Why You Can't Tickle Yourself

Run your own fingers along your ribs and almost nothing happens. Let someone else do exactly the same thing and you squirm. The difference isn't in your skin. It's in a quiet forecast your brain makes every time you move.

Go on, try it. Run your fingertips lightly along your ribs, or the sole of your foot, or wherever you're most ticklish.

Nothing much, right? A bit of a sensation, maybe. Nothing worth squirming over.

Now imagine someone else doing precisely the same movement, on precisely the same spot. Same pressure, same speed. You'd be wriggling.

It's a strange thing when you stop to think about it. The touch on your skin is the same. The nerves are the same. So whatever is going on, it isn't happening at your ribs. It's happening in your head.

The copy your brain keeps

Here's the trick. Every time your brain sends out a command to move a part of your body, it doesn't just send the command and forget about it. It also keeps an internal copy of that outgoing, movement-making signal.

Neuroscientists call this an efference copy. "Efferent" just means outgoing, travelling from the brain out to the body. An equivalent term with a different history is corollary discharge, which describes the signal fed into your sensory system to cancel out the sensations your own movements produce.

You can think of it as your brain sending a memo to itself. Not "move the hand" but "I'm about to move the hand, so expect to feel this".

Cancelling the expected

So what does the brain do with that memo? It uses it to predict what you're about to feel. And when the prediction matches what actually happens, the sensation is turned down.

That's why you can't tickle yourself. When your own fingers move along your ribs, your brain already knows they're coming. It has predicted the touch, and that prediction is used to dampen the response.

Part of the forecasting is thought to happen in the cerebellum, a crinkly structure at the back of the brain. It can predict sensations when your own movement causes them, but not when someone else does. When someone tickles you, there's no memo. The touch arrives unannounced, and you get it at full strength.

You can even see the difference in brain scans. Brain regions that process touch, and how pleasant it feels, are less active during self-tickling than when someone else is doing the tickling.

Making yourself ticklish

Now for the fun part. If the reason you can't tickle yourself is that your brain predicts the touch, then it should be possible to sneak past the prediction.

And it is, a little. Researchers built a set-up in which people's feet were tickled by a robotic arm that was controlled by their own arm movements. So the person was still the one doing the tickling, just through a machine. When the robot copied their movement straight away, it didn't feel very tickly.

But then the researchers added a small delay between the person's movement and the robot's touch. And the tickle started to work. Even a short delay made the sensation feel more tickly, and the longer the delay, the more tickly it felt.

That's a lovely result, because it shows just how precise the forecast is. Your brain isn't just predicting "a touch is coming". It's predicting exactly when. Shift the timing even slightly, and the prediction no longer lines up, so the touch is no longer cancelled. Tickling needs a bit of surprise.

Not just tickling

What's really going on here is far bigger than tickling. Your brain is constantly separating sensations you caused from sensations the world caused. And it uses the same kind of internal copy to do it.

Take your eyes. Every time you glance around the room, the image landing on the back of your eye slides about. Yet the room doesn't seem to lurch. It stays perfectly still.

In the nineteenth century, the scientist Hermann von Helmholtz pointed out a telling contrast. If your eyeball is moved passively, say nudged from the outside, the world appears to move. If your own eye muscles move it, the world is perceived as still. The difference is that when your eye muscles do the moving, your brain knows it's happening and accounts for it. Helmholtz was the first to propose that the brain keeps copies of its own movement commands.

Animals do it too, and one of the neatest examples is the cricket. A male cricket chirps astonishingly loudly; one description compares the racket to a pneumatic drill. So how does it avoid deafening itself? Recordings from the nerves in singing crickets show that, in time with each chirp, the cricket's nervous system dampens down its own hearing. The signal from the singing system inhibits the hearing pathway, softening the cricket's own voice in its ear and protecting its hearing from being swamped, while still letting it pick up quieter sounds from around it.

What it doesn't explain

One caveat. The prediction idea does a good job of explaining why your own touch feels weaker. It explains why self-tickling falls flat.

What it doesn't do, on its own, is explain everything about tickling. It tells you why the sensation is dampened when you do it yourself. It doesn't tell you why being tickled by someone else makes you laugh in the first place. That's a different question.

Me and not me

Still, there's something rather wonderful in the bit it does explain.

Your brain is constantly sorting the world into two piles: the things you're doing, and the things being done to you. Most of the time, you never notice it happening. The world stays steady when you look around. Your own movements don't keep startling you.

A tickle is one of the few places where you can actually feel that sorting at work. When your own fingers fail to make you laugh, that's your brain quietly saying: relax, that one was you.

SOURCES

1. Scientific American, "Why can't a person tickle himself?" https://www.scientificamerican.com/article/why-cant-a-person-tickle/ (accessed 25 Oct 2026)

2. Wikipedia, "Efference copy." https://en.wikipedia.org/wiki/Efference_copy (accessed 25 Oct 2026)

3. J. F. A. Poulet and B. Hedwig, "A corollary discharge maintains auditory sensitivity during sound production," Nature 418, 872–876 (2002). https://ideas.repec.org/a/nat/nature/v418y2002i6900d10.1038_nature00919.html (accessed 25 Oct 2026; abstract)

4. Journal of Experimental Biology, "RACKET? WHAT RACKET?" (Inside JEB summary of cricket hearing research). https://cob.silverchair.com/jeb/article-split/206/17/2908/13841/RACKET-WHAT-RACKET (accessed 25 Oct 2026)