The Tickling Paradox

Tickling someone is somewhat of a divisive practice. Some love the sensation and burst out into uncontrollable laughter, some like it initially but then find a prolonged onslaught distressing while others positively hate the feeling. One curious feature of tickling is that you cannot, with a few rare exceptions, tickle yourself. Why?

The short answer is that it is all to do with our brain, which, as well as being reactive, tries to predict what is going to happen next and uses the knowledge that you are about to tickle yourself and downplays any reaction to the assault.

If you want a longer explanation, when we perform an action, that part of the brain which is responsible for initiating a message, the primary motor cortex, tells other parts of your brain that it should prepare for sensory information that will follow that action. As well as an anticipatory role, the brain also seems to adjust the level and degree of feeling from an action inflicted by an outside agency compared with those that are self-inflicted.

Using brain imaging techniques, scientists have been able to establish that people perceive the intensity of their own touch as weaker than that of an external touch. Neuroimaging confirms that this is not just a perception but that the brain responds less strongly to touches that are self-generated. They are tuned down because they are predictable.

People are sensitive to external stimuli and are on the alert for something that seems, feels or sounds out of the ordinary, a basic survival response. When you come to tickle yourself, the brain knows where your hand is going before you even move it, simultaneously telling those parts of the brain that will sense your fingers attempting to tickle that there is nothing to worry about. The sensation is accordingly attenuated. However, someone else attempting to tickle you catches the brain unawares and in response it amplifies the sensation.

You cannot get the same sensation from tickling yourself simply because of this basic survival instinct.  

Curiously, though, people with schizophrenia are able to tickle themselves and get a reaction. They struggle to recognise things they initiate from those they did not and being unable to predict their movements and the consequent sensations, the brain is tricked into responding in a way that it would had the tickling been initiated by another person.

Fascinating.