Why Can't You Tickle Yourself? The Cerebellum Spoils The Fun

First off, it turns out there are two different types of tickling, known as knismesis and gargalesis. The soft version of tickling – where a light touch, such as from a feather, produces a weird sensation but rarely any laughter – is knismesis, and it's pretty useful, for example, allowing you to detect any creepy crawlies that happen to be sneaking along your elbow. 

Then there is gargalesis, the classic version of tickling where laughter is produced as someone goes to town on your armpits, ribs, tummy, or knees (other body parts are available). When this is done by someone you know and trust or feel safe around, it can stimulate your hypothalamus.

“Your hypothalamus controls that adrenaline rush you get when something abrupt, exciting or challenging happens to you,” Dr Neha Vyas explained to the Cleveland Clinic in 2024. “So it’s geared toward protecting you.”

A comfortable social context appears to be somewhat necessary for the tickling sensation to occur. As wisely noted by Charles Darwin in 1872 "in that of laughter from being tickled the mind must be in a pleasurable condition; a young child, if tickled by a strange man, would scream in fear."

There are a few ideas about how the tickle sensation evolved, with the main ones being that it encourages social bonding or helps children develop a sense of humor. Going the other way, another suggests it is essentially combat training.

"One plausible theory suggests that tickle may be an evolutionary adaptation, evident as it is in the social interaction among primates," one paper explains. "Thus, the discomfort and pleasure elicited by tickling might be adaptive and help a child develop skills that can be used in defense and combat."

But why can't we tickle ourselves? While there is plenty of debate around the function and origin of tickling, there is a broad consensus around why we cannot induce this sensation in our own bodies. Essentially, it is because we cannot surprise ourselves. You know where your hand is going to move and get ready for that motion.

"We can readily distinguish between sensations that are produced by our own movements and sensations that are caused by a change in the environment," a paper looking into why we can't tickle ourselves explains. "This ability is important because it enables us to pick out stimuli that correspond to potentially biologically significant external events from stimuli that arise simply as a consequence of our own motor actions."

One study demonstrated this through the use of a tickle machine. With one hand, subjects could control a tickle device that would then activate a tickle rod in the patient's open palm. The team then introduced a delay to the proceedings.

"Under all delays and trajectory rotations the left hand made the same sinusoidal movements and the right hand experienced the tactile stimulus," the team explained in their paper. "Only the temporal or spatial correspondence between the movement of the left hand and the sensory effect on the right palm was altered."

The team found that when the device was used with no delay, little tickle sensations were produced. But when a delay of 1, 2, and 3 seconds was introduced, there was a progressive increase in tickly sensations, supporting the idea that the reason we cannot tickle ourselves is because we know exacly when and where it will happen.

"The brain responds differently to self-generated and externally generated sensations, disregarding the former and accentuating the latter," Sarah-Jayne Blakemore at University College London told the British Association Festival of Science at Imperial College, London, per the Telegraph. "The cerebellum spoils the fun by predicting the sensory consequences of movements and sends signals to the rest of the brain, instructing it to ignore the resulting sensation."

So if you do want to tickle yourselves, you can't. But get a tickle machine involved and put it on a slight delay, and you're back in business.