Appliance of Science: Why can't we tickle ourselves?

How ticklish are you? Do you squirm at the mere mention of a tickle or can you hold out a full-force tickle attack with just the slightest giggle response? Regardless of how ticklish you are, you may have noticed something we all share and that is the fact that we cannot tickle ourselves.

WHY CAN’T WE TICKLE OURSELVES?

It is all down to a part of the brain called the cerebellum, which distinguishes our movements and touch from that of others.

WHY ARE WE TICKLISH?

The body is covered in millions of nerve endings, many sitting right under our skin. They detect all kinds of sensations and touch. Some areas of our bodies are more sensitive than others, especially when it comes to light touches that induce a tickle response. Usually, these more sensitive areas are parts of our bodies that are more vulnerable to injury.

The tickle response probably developed in early humans to detect and respond to predators and potentially threatening touch. Tickling alerts us to potential danger.

WHAT HAPPENS WHEN WE ARE TICKLED?

When something or someone brushes lightly against a part of our body it is detected by nerve endings that lie just below the skin. The stimulated nerve endings send a signal to the brain, causing a response in two particular areas, the somatosensory cortex (that processes touch) and the anterior cingulate cortex (that processes pleasure). These areas trigger our physical response to the tickle and we laugh, move uncontrollably, shudder or flinch, depending on the tickle type.

There are two different types of tickles, gargalesis, a heavy touch tickle which causes laughter and uncontrollable body movement, and knismesis, a lighter tickle, when something light touches gently against the skin; this type of tickle causes a flinch or shudder response.

WHY DO WE LAUGH WHEN TICKLED?

It’s probably an evolutionary trait that has been passed down from our ancestors. Early humans may have used it in response to a tickle to show submission to a potentially aggressive attack. Laughter would show they were not willing to retaliate physically which may have been enough to calm an aggressor.

SO, WHY CAN WE NOT TICKLE OURSELVES?

This brings us back to the cerebellum. This part of the brain controls movement and can distinguish between expected and unexpected movement. It can anticipate the action of a self-tickle and alerts the rest of the brain — thereby muting the intensity of the sensation. This makes a lot of sense, otherwise we could constantly be triggering a tickle response every time we touch our own bodies. In order for a tickle response to be triggered, we need an element of surprise or anticipation. The cerebellum stays one step ahead of our own movement, removing any surprise potential from the self-tickle; we will always know it is coming.

Sometimes science gives a helping hand...

A team of British scientists have developed a tickle robot. Using a joystick, a person can get the robot to tickle them. There is a slight delay in the robot’s response, maintaining the element of surprise, resulting in a successful tickle.

Naomi is a science communicator and mother to three inquisitive children. She can be found at sciencewows.ie

Feel free to email your questions to drhowsciencewows@gmail.com


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