Why can't you tickle yourself?

Hi there Konstantina Kilteni, can you explain why it is difficult to tickle yourself?

“The reason you can´t tickle yourself is that the brain can anticipate and suppress the sensory effects of your body's movements. For example, when you reach for an object, your brain will anticipate how touching it will feel. But if someone else touches you, or a spider crawls up your arm, your brain can't predict what's going to happen based on your movements, so it tickles you more."

Why is it important to study this phenomenon?

"It gives us access to the mechanism that the brain uses to distinguish between signals from within and outside the body. This could be of clinical interest because we know, for example, that people with schizophrenia have difficulty distinguishing between sensations generated by their own body and those generated by other people. One possible explanation for the voices heard by some schizophrenics is that the brain interprets its own thoughts as being someone else's voice. In fact, compared to healthy control persons, they also find it easier to tickle themselves."

You work in a 'touch and tickle' lab at Karolinska Institutet. What do you do there?

"We carry out experiments on healthy people where they are asked to tell us how intense or ticklish it feels to be touched, depending on whether it comes from themselves, from a machine or another person. For example, we use robots that can generate touch on different parts of the body, and ask the subjects to describe how it feels compared to when they control the robot themselves. We are also carrying out brain imaging studies to find out which parts of the brain distinguish between self-touch and external touch."

What are your findings?

"We have recently found in our tests that even healthy people with certain personality traits that resemble the clinical symptoms of schizophrenia have reduced ability to predict how self-generated movements will feel. This could mean an increased risk of schizophrenia, but we need more research to confirm this."  

Why do we laugh when we are tickled? It actually feels quite uncomfortable.

"That's an interesting question that we don't know the answer to. Typically, the person being tickled tries to pull away from the tickling, while laughing as if it's enjoyable. Although many people actually find it unpleasant. One suggestion is that laughing while being tickled is a nervous reflex that differs from the laughter when we hear a joke, for example. This has not been fully clarified, but it's probably a question of two different reactions."