Two systems of laughter: how the brain controls emotions and speech

Laughter is not always associated with humor: people laugh to keep up a conversation, express agreement, or strengthen a relationship, but sometimes emotions turn out to be so strong that a person loses control of himself. Scientists have found that two separate neural systems formed at different stages of evolution may be responsible for these different manifestations of laughter. About how involuntary laughter differs from ordinary laughter and how it is related to speech and social connections, see the Izvestia article.

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Most of the laughter does not arise in response to jokes, but during communication. People laugh to show the other person that they understand him, to express agreement, or to emphasize intimacy. In addition, laughter can help reduce stress.

According to the data provided in the article, the probability of laughing in the company of another person is about 30 times higher than when alone. At the same time, people laugh more often next to those they know and sympathize with. The work was published in the journal Trends in Neurosciences (TN).

On average, laughter occurs about six times in 10 minutes during a conversation. These reactions are usually short.: they start and end quickly, and the voice sounds relatively low. However, there is another type of laughter — involuntary. It can last longer, accompanied by high-pitched sounds, squeaking and whistling. A person is not always able to stop laughing, even if the situation requires it.

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Two neural networks — two types of laughter

The researchers analyzed scientific papers that studied people's reactions to electrical stimulation in various parts of the brain. Such procedures are carried out, in particular, when examining patients with epilepsy before surgery. Exposure to certain areas of the brain allows you to identify their functions, and patients can describe their feelings during stimulation.

Scientists have noticed that exposure to several different areas of the brain can cause laughter. At the same time, the reactions differed: in some cases, laughter was accompanied by pleasant sensations and a sense of joy, in others it arose without a pronounced emotional component.

Based on the analysis, the researchers identified two neural networks. The first includes the anterior cingulate cortex, the temporal pole, and some subcortical regions. Her stimulation is associated with emotional, sometimes uncontrollable laughter. The second network is located primarily in the motor and premotor areas of the brain involved in motion control. Its activation can cause laughter without a sense of fun and be accompanied by speech disorders.

Thus, laughter, which a person uses in everyday communication, and an involuntary emotional reaction can rely on different mechanisms of the brain.

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From animal behavior to human speech

According to the authors of the work, the two systems of laughter differ not only in functions, but also in their evolutionary origin. The first, related to emotional reactions, correlates with the neural network involved in vocal expressions common to humans and other mammals. It may also be responsible for other involuntary emotional sounds, such as screams.

When spontaneous laughter occurs, a chain of neurochemical processes is triggered, affecting, among other things, the opioid system of the brain. This may explain the pleasant sensations that accompany such a reaction. The serotonin system, which regulates sensitivity to pain, is also affected, which, according to the authors, may be associated with a temporary decrease in physical pain.

This neural network is considered to be more ancient. Researchers attribute its origin to the emotional reactions of animals and the playful behavior during which animals interact with each other.

The second system is associated with voluntary movements and complex vocal actions, including speech, singing, and beatboxing. It is especially important for communication, because it allows a person to control laughter and use it in conversation, for example, to mark the end of a phrase or to support the interlocutor.

The authors of the review refer to a study by the journal Philosophical Transactions of the Royal Society B: Biological Sciences, in which scientists compared the movements of the vocal tract during spoken and involuntary laughter. In the first case, they were similar to movements when pronouncing words, whereas with uncontrolled laughter they were noticeably different from speech.

When the ability to laugh is preserved, but speech is impaired

The differences between the two systems help explain why some brain disorders have different effects on laughter and speech. According to the data reviewed by the authors, after a stroke that damaged the network associated with voluntary laughter, a person may experience serious speech disorders. At the same time, the ability to laugh, cry, and swear may be preserved. The authors attribute this to the fact that the older neural system remains intact, even if the network necessary for complex control of movements and speech is disrupted.

Researchers believe that studying laughter can help to better understand not only emotional reactions, but also the mechanisms of social interaction. It allows us to explore how connections between people are formed, how emotional contagion occurs — the tendency to involuntarily adopt the emotions of others — and what role laughter plays in empathy and everyday communication.

Despite the apparent simplicity of this phenomenon, the authors consider it as a tool for studying a wide range of processes, from the evolution of social behavior to the mechanisms of speech and pain regulation.