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Why it’s impossible to tickle yourself

Most of us love to be tickled, although some of us may be more ticklish than others. However, one thing is for sure, we can’t tickle ourselves. But why is that so? Well, it’s all down to how we see, and how we perceive movement.

Try this for starters. Close one of your eyes, then carefully push against the side of your open eye, gently moving your eyeball from side to side. For most of us, it will appear as though what you see is actually moving, even though you know that it’s perfectly still. Now repeat this without your hand, just by moving your eye. Now everything is stable again. While what you are actually seeing is the same in both instances, somehow everything was changed when you moved your eyeball with your hand.

The reason for this?

When you move your eyes in the natural manner, your brain sends simultaneous messages to the eye muscles and to the visual system so that it can predict what’s going to happen when the eye moves. This allows your visual system to compensate for the changes caused by the motion of the eyeball on the retina, and your brain knows that the changes in what you see are due to the eye’s own movement. However, when you moved your eyeball, the visual system was unable to predict this, therefore there was no compensation, thus the image seemed to move around.

So what has all this got to do with tickling?

In the same way as your visual system predicts what is going to happen when you move your eye, your motor system is also able to predict what’s going to happen when you’re tickled. Because your brain can accurately predict the sensation, when you tickle yourself it results in a less intense experience than when someone else does it for you.

However, it is possible to tickle yourself, but you need a technical aid of some kind. By using a robot, researchers at University College London have been able to recreate the feeling of someone else doing the tickling. To instigate the tickling, the researchers had to move a mechanical arm on the robot back and forth. This movement was then transferred to a second mechanical arm which had a soft piece of foam at the end, which stroked the palm of the researcher’s other hand. While this wasn’t considered to be a particularly ticklish sensation, when the researchers added a slight delay into the tickling movements, it felt much more ticklish. Just this small time delay affected the brain’s ability to predict the sensation, making it more like the feeling we experience when someone else tickles us.

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