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Speaker 1: Welcome to brain stuff from how stuff works, Hey, brain stuff,

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Speaker 1: it's Christian Seger here. Deja vu is French for the

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Speaker 1: term already seen, and the term was coined by a

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Speaker 1: scientist named A Meal bureau Rock in eighteen seventies six,

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Speaker 1: and what it refers to is the feeling that you've

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Speaker 1: experienced something before. There's actually a lot of different terms

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Speaker 1: that can be used to specify this type of experience,

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Speaker 1: from deja goat, which means already tasted, to deja chante,

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Speaker 1: which means already sung. Now, these episodes of deja vu,

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Speaker 1: they usually last ten to thirty seconds long, and about

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Speaker 1: two thirds of people say they've experienced it, and rates

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Speaker 1: seem to be higher in people who are fifteen to

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Speaker 1: twenty five years old, have higher incomes, travel more, are

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Speaker 1: more educated and more open minded, are politically liberal, and

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Speaker 1: have psychiatric disorders like anxiety, depression, dissociative disorders, and schizophrenia.

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Speaker 1: Fun science doesn't know exactly what causes deja vu, and

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Speaker 1: there are over forty theories about it. That's a lot

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Speaker 1: researchers don't even agree on how to categorize it, but

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Speaker 1: broadly we can talk about two types. Today, we have

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Speaker 1: associative deja vu, in which stimuli trigger and associative memory,

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Speaker 1: and biological deja vu, in which people with brain dysfunction

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Speaker 1: experience strong deja vu. So an example of this, Lots

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Speaker 1: of people with temporal lobe epilepsy report having deja vu

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Speaker 1: right before seizures, and some of them deja vu can

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Speaker 1: even be triggered with electrical stimulation to the brain. Some

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Speaker 1: people with conditions like anxiety and dementia have reported chronic

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Speaker 1: deja vu, in which the feeling is so common and

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Speaker 1: persistent that it disrupts their daily life. And there is

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Speaker 1: a case study of a healthy guy who started taking

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Speaker 1: opamine increasing drugs to fight the flu immediately getting a

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Speaker 1: bunch of deja vu, and it stopped when he stopped

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Speaker 1: the drugs. Weird researchers think structures in the medial temporal lobe,

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Speaker 1: which is located behind the top part of your ears

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Speaker 1: towards the middle of your brain, are involved because it's

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Speaker 1: involved in our sensory perception in the establishment of our memories.

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Speaker 1: The hippocampus and the rhinal cortex help us consciously form

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Speaker 1: and recall memories. They might save on brain processing power

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Speaker 1: in time by sorting out familiar things from novel things,

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Speaker 1: so they denote I don't know energy to the novel things.

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Speaker 1: The para hippocampal gyrus, though, that helps us determine what's

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Speaker 1: familiar and what's not, and it doesn't retrieve memories to

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Speaker 1: do so, while the amygdala helps process emotional reactions. So

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Speaker 1: here's some popular theories for what is going on with

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Speaker 1: deja vu. Are first is called divided attention theory. You

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Speaker 1: actually have seen the oddly familiar thing before, you just

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Speaker 1: weren't paying enough attention the first time around to record

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Speaker 1: a full memory of it. This was proposed by a

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Speaker 1: guy named Dr Alan Brown, who tested subliminal familiarity with

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Speaker 1: briefly seen images. Our next theory is called hologram theory. Cool, right, Okay,

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Speaker 1: so this is a thing you maybe don't know about holograms.

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Speaker 1: It's that you can cut them up and each piece

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Speaker 1: will display the full image, just at a lower resolution.

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Speaker 1: Dutch psychiatrist Herman Snow proposed that maybe deja vu happens

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Speaker 1: when some fragment of a memory, maybe a familiar smell

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Speaker 1: or an object, triggers the feeling of remembering a full scene.

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Speaker 1: Then we have dual processing theory. The temporal lobes sort

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Speaker 1: of works on incoming information, but twice once upon receipt

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Speaker 1: and again after a quick shunt through the right hemisphere.

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Speaker 1: Maybe sometimes the temporal lobe mislabels data from that second stream,

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Speaker 1: accidentally identifying it as something old rather than something new,

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Speaker 1: giving you a feeling of familiarity. Now, this one was

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Speaker 1: proposed by Robert Efron in nineteen sixty three. And we

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Speaker 1: have one last theory. It's called leaky processing theory. That

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Speaker 1: sounds dangerous maybe dirty. Our brains store current input in

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Speaker 1: short term memory and then transfer the important stuff for

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Speaker 1: you know, like bagel bites, jingles some kind of song

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Speaker 1: to your long term memory. Maybe sometimes a bit of

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Speaker 1: information leaks or jumps or or miss routes directly from

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Speaker 1: short to long term storage, and that is what creates

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Speaker 1: a feeling of familiarity. Check out the brain stuff channel

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Speaker 1: on YouTube, and for more on this and thousands of

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Speaker 1: other topics, visit how stuff works dot com.