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What happens to

memories over time?

EMORIES fade quickly, as we all know an interconnected network of brain cells.
too well. “All things being equal, it’s To retrieve a memory, you need some part of
M harder to remember things from a its content: for example, to recall who came
long time ago compared to more recent to your last birthday party, you might start
events,” says neuroscientist Marc Howard by picturing where the party took place.
of Boston University. Artificial intelligence researchers have
But forgetting doesn’t just happen by built computer programs that work on the
accident. Evidence suggests that it is largely same principles, known as neural networks.
down to active processes in the brain. They have found that when memories are
In the hippocampus, for instance, which distributed across interconnected units like
plays an important role in memory, new this, there is a lot of potential for what’s
cells are formed throughout life. It takes called interference, in which one memory
energy to do this, yet these cells seem to effectively impedes the recall of another.
overwrite established memories and This is especially true if they share some
induce forgetting. of the same content, so you might end up
Why should the brain invest energy in confusing memories of two birthday parties
dismantling its own memories? The issue that happened at the same venue. In
isn’t storage space: given the number of addition, if you store memories that are no
cells and connections in the brain, there is longer useful, there’s a high risk that they
reason to think we could remember much will hamper the storage of new memories.
more than we do. Having fewer memories can also make it bodies simply aren’t adapted to living quite
According to Blake Richards at the easier to spot important patterns that help as long as we do, says Aoife Kiely from UK
University of Toronto, Canada, the goal us plan for the future. By remembering charity the Alzheimer’s Society.
of memory isn’t to store information instances when traffic was bad on your Aside from some new cells in the
indefinitely, but to optimise decision- commute, for example, you would learn hippocampus, “the neurons you are born
making in the future (see “What is memory which times to avoid. Remembering every with are pretty much the ones you are going
for?”, page 32). And it seems that forgetting single journey would make it impossible to to live your whole life with”, she says. “It is
most of our experiences actually helps us identify such patterns. certainly an issue of wear and tear of the
learn important lessons. Even so, there are less practical reasons brain.” As we age, we lose many of the
Each memory is thought to be stored in for forgetting, especially as we age. Our connections between these neurons,

FAQ. DOES CLOSING YOUR EYES WHY IS IT THAT YOU ONLY the box — it activates the connections

that memory fragments are attached to.
But sometimes, a friendly prompt can
TRULY HELP YOU REMEMBER? REMEMBER SOME THINGS mess with your memory. Imagine you

said to you: “Remember they sang such-
Yes. Vision is our dominant sense and WHEN OTHER PEOPLE went to a concert with a friend who later
a key source of new information. When and-such song?” Each time you recall a
you try to think of something, seeing TRIGGER THE MEMORY? memory, it becomes fragile and vulnerable
the world in front of you is a major to change. Even though you don’t actually
distraction. So, closing your eyes helps We store a lot more information in the remember, you’ve heard of this song,
limit the distraction, especially when brain than we can intentionally recall. your friend looked very confident and you
you try to retrieve a highly visual piece What we can retrieve depends largely on may end up convincing yourself about
of information. But it’s highly individual. the cues given, either from other people or this experience. And this becomes a new
Some people may find it works while the environment. If memories are a pile of memory (see “Can I trust my memories?”,
others don’t. YY jigsaw puzzle pieces, cues are the picture on page 36). YY

40 | NewScientist | 27 October 2018