When I walk into my lab on a weekday morning, it’s not uncommon to hear uncontrollable squeals of joy or fits of giggles. Laughter is not traditionally thought of as the noise of neuroscience, but my research group is somewhat unusual. In the Touch & Tickle Lab, we invite participants to experience Hektor, the tickling robot, in the name of scientific progress.
In a typical visit, participants take off their shoes and socks and then sit in what looks like a dentist’s chair. My colleagues and I place their feet on a platform, below which lies Hektor, a robot consisting of three electric motors. During a tickling session, Hektor pushes probes along the soles of the participants’ feet, and they report how much each stroke tickled on a scale of one to 10. Through this process, we track people’s facial expressions, heart rate, muscle activity, breathing and skin conductance (which tells us if they are sweating). Electrodes placed on participants’ scalps reveal their brain activity.
Being tickled is a sensation most of us instantly recognise, and some of history’s greatest thinkers were fascinated by this strange phenomenon. Socrates described the feeling as a mixture of pain and pleasure. Aristotle thought tickling was a consequence of people’s delicate skin. And Charles Darwin wrote extensively on the subject, hypothesizing that we may be most ticklish on spots that are not often touched and only in certain psychological contexts.
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Today, I and other neuroscientists still wonder about many fundamental mysteries: Does tickling have any biological function—and if so, why did we evolve to have this experience? What happens in our nervous system that causes this unique sensation? Why are some areas of the body more sensitive than others? Why do people react differently to potentially tickling touches? Answering these questions can expand our knowledge of the way the human body perceives and processes physical sensations. Tickling gives neuroscientists an opportunity to study how complex systems in the brain and body, including those involved in emotion, movement and sensation, interact – all while answering questions that can help us understand differences in human behavior and development.
Tickling—what we scientists sometimes call gargalesis—may be an evolutionarily ancient behavior.
The research so far suggests that tickling – what we scientists sometimes call gargalesis – may be an evolutionarily ancient behavior. Many primates, including chimpanzees, bonobos, gorillas, and orangutans, do as well. And rodents show responses to certain forms of touch that may be relevant to tick research. When rats are stroked on the stomach, for example, they produce far more vocalizations than they do when gently touched, and the stimulation appears to activate certain areas of the brain that also light up when humans are tickled.
Tickling also seems to transcend culture. In one study, participants from more than 20 cultural backgrounds, including people from Britain, Poland, India and Hong Kong, listened to recordings of German speakers laughing spontaneously and were able to recognize which laughter was induced by tickling, as opposed to joy or schadenfreude.
Studies have led to several theories about how and why tickling may have evolved. It may simply be a reflex response with no apparent function—perhaps it’s just a byproduct of the way our systems for perceiving touch have evolved. Or it can help build social bonds between people, such as parents and children. Touch is an incredibly important social signal for our species that can help us communicate with each other and increase feelings of closeness. Tickling can make us feel especially connected to others because it makes us laugh, a response that often comes with joy.
Another theory is that tickling is a behavior our ancestors used to teach their young where to attack others or how to defend themselves in a fight. This idea is based on observations that the playful back-and-forth interactions involved in tickling children and young monkeys resemble a “mock fight”, and that some of the tickling areas of our bodies (such as the armpit) would be vulnerable if attacked in a real fight.
However, not everyone reacts to being tickled in the same way – people with certain neurodevelopmental or psychological conditions can experience it very differently. For example, in a study published in 2024, researchers in Japan observed that children with higher scores on tests for autistic traits were less responsive to being tickled and less likely to approach their parents with a positive emotional response to the tickling than peers with lower scores. Such studies show how researchers can use tickling as a tool to understand differences between people that may one day shed light on important differences in how we process and perceive sensations.
People with schizophrenia may also experience tickling differently. When you make a movement—for example, to scratch your head—your brain can usually predict when and where parts of your body will make contact before it actually happens. This ability generally makes people feel their own touch on their body as less intense than when someone else touches them, and is considered part of why most people cannot tickle themselves. But some people with schizophrenia struggle to predict and process the sensation of touching themselves. As a result, they perceive self-touch as more intense and more likely to tickle than people who process touch in a typical way. Something similar can be seen in people with a high score for schizotypal personality traits, who tend to show unusual thought patterns and social behavior without fulfilling criteria for a mental disorder.
In our lab, we are currently investigating how and why the brain can cancel some sense of self-generated touch in certain people. As with our work with the robot Hektor, we hope our experiments help create a clearer picture of the way people predict and perceive physical touch, and uncover some of the mysteries of tickling along the way. Behind every giggle is a fascinating bit of neuroscience waiting to be discovered.
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