WEBVTT - BrainStuff Classics: How Does Déjà vu Work?

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<v Speaker 1>Welcome to brain Stuff from How Stuff Works. Hey, brain Stuff,

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<v Speaker 1>I'm Lauren Voke Obama, and I've got a classic episode

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

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<v Speaker 1>talking about how deja vu works. He's talking about how

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

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<v Speaker 1>Deja vu is French for the term already seen in

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<v Speaker 1>the term was coined by a scientist named A Meal

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<v Speaker 1>bureau Rock in eighteen seventies six, and what it refers

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

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<v Speaker 1>actually a lot of different terms that can be used

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<v Speaker 1>to specify this type of experience, from deja goat, which

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<v Speaker 1>means already tasted, to deja chante, which means already sung. Now.

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<v Speaker 1>These episodes of deja vu, they usually last ten to

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<v Speaker 1>thirty seconds long, and about two thirds of people say

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<v Speaker 1>they've experienced STD and rates seem to be higher in

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<v Speaker 1>people who are fifteen to twenty five years old, have

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<v Speaker 1>higher incomes, travel more, are more educated and more open minded,

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<v Speaker 1>are politically liberal, and have psychiatric disorders like anxiety, depression,

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

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<v Speaker 1>causes deja vu, and there are over forty theories about it.

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<v Speaker 1>That's a lot researchers don't even agree on how to

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<v Speaker 1>categorize it, but broadly we can talk about two types. Today.

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<v Speaker 1>We have associative deja vu, in which stimuli trigger and

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<v Speaker 1>associative memory, and biological deja vu, in which people with

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<v Speaker 1>brain dysfunction experience strong deja vus. So an example of this,

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<v Speaker 1>Lots of people with temporal lobe epilepsy report having deja

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<v Speaker 1>vu right before seizures, and some of them deja vu

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<v Speaker 1>can even be triggered with electrical stimulation to the brain.

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<v Speaker 1>Some people with conditions like anxiety and dementia have reported

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<v Speaker 1>chronic deja vu, in which the feeling is so common

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<v Speaker 1>and persistent that it disrupts their daily life. And there

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<v Speaker 1>is a case study of a healthy guy who started

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<v Speaker 1>taking dopamine increasing drugs to fight the flu immediately getting

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<v Speaker 1>a bunch of deja vu, and it stopped when he

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<v Speaker 1>stopped the drugs. Weird researchers think structures in the medial

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<v Speaker 1>temporal lobe, which is located behind the top part of

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<v Speaker 1>your ears towards the middle of your brain, are involved

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<v Speaker 1>because it's involved in our sensory perception in the establishment

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<v Speaker 1>of our memories. The hippocampus and the rhinal cortex help

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<v Speaker 1>us consciously form and recall memories. They might save on

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<v Speaker 1>brain processing power in time by sorting out familiar things

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<v Speaker 1>from novel things, so they denote I don't know energy

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<v Speaker 1>to the novel things. The para hippocampal gyrus, though, that

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<v Speaker 1>helps us determine what's familiar and what's not, and it

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<v Speaker 1>doesn't retrieve memories to do so, while the amygdala helps

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<v Speaker 1>process emotional reactions. So here's some popular theories for what

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<v Speaker 1>is going on with deja vu. Our first is called

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<v Speaker 1>divided attention theory. You actually have seen the oddly familiar

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<v Speaker 1>thing before, you just weren't paying enough attention the first

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<v Speaker 1>time around to record a full memory of it. This

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<v Speaker 1>was proposed by a guy named Dr Alan Brown, who

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<v Speaker 1>tested subliminal familiarity with briefly seen images. Our next theory

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<v Speaker 1>is called hologram theory. Cool, right, Okay, so this is

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

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<v Speaker 1>you can cut them up and each piece will display

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<v Speaker 1>the full image, just at a lower resolution. Dutch psychiatrist

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<v Speaker 1>Herman Snow proposed that maybe deja vu happens when some

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<v Speaker 1>fragment of a memory, maybe a familiar smell or an object,

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<v Speaker 1>triggers the feeling of remembering a full scene. Then we

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<v Speaker 1>have dual processing theory. The temporal lobe sort of works

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<v Speaker 1>on incoming information, but twice once upon receipt and again

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<v Speaker 1>after a quick shunt through the right hemisphere. Maybe sometimes

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<v Speaker 1>the temporal lobe mislabels data from that second stream, accidentally

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<v Speaker 1>identifying it as something old rather than something new, giving

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<v Speaker 1>you a feeling of familiarity. Now, this one was proposed

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<v Speaker 1>by Robert Efron in nineteen three. And we have one

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<v Speaker 1>last theory. It's called leaky processing theory. That sounds dangerous.

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<v Speaker 1>Maybe dirty our brains store current input in short term

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<v Speaker 1>memory and then transfer the important stuff for you know,

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<v Speaker 1>like bagel bites, jingles, some kind of song to your

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<v Speaker 1>long term memory. Maybe sometimes a bit of information leaks

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<v Speaker 1>or jumps or or miss routes directly from short to

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<v Speaker 1>long term storage, and that is what creates a feeling

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<v Speaker 1>of familiarity. Today's episode was written by me and produced

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<v Speaker 1>by Tyler Clang. For more on this and lots of

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<v Speaker 1>other memorable topics, visit our home planet, how stuff works

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<v Speaker 1>dot com