After centuries of debate, we still don't know how tickling works

Most of us have laughed uncontrollably when tickled. Yet almost none of us know why. Tickling sits at a strange crossroads – it’s universal, ancient, and deeply familiar, yet still barely understood by science. Socrates and Aristotle debated its meaning.

Charles Darwin believed it could reveal something about laughter and emotion. Even today, neuroscientists are still asking: what is tickling, and why does it matter?

Neuroscientist Konstantina Kilteni from Radboud University believes this question deserves more attention. “Tickling is relatively under-researched,” she noted. To her, this isn’t just a gap – it’s an opportunity.

“It is a complex interplay of motor, social, neurological, developmental and evolutionary aspects,” said Kilteni.

By studying tickling, we may unlock new answers about how the brain develops, how we relate to others, and how emotions are wired into our skin.

Two types of tickling

Kilteni’s research distinguishes between two kinds of tickling. Knismesis is the light, feather-like sensation. Gargalesis is the intense, laughter-inducing kind from strong, repetitive touches – like fingers on the armpits or soles.

Most studies focus on knismesis. It’s easier to replicate and measure. But gargalesis, the one that causes squirming and laughter, remains neglected. That’s the version Kilteni wants to study closely.

Why should we study tickling?

Tickling has implications far beyond laughs. It may explain how we learn to distinguish self from others. This is key to understanding conditions like autism or schizophrenia. It also appears early in life – infants react to tickles by the end of their first year.

Besides humans, gorillas, bonobos, and even rats respond to tickling. That makes it a good subject for evolutionary studies. According to Kilteni, tickling can strengthen the bond between parents and children. But it also offers insight into early brain development.

To study gargalesis, Kilteni created a tickling lab. A subject places their feet through holes in a plate. A mechanical stick delivers a controlled tickle. This lets her track consistent reactions – heart rate, breathing, sweat, and brain activity.

“By incorporating this method of tickling into a proper experiment, we can take tickling research seriously. Not only will we be able to truly understand tickling, but also our brains.”

Tickling and sensory processing

Research confirms that individuals with autism often react more strongly to tickling. This might reflect differences in sensory processing or brain wiring. These insights may help develop better sensory therapies and deepen our understanding of the autistic experience.

When you try to tickle yourself, your brain already knows what’s coming. It uses a process called “predictive attenuation” to cancel out the expected sensation.

As your hand moves, your brain sends motor signals to control it – but it also predicts the resulting touch. Because it can accurately guess the timing, location, and pressure, the brain reduces your sensitivity in advance. This means the tickling sensation doesn’t fully register.

Kilteni highlights this effect to explain why externally generated touches feel more intense and unpredictable. Your brain filters out sensations it can predict, so it can stay alert to unfamiliar or potentially harmful stimuli.

This internal filtering system is essential for reacting quickly to surprises – like a sudden poke or a crawling insect. It also plays a role in understanding the difference between self and other, which is crucial for social interaction and personal awareness.

An evolutionary mystery

Some people can’t stop laughing when tickled. Others barely flinch. This may depend on genetics, skin sensitivity, brain wiring, or even personality traits like extroversion.

Children are usually more ticklish, possibly because it helps them learn body awareness and humor.

Tickling may have served many roles. One theory says it taught children to protect sensitive body parts. Another sees it as a way to build social bonds. Some scientists say it’s just a reflex – like sneezing. But no theory has been proven.

Tickling might even have sexual or emotional dimensions. “Tickle sensations can only be induced by people with whom we have close social relationships,” noted Kilteni. The same touch from a stranger would likely feel unpleasant.

New tools and ideas for future research

The review proposes three key challenges: defining what tickling really is, recreating it reliably in labs, and mapping its brain mechanisms.

Kilteni’s solution is to use automated tools like robots or haptic devices. This helps remove human error and makes the tickling consistent.

She also encourages combining physical, emotional, and brain data to better understand the experience. Future work may use imaging techniques to track exactly what happens from skin to brain.

Still laughing, still wondering

From Plato to PET scans, tickling has fascinated thinkers for millennia. Yet it remains one of the least understood sensations.

Thanks to researchers like Kilteni, that may soon change. “We are only at the very beginning of this journey,” she said.

With better tools and clearer definitions, tickling might soon reveal more about emotion, evolution, and how the brain tells self from other.

The study is published in the journal Science Advances.

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