Tickling, because you can't do it yourself

Tickling

In a neuroscience lab in Berlin one day last year, Subject one sat in a chair with his arms raised and toes uncovered and pointing down. Lurking next to him was Subject Two. Once ready and after a signal, Subject Two was instructed to tickle their partner.

To capture the moment, a high-speed GoPro was aimed at the first subject's face and face. to which was added another camera directed at his feet and a microphone installed nearby. As expected, Subject One couldn't help but laugh. It was precisely this aspect that prompted Michael Brecht, leader of the research group at the Humboldt University of Berliano, to devote himself to neuroscience applied to tickling and play. In addition to being a fun phenomenon, tickling is also mysterious and poorly studied. After all, brain and behavior research is typically geared towards somber themes, such as depression, grief, and fear. "But I think there are also deeper prejudices against play, which is seen as a thing for children," explains Brecht.

New methods for an ancient mystery

Laughter is commonly considered a widespread social behavior in some mammalian species. It is a way to disarm others, ease social tensions and create bonds. Chimpanzees are capable of laughing, as are dogs and dolphins. Rats are the frequent subjects of tickle studies. If you turn them upside down and tickle their bellies, they squeak at more than twice the level that human ears can detect. But many mysteries remain around tickling, both in regards to rats and people. The greatest of all is because we can't tickle ourselves.

"If you read the ancient Greeks, Aristotle wondered about tickling. Socrates, Galileo Galilei and Francesco Bacone too," says Konstantina Kilteni, a cognitive neuroscientist who studies touch and tickle at the Karolinska Institutet in Sweden and who she is not involved in Brecht's research. We don't know why contact is capable of causing tickling, nor what happens in the brain. We don't know why some people, or parts of the body, are more ticklish than others. "These questions are very old - continues the author -, and after almost 2,000 years we still do not have an answer".

It is not easy to collect objective measurements on how human beings respond to tickling and to correlate them with the perception of phenomenon. That's why Brecht's group involved twelve people in a studio designed to observe tickle with non-Aristotelian instruments like GoPro and microphones. The footage the team collected would help them understand what happens when people are tickled and what changes when they are tickled alone. In the journal Philosophical Transactions of the Royal Society B, the team reports observations on reaction times, laughter and breathing and, for the first time in a human study, shows that trying to tickle oneself while being being tickled by another person cancels the phenomenon.

Tickling, Brecht argues, is "a very strange kind of touch and reaction to it". In an 1897 article entitled The Psychology of Tickling, Laughing, and the Comic, he notes that all people generally tickle in the same places. Feet come first. Armpits, neck and chin follow. As children, we instinctively tickle, and even if some of this predilection for play fades as we grow up, we continue to understand this mysterious language. Brecht believes that this is a form of social signal in the context of the game: "With your laughter signal that it is okay to touch, when it would normally be inappropriate to do so," the researcher points out.

A question of feeling

In the first phase of the new study, each subject had to walk in front of the GoPro and the microphone. Previous studies have established that tickling depends on mood: anxiety and lack of familiarity, in fact, repress the phenomenon. Since the participants had to tickle each other in turns, Brecht's team made sure that each couple knew each other in advance and felt comfortable.All participants were still surprised by the tickle attack from the partner. The "tickler" always hid behind the subject, receiving randomized indications on the parts of the body to be touched from a screen. Neck, armpit, lateral trunk, sole of foot and head: each point was tickled rapidly five times.

The first observation recorded by the team was that the subjects' facial expressions and breathing changed approximately 300 milliseconds later. tickle. Then, about 500 milliseconds, came the vocalization, surprisingly delayed (normally the vocal reaction time to a touch is about 320 milliseconds). The research team suspects that laughter takes longer to arrive as it requires more complex emotional processing. The subjects also rated the ticklishness of each touch. Since it is not usually susceptible to tickling, the top of the head served as a control area for understanding what happens when tickling an unresponsive spot on the body. The volunteers laughed audibly after about 70 percent of the touches, with an intensity directly proportional to the strength of the sensation. The volume of the participants' laughter turned out to be the parameter that best matched their subjective evaluations.

In the next phase of the experiment, the "ticklers" repeated the action of the previous stage, while their partners have tried to tickle themselves (in the same spot but on the opposite side of the body, just next to it or by simulating the act without touching the skin).

As expected, the self-tickling attempts did not had effects. However, the team noticed something strange: the act made the other person's tickle less intense. On average, laughter decreased by 25 percent and was delayed by nearly 700 milliseconds when the same areas were affected. "It was a surprise - explains Brecht -. But it emerged very clearly in the data".

Predictability and inhibition

How can this phenomenon be explained? To answer, we need to go back to the question of why we can't tickle ourselves. The main theory holds that tickling causes laughter thanks to a prediction error of the brain, which is confused by an unexpected touch and leads to fibrillation. Attempts to tickle oneself on the other hand are always predictable.

But Brecht thinks that the point is not the ability to predict. The researcher suggests instead that when a person touches their body, the brain sends a message to the whole body by inhibiting the sensitivity to touch. If this were not the case, Brecht argues, we would continually tickle ourselves every time we scratch an armpit or touch our toes.

The theory makes sense, says Sophie Scott - cognitive neuroscientist of ' University College London not involved in research - because our brain learns to attenuate sensory perceptions when our actions contribute to causing them. The same darkening effect, he continues, occurs with hearing. As we speak, the parts of the brain that other people listen to are suppressed. (This is why, continues Scotto, "people are not able to judge the volume of their voice"). Kilteni notes that it is not yet clear what exactly happens in the nervous system when a person is tickled, even self-inflicted. However, the neuroscientist is impressed by the data that Brecht's team has been able to collect.

The face does not say everything

The contribution to the science of the tickling sessions in the laboratory goes beyond the funny side. They also clarify little-studied aspects of emotional processing. "People say that we do not express emotions very intensely with our voice, that it is the job of the face - says Scott, who could not disagree more -. The voice expresses words, moods, identity, health, age. , sex, gender, geographical origins and socio-economic status: they are just more difficult to study than faces ". Scott adds that touch is also greatly underestimated. Compassion and affection are expressed much more clearly with touch than with faces or words.

Brecht's team intends to continue studying the game through neuroscience in future studies. Experts have speculated that the level of susceptibility to tickle reflects the perception we have of ourselves regarding our playfulness. While this aspect seems true for other animals - a rat that is very ticklish is also more playful - it is more questionable for humans. "My wife suffers more from tickling - says Brecht -. But I'm very playful!" .

This article originally appeared on sportsgaming.win US.