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A Familiar Feeling with an Unsettled Explanation

Tickling is instantly recognizable but scientifically slippery. It blends touch, laughter, anticipation, emotion and social context into a sensation that can feel playful in one moment and unbearable in another. In “The Surprising Science of Tickling,” neuroscientist Konstantina Kilteni argues that this odd experience offers a useful way to study how the brain combines bodily signals and predicts what a touch will feel like.

Kilteni’s Touch & Tickle Lab approaches the question with unusual rigor. Its robot, Hektor, moves probes across the soles of participants’ feet while they rate how ticklish each stroke feels. Researchers simultaneously measure facial expressions, heart rate, breathing, muscle activity, skin conductance and electrical activity in the brain. A machine cannot reproduce every part of an interaction between people, but it can deliver touches consistently. That control helps separate the physical properties of a stroke from the expectations and relationships that shape the response.

The basic questions remain open. Scientists do not yet know whether tickling has a specific biological function, why some body regions are especially sensitive, or why people respond so differently. The subject nevertheless connects systems that are often studied separately: sensation, movement, emotion, laughter and the sense that a body belongs to oneself.

An Ancient Reflex, a Social Signal or Both?

Tickling may have deep evolutionary roots. Chimpanzees, bonobos, gorillas and orangutans engage in tickling-like play. Rats also vocalize much more when stroked on the belly than during ordinary gentle touch, and relevant stimulation activates some brain areas that respond when humans are tickled. These findings do not establish a single origin for tickling, but they suggest that the behavior is older than human language or culture.

Human responses also cross cultural boundaries. In one study, people from more than 20 cultural backgrounds listened to recordings of German speakers laughing. They could distinguish laughter caused by tickling from laughter associated with joy or delight at another person’s misfortune. Even without understanding the speakers’ language, listeners recognized something distinctive in the sound.

Several evolutionary explanations could fit the evidence. Tickling might be a side effect of how nervous systems detect unexpected touch, with no special function of its own. It might strengthen bonds between parents and children or between playmates by coupling touch with laughter and closeness. Another proposal treats tickling as a form of mock combat that helps the young practice protecting vulnerable areas such as the armpits. The article does not declare a winner. Tickling could serve more than one role, or its modern social uses could have grown from a simpler sensory reflex.

Why People Usually Cannot Tickle Themselves

The most revealing clue is the difference between self-generated and external touch. When a person reaches up to scratch their head, the brain predicts when the hand will arrive, where contact will occur and roughly how the sensation should feel. It then reduces the intensity of the expected signal. That sensory dampening helps explain why touching oneself normally feels weaker and why most people cannot tickle themselves: the nervous system has already accounted for the movement.

Differences in this prediction process may illuminate broader variations in bodily experience. Some people with schizophrenia have more difficulty anticipating and interpreting self-generated touch, so their own touch can feel unusually intense and more ticklish. Similar patterns have been reported among people with high levels of schizotypal traits, which can include atypical thought and social patterns without a diagnosis of schizophrenia.

The article also describes a 2024 study in which children who scored higher on measures of autistic traits responded less strongly to tickling and were less likely to approach their parents with a positive emotional reaction afterward. This result does not make ticklishness a diagnostic test, nor does it imply that one response characterizes every autistic person. It shows how a controlled, familiar sensation might help researchers investigate individual differences in sensory processing and social touch.

The larger lesson is that tickling is not merely a funny reflex. It exposes the brain’s constant effort to decide where a sensation came from, whether it was expected, what it means socially and how strongly it should enter awareness. Kilteni’s work is still mapping that territory, but the phenomenon’s very strangeness makes it valuable: behind a giggle lies a compact experiment in how the brain constructs bodily experience.