Just Explain It: What Is Déjà Vu?

Have you ever experienced déjà vu? You know, the strong feeling an experience is familiar, while at the same time knowing it hasn’t happened before. Where does it come from

That’s the subject of today’s Just Explain It.

The truth is, even though 60 to 80 percent of us say we’ve experienced it, déjà vu stumps science as much as it stumps the rest of us. That’s because it happens so quickly and so randomly, it’s very difficult to study.

Because it’s so hard to study, scientists haven’t singled out a definitive reason as to why déjà vu – which means "already seen" in French – happens. There are, however, two prevailing theories.

One theory has to do with the areas of the brain that recognize familiarity and recall memories. Although they occupy different parts of the brain, they’re normally in sync. Some scientists theorize that déjà vu occurs when the part that recognizes familiarity misfires and creates a strong sensation of familiarity. They don’t know why it misfires, but it could be triggered by something very, very subtle, even more subtle than a slightly familiar stand-up at the top of an online video. Perhaps it’s a room at your office that’s arranged similarly to one from your childhood. 

[Related: Mind Games: 5 Things You Can Do To Improve Your Memory]

Another déjà vu theory is based on the way we process memories. In it, a new experience doesn’t go through the part of the brain that processes short-term memories. It goes directly to the part that processes long-term ones. When this happens, the memory feels old and familiar, even though it is in fact a new memory.

One thing scientists seemed to have figured out about déjà vu is who’s more likely to encounter the sensation. People aged 15-25 tend to have déjà vu more often than older people. Younger people could experience it more because their brains are more active and they produce more dopamine, which has been linked to déjà vu.

But why is it important to study this fleeting and seemingly harmless feeling? As scientists find out more about déjà vu, they learn about how we retain memories and how some people lose the ability to recall them, like those who suffer from Alzheimer’s disease.

[Related: Could A Drug Prevent Brain Aging?]

Whatever causes this strange sensation, it will continue to challenge scientists and make the rest of us wonder, "Did this already happen?"

Tell us. Have you ever experienced déjà vu? You know, the strong feeling an experience is familiar, while at the same time knowing it hasn’t happened before. Seriously, we’re asking! It's not déjà vu all over again. Give us your feedback in the comments section below, or on Twitter using #JustExplainItNews.

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