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Speaker 1: Welcome to brain Stuff from How Stuff Works. Hey, brain Stuff,

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Speaker 1: I'm Lauren Voke Obama, and I've got a classic episode

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Speaker 1: for you today from our former host, Christian Sager. He's

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Speaker 1: talking about how deja vu works. He's talking about how

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Speaker 1: deja vu works. Hey, brain Stuff. It's Christian Sager here.

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Speaker 1: Deja vu is French for the term already seen in

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Speaker 1: the term was coined by a scientist named A Meal

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Speaker 1: bureau Rock in eighteen seventies six, and what it refers

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Speaker 1: to is the feeling that you've experienced something before. There's

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Speaker 1: actually a lot of different terms that can be used

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Speaker 1: to specify this type of experience, from deja goat, which

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Speaker 1: means already tasted, to deja chante, which means already sung. Now.

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Speaker 1: These episodes of deja vu, they usually last ten to

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Speaker 1: thirty seconds long, and about two thirds of people say

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Speaker 1: they've experienced STD and rates seem to be higher in

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Speaker 1: people who are fifteen to twenty five years old, have

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Speaker 1: higher incomes, travel more, are more educated and more open minded,

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Speaker 1: are politically liberal, and have psychiatric disorders like anxiety, depression,

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Speaker 1: dissociative disorders, and schizophrenia. Fun science doesn't know exactly what

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Speaker 1: causes deja vu, and there are over forty theories about it.

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Speaker 1: That's a lot researchers don't even agree on how to

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Speaker 1: categorize it, but broadly we can talk about two types. Today.

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

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Speaker 1: associative memory, and biological deja vu, in which people with

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Speaker 1: brain dysfunction experience strong deja vus. So an example of this,

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

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

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

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

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

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

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

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Speaker 1: taking dopamine increasing drugs to fight the flu immediately getting

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

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Speaker 1: stopped the drugs. Weird researchers think structures in the medial

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Speaker 1: temporal lobe, which is located behind the top part of

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Speaker 1: your ears towards the middle of your brain, are involved

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Speaker 1: because it's involved in our sensory perception in the establishment

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Speaker 1: of our memories. The hippocampus and the rhinal cortex help

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Speaker 1: us consciously form and recall memories. They might save on

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Speaker 1: brain processing power in time by sorting out familiar things

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Speaker 1: from novel things, so they denote I don't know energy

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Speaker 1: to the novel things. The para hippocampal gyrus, though, that

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Speaker 1: helps us determine what's familiar and what's not, and it

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Speaker 1: doesn't retrieve memories to do so, while the amygdala helps

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Speaker 1: process emotional reactions. So here's some popular theories for what

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Speaker 1: is going on with deja vu. Our first is called

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Speaker 1: divided attention theory. You actually have seen the oddly familiar

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Speaker 1: thing before, you just weren't paying enough attention the first

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Speaker 1: time around to record a full memory of it. This

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Speaker 1: was proposed by a guy named Dr Alan Brown, who

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Speaker 1: tested subliminal familiarity with briefly seen images. Our next theory

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Speaker 1: is called hologram theory. Cool, right, Okay, so this is

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Speaker 1: a thing you maybe don't know about holograms. It's that

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Speaker 1: you can cut them up and each piece will display

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Speaker 1: the full image, just at a lower resolution. Dutch psychiatrist

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Speaker 1: Herman Snow proposed that maybe deja vu happens when some

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Speaker 1: fragment of a memory, maybe a familiar smell or an object,

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Speaker 1: triggers the feeling of remembering a full scene. Then we

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Speaker 1: have dual processing theory. The temporal lobe sort of works

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Speaker 1: on incoming information, but twice once upon receipt and again

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Speaker 1: after a quick shunt through the right hemisphere. Maybe sometimes

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

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

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

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Speaker 1: by Robert Efron in nineteen three. And we have one

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Speaker 1: last theory. It's called leaky processing theory. That sounds dangerous.

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Speaker 1: Maybe dirty our brains store current input in short term

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Speaker 1: memory and then transfer the important stuff for you know,

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Speaker 1: like bagel bites, jingles, some kind of song to your

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Speaker 1: long term memory. Maybe sometimes a bit of information leaks

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Speaker 1: or jumps or or miss routes directly from short to

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Speaker 1: long term storage, and that is what creates a feeling

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Speaker 1: of familiarity. Today's episode was written by me and produced

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Speaker 1: by Tyler Clang. For more on this and lots of

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Speaker 1: other memorable topics, visit our home planet, how stuff works

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Speaker 1: dot com