Subject 1 sat on a chair with their arms raised and their bare toes pointed down at a Berlin neuroscience lab on a day in December of last year. Subject 2 waited, fingers curled, behind them with access to their feet. Subject 2 was told to take the open shot whenever they wanted to: tickle their spouse severely.
A high-speed GoPro was aimed towards Subject 1 with the intention of filming his or her face and body to preserve the moment. An additional one right beneath their feet. There was a microphone nearby. Subject 1 cracked up just as we’d hoped. Michael Brecht, head of the Humboldt University study group, was intrigued to the neurology of tickling and play because he couldn’t help but do it. It’s humorous, but it’s also incredibly mysterious—and understudied. Brecht acknowledges that “it’s been a bit of a stepchild of scientific study.” After all, studies of the brain and behaviour tend to focus on depressing subjects like pain and fear. On the other hand, he argues, “I think there are also deeper basic prejudices against play— it’s something for children.”
Many people believe that laughter is a social activity shared by many mammals. It’s a technique of disarming others, alleviating social tensions, and uniting. Even chimpanzees are capable of it. Dogs and dolphins too. Tickling experiments are often conducted on rats. If you turn them over and start poking at their stomachs, you’ll hear a squeak that’s more than twice as high as the upper limit of human hearing. However, there are still many unanswered questions regarding tickling, whether in rats or humans. The largest of all of them is the inability to tease oneself.
“If you study the ancient Greeks, Aristotle was worrying about ticklishness. Cognitive neuroscientist Konstantina Kilteni, who investigates touch and tickling at Sweden’s Karolinska Institutet, adds that “Socrates, Galileo Galilei, and Francis Bacon” all fit this category, too. Neither the causes nor the brain mechanisms of ticklish responses to touch are fully understood. As of yet, we have no idea why certain people, or anatomical regions, are more sensitive to tickling than others. Her next statement is that “these questions are really old,” and that “after approximately 2,000 years, we truly don’t know the solution.”
The problem lies in the fact that it is challenging to collect objective data of how people react to tickling and correlate them with reported ticklishness. Because of this, Brecht’s team enticed 12 participants to participate in a study that aimed to examine the occurrence using non-Aristotelian gadgets like GoPros and mics, despite having a rather small sample size. The data his team gathered about what happens when individuals are tickled and when they tease themselves would be invaluable. For the first time in a human investigation, the researchers reveal that tickling oneself while being tickled lowers ticklishness. They describe their findings on reaction times, laughter, and respiration in September’s Philosophical Transactions of the Royal Society B. You don’t see that very often. The studies don’t usually include things like that,” explains Kilteni. You may say “it advances the state of the art” with confidence after reading this.
Tickling is “a really weird form of touch and reaction to touch,” according to Brecht. He is amazed by how fundamental these complex behaviours are. A article published in 1897 titled “The Psychology of Tickling, Laughter, and the Comic” made the observation that everyone has the same tender points. The feet take first place. Afterwards, we get to the pits of our arms, necks, and chins. As children, we have an innate need to play and tickle; as adults, this desire may wane, but our innate understanding of this enigmatic language remains. In the context of play fighting, Brecht thinks this is a type of social signalling: “You indicate with your giggles that it’s alright to touch, while ordinarily would be wrong to contact.” (Your laughter signals need not precede physical contact. “They giggle like hell before you really get there,” one may say to a child who is going to be tickled by a parent.
Each participant was given their turn in front of the cameras and microphones at the beginning of the new trial. Previous research has shown that the response to tickling depends on the subject’s mood, with anxiety and unfamiliarity acting as a damper. Brecht’s team made sure participants in each pair were acquainted with one another before the experiment began so that they would feel comfortable tickling one another, but everyone was nonetheless taken aback by the surprise of being tickled. The tickler would hide behind their companion at all times while being fed random sequences of body regions to touch from a videoscreen. A total of five fast tickles were applied to the neck, armpit, lateral trunk, plantar foot, and top of the head.
The first thing that was noticed was that the person’s facial emotions and breathing morphed into a tickling in around 300 ms. Poetry captured on GoPro film is described in the article. The person being tickled reacts with a lifted cheek and an outwardly drawn corner of the mouth, which “occur in conjunction to express a joyful smile.”
Then, after roughly 500 milliseconds, came the vocalization—surprisingly late. (The average response time for a human voice when touched is 320 ms.) The group hypothesises that the reason laughter takes longer is due to the complexity of the emotional processing it entails.
The subjects also assessed how ticklish each touch was. The crown of the head is not generally ticklish, therefore it served as a control for what occurs when you tickle someone in a not-responsive location. About 70% of the time, volunteers were heard laughing in response to the tickling, and the more they felt it, the louder and higher pitched their laughter became. According to a study, participants’ subjective judgments of the intensity of each tickle were most strongly connected with the volume of their laughing.
The next section of the experiment had the ticklers repeat their actions while their partners tickled themselves, either in the same location on the other side of the body, immediately adjacent to it, or with a floating pretend-tickle that never made contact with the skin at all.
Self-ticking went as smoothly as could be expected. However, the group realised something peculiar: tickling oneself diminished the intensity of the tickle from the other player. On average, the prevalence of ticklee chuckling reduced by 25 percent, and was delayed to over 700 milliseconds while self-tickling the same side. “We were taken aback by it,” Brecht adds. “But it’s really evident in the data.”
We can only speculate as to the reason behind this. Once again, we’re left wondering why it is that we’re unable to tickle ourselves. The most popular explanation proposes that the brain makes a prediction error when tickled, causing the recipient to laugh. It goes into a brief state of panic when touched in a way that throws it off. As expected, self-touch causes little panic.
Brecht, however, is of the opinion that this is not primarily a predictive exercise. He proposes instead that self-contact triggers a brain-wide message that dulls touch receptors. We believe the brain is using a tactic it has learned: “Don’t pay attention to me after I touch myself,” he says. He claims that if this weren’t the case, people would continuously be tickling themselves by doing things like scratching their armpits or toes.
Sophie Scott, a cognitive neuroscientist from University College London who was not involved in the study, explains that this makes sense given that our brains learn to suppress sensory inputs when our actions are influencing them. When I move about while sitting, I feel a lot of different things in my body. To her, knowing who else entered the room and touched her is more pertinent. She goes on to say that the same thing happens to one’s hearing. The areas of your brain responsible for taking in speech are turned off when you’re talking. According to her, this is why “people are quite lousy at assessing how loud they are speaking.” Because the brain suppresses its own responses when self-tickling, it also likely does the same when someone else tickles the person.
When a person is tickled, even by oneself, it’s not apparent what happens in their nerve system, as pointed out by Kilteni. It will be difficult to know for sure without monitoring muscle activity, recruiting more than 12 participants, or automating the tickling procedure. She is, nevertheless, amazed by the information Brecht’s group was able to gather. Kilteni has learned, for example, that the sound of laughter correlates well with the intensity of a tickling; she intends to use recordings and video of giggles in her future projects.
While “Ticklees were told to act as naturally as possible” and other like lines provide some much-needed humour to technical writing, lab-based tickle sessions give more to science than just that: They shed light on previously mysterious facets of the emotional processing system. Scott argues that the face is more effective at conveying feelings than the voice. She strongly disagrees and says so: Words, emotions, identities, health, ages, sexes, genders, nationalities, and socioeconomic position may all be inferred from a person’s voice; it’s just more difficult to analyse than facial features.
Scott chimes in to say that the importance of touch is often overlooked as well. Kindness and love are communicated more effectively via physical contact than through words or even facial expressions. When a friend is in distress, she recommends either saying “I feel terribly terrible for you” or giving them a hug. That physical contact and comfort are probably crucial.
Brecht and his team hope to keep exploring the neurobiology of play in future research. Researchers have hypothesised that your tolerance for being tickled can provide insight into your sense of humour. Despite the apparent truth of the statement (a ticklish rat is also a playful rat), the extent to which this holds true for humans is open to debate. A more ticklish person than I am is my wife,” Brecht remarks. “But I’m really quite jovial!”