<p>Thiashya Jayasekera presents a column about the big questions in science. This edition is all about why some people are ticklish.</p>
Why do we laugh when we’re tickled? One thing’s for sure, it’s not because we find it funny.
The lightest brush of a feather against your toes or the approach of wiggling fingers to your armpits can send you into hysterics. And not the fun kind. The fit of laughter which erupts from an episode of tickling is far from voluntary.
It may seem like an inconsequential behaviour, yet scientists have puzzled over this silly, almost inexplicable physical tic for centuries. But tickling is far from insignificant. It has an important social function, is hypothesized to be part of a defence mechanism and perhaps helps us along our journey of self-discovery. It’s intrinsic to who we are.
For nearly a century, it was common belief that humour and tickling went hand in hand. It was thought that a good mood was a necessary prerequisite for a successful tickling bout. However, this theory – called the Darwin-Hecker hypothesis – has since been debunked. Studies conducted to test the Darwin-Hecker hypothesis have consistently shown that techniques to improve humour (such as watching stand-up comedy clips), do not affect someone’s susceptibility to tickling. So why do we laugh?
Functional MRI studies show that both tickling and laughing stimulate the same area of the brain, the rolandic operculum – which controls our facial movement, vocal and emotional reactions. However, tickling also stimulates the hypothalamus – the part of the brain responsible for regulating our ‘fight or flight’ response,and fires when we anticipate pain.
Because of this, some scientists believe that tickling is a means of teaching self-defence and that the laughter that follows is a natural sign of submission to an attacker. It’s not just fun and games – when you laugh, you effectively dispel a potentially tense situation and the unpleasant tickling episode ends. It’s no coincidence that our most ticklish parts are also the most vulnerable – the soles of your feet, armpits and neck. ‘When you tickle someone, you actually stimulate the unmyelinated nerve fibres that cause pain,’ says Dr. Alan Hirsch, founder of the Smell & Taste Treatment and Research Foundation in Chicago. As your amicable attacker approaches you, with threatening fingers and arms outstretched, your instinct is to draw your arms close and squirm to escape. So maybe tickling is simply a primal, somewhat gentle means of teaching someone how to defend themselves. Amongst all the laughter and giggling, the tickle attack remains inoffensive and (relatively) painless. As Robert R. Provine – a neuroscientist and a prominent figure in the tickling discourse – writes, “tickling attacks are the most benign form of human conflict”.
At the opposite end of the spectrum, tickling also plays a role in forging relationships. Take, for example, a parent fondly eliciting a giggle from a child. Or a middle-schooler flirting with bae on the playground. So whether it’s a parent and a child – or two potential romantic partners – tickling seems to have an inherently social function. As Provine aptly puts it, “If you think the social component [of tickling] is not important, try tickling a stranger”. If you’ve ever tickled a child it’s probably gone somewhat like this. You tickle them – they laugh. You tickle them more – they shriek. You tickle them even more – they wail. You stop. It’s a near-primal dialogue between adult and child, a strange neurologically charged interaction – establishing close bonds, along with a lesson in self-defence.
It’s not unique to humans. This little tickle tango occurs in chimpanzees as well. Rats too, let out a cheeky giggle when tickled. It’s a mammalian thing.
The social aspect of tickling is made all the more evident because you can’t really tickle yourself. In short, that’s because your brain knows whats coming and so it suppresses your tickle response. Knowing this, placing your hands on top of your tickler’s will cause your brain to protect you from the unpleasant tickling sensation that follows.
The question of why we can’t tickle ourselves leads to bigger questions of consciousness and self-awareness. Provine suggests that tickling is intrinsic to recognising our sense of self and forms the neurological basis for the separation of self from the other. When a baby feels a featherlight touch at the sole of their foot, they recognise something that is noticeably foreign – and following from that, what isn’t foreign. There’s themself too.
This seemingly mundane, yet curious behaviour seems to be at the very heart of who we are as conscious beings and as social animals.