What is it about tickling?

In a recent entry (“Let’s talk about feet”), I discussed some of the amazing features of human feet, including the fact that feet are ticklish. That sparked a question in my mind – what makes us ticklish? Why are some parts of our bodies more ticklish than others? Why are some people extremely ticklish, while others can stand seemingly hours of feathers-on-the-toes temptation without even cracking a smile? And is it really true that you can’t tickle yourself?

Ticklishness is neurologically hardwired into our brains. The sensation of tickling is controlled by a highly developed part of the brain called the cerebral cortex. The cerebral cortex is one of the largest parts of the brain; it contains all of the centers that receive and interpret sensory information, initiate movement, analyze information, reason and experience emotions. Neurologically, a ticklish response is similar to a developed defense response against dangerous creepy-crawly critters like poisonous spiders and bugs. This explains why we tend to be ticklish on exposed or vulnerable parts of our bodies – like our feet, armpits and stomachs. Make sense, right? The sensation of tiny little legs crawling across my toes would easily make me jump, brush the area vigorously, and remove whatever’s causing the feeling. Sounds a lot like what happens when someone tries to tickle my feet!

Ticklishness might be more than simply a neurological phenomenon, though – scientists also believe that it is a learned response. Two essential factors must be in place for tickling to occur. First, there must some form of a mock attack. Someone else must be coming at you in such a way that your brain interprets as potentially hostile. But second, and equally importantly, there must be a perceived lack of real threat. In other words, I must believe both that you can make me laugh uncontrollably and that you won’t actually hurt me in the process. If a good friend suddenly tickles you from behind, both of those criteria are met – it’s startling, surprising, and maybe initially scary, but there’s also no real threat. As the Encyclopedia Britannica says to describe when a child will find tickling enjoyable, “The child will laugh only – and this is the crux of the matter – when it perceives tickling as a mock attack, a caress in mildly aggressive disguise.”

Tickling also has a relational aspect. Robert Provine, professor of neuroscience at the University of Maryland, Baltimore County and author of "Quest for Laughter", believes that tickling is an important form of non-verbal communication. For children, tickling is most often done during a time of playing, either with their parents, siblings, or playmates. Above the age of puberty, tickling usually is a form of flirtation, and is often done in the context of a sexual relationship. All in all, Dr. Provine points out that tickling is always done between people who have a good relationship – parents and children, siblings, good friends or spouses. Strangers or coworkers don’t usually try to launch a tickle attack!

So what about the idea that you can’t tickle yourself? Once again, our brains provide the answer. The human brain knows what feelings to expect whenever the body performs a certain motion. The region of the brain that controls this is called the cerebellum. The cerebellum is a relatively primitive region at the base of the brain that monitors movement and sensation. We don’t pay attention to most of these things – for example, our brain ignores the feeling of clothes on our skin. If we had to pay attention to every sensation our bodies experienced, we’d be overwhelmed! Instead, our brains are wired to pay attention to startling, surprising or unexpected sensations. This is the neurological reason why we can’t tickle ourselves. When you move your hands towards your feet, your brain expects the associated sensations, realizing “Oh, it’s just me. No problem.” Without the surprise, unease, or feeling of mock attack, it simply doesn’t tickle. That’s not to say that you can’t stimulate the nerves in your feet to feel funny when you try – but you’re probably not going to break out laughing in the same way as if someone else was doing it to you.

And just in case you were wondering, humans are not the only ones who are ticklish. Chimpanzees have been observed tickling each other when playing. (Does that qualify as monkeying around?) And even other animals can get in on the fun. In 1999, two neurobiologists at Bowling Green State University published results from a tickling study on rats. When the rats were tickled at the napes of their necks, they chirped and kicked their feet. I guess that’s what it sounds like when a rat giggles!