“Studying fun is a serious matter,” says neuroscientist Michael Brecht

German researcher and Leibniz Prize winner delivered a lecture at FAPESP on research designed to understand playful behavior and the effects of sexual touch on the brain.

By Karina Toledo  |  Agência FAPESP – German neuroscientist Michael Brecht spends much of his time tickling rats. This activity is neither a hobby nor a game but is research designed to explore play and the predilection for fun shared by rodents and humans after millions of years of evolution.

“Most people think it’s more important to study pain, depression or autism. Classically speaking, these have been the subjects that get the funding. The neuroscience of fun is still relatively unexplored. It’s thought to be simple and not a very serious matter. Both assumptions are wrong,” Brecht said in an interview given to Agência FAPESP.

Winning a Leibniz Prize, he added, gave him the freedom to do research into phenomena that are not usually taken seriously by academia. Leibniz Prizes, Germany’s equivalent of the Nobel awards, give scientists €2.5 million from DFG, the German Research Foundation, to spend on their research work as they wish for up to seven years. 

Brecht won the award in 2012 for developing the “in vivo whole-cell” method of measuring neuronal activity in freely moving animals. “The method opened up new research possibilities, such as investigating the effects of social interaction and sexual touch on the brains of rats,” he said.

Brecht is a professor at the Bernstein Center for Computational Neuroscience (BCCN) and at Humboldt University, both in Berlin. On April 24, he visited FAPESP’s headquarters in São Paulo to deliver a lecture entitled “Sex, Touch & Tickle – The Cortical Neurobiology of Physical Contact”. 

The event was part of DFG's Gottfried Wilhelm Leibniz Program, which includes Leibniz Lectures and aims to foster a dialogue between prizewinners and the scientific community. 

In an interview with Agência FAPESP during his visit, Brecht spoke about studies that help understand the social function of tickling and playful behavior among mammals and the dramatic changes sexual touch in the prepubertal stage can produce in the brain and the rest of the body. A slightly abridged transcript of the interview follows.

Agência FAPESP – The title of your lecture includes the words sex, touch and tickle. How are these three elements connected in your line of research?
Michael Brecht – We’re interested in social interaction, and one way to approach this question has been through touch. For my postdoctoral research, I studied very simple tactile stimuli. For example, what happens when you touch a single rat whisker? At that time, I discovered that a simple stimulus like this one couldn’t give me a broad idea of what happens in the animal’s brain in real-life situations. Recently, we’ve explored aspects relating to social touch and how it’s represented in the brain. We focus mainly on sexual touch and tickling.

Agência FAPESP – What kinds of experiments with animals have been performed to explore this topic?
Brecht – We study rats because they’re very playful animals. It was a great surprise to me when a research paper that was published 20 years ago suggested that rats are ticklish and enjoy being tickled. Initially, the scientific community was highly skeptical. The idea that a rat could be ticklish and respond by giggling, or rat-like laughter, was astounding. One of the first things we noticed is that it makes all the difference to isolate the animal from its group for a day or two before the experiment. It’s much more ticklish and sensitive to touch. When the animal is tickled immediately after being taken from a group it’s less keen to be touched. We think some kind of interaction among rats in a group may satisfy the need to be tickled. When we tickle them, the rats make very similar sounds to those we hear when they play with each other. They’re ultrasonic chirps [too high in frequency for human ears to pick up]. They make these sounds when they’re excited, when they get food, and when they’re in a good mood. 

Agência FAPESP – Why are some rats or people more ticklish than others?
Brecht – It’s clear that there are big individual differences in ticklishness. We don’t know why some people aren’t even ticklish at all. It’s a strongly age-dependent phenomenon in both rats and humans. Children are much more ticklish than adults, and this finding correlates with playfulness. These kinds of differences between ages make sense in a general behavioral context. What doesn’t make sense to me is that there are equally young rats that are very non-ticklish, very unimpressed, and others that are very eager to be tickled. Typically, the playful ones are also more ticklish. This kind of behavior has been preserved for at least 100 million years, since we diverged from rats, so we think ticklishness must be relevant to mammals. 

Agência FAPESP – What do you think the social function of tickling could be?
Brecht – In rats, we have some evidence that it has a lot to do with play and playful behavior. The responses we see in the brain are similar. We tend to think ticklishness may be a trick of the brain to make animals interact playfully.

Agência FAPESP – What has your group found out about sexual touch?
Brecht – Studies conducted with rodents in the 1970s showed that the onset of puberty can be advanced by weeks when a young female is placed in direct contact with an adult male. After that, research focused for many years on pheromonal factors. For example, it was discovered that puberty is advanced when a young female smells the urine of an adult male, but this effect is weaker than when there is direct contact. This finding made us think it was worth looking into tactile effects. Our work showed that stimulating the genitals of a young female advanced puberty as much as when the same female was put in direct contact with an adult male. We studied the brains of these animals, especially a region called the somatosensory cortex, where there’s a map of the entire body, and we found that the part that corresponds to the genitals increases more than twofold in size after tactile stimulus. We’re particularly interested in studying the part of the somatosensory cortex that represents the genitals. In rats, it has a very interesting structure. By anatomical methods, we observed that in both males and females, this brain structure is phallic in shape. Amazingly enough, it resembles the sexually excited male organ. This finding was a most intriguing discovery for us, as the genitals are the most different body part in males and females, but when we look at the representation of this body part in the brain, we see that it’s very similar in both sexes. We observed this first in rats and then in other species, such as rabbits.

Agência FAPESP – Do males and females respond similarly to sexual touch?
Brecht – We haven’t yet investigated the role of sexual experiences in males in great depth. This investigation is something we want to do. One thing we have observed is that in castrated animals, both males and females, this expansion in the genital area of the somatosensory cortex during puberty doesn’t occur. But we don’t yet know whether males and females respond the same way to touch. There are clear differences in behavior between the sexes during puberty. Males tend to touch their own genitals more, for example.

Agência FAPESP – Can this kind of study help understand what happens to the brains of sexually abused children?
Brecht – Christine M. Heim [a researcher at Charité Medical School, Berlin] showed in a study published in 2013 that this part of the somatosensory cortex that represents the genitals is usually atrophied in women with a history of childhood sexual abuse. Cortical density is reduced in this specific area. In animals, we’ve found that the area expands when the genitals are stimulated, but in humans, it appears that experience of abuse may impair the development of this brain region. All these findings are evidence that sexual touch clearly goes far beyond the effects felt on the skin. It really changes the brain in a dramatic way, and in fact, it changes the body as a whole. So touching children can have a very negative effect on their development.

Agência FAPESP – What techniques does your group use to find out how tactile stimulus affects the brain?
Brecht – First, we analyze the animals’ behavior. We make videos and ultrasound recordings. We also record the activity of different brain structures. All this analysis has shown us that the region of the somatosensory cortex that represents the trunk or abdomen, where the animals are most sensitive to tickling, is deeply involved in creating the feeling of ticklishness. When we touch animals on the belly, we see strong responses in this region, and they’re very mood-dependent. When the animals are afraid, these cells don’t respond to touch. We also perform many anatomical studies, and a few optogenetic tricks [using light to activate and deactivate these neurons].

Agência FAPESP – You won a Leibniz Prize for developing in vivo whole cell recording. Could you explain how it works and what kind of research it has made possible?
Brecht – Whole cell recording and patch clamp are techniques that have been used in cell cultures or brain slices for a long time. Basically they consist of carefully inserting an electrode into the cell with a glass pipette to record electrical events inside the cell. What I did was adapt these techniques for use in vivo. Initially the method required that the animal’s head remained fixed. Later we miniaturized the equipment so that the animal could move about freely. Another challenge was making cell recording stable even with motion. We use a few tricks. We cement the pipette once the recordings have been obtained, and this enables us to study animals even while they’re running about in arenas. This has opened up new research areas, such as this one that explores sexual touch. We’ve also deployed it in the study of brain structures associated with spatial memory, such as the hippocampus. We found that some cells in the hippocampus fire when the animal is in a certain place but others don’t. We always thought this was due to different spatial information received previously, but we were able to show that intrinsic properties of the cells are involved as well.

Agência FAPESP – How did winning a Leibniz Prize change your personal and professional life?
Brecht – Winning the prize gave me money and the freedom to dedicate myself even more to what I wanted to do, which was curiosity-driven research. I’ve always worked on unusual topics, but studying ticklishness, for example, is out of the ordinary and has been financed by this prize. Most people think it’s more important to study pain, depression or autism. Classically speaking, these have been the subjects that get the funding. The neuroscience of fun is still relatively unexplored. It’s thought to be simple and not a very serious matter. Both assumptions are wrong. If we don’t study the normal behavior of animals, we won’t be able to cure diseases. In addition, understanding fun is quite complicated. It’s a highly elusive feeling. It’s easy to cause pain in an individual, but it isn’t so easy to promote fun. When you tell the same joke a second time, it isn’t so funny. Studying playful behavior is necessary. Our brains are somehow configured to be playful, and I think learning mechanisms are involved. Depending on educational context, people show more or less appreciation for this capacity to play. Being playful and fun-loving can also be a problem when individuals can’t control it. Research has shown that drugs like Ritalin given to hyperactive children lead to a huge decrease in playfulness and as a result they become able to stay quiet. If we give these substances to rats, they stop playing with each other. I’m not saying children shouldn’t take these drugs, but I think we need to understand more about how they work. This can help us make more appropriate choices.