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Welcome to brain Stuff from How Stuff Works.

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Hey, brain Stuff, I'm Lauren Voke Obama, and I've

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got a classic episode for you today from

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our former host, Christian Sager. He's

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talking about how deja vu works. He's

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talking about how deja vu works. Hey,

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brain Stuff. It's Christian Sager here. Deja

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vu is French for the term

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already seen in the term

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was coined by a scientist named

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A Meal bureau Rock in eighteen

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seventies six, and what it refers to is

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the feeling that you've experienced

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something before. There's actually

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a lot of different terms that can be used to specify

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this type of experience, from deja

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goat, which means already tasted,

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to deja chante, which means

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already sung. Now. These

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episodes of deja vu, they usually

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last ten to thirty seconds long, and about

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two thirds of people say they've

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experienced STD and rates seem

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to be higher in people who are fifteen

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to twenty five years old, have higher

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incomes, travel more,

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are more educated and more open

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minded, are politically liberal,

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and have psychiatric disorders like

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anxiety, depression, dissociative disorders,

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and schizophrenia. Fun science

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doesn't know exactly what causes deja

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vu, and there are over forty theories

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about it. That's a lot researchers

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don't even agree on how to categorize

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it, but broadly we can talk about

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two types. Today. We have associative

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deja vu, in which stimuli

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trigger and associative memory,

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and biological deja

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vu, in which people with brain dysfunction

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experience strong deja vus.

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So an example of this, Lots of people

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with temporal lobe epilepsy report

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having deja vu right before seizures,

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and some of them deja vu can even

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be triggered with electrical stimulation

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to the brain. Some

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people with conditions like anxiety and

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dementia have reported chronic deja vu,

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in which the feeling is so common and persistent

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that it disrupts their daily life. And

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there is a case study of a healthy guy

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who started taking dopamine increasing

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drugs to fight the flu

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immediately getting a bunch of deja vu, and

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it stopped when he stopped the drugs.

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Weird researchers think

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structures in the medial temporal

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lobe, which is located behind the top

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part of your ears towards the middle of your

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brain, are involved because

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it's involved in our sensory perception

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in the establishment of our memories.

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The hippocampus and the rhinal cortex

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help us consciously form and recall

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memories. They might save on

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brain processing power in time

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by sorting out familiar things from novel

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things, so they denote I don't

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know energy to the novel things. The

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para hippocampal gyrus, though,

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that helps us determine what's familiar

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and what's not, and it doesn't retrieve

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memories to do so, while

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the amygdala helps process

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emotional reactions. So

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here's some popular theories for what is

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going on with deja vu. Our

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first is called divided attention

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theory. You actually have seen

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the oddly familiar thing before, you

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just weren't paying enough attention the first time

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around to record a full memory of it. This

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was proposed by a guy named Dr Alan Brown,

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who tested subliminal familiarity

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with briefly seen images. Our

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next theory is called hologram theory.

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Cool, right, Okay, so this is

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a thing you maybe don't know about

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holograms. It's that you can cut them

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up and each piece will display

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the full image, just at a lower

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resolution. Dutch psychiatrist

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Herman Snow proposed that maybe deja

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vu happens when some fragment

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of a memory, maybe a familiar smell

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or an object, triggers the

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feeling of remembering a full scene.

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Then we have dual processing theory.

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The temporal lobe sort of works

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on incoming information, but twice

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once upon receipt and again after

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a quick shunt through the right hemisphere.

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Maybe sometimes the temporal lobe

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mislabels data from that second

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stream, accidentally identifying

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it as something old rather

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than something new, giving you a feeling

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of familiarity. Now, this one

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was proposed by Robert Efron

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in nineteen three. And

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we have one last theory. It's

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called leaky processing theory.

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That sounds dangerous. Maybe dirty

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our brains store current input

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in short term memory and then transfer

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the important stuff for you know, like

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bagel bites, jingles, some kind of song

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to your long term memory.

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Maybe sometimes a bit of

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information leaks or jumps

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or or miss routes directly from

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short to long term storage,

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and that is what creates a

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feeling of familiarity. Today's

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episode was written by me and produced by

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Tyler Clang. For more on this and lots

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of other memorable topics, visit our home planet,

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how stuff works dot com