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October 1, 2015

What the Heck is Déjà Vu? Why Do I Get It and Some People Never Do?

This is the latest post in my #BrainBits series, where I'll answer your burning neuroscience questions in 60 seconds or less. If you have a question you'd like me to answer, you can e-mail me, tweet me, or submit your questions anonymously here.

Erika Wittlieb (Pixabay)
What is déjà vu?  Many of us know the feeling. You'll be going about your day, minding your own business, folding some laundry...nothing out of the ordinary. Suddenly a sensation of familiarity washes over you, and you're completely aware that it's happening. I've been here before. Except you haven't. Or have I? You might try to think back and pinpoint when you'd experienced this moment before. But just as quickly as the feeling hits you, it's gone again.

Did you predict the future? Were you seeing something from a past life? What the heck is déjà vu, anyway?

Perhaps unsurprisingly, déjà vu (French for "already seen") is, scientifically, pretty poorly understood. There are a few theories, however:

University of Bristol
  • Déjà vu may be the result of some sort of "mismatch" in how we're simultaneously sensing and perceiving the world around us. Perhaps we smell something familiar, for example, and our mind is instantly transported to the first time we smelled it. (It's a vague theory, though, and doesn't explain why most déjà vu episodes don't reflect true past events.)
  • Déjà vu may be a fleeting malfunctioning between the long- and short-term circuits in the brain. The information our brain takes in about its surroundings may "shortcut" its way straight to long-term memory, bypassing typical storage transfer mechanisms. When we have a moment of déjà vu, it feels as though we're experiencing something from our distant past. 
  • A region of the brain called the rhinal cortex, involved in detecting familiarity, may be inexplicably activated without actually activating memory (hippocampal) circuits. That may explain why déjà vu episodes feel so non-specific when we try to figure out where and when we had previously experienced a particular moment. In fact, some patients with epilepsy reliably experience déjà vu at the beginning of a seizure. For these individuals, experimental stimulation of the rhinal cortex — and not so much the hippocampus itself — induces déjà vu.

Déjà vu is estimated to occur in 60-70% of people, and most commonly in those between the ages of 15 and 25 years. (Why? No idea.) Interestingly, I had previously written about déjà vu years ago out of my own curiosity on the matter, having experienced it fairly frequently. I'm now 26, though, and can't remember the last time I had an episode.

Are any of these theories correct? We may never know. After all, an episode of déjà vu is completely unexpected and, for most of us, extremely rare. Empirical research on the topic is next to impossible.

The most parsimonious explanation, then, is likely the following:


What about you?
Do you experience déjà vu?
Let us know
In this anonymous poll!

Stay tuned for the next #BrainBits: "What are hiccups?"

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