The science of tickling

It turns out that tickling is much more complex of a behavior than we could imagine. In fact, it may even be a way to study human consciousness. Let’s start with the basics. There are two forms of tickling: knismesis and gargalesis. Knismesis is more of a light sensation that rarely produces actual laughter, like when a feather is run across your skin or a pesky fly lands on you. The other type, gargalesis, is the sensation you feel when someone else tickles you more aggressively. Try as you might, you can’t induce the same exhilaration and laughter, or even fear and irritation, brought about when another person tickles you if you try to tickle yourself. Go on, try it. Nothing, right?

We’ve only recently begun to understand this mechanism in the brain. Neuroscientists have revealed that we cannot tickle ourselves (the gargalesis type) essentially because we can’t surprise our own brain. During a tickle, the skin’s nerve endings shoot electrical signals to the somatosensory cortex, a part of the brain that processes touch. Meanwhile, the anterior cingulate cortex analyzes these signals as either harmful or playful. But in the back part of the brain, the cerebellum gives you away. It tells your cortex that you are about to attempt a self-tickle, and not to worry, it should suppress the signals from the tickle. So there is a brain system in place that analyzes the sensory input together with the motor output, basically telling us whether what we feel is due to ourselves or others. And in doing so, it also helps us understand how the brain separates “me” from “them.” In fact, some people with dissociative disorders like Schizophrenia can tickle themselves silly. Being able to differentiate the actions of others and ourselves is central to our sense of self.