In their study, Xiong and Kilteni surveyed 448 people from three cultural backgrounds: Chinese, Dutch, and Greek. "We found remarkably similar patterns regardless of where participants came from," says Kilteni. "More than 95% of the people we studied had either been tickled themselves or had tickled someone else, suggesting that tickling behaviours are widespread". Across all three groups, participants described remarkably similar experiences. Most reported laughing when tickled, and most said they had been tickled by family members or friends. During childhood, people were most often tickled by someone older than themselves, while in adulthood being tickled by people of the same age became more common.
We laugh, but not because we enjoy
The researchers also examined how much people enjoyed being tickled. “Here we see a small age-related difference" says Kilteni. 42% of participants said they enjoyed being tickled during childhood, compared with 35% as adults. More than a quarter of respondents found being tickled unpleasant, while most adults remained neutral. For many adults, being tickled is neither particularly enjoyable nor especially unpleasant.”
The researchers also asked participants whether they thought people tickle others in order to make them laugh. 77% believed this was the case. “However, when we asked whether participants think people laugh because they genuinely enjoy being tickled, most respondents thought the answer was no. That is interesting: people clearly associate tickling with laughter,” says Kilteni, “but they do not necessarily think that laughter reflects pleasure.” The researchers noted that fully understanding these mixed responses to tickling will require dedicated laboratory experiments.
Ticklish bodyparts
Alongside the survey, participants coloured body diagrams to indicate where they feel most ticklish on their body. The resulting ‘body maps’ were strikingly similar across all three cultural groups. The armpits, soles of the feet, abdomen, and sides of the torso consistently emerged as the most ticklish regions. The researchers then compared these tickle maps with maps of other bodily characteristics and sensations, including touch sensitivity, skin thickness, pleasure, and how often different body regions are touched in everyday life. This allowed them to test several long-standing theories about why some parts of the body are especially ticklish—a question that has intrigued thinkers from Aristotle to Darwin.
“Several popular explanations simply don't fit the data,” says Xiong. “For example, the most ticklish areas do not have the thinnest skin—our lips and eyelids are much thinner, yet they are not especially ticklish. Nor are the most ticklish regions simply the most vulnerable parts of the body.” The researchers also found that the body's most ticklish regions do not coincide with the areas that are most sensitive to ordinary touch or those where touch is generally experienced as most pleasurable. Instead, the strongest support was found for Charles Darwin's idea that body regions that are touched less often tend to be more ticklish. “But that is not the whole story,” says Xiong. “No single theory can fully explain why some parts of the body are more ticklish than others.”
Together, the findings suggest that ticklishness depends on a more complex combination of social, sensory, and physiological factors than previously thought. “More research is needed before we can fully explain the phenomenon,” Kilteni explains.
Tickling lab
Xiong and Kilteni are conducting research in their Tickle Lab at the Donders Centre for Cognition. There, participants sit in a chair and place their feet through two openings, after which a robotic device tickles the soles of their feet under controlled conditions. "Our findings show that ticklishness sits at the intersection of sensorimotor processing, social behaviour, emotion, and evolution," says Kilteni. "Understanding how the brain generates ticklishness could help us understand how these different systems work together."