Craig: Hi, I'm Craig. Tehehehe. And this is mental_floss on YouTube. Today I'm gonna answer Tim B's big question: Why are people ticklish?

No one knows for sure why people are ticklish but luckily for us there are people who study this for a living. Lucky for them too, that sounds like a great job. So I'm gonna talk about some of their findings today to tickle your fancy. What's a fancy? Let's get started.

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(laughing) oh, oh stop it. Oh, stop. In 1997 the writers of a study published in the journal Cognition and Emotion hypothesized that because people who are tickled laugh, they must already be in a happy mood. They tested their theory by dividing 72 undergraduates into two groups.

One group was shown comedy and Saturday Night Live clips before being tickled, another group was shown an un-funny video before being tickled. It was probably a WheezyWaiter video. For their theory to be correct, subject would have had to laugh more while being tickled after the comedy clips, but the groups laughed in equal amounts.

That's science-talk for, "People laugh while being tickled no matter what mood they're in," meaning the laughter has nothing to do with actually being happy, tickling was nothing more than a reflex."

Another study done in 2013 at the University of Tuebingen in Germany found that tickling primarily activates two parts of the brain: the rolandic operculum and the hypothalamus.

The rolandic operculum is also stimulated during regular laughter and emotions in general, but the hypothalamus only activates during tickling, not other kinds of laughter. Interestingly, it's the same part of the brain that also deals with pain and instincts like fight or flight.

These two studies show that tickling is a reflex, so it probably evolved over time. We can't know exactly why, but scientists have some theories, as they tend to.

According to expert Dr. Glenn Weisfeld-- is he German, what should my accent be? Sh-- I'll just do American, "The structures of the body that are most vulnerable to tickling are also the ones that are most vulnerable to attack. We may be responsive to tickling because it gives us practice in defending ourselves." Ye-haw.

The scientists behind the University of Tuebingen study had a similar theory. They believe that parents began tickling their children to prepare them to defend themselves. That's why I tickle myself. Tehehe--haCHA

Another possibility comes from the book Laughter: A Scientific Investigation, by neuroscientist Robert R. Provine. He wrote that tickling originated as a form of social bonding. A parent tickles their baby, then the baby laughs in response. The tickling tends to stop when the baby starts a fuss, so the laughter ends.

Thanks for watching mental_floss on YouTube, which is made with the help of all of these tickle monsters. If you have a big question of your own that you'd like answered, leave it below in the comments. I'll see you next week.

Tehehe. You knew I was gonna do that, come on.

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