Are they laughing at you or laughing with you? Your brain can tell the difference.
Curious about how different types of laughter — mocking, joyful or ticklish — are understood, researchers led by Dirk Wildgruber, professor of neuropsychiatry at Eberhard Karls University of Tübingen in Germany decided to explore what these different expressions of hilarity looked like in the brain.
They recruited 18 young men and scanned their brain activity as the volunteers listened to three types of recorded laughter. The laugh tracks were generated by professional actors, who were given three specific scenarios — being tickled, feeling joy and taunting someone — and asked to produce the appropriate laugh for those situations. As the participants heard the laughter, they were asked to categorize whether it was happy, mocking or a consequence of being tickled. The men were able to correctly identify the laughs in the majority of cases, though they were slightly less accurate at correctly labeling tickling.
In a second test, the men counted the number of bouts of laughter in each recording, using the actor’s audible inhalation as a signal for when a bout ended. This provided the researchers with a way of distinguishing between types of laughter. Again, the participants were better at identifying the two types of social laughter, as compared with tickling. Why? “Perception of these types of laughter activates a partially overlapping network of brain regions,” says Wildgruber. These types of laughter include areas involved in processing sound and vision, as well as those that allow people to consider what others might be thinking or feeling.
Oddly, however, in terms of blood flow to specific brain regions — which is how scientists generally measure whether an area of the brain is activated — the researchers found no distinction between joyous and taunting laughter. Wildgruber suggests that the same regions may be used to process a broad range of social information, just as a computer might use the same hardware for word processing or games.
The researchers did, however, see changes in the strength of the connections between regions. When participants listened to taunting laughter, for example, the data showed a stronger connection between auditory areas and those involved in analyzing other people’s intentions, which is known technically as “mentalizing.” But during joyous laughter, the visual areas were more highly connected with the mentalizing regions. “The stronger connection between the ‘voice area’ and the ‘mentalizing area’ during perception of taunting laughter might indicate that the social consequences of this signal are primarily inferred from the acoustic signal,” says Wildgruber.
In contrast, seeing facial expressions (even if you are just imagining them when you are listening to laughter) might be more important in recognizing joy. Jaak Panksepp, professor of integrative physiology and neuroscience at Washington State University and a leading researcher on laughter, who was not associated with the study, called it “wonderful.” He says, “It is remarkable that joyful and taunting laughter could not be observed with traditional blood-flow measures but could by more modern connectivity analyses that tell us how quite different brain regions are working together when listening to various kinds of laughter.”
All this focus on the physiological basis of laughter might seem, well, silly, but it actually has important clinical implications. Misperceiving neutral or positive information as threatening, for example, is a key problem in schizophrenia — and it may involve hearing happy laughter as mocking. In depression, smiles are often seen as smirks and interpreted as a sign of social rejection, so here, too, understanding how the brain recognizes the social information in laughter could be informative. Autism also involves problems with recognizing and decoding social information like the emotional tone of laughter. Wildgruber suggests that if differences in connectivity during laughter are seen in these conditions, it might lead to better diagnosis and treatment.
Understanding laughter might also offer insight into human evolution. Panksepp found that even rats could laugh when tickled (they do so at a frequency too high to be perceived by human ears). So he believes this stimulates joyful play, which helps animals bond and learn adult social behavior in a fun way that allows them to make mistakes that can be corrected in a safe and encouraging environment.
“The findings of our study are in line with the hypothesis that [complex social laughter is a] diversification from an ancient reflexlike tickling laughter expressed during play,” notes Wildgruber. He says the ability of laughter to express such divergent social signals as the rejection from taunting, and the connection from enjoying a joke with others may link it to the development of language. “Laughter seems to represent a direct link between animal communication and the origin of human language,” he says, “The diversification of this ancient signal throughout evolution might have been the starting point for human language capacity.”
Panksepp is also intrigued by how laughter echoes throughout both higher cognitive and more primitive emotional brain regions and how the antisocial side of laughter is actually more complex. “The primal laughter [and] joy generators of the brain are in very low [less evolved] regions,” which represents their earlier evolution, he says, “but such primal forces of the mind can developmentally mature in many different directions in upper brain regions.”
So while even infants can experience social joy in laughing, it takes a more mature and socially sophisticated mind to understand the complexity of taunting. “The dark side of laughter is that with maturation one can obtain in-group social joy at the cost of marginalizing others with taunting laughter,” Panksepp says. “Joyful laughter is infectious and brings people together; taunting laughter is not, since it is discriminatory. Clearly, we are still just barely beginning to fathom the many ways laughter [affects] our brains.” And as we do, we may understand a lot more about how laughing helps us to connect — or not — with others.
The study was published in PLOS One.