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Steve Turnbull
November 2016.
266
Where are our memories stored?
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There isn’t a single place in the brain where memories are stored. We can say that because there’s never been evidence of someone who has damaged a particular part of the brain and lost all their memories, but has everything else intact. Memory, therefore, seems to be distributed across the brain.

What we’re getting better at understanding is the areas that are needed for the formation or consolidation of new memories. There do seem to be areas of the brain that are specifically needed for the formation of new memories. There are patients who have what’s called anterograde amnesia, which is the inability to form new memories because of damage to the hippocampus - there’s one on each side the brain. If the hippocampi are damaged it seems to stop us forming new memories.

"It does seem that newer memories are more vulnerable than older ones. So if you have a trauma - a head injury for example - the memories that could be lost are those formed immediately before the injury."

There doesn’t seem to be a different location for newer and older memories. But it does seem that newer memories are more vulnerable than older ones. So if you have a trauma - a head injury for example - the memories that could be lost are those formed immediately before the injury. And then it works back. So if you have a bump on the head you might not remember exactly what happened before it. Quite a big bump might mean you don’t remember what happened that day. Bigger than that and you might lose a year.

Sometimes those memories come back, and if they can come back you would say it’s not the storage that has gone but the ability to recall it. But it does seem there is a tendency for newer memories to be more vulnerable than older memories. But we don’t think that’s because they’re stored in a different place, we think they’re less consolidated.

"A person’s face, their name, their smell, how they walk or a place you once went with them… any of those elements in your set of memories can trigger the rest of the memory."

One of the properties of human memory is that it is content addressable. Normally in a filing system you would store your records or the people that you have met in alphabetical order - by their name, and then having dug up the name you would get all the associated information: phone numbers, addresses and so on. Human memories are not like that. A person’s face, their name, their smell, how they walk or a place you once went with them… any of those elements in your set of memories can trigger the rest of the memory. So filing doesn’t seem to happen in any name order or by any other single attribute.

In terms of what you choose to remember and what you don’t, there is some evidence that you encode things that you’re not even aware of. We are carrying around images and things that we’re not even aware that we’ve seen - maybe things that we didn’t focus on or tend to at the time, and they can enter our memory without conscious awareness.