There are many forms of touch in the human vocabulary: caresses, squeezes, slaps, pinches, and more. But the only touch known to routinely elicit laughter is tickling. From the time we are babies in our caregivers’ arms to adulthood, wiggling a few fingers on our bellies is enough to elicit squeals of laughter. But why? Why does being tickled elicit uncontrollable laughter?
“It’s a very unique response.” Sandra Proels“Tickling has some interesting quirks,” says Proels, a PhD student at the Bernstein Center for Computational Neuroscience in Berlin, Germany. Proels has studied the human tickle response in her neuroscience research. While there are still some big mysteries and unknowns, scientists like her are coming up with some intriguing answers and explanations for why we’re ticklish and what happens when we’re tickled.
What is tickling?
First, there’s an important distinction: the word tickle refers to two very different sensations. The first is the sensation of a light touch on the skin, like a hair falling down your back or a feather on your arm. The technical term is tickling. Tickling might prompt you to brush something away or scratch the area, but it has more in common with an itch than anything else, and it probably won’t make you laugh.
In contrast, gargalesis is tickling induced by repeatedly applying firm pressure to particularly sensitive parts of the body. “These two should be considered completely separate,” he says. Ishiyama ShinpeiHe is a neuroscientist at the Central Institute of Mental Health in Mannheim, Germany, and studies the neural mechanisms of tickling.
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The purpose of knysmesis is clear: to reduce the chances of being bitten or burrowed into by unwanted animals. “They need to protect the surface of their body from parasites,” says Ishiyama. It’s the same as a cow wagging its tail to scare off flies. The explanation for gargalesis is less simple.
What is the purpose of tickling?
No one knows for sure why this ticklishness exists, but there are a few theories. One, Ishiyama says, is that it’s to protect weaker parts of the body. An exaggerated, soothing response of pleasure might deter would-be aggressors. Or maybe the ticklishness primes us to better protect our soft, fragile core. But he’s skeptical, since the weakest parts of the body don’t always match up with the most ticklish. For example, Ishiyama points out that while most people find the soles of their feet extremely ticklish, that’s not the part of our bodies that needs the most protection. “There are a lot of exceptions… I don’t think it’s really a conclusive theory,” he says.
He speculates that tickling and tickling may be a form of play, a social bond, and combat training a side benefit. First, humans are not the only ticklish animals. Great apes Some rodents, particularly rats, respond similarly to tickling. What ticklish animals have in common is that they are “highly social mammals” that play, fight, and communicate with each other.
Other findings seem to support the play theory. Tickling depends on emotion and situation, Proels says. People and animals feel more ticklish when they’re in a positive, playful mood. Responses vary, too. Familiarity-basedShe adds that people are less likely to respond with laughter if a stranger tickles them. Can relieve tickling sensationAnd with a few exceptions related to disorders such as schizophrenia, we cannot tickle ourselves: it is a response that is only present in social situations.
Finally, neuroscientists have traced some of the brain regions involved in tickling sessions. Studies on rats have shown that the same somatosensory circuits involved in play behavior It also glows when the subject is tickledOther brain areas activated by tickling include areas that process touch, areas associated with the fight-or-flight response and vocalization, and emotional regions such as the amygdala and anterior cingulate cortex.
Is tickling always fun?
Laughter is a sign of joy and amusement, and tickling is mostly a pleasurable activity (although it can also have unpleasant aspects). This is best demonstrated by experimental and anecdotal observations, which show that both humans and rats tickle. Pursue opportunities to be tickledTickling works even if the rat thrashes about as if trying to escape the tickle monster’s claws the moment it comes into contact, Ishiyama says. As a reward system During training, Proels says, the tickling sensation turned into a pleasurable sensation. Sexual fetish(Documented in a 2024 study co-authored by Ishiyama.)
Curiously, both humans and rats show signs of ambivalence and fear when faced with the prospect of being tickled. But neither species can stop coming back for the tickle, Ishiyama says. The range of emotions generated by the anticipation of tickling may be similar to those experienced by people who look forward to a haunted house tour or a scary movie. “Having a little bit of fear in the midst of the pleasure makes the play more enjoyable. Otherwise, it’s not really thrilling,” Ishiyama explains.
But too much of a good thing can be bad. Tickling provokes profound neurological and physical responses. It stimulates involuntary movements, alters breathing rhythm, activates multiple areas of the brain, often leaves people breathless, and quickly becomes a source of stress. Historical records show that tickling was used A type of torture Because, again, outside the positive context of play and familiar environments, it can be an extremely unpleasant sensation, especially when it’s something you have no control over. In these cases, Proels says, the victim’s reaction will be different: It will be more like pain than laughter.
Even fetishists surveyed by Ishiyama who seek tickling for sexual gratification noted that tickling combines pain and pleasure in a way similar to BDSM: About 40 percent of study participants said they experienced pain during consensual tickling.
What don’t you understand?
Despite being studied by a small number of scientists, tickling remains an understudied phenomenon, Ishiyama says. “I advocate the study of positive emotions. My ultimate goal is to understand the brain mechanisms of enjoyment.” But most neuroscience research focuses on diseases and disorders, he says. Perhaps as a result, there is still a lot unknown about tickling.
For example, some people are very ticklish, while a few others are not. Proels adds that this likely has some genetic component, but “it’s one of the big mysteries.” There is also the exact neurophysiological mechanism behind tickling self-inhibition, which we’re getting closer to but still need to figure out. Ishiyama points out that it’s not known how many other animals experience tickling, and they’re just starting to work with mice. Age dependency remains a question, and ticklishness seems to decrease with maturity, but it’s unclear why. Furthermore, the evolutionary path that led to tickling in multiple species is unclear.
We’ve gained some insights through tickling, but it’s going to take a lot more laughing rats, chimpanzees, and humans before we can untangle this tangled tickling mess.
This story is part of Popular Science’s “Ask Me Anything” series, in which we answer your wildest, most mind-bending questions, from the mundane to the bizarre. Is there something you’ve always wanted to know? inquiry.
