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Hank explains the little we know about the perceptual condition known as synesthesia, where a person involuntary associates one sensation or experience with another sensation.

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You might think you'd have to be on some kind of psychoactive street drug to see music or taste the feeling of the wind in your hair. Not the case! You could instead have synesthesia. A neurological condition in which two senses are perceived simultaneously. Synesthesia is Greek for 'joined perception', and it can involve mixing any of our senses, sometimes even three or more of them at once, although that's more rare.   Researchers have found that synesthesia is often inherited. Though members of a family will sometimes have different types. Scientists at Baylor University think that they've identified a region of DNA on chromosome 16 as the culprit, at least for the most common form called 'colored sequence synesthesia'. This is when people perceive letters, or numbers, or words, or days of the week -- whatever -- as being inherently colored. Like the letter A is red and the number 4 is brown.   And you might be thinking "Psshh yeah, that person probably just had a red A magnet on their refrigerator when they were a little kid, so they think of A's as being red." But most studies suggest that there is something funny going on with the synesthetes' brain.    Although there is no established way to diagnose synesthesia, true synesthetes have a few things in common. One: their mixed perception of senses is involuntary, it happens without them thinking about it. Two: their condition is experienced rather than imagined. Like if I asked 'what color is a triangle?', a synesthetes would see a color, say yellow, immediately and they wouldn't have to think about it before their brain made the association. Three: the sensory mix up is durable, meaning that the associations are always the same. Bacon can't taste like Bach one day and Beethoven the next. Four: often the secondary perception will be more memorable than the primary one. So if a synesthete always associates the name Dave with the color purple, they'll usually remember the purple first, which tells them that it's Dave. And finally number five: the perceptions may be really emotional. Like "Oh my god, this Elton John song playing in the T.J.Maxx smells like gasoline! Get me out of here!"   Now of course the question is: what are these people's brain up to? One idea is that it might be a defect in the neural structure. Scientists theorize that we're born with our senses sort of all tangled up and then over time, our brains shut down the neural bridges between our senses so we experience them separately. But synesthetes might not be properly shutting down those bridges, making their lives a little bit trippier than everybody else's.   Another theory suggest that synesthesia is caused by neurochemistry. Our neurons communicate with each other through chemicals called neurotransmitters. So it could be that synesthetes have neurotransmitters meant for one part of the brain way over in a different part, or they could lack chemicals called inhibitors that help keep neurotransmitters in check.   This would explain why a lot of synesthetes have different sensory experiences when they're really tired or really hungry, or why it happens to people on hallucinogenic drugs. And of course, because our brains are complicated places, it could also be a combination of all of these things. For now, synesthesia is yet another thing that we don't completely understand about the delicious, amazing things, that are our brains.   Thanks for watching this episode of SciShow. Just because I said that brains are delicious, that doesn't mean that I'm a zombie! And thank you to everyone who suggested that we do this episode on synesthesia. The reason that I didn't want to is that I didn't want to have to say 'synesthesia' 25 times in one episode. But I think I did a pretty good job.   If you have any questions, or ideas for future topics for a SciShow, we're on Facebook and twitter and of course in the comments below. And if you want to continue getting smarter with us, go to youtube.com/scishow and subscribe.