Tickling is a unique application of the sense of touch that surprisingly has developmental and cultural importance. Experts discuss the science and sociology of tickling.
- Dr. David Linden, Professor of Neuroscience, Johns Hopkins University School of Medicine and author, Touch: The Science of Hand, Heart and Mind
- Dr. Robert Provine, Professor of Psychology and Neuroscience, University of Maryland, Baltimore County and author, Curious Behavior: Yawning, Laughing Hiccuping, and Beyond
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Nancy Benson: There’s one way that’s guaranteed to make most people laugh. You’ll need a feather, but fingers have been proven to work fine as well. Run them over the bottom of a person’s feet, the sides of the torso, or along the side of the neck. Almost instantly, you’ll have them doubled over in laughter. It’s as effective on a 300-pound bodybuilder as it is on a newborn baby. Dr. David Linden is professor of neuroscience at Johns Hopkins School of Medicine, and author of Touch: The science of hand, heart, and mind.
Dr. David Linden: Tickling is a unique tactile sensation that results typically from light touching of certain areas of the body and can evoke defensive responses and sometimes laughter.
Robert Provine: Tickling is probably the primal, the original stimulation for laughter. Where laughter, being a vocalization that produced in physical play situations, whereby it’s a signal that this is play, I’m not attacking you.
Benson: That’s Robert Provine, professor of psychology and neuroscience at the University of Maryland, Baltimore County, and author of Curious Behavior: Yawning, laughing, hiccupping, and beyond. But what exactly causes the unique sensation of being tickled? Linden explains.
Linden: The tickle sensation is not conveyed by a special class of nerve ending in the skin, it seems to be conveyed by the same nerve endings that convey many other forms of touch, though the tickling sensation appears to result from a pattern of activation of nerve endings. Not a unique set of nerve endings that are dedicated to tickling.
Benson: But even though people like to laugh, a lot of us simply can’t stand to be tickled. That shows the two sides of tickling—the laughter…and the threat.
Provine: We distinguish between being touched and touching something. That’s an important distinction because you don’t defend yourself from the contact of your body if you brush against a tree, a branch, the wall of your house. That’s very different than something coming, approaching you and touching you. So we have to make this distinction between “self” and “other.” Otherwise we’d be going through life in a chain reaction of false alarms, where you’d be startled by your clothes, a breeze blowing on your skin.
Benson: But the social part of tickling is how most people think of it. Linden says tickling is an easy way for parents to get their children to laugh. And they may end up liking you more for it, too.
Linden: There are particular sets of nerve endings in the skin that are designed to convey a caress; designed to convey affiliative social touch and they project in particular parts of the brain involved in social cognition. And we know that among young children that this is really crucial for development.
Benson: As we get older, Provine says the purpose of tickling starts to move into the bedroom.
Provine: We often think of a tickle as being something that has a definite developmental course whereby children engage in a lot of rough-and-tumble play and adults don’t. But something we forget is that the rough-and-tumble play and tickle of childhood morphs into sexual foreplay and sexual acts themselves. So tickle doesn’t go away in adults, it’s simply the arena for its performance changes.
Benson: But even with that, adults eventually seem to lose most of their interest in tickling.
Linden: Ticklishness declines with age because all forms of touch decline with age. As we get older, we have kinds of peak touch sensation about age 20, and then about every year after 20 we lose about one percent of our touch nerve endings. And we lose all of them. In other words, we lose the ones for fine touch, for vibration, for texture, for sexual sensation, for pain. We lose all of them together. I found a sharp drop-off in tickling and being tickled in individuals after the age of 40. It’s a rather striking decline. And this is probably associated with a lowered sexual desire and also decreased social opportunity.
Benson: Those social opportunities are important. You might not think of it this way, but Provine explains that tickling helps strengthen the bonds between humans—but only if both sides are on board with the tickle.
Provine: You’re not tickled by random people. When’s the last time someone came up to you in the street and tickled you? Probably never. We tickle and are tickled by friends, family, lovers, children. We wouldn’t be doing this to other people if we didn’t have positive feelings toward them. Tickling is a neurological form of physical bonding. When someone tickles us, the typical response is to reciprocate. It binds people together in a very primitive way.
Benson: But why are some people so squeamish about tickling? Linden admits we don’t know. In fact, he says that there are very few studies that provide solid conclusions about any aspect of tickling, why some people are more ticklish than others, or why the bottom of the feet are so universally ticklish. There just isn’t enough evidence. However, Provine and Linden do provide a theory to one key question: what makes us laugh when being tickled?
Provine: Laughter is a sound that we make. It’s innate; you don’t have to learn to do it. Individuals in all societies do it and it develops early in life between three and four months after birth. But the sound of laughter is really the sound of labored breathing of rough-and-tumble play, which involves tickle. So in the rough-and-tumble, the sound of laughter – ha, ha, ha, ha – is a sign that I’m not attacking you. This is really play.
Linden: Most people think that it’s an innate response because little babies seem to have this response fairly strongly, and it also, when cultural anthropologists go all over the world and they ask about this and they do this, it seems to be that most places have a tickling response that is the same.
Benson: Laughing is an unavoidable response when someone else tickles you, but don’t expect to laugh if you try to tickle yourself.
Linden: Most people, if they go to try to tickle themselves, it fails. It doesn’t feel very ticklish. And this seems to be because the commands that your brain sends to your tickling fingers in order to initiate the tickle, are also being sent to a brain region called the cerebellum. And the cerebellum turns that into inhibitory signals that are sent to the part of the brain called the somatosensory cortex that processes the touch sensations, and it seems to damp them down. So when you go to tickle yourself, you’re kind of inhibiting your own brain and dampening it down which is why for most people, it’s very hard to get a strong tickle sensation from self-stimulation.
Benson: The act of tickling has been around for millennia. It has an evolutionary reason—as a defense, keeping our bodies safe from invaders, like insects crawling on our skin. But now we think of it as a social mechanism for friends, family, and lovers… a simple action with the power to bond us together through the touch of our skin. Our writer-producer this week is Michael Wu. Our production director is Sean Waldron. I’m Nancy Benson.