Chris Moulin, PhD, Professor of Cognitive Neuropsychology at Grenoble Alpes University, France:  During a déjà vu there is a conflict of two signals in the brain. One signal saying, this is something familiar, something I have seen before, and the other signal, which may arise a little later, says, this is not possible, I cannot remember this, this is something I haven’t seen before. So, it is a conflict or mismatch between two different evaluations at the same moment. 

Our thinking about déjà vus is well informed by how memory systems in the brain work. We know there is a system that is always active, trying to detect things in the environment that we know and that directs our attention to new things. This system works very quickly and automatically. Then there is a slower, more sophisticated system that tries to retrieve information and recalls things from the past. Déjà vus show the functions of these two systems. It is very rare, but sometimes these two systems fall out of sync. When they do, one has the strange feeling that something is familiar, but one can’t explain why. Or one is even sure it has not happened before. This view is inspired by how we think the brain works in general regarding memory.

The analysis of a déjà vu is difficult. There have been advances in about the last five years because a few teams – there is a team led by Anne Cleary in America, Colorado, and another team by Akira O’Connor in Scotland at St. Andrews University – have been developing experiments that provoke something very similar to déjà vu in healthy people. Anne Cleary presents participants virtual reality environments that can make people think they are experiencing something very similar to what they have already experienced. This similarity is interpreted as familiarity. People think it is something they have experienced before, but in reality, they haven’t.

Akira O’Connor’s team in Scotland does something similar but with words, creating the same sense of conflict. Their latest work on déjà vu involved scanning people’s brains using functional magnetic resonance imaging. This way, they can see what happens when someone has such a conflict described as déjà vu. The method has been a breakthrough in recent years. But it is still the case that when people experience something like déjà vu in experiments it is only like an analogue of déjà vu but not as impressive or unusual as the real déjà vu that occurs spontaneously and infrequently as in daily life.  We are therefore very cautious after conducting the experiments to ask the participants how comparable the experience was to a déjà vu. Although people are saying it is like a déjà vu when asked on rating scales how intense it is, they say it is quite weak compared to some very strong déjà vus that we can experience in real life. If you enter an experiment expecting to have something unusual, it obviously will not be as surprising or impressive as it otherwise would be. And you never know in which situations people feel a déjà vu. 

We have also worked on comparing déjà vus with other experiences and searched in different countries and languages. We have tried to put people’s experiences together and provide them a definition to see if, when they say they have déjà vu, it fits our definition of what we call déjà vu. And mostly the results are reassuring, but there are some differences. Many people say they had déjà vu, but when asked how much they agree with our definition of déjà vu, they do not use the same definition of déjà vu.

All over the place, people seem to use the word déjà vu. To our knowledge, even in Russia. It seems that almost everyone who uses the term déjà vu uses it the same way. 

What is interesting is that in French the term déjà vu simply means “already seen,” which does not necessarily mean this strange experience. So, we researched and found differences between how English speakers and French speakers describe déjà vu. I think this is because for an English speaker, once you talk about déjà vu, which is this mysterious French word, you talk about something specific, something strange, and something different. While for French speakers, you talk about something that is a continuation of normal memory experiences and normal feelings that they have already seen something. French speakers use “le phénomène de déjà vu” for the feeling of what we just call déjà vu. The linguistic element is an interesting point. 

Relatively recently we worked on the opposite of déjà vu, which is jamais vu. We asked people to say the same word over and over again until it sounds strange. This feeling of strangeness is the opposite of déjà vu because it is when you know something very well, but then it feels unreal or unfamiliar. We even won an Ig Nobel Prize for Literature for this research. We have worked a bit on these kinds of things to build a bridge between all these different weird experiences. We are now trying to argue that they are all quite normal. They do not happen often, but when they do, it is a sign that something good is happening, that you have a certain awareness of how your mind works. 

Recorded by Stefanie Flunkert.

Question first published on 25.10.2011

Question answered again on 20.9.2026