Washington State University

Ask Dr. Universe


January 3rd, 2013

Dear Dr. Universe,

Please, we need your help!!! We want to know what makes people ticklish? Why do we laugh when we are tickled? And why are we sometimes ticklish and sometimes not?

Michelle, Sarah, Jacob, Micah, Jeremy, Austin and Taylor
Phoenix, Arizona

Laughter from tickling. David Shankbone, Wikimedia

Laughter from tickling. David Shankbone, Wikimedia

“Tickle” might just be a side effect of some other effect way back in our evolutionary history, says Patrick Carter, who studies the evolution of physiology here at WSU. That means he studies how and why we came to look and operate the way we do.

Professor Carter admits that thinking about tickle can be a lot of fun, and a lot of scientists and philosophers have even thought pretty seriously about it. Socrates, Plato, Francis Bacon; Galileo, and Charles Darwin all thought and wrote about tickle. Because none of them figured it out, though, we’re still working on it.

First, let’s think about types of tickles. I’m sure you’ve thought about how a little tickle, say with a feather under the chin, is different from a serious tickle, like when your buddies tickle torture you.

Scientists call the light tickle KNISMESIS and the heavy tickle GARGALESIS.

Great words, huh? Hey, how about a little gargalesis?

So anyway, where did tickle come from? Depending on who you talk to, the knismesis variety is pretty clear. It probably has to do with the feeling when a tick or other insect is crawling on your body. It tickles, and you brush it away or squash it.

That’s probably too neat an explanation, but what can I say?

Gargalesis is definitely more complicated. WHY would we start laughing hysterically when somebody digs her fingertips into our sides? It seems pretty ridiculous.

Charles Darwin thought that the tickler’s and the ticklee’s relationship had something to do with whether gargalesis was pleasurable or not. Even though a child might enjoy being tickled by a parent, being tickled by a stranger would be frightening.

To test this, psychologist Christine Harris at the University of California, San Diego, built a tickle machine. She figured that if Darwin was right, people would at LEAST need to think they were being tickled by a person, not a machine.

What she found out, however, was that it didn’t make any difference what the subjects thought they were being tickled by.

Another thing that Professor Harris has found is that tickling and humor are not related. She had a bunch of students watch a funny video and then tickled them. Others watched a not-so-funny video and then got tickled. This relied on the “warm-up effect” – if you think something’s funny, the next funny thing that happens is even funnier, and so on.

The result of the experiment? No effect. Tickling does not create a pleasurable feeling, says Professor Harris, just the outward appearance.

So where does that leave us? What IS gargalesis?

Maybe it’s just a reflex, like your leg jerking up when you tap yourself on the knee. But if so, why can’t you tickle yourself? Well, why can’t you say BOO! in the mirror and scare youself?

Actually, some scientists at the Institute ofNeurology in London decided to figure this one out. They used an MRI machine to look at a person’s brain when the person was subjected to knismesis. MRI stands for magnetic resonance imaging. It uses a very powerful magnet to look inside the body. Problem is, you have to lie very still for it to work, so studying gargalesis was out.

However, what they found was when someone else was doing the tickling, there was a lot of activity in the somatosensory cortex, the part of the brain that handles touch.

When the person tickled herself, the cerebellum lit up. So what? Well, the cerebellum handles planning. What the scientists reasoned from this is that the cerebellum knew that its person was going to tickle herself, so it WARNED the somatosensory cortex!

Okay, that’s pretty cool – but still, WHY?

Well, maybe tickling helps establish a good feeling between parent and baby – mom tickles baby, baby laughs, mother smiles and tickles some more …

Or MAYBE, says Professor Harris, gargalesis has to do with developing fighting skills. HUH? Well, your buddy tries to tickle you, and you fight her off and tickle her back and you wrestle, like kittens fighting.

You know that tickling ISN’T all that pleasant, even though you laugh. Maybe the laugh is a signal that you’re not mad. Jaak Panksepp, a scientist at Bowling Green State University, has found that rats give off a real high-pitched chirp when they’re tickled. He thinks this is like rat laughter and helps distinguish play from threat.

ON THE OTHER HAND, says Professor Carter, maybe none of this is correct.

Not everything is an obvious result of something that happened in evolution. Maybe tickle is just a side effect of something we haven’t a clue about.

In other words, we may never know for sure why we tickle. Sorry.

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