What is memory, and how does it work?

What exactly is memory? Catherine Loveday is a neuropsychologist at the University of Westminster and author of several books exploring the brain and human memory.

Catherine - So that's a really interesting question because a lot of people, I think, think of memory as the last time I rode a bike, I remember what happened or the first time I rode a bike. So they can vividly picture what they were doing and re-experience it. And that is a really important part of memory, but memory is a lot more than that. So the knowledge of what a bicycle is, and how to spell it, that kind of knowledge is part of our memory system. Knowing how to ride a bike is also a different part of our memory system. And even being able to kind of follow a set of directions and hold those in our head for a temporary period of time, that is also using yet a different part of our memory system. And what people may be surprised about is that even planning a trip in the future or planning anything involves using our memory system because we have to think back. And then of course there's all the unconscious ways in which our memories impact us. You know, the way we are affected by advertising our kind of intuitive sense that somebody isn't feeling very happy. All of those things are the kind of unconscious part of our memory system. So I guess I would say that memory really is any way in which the past experiences we've had affect the way we are thinking or feeling or behaving in the present moment.

Chris - And it's all interconnected, isn't it? Because I know someone did a test on me once where they gave me a piece of paper and said, write out all the letters on a computer keyboard. And I said, well I've no idea where they all are. And they said type your name on your imaginary keyboard. And suddenly I realised I knew where all the letters were and I could write them down. And so it's, we use one form of memory to influence another in that respect, don't we? Are there different parts of the brain though that segregate with this sort of memory function tends to happen here?

Catherine - Yeah, so I think that's another thing that's really interesting about memory because it's distributed across a lot of the brain. So lots of different areas of the brain are involved in remembering, but there are some structures in the brain that are particularly important. So the hippocampus, which is a small seahorse shaped structure towards the middle of our brain, that's really important for kind of encoding the memories and consolidating them. But then the prefrontal cortex at the front, I think of that as being a little bit like a librarian who's sort of in charge of the memory system and then who've got the cerebellum at the back, which is more involved in those kind of procedural memories that you were talking about. Things like learning, knowing how to ride a bike or even just walking and talking. All of these things involve that area of the brain. And then there's the amygdala, which is really important for emotional content. So these structures are all connected, but they all contribute in different ways to each memory task that we're doing.

Chris - And do we know, when we physically make a memory, what that looks like in the network of brain cells we have, how do we actually remember stuff?

Catherine - Essentially imagine you're sitting in a nice park, for example, eating a nice piece of chocolate cake or something. And the experiences that you are having are, you are holding them in your consciousness and after, if you kind of pay attention to that for any length of time, the hippocampus starts to kind of combine these together into a connected trace so that really any one part of that will sort of trigger the rest of the trace so that the whole memory can come back to us. But also it starts to connect it with memories from the past. So whether you've been to this place before or whether you've eaten chocolate in the past and gradually it creates these sort of strong memory traces where it connects as a cellular network. It connects these different sensory experiences together into a combined trace. And then ultimately that kind of shifts out and is is kind of stored across the outside of the brain.

Chris - And when we forget something, we've made a memory like that but then we can't remember it. What happened there?

Catherine - The main reason that we forget something is that we didn't rehearse it. So you can think of this a little bit like revising for an exam and if you go to the lesson and then you never look at the stuff again, you kind of forget it. But if you go back and you go over it again, then you are more likely to remember it and basically we do this with pretty much everything in life. So if you've had that nice sort of sitting in the park, chocolate ice cream or chocolate cake kind of moment, then if you reflect back on that later in the day or you have a conversation with someone, you are rehearsing it, you are activating those cells again. And what we know from memory is the more often you activate that memory trace, the stronger it becomes and the easier it is to remember. But if we don't activate it, we essentially forget about it. So we forget things either because we haven't thought about them again, maybe because they weren't important enough or sometimes because we haven't had the time, we haven't had any relaxation space or any rest or whatever and we are just not practicing and rehearsing and reactivating those memory traces. And sometimes there's a memory trace that we can't activate because I mentioned earlier on the prefrontal cortex, this kind of librarian part, we can't sort of quite reach it. So I think of it as the librarian not being able to quite be able to find that book. But given time often it will, it will come back to us. Sometimes we forget something because we didn't actually pay attention in the first place, of course.