Why you can't tickle yourself: what your brain knows that your skin does not
Why your own fingers can't tickle you, but a friend's can
Your skin feels the same fingers either way, yet only someone else's make you laugh. Even a touch you believe comes from a machine can tickle you. So where is a tickle really made?
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1
A night train crosses the mountains. You and your friends Miva and Rono share a small sleeper, and nobody can sleep. Rono says he is the one person in the world who is not ticklish.
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2
Miva does not argue. She runs her fingers along his ribs, and Rono bends over, laughing.
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3
Then he tries it on himself: the same spot, the same quick fingers. Nothing. He shrugs: of course, he knows where his own hand will go. Try it on your own side, right now. It is only a touch.
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4
Maybe a tickle only works when you believe a person is doing it? Scientists in San Diego tested that in the 1990s. People wore a blindfold, and a "tickle machine" tickled their bare feet. In truth, a helper hid under the table and did it. People laughed and pulled away about as much as when they knew a person was there.
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5
So you do not need to think a person is tickling you. You only need a touch that does not come from your own hand. Your skin gets the same touch both times, so the difference is made further up, in your brain. Somehow, it knows which hand is yours.
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Go further
A tickle in animals.