Why do I feel I know what is going to happen?

Ginny - So, Déjà vu is a really common experience, but scientists really don't understand what causes it. The main reason for that is that it's very hard to predict when someone is going to have a déjà vu experience or to induce them. So, what we would love is to get someone in an MRI machine having déjà vu and look at what's going on in their brain, but it's really, really difficult to do. Some researchers at Colorado State University recently actually did manage to provoke déjà vu using a kind of immersive visual technology, sort of 3D.

Chris - Like virtual reality.

Ginny - Yeah, sort of virtual reality thing, but very immersive and they showed them various scenes. They found that déjà vu was provoked most regularly when the layout of a scene was similar to one they'd seen previously. So, the participants knew that the scene was new because they knew that they were only going to see the scene once. So, they have that feeling of, "I can't recognise this scene" because they haven't seen it before. But because the layout was similar, they got that déjà vu experience. So, that suggested that it might be that you get it when you've seen elements that are seen before, when there's something familiar about it, but you can't quite place where that familiarity is coming from and you know that the scene is new, that you shouldn't recognise it, and that's what gives you the weird feeling of déjà vu.

Dave - I once had a bike accident. I hit my head rather hard and for a while after, I got this kind of, "I've met this person before" someone I'd meet someone at a party or something. And after about 15 minutes, I was sure I've met them ages ago, but I wasn't sure whether it was Cambridge I probably them ages ago because Cambridge is a very small town or whether there was something. It was like my brain, my memory wasn't quite working properly.

Ginny - Well, we actually know a bit about what area of the brain is involved because some people who have epilepsy get déjà vu as part of their symptoms and that happens when you get epilepsy that occurs in your temporal lobe which is a bit sort of just above the ear. So, it could be that if you had a bit of damage going on there because you'd hit your head, that might make you more likely to have these feelings.

Chris - Has anyone else ever had déjà vu?

Dominic - I think I had it with sorts of memories sometimes, things that I don't remember perfectly and I think, why do I feel slightly familiar in this place and I think actually, when I was 5, maybe I was here.

Chris - It happens to me when I get sleep deprived and that, I think is interesting because also, sleep deprivation does trigger brain patterns of activity that we know also trigger epilepsy and people who are epileptic. So, it's interesting that you said epileptics get it but also sleep dep can do it, Ginny.

Ginny - Yeah, they've done quite a lot of sort of retrospective studies where they ask people, when do you get déjà vu? How often do you get it? So, they found that people do get it more often when they're tired and also, when they're stressed. But there was some other interesting things like it's more common in young people and it's more common in well-educated people which doesn't really seem to make that much sense. But also, people who travel a lot, which you can kind of understand a bit more because you're more likely to go to places that are new. And of course, you can only actually have déjà vu in a place that's new. You can't have it in your home because you know you've already been there. You know why it's familiar. So, that one kind of makes sense, but I can't get my head around why it's young, well-educated people who seem to get it more.