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Ask an expert: Why can’t you tickle yourself?

Wolfgang Stein

Wolfgang Stein

Have you ever had a question even the Internet couldn’t answer? Some of the Illinois State community did. And we put the University’s faculty experts to work answering their inquiries. To submit a question, email it to Kevin Bersett at kberse@IllinoisState.edu or tweet it to @ISUResearch.

Question: Why can’t I tickle myself? I’m one of the most ticklish people I know! My friends (and wife) can’t tickle themselves either. How come?

—J Thomas (Tom) Stoltz ’90, Bangkok, Thailand

Answer: What you think you are seeing or feeling is not the real world. It is being preprocessed by your nervous system.

Your nervous system does not work like a storage device. It is not a camera, taking in everything around you. Your brain only pays attention to important things—when something is novel or new. Anything that is familiar, your brain sees as useless or unnecessary information.

When you are performing an action, your brain sends signals to your muscles, and the muscles move. But that is not all—a copy of that signal, called an “efference copy,” is kept and subtracted from signals of your sensory system. If your actions happen as expected, the efference copy matches the sensory information and no sensory information reaches the brain.

I touch the computer mouse, and it is only the computer mouse. But say you reach down for your computer mouse, and there is a spider on it. That is very different than what you expect. You feel that spider. Your “efference copy” does not match; your brain realizes the difference and pulls your hand back.

When we try to tickle ourselves, we have an expectation of what will happen. The expectation is met. That means the efference copy matches, so the tickling sensation does not reach the brain. No reaction.

On the flip side, the expectation has to come from our own nervous system for the brain to have a chance to ignore it. If we see someone coming to tickle us, we will still laugh because it was not our brain that sent the signal, so there is no efference copy, and the message reaches the brain. You laugh.

Wolfgang Stein, associate professor of neuroscience, School of Biological Sciences

To read all of the “Ask an expert” questions and answers, check out the inaugural issue of the Redbird Scholar. The University’s new biannual magazine focused on faculty and student research and creative expression will be published in print and online (IllinoisState.edu/RedbirdScholar) for the first time in September. Follow us on Twitter at @ISUResearch.

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