BBC Focus - 09.2019

something that is new, that we have not
seen before in this way, has a high chance
of being retained. This is because novelty
triggers systems that release substances
like dopamine, which increase the lifetime
of memories formed during this time. Each
surprise is a novelty because based on our
existing knowledge and memories we did
not predict it. And these kind of emotional
reactions like surprise, fear, happiness and
so forth, trigger the release of substances
and certain other processes that somehow
strengthen the connections between
neurons, resulting in longer-lasting
memories. In other words, these memories
last longer because they are more resistant
to active forgetting processes.
Another way how memories have a
higher chance of survival is repetition.
I think that this is especially a feature
of humans. We talk a lot, and we live in
groups. For 30,000 years now we have
DGGPUKVVKPICTQWPFVJGRTQXGTDKCNTG
at night, talking to our kin or loved ones

about what happened during the day

when we get back home from hunting and

HQTCIKPIQTVJGQHEGPQYCFC[U9JCVYG

experienced we explain to other people,

and they ask us probing questions during

this reporting, things that interest them

particularly. This kind of guided repetition

KUCPQVJGTYC[QHNVGTKPIQWVYJCVKU

important and what can be forgotten.

We usually only talk with people about

YJCVYGPFKORQTVCPVCPFKPVGTGUVKPI

but when others start to ask us targeted

questions to tickle out more information

about a certain event, it is a way of making

sure that the knowledge of everybody is

used to extract the most relevant aspects

from your experience and commit this to

the memory of many.

This repetition and sharing strengthens

the memories of the narrator and

distributes it across the brains of the

listeners, making the acquired knowledge

resistant against the brain’s forces of

forgetting by way of strengthening and

distribution. But the question of how, on

the biological level, repetition, surprise or

other emotional reactions protect against

forgetting has not been fully answered.

The way my group is looking at this

currently is trying to understand how

these ways of making memories stronger

affect the systems that convey the message

‘forget’ in the brain.

IS IT POSSIBLE THAT THE FORGETTING

MECHANISM GOES HAYWIRE IN

SOMEBODY WHO SUFFERS FROM A

DISEASE SUCH AS DEMENTIA?

That is a hypothesis I have been proposing

for a couple of years now. If there is

a hardwired forgetting process in the

brain, then, like any other processes

of the brain, it can get dysregulated,

and this dysregulation could promote

diseases of forgetting. I have suggested

that Alzheimer’s disease might not start

as a problem of making memories, but as

excessive forgetting. Thus, to approach

this disease, it may be helpful to try

to tone down an overactive forgetting

process. One group has done just that.

They used the approach that we used to

stop normal forgetting in a healthy rat,

and used it in a transgenic [genetically

altered] rat that expresses some symptoms

of Alzheimer’s disease, such as the famous

plaques [fragments of protein that clump

together and interfere with signals from

neurons]. They found that blocking the

forgetting process reduced the plaques

and normalised memory retention in this

transgenic rat. Thus, I think it is at least

a plausible alternative hypothesis that

excessive memory loss in certain neuro-

degenerative conditions can result from

the overactive and dysregulated forgetting

process we have discovered.

PROF OLIVER HARDT

Oliver is assistant professor in the Department

of Psychology at Canada’s McGill University.

Interviewed by BBC Science Focus commissioning

editor Jason Goodyer.