Welcome to brain Stuff from How Stuff Works. Hey, brain Stuff, I'm Lauren Voke Obama, and I've got a classic episode for you today from our former host, Christian Sager. He's talking about how deja vu works. He's talking about how deja vu works. Hey, brain Stuff. It's Christian Sager here. Deja vu is French for the term already seen in the term was coined by a scientist named A Meal bureau Rock in eighteen seventies six, and what it refers
to is the feeling that you've experienced something before. There's actually a lot of different terms that can be used to specify this type of experience, from deja goat, which means already tasted, to deja chante, which means already sung. Now.
These episodes of deja vu, they usually last ten to thirty seconds long, and about two thirds of people say they've experienced STD and rates seem to be higher in people who are fifteen to twenty five years old, have higher incomes, travel more, are more educated and more open minded, are politically liberal, and have psychiatric disorders like anxiety, depression,
dissociative disorders, and schizophrenia. Fun science doesn't know exactly what causes deja vu, and there are over forty theories about it. That's a lot researchers don't even agree on how to categorize it, but broadly we can talk about two types. Today. We have associative deja vu, in which stimuli trigger and associative memory, and biological deja vu, in which people with
brain dysfunction experience strong deja vus. So an example of this, Lots of people with temporal lobe epilepsy report having deja vu right before seizures, and some of them deja vu can even be triggered with electrical stimulation to the brain. Some people with conditions like anxiety and dementia have reported chronic deja vu, in which the feeling is so common
and persistent that it disrupts their daily life. And there is a case study of a healthy guy who started taking dopamine increasing drugs to fight the flu immediately getting a bunch of deja vu, and it stopped when he stopped the drugs. Weird researchers think structures in the medial temporal lobe, which is located behind the top part of your ears towards the middle of your brain, are involved because it's involved in our sensory perception in the establishment
of our memories. The hippocampus and the rhinal cortex help us consciously form and recall memories. They might save on brain processing power in time by sorting out familiar things from novel things, so they denote I don't know energy to the novel things. The para hippocampal gyrus, though, that helps us determine what's familiar and what's not, and it doesn't retrieve memories to do so, while the amygdala helps process emotional reactions. So here's some popular theories for what
is going on with deja vu. Our first is called divided attention theory. You actually have seen the oddly familiar thing before, you just weren't paying enough attention the first time around to record a full memory of it. This was proposed by a guy named Dr Alan Brown, who tested subliminal familiarity with briefly seen images. Our next theory is called hologram theory. Cool, right, Okay, so this is
a thing you maybe don't know about holograms. It's that you can cut them up and each piece will display the full image, just at a lower resolution. Dutch psychiatrist Herman Snow proposed that maybe deja vu happens when some fragment of a memory, maybe a familiar smell or an object, triggers the feeling of remembering a full scene. Then we have dual processing theory. The temporal lobe sort of works on incoming information, but twice once upon receipt and again
after a quick shunt through the right hemisphere. Maybe sometimes the temporal lobe mislabels data from that second stream, accidentally identifying it as something old rather than something new, giving you a feeling of familiarity. Now, this one was proposed by Robert Efron in nineteen three. And we have one last theory. It's called leaky processing theory. That sounds dangerous.
Maybe dirty our brains store current input in short term memory and then transfer the important stuff for you know, like bagel bites, jingles, some kind of song to your long term memory. Maybe sometimes a bit of information leaks or jumps or or miss routes directly from short to long term storage, and that is what creates a feeling of familiarity. Today's episode was written by me and produced
by Tyler Clang. For more on this and lots of other memorable topics, visit our home planet, how stuff works dot com