Scientists develop “tickle robot” to solve touching mystery

Researchers in Nijmegen have set up a laboratory to try to answer one of the oldest questions known to science: why are people ticklish?

Aristotle, Erasmus, Galileo and Darwin all tried to put their finger on the purpose of tickling, or gargalesis to use its scientific name, without finding a definitive reason.

Now two researchers at Radboud University in Nijmegen are using robots and sensors to try to shed more light on the phenomenon.

Tickling exists across cultures and throughout history, but with few variations and little difference between men and women, indicating that it has its roots in biology. Tickling has been observed in other primates such as bonobos and chimpanzees.

Ziliang Xiong and Konstantina Kilteni have set up their lab in a windowless basement in the Maria Montessori building, an environment stripped of any other stimuli that could make their test subjects laugh.

The robot uses a metal pin to simulate tickling, with settings that can be adjusted to measure the effect of different types of contact from gentle stroking to prodding. The participants wear a cap equipped with electrodes that measure their brain responses.

Families and partners

The researchers also asked the 448 subjects to fill in surveys about how they experienced tickling, which revealed strong similiarities.

Most tickling is by adults on children, usually within families, or between siblings. Partners and friends also tickle each other, but this is less common.

Most respondents said they reacted to tickling by laughing, squirming or trying to turn away. The vast majority named the same body parts as most susceptible to tickling: the sides, armpits, belly and the soles of the feet.

The researchers noted that while tickling is associated with play and laughter, many people find it unpleasant and it can quickly become overwhelming. The Nazis even used it as a torture method.

There are indications that people diagnosed with autism are more sensitive to tickling and that ticklish people may even live longer.

Other theories suggest a link between tickling and sexual stimulation, given that couples often tickle each other and it tends to be directed at body parts that are rarely exposed.

Thin skinned

Darwin speculated that tickling felt uncomfortable because it involved touching parts of the body that are unused to being touch, while Aristotle believed it worked on places where the skin is thinner.

But the researchers in Nijmegen said none of the theories provided a complete answer to the reasons why people are sensitive to tickling. “You rarely get touched on your back, but the back is pretty resistant to tickling,” Xiong pointed out.