Are you ticklish? Ever wondered why some people are more ticklish than others? And why are some parts of our bodies more vulnerable to tickling? There have been a number of theories proposed over the years as to why we are ticklish and why we laugh when we’re tickled. But the fact remains: most of us can’t tickle ourselves.
Who doesn’t love a good tickle fight? Image credit Dominic Casario via Flickr
A long history
Aristotle wrote about it and so did Darwin: tickling. Touch is the most sensitive of the human senses, and tickling is a very particular kind of touch. In fact, tickling is a name used for two distinct kinds of sensation. The first, called knismesis, is the light kind of tickling that almost feels itchy. Like when someone touches you with a feather. It might make you shiver and feel tingly, but knismesis won’t make you laugh. The rougher tickling we use in tickle fights is known as gargalesis. Our responses to both appear to be reflexes.
Many animals are also ticklish, but most of them only experience knismesis. Think of a horse shuddering to get a fly off its back. Few animals are known to experience gargalesis. Unsurprisingly, most of those that do are the apes. For example, chimps and orangutans have also been observed to engage in tickle fights. But why are we ticklish?
Feeling social, or having a fight?
Think about the last time you were tickled. Was it on your neck, under your armpits, maybe around your ribs? The fact some of the most vulnerable parts of our bodies are the most ticklish has led to the suggestion tickling is a way we learn to protect ourselves. The argument is that we evolved to be ticklish so we would learn to defend ourselves as children (when most tickle fights happen.) We squirm and attempt to get the tickler’s hands away from us and learn self-defense along the way.
Another explanation for tickling is that it plays an important role in social bonding between family members and other close companions. It’s unlikely you would feel comfortable tickling a complete stranger. But babies begin laughing in response to tickling in their first few months. Psychologists suggest tickling and laughter are important forms of communication between babies (who can’t yet talk) and the adults who look after them.
Others say tickling is an alarm to alert us to the fact something is crawling on our skin. It becomes funny when we realise the sensation is a result of the touch of another person, rather than a spider or something else we fear.
As to why some people are more ticklish than others, it’s probably partly due to the density of touch receptors a person has in their skin, but it’s also context dependent. You may be more or less ticklish depending on who is tickling you.
Why tickling and giggling go together
Do you like being tickled? Most people say no and many go so far as to say being tickled is painful. So why on earth do we laugh when we’re being tickled? Laughter usually signals pleasure.
Scientists looked at what was going on in the brain when we laugh while being tickled and when we laugh for other reasons and found both kinds of laughter activate a part of the brain by the name of the Rolandic operculum. But only laughter in response to tickles activates our hypothalamus – which among many other things, is responsible for our fight or flight response. One possibility is that we laugh to signal submissiveness in the hope our ‘attacker’ will leave us alone.
And it’s not just humans who laugh when tickled. Apes laugh too, although the sounds are technically called ‘tickle-induced vocalisations’. The humble rat is also known to do something akin to laughing when tickled. If you tickle rats, they make the same chirping sounds they use during play. Fascinating studies have also shown rats are more optimistic after they’ve been tickled.
It’s hard to trick your own brain
Have a go at tickling yourself. For most of us, the result is decidedly boring – nothing happens. Why? We think it’s because our brains have a lot of experience at making good guesses about what’s going to happen next. Every time you move one of your limbs, a structure at the back of your brain called the cerebellum predicts your body’s movements and then reduces the sensations you experience as a result of your own touch.
So when you try to tickle yourself, your brain already knows what’s coming and the sensations barely register: the tickling response is suppressed. If you use a machine which delays how long it takes for you to be tickled after moving your hand, you can trick yourself into feeling tickled. The longer the delay, the more likely you feel tickled by your own movements. But research has shown people with schizophrenia can successfully tickle themselves. It appears that people with schizophrenia are less able to tell the difference between a sensation coming from themselves or elsewhere and confuse the source of the tickle.
And is there anything you can do if want to stop feeling ticklish? You bet! All you need to do is put your hands on top of the hands of whoever is tickling you – then your brain can better judge what’s coming next. And hey presto, all of a sudden you aren’t ticklish anymore.
Espresso Science 
Mmmm, interesting tickle studies with animals. Can I therefore assume we are closer in evolution to rats, and not just the classic ape? Or is it that scientists like to torture poor rats with their experiments, rather than a cute and cuddly koala?
I think there are many reasons why rats are more often involved in scientific research than some other animals!