Why can’t you tickle yourself and how does the brain know?

The brain can tell which tickling sensations are caused by one’s own actions and gives them low priority, so that it can be more receptive to sensations from outside sources that may be more urgent. One study suggests how brain areas may interact to do this.

In the study, a magnetic resonance imaging device scanned brain activity while volunteers had a palm tickled either by themselves or by the experimenters, using a tickling machine, a box with a pivoting rod. A piece of soft foam at the end of the rod could be moved by either the subject or an unseen experimenter.

The researchers found that the areas of the brain that process touch information, the somatosensory cortex, were more active when subjects were tickled by someone else than when they tickled themselves.

The cerebellum was less active when the subject was making a movement that resulted in a touch sensation than when the movement did not produce a sensation.

This suggests that the cerebellum anticipates the sensation caused by the movement made by subjects tickling themselves and sends a message to the somatosensory cortex telling it to decrease its activity, so that the sensation is dulled.