FORGETFUL?
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Charan Ranganath
March 25, 2024
Guardian
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_ A failing memory can be frustrating, but it may be a sign your
brain is working exactly as it should _
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Every day, people across the planet ask themselves this question,
myself included. When we are desperately searching for our glasses,
wallet or keys, we might wish to have a photographic memory, but the
truth is we are designed to forget.
In fact, the majority of what we experience in a given day is likely
to be forgotten in less than 24 hours. And that is a good thing. Think
of all the passing encounters with people you will never see again,
the times you spend waiting in a queue at the supermarket, and those
awkward times when you find yourself looking at the floor while stuck
in a crowded elevator. If our brains hoarded away every moment of
every experience, we would never be able to find the information we
need amid an ever-increasing pile of detritus.
So, if memory is not supposed to be a comprehensive archive of the
past, what is the point of remembering at all? To answer this
question, it helps to think about what it means to remember in the
first place.
For more than 25 years, I have studied how we are able to recall past
events, an ability known as “episodic memory”. Endel Tulving, the
pioneering cognitive psychologist who coined the term, described
episodic memory as the uniquely human capability for “mental time
travel, roaming at will over what has happened as readily as over what
might happen, independently of the physical laws that govern the
universe”.
I first read this description of mental time travel when I was a
graduate student, and I was deeply sceptical. Now, with the wisdom of
age (something I will come back to later), I understand what he meant.
When you recall a rich episodic memory, there is a palpable feeling of
being transported back to a point in your past, a specific time and
place. For instance, the smell of freshly baked pastries might remind
you of having breakfast with your grandmother, or a song by the Stone
Roses might conjure up your first kiss. Findings from my lab and
others have shown that, at the moment of remembering, the brain
appears to revert a bit to the state that it was in at the time,
enabling us to relive these past experiences. This is why, if you have
misplaced your keys, it can be helpful to put yourself, mentally, into
the context where you last saw them. Getting in touch with the sights,
sounds and thoughts from an earlier time period can be an effective
way of accessing those memories.
Ageing is a bit like having a dysfunctional time machine that sends us
to the wrong place
Mental time travel isn’t just about reflecting on the past; it also
orients us in the present. Consider what happens when you wake up,
jet-lagged and confused, in a hotel room. After a second spent
recapping the recent past, you can reassure yourself that you’re
there on holiday, and then go back to sleep. People
with Alzheimer’s disease cannot use episodic memory as a lifeline,
and, as such, may feel frighteningly disoriented, floating in space
and time.
Crucially, Tulving also proposed that mental time travel allows us to
consider what might be coming round the corner. He came to this
conclusion, in part, from getting to know Kent Cochrane, who had
profound amnesia after a motorcycle accident. Surprisingly,
in addition to his severe episodic memory deficits, Cochrane was also
unable to contemplate the future. Tulving’s ideas have been
substantiated by further research. In the UK, Demis Hassabis
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went on to co-found the AI company DeepMind) and Eleanor Maguire
published studies of patients with an impoverished ability to imagine
events, and others reported a stunning degree of overlap in the brain
networks that are active during remembering and during imagining the
future. Further studies have shown that episodic memory can allow us
to construct alternative realities, to consider what might have
happened if we’d made different choices in the past.
On average, episodic memory gets worse as we get older, and that is
due, at least in part, to the strange developmental trajectory of the
prefrontal cortex – an area of the brain that helps support episodic
memory. In humans, the prefrontal cortex continues to develop
throughout childhood and adolescence, only reaching maturity in young
adults. Then it begins to decline in function, starting as early as
your 30s (depressing, I know). Consequently, ageing is a bit like
having a dysfunctional time machine that frequently sends us to the
wrong place. For many years, I pondered why it is that the full extent
of mental time travel is only available to young adults, with the rest
of our lifespan spent making do with a suboptimal episodic memory.
But what is “optimal”, anyway? Perhaps episodic memory is
functioning exactly as it should through our lifetime. Consider that
for much of human history young adults would have needed to care and
provide for their children. At this age, they would require a more
focused episodic memory to keep track of the most current information
about foraging or hunting sites, to differentiate between allies and
rivals, and so on. Elders, in contrast, have traditionally played a
different role, guiding and giving advice to younger generations.
During this period, forming new episodic memories is less important
than passing on the wisdom accrued from existing ones.
So, the next time you find yourself wondering “Why am I so
forgetful?” perhaps you can take some comfort from the idea that
your brain is probably doing just what it evolved to do.
Professor Charan Ranganath is the author of Why We Remember: The
Science of Memory and How It Shapes Us (Faber). To support the
Guardian and Observer, order your copy at guardianbookshop.com
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Delivery charges may apply.
Further reading
Remember: The Science of Memory and the Art of Forgetting
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Lisa Genova (Atlantic, £10.99)
The Memory Illusion: Remembering, Forgetting, and the Science of False
Memory
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Dr Julia Shaw (Cornerstone, £10.99)
Being You: A New Science of Consciousness
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Prof Anil Seth (Faber, £10.99)
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* psychology
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