Alexander Image/Shutterstock
Source: Alexander Image/Shutterstock

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, when 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 you?

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.

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

The phenomenon of déjà vu (French for "already seen") is, scientifically, pretty poorly understood, but there are a few theories:

  • 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, so 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.
University of Bristol
Source: University of Bristol

Déjà vu is estimated to occur in 60-70% of us, most commonly in those between the ages of 15 and 25. Why? We have no idea. Interestingly, though, 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, since episodes of déjà vu are completely unexpected—not to mention, for most of us, extremely rare—real empirical research on the topic is next to impossible.

What are your experiences with déjà vu? 

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