Do you remember the last time you were laughing and couldn't stop? Perhaps it was in asituation where you shouldn't even be laughing.
This happened to one of us while accompanying a friend to a family court, in the middle of an unpleasant divorce process. This led us to a quick sprint to the bathroom, while we desperately (and unsuccessfully) tried to regain control — it wasn't exactly the kind of emotional support that friend was looking for!
Another classic example is the cricket commentators Brian Johnston and Jonathan Agnewwho laughed so muchwhile describing a match in 1991 thatthey couldn't say anything. But how and why does this happen?
In fact, although we usually associate laughter with amusement, most laughter occurs for other social reasons. For example, you are30 times more likely to laughif you are with someone than if you are alone. And you will laugh moreif you get to know the person you are withand like them.
Most of the laughter occurs during conversations, when people canlaugh through contagion— being infected by another person's laughter.Studies showthat, when we see or hear someone laughing, it can almost automatically trigger laughter in us, promoting social bonding.
We often laugh to show agreement and understanding, and to strengthen friendships – for example, when we recall shared moments. We also laugh to reduce stress.
These common laughs in conversations occurapproximately six times every ten minutes of conversationon average. They are short, with a more serious tone, and tend to start and stop quickly.
These types of laughter, which we refer to as voluntary, differ from uncontrollable laughter that incapacitates us and that we cannot prevent. Uncontrollable or involuntary laughs are longer and have a more acute tone, involving strange snorts and whistles.
In our latest research, we investigated whether these two different types of laughter could originate from completely distinct brain systems.
Things get complicated
When trying to understand the underlying brain networks involved in the production of laughter, things can quickly become complicated.
To start, people move around a lot when they laugh. This can cause problems for brain imaging techniques, such asfMRI(functional magnetic resonance imaging). It can also be extremely difficult to get people to laugh naturally in a laboratory setting.
Another issue is that different regions of the brain seem to all be connected to laughter. One of us (Fausto) collaborates with theepilepsy surgery unitfrom the Niguarda Hospital in Milan, where patients with drug-resistant epilepsy are undergoing electrical stimulation of the brain for clinical purposes. The electrical stimulation is highly precise and is not affected by movement.
Normally, if you stimulate the motor system, the patient will move. If you stimulate the visual system, they may experience visual hallucinations. And if you stimulate the auditory system, they will hear sounds. However, there are five or six areas of the brain where stimulation causes the patient to laugh loudly. So, why does this happen?
Recently,We reviewed all studies on brain stimulation.involving people laughing and how they felt when laughing. These studies provide evidence that the brain areas where stimulation evokes laughter form two different laughter networks.
In one, encompassing the anterior cingulate cortex, the temporal pole, and certain subcortical regions, stimulation led to laughter accompanied by pleasant sensations and feelings of happiness—this is the most uncontrolled and acute form of laughter. When stimulation occurred in the other network, located in the motor and premotor regions of the brain, the laughter resulted in speech disturbances and was not associated with any emotional state.
Evolutionary differences
The areas that constitute the first laughter network, which is more joyful, correspond to a vocalization network that humans share with all other mammals. This network is also potentially responsible for other spontaneous emotional vocalizations, such as screams.
Activation of this network during spontaneous laughter triggers a neurochemical cascade that involves, among other things, the opioid system. This helps to explain the feeling of pleasure and reward that comes from this joyful and uncontrollable laughter. The serotonin system, which regulates our sensitivity to pain, is also affected, which may explain why this laughter can temporarily alleviate physical pain.
From an evolutionary perspective, this network is older. It originates in spontaneous emotional responses and systems ofplayful anticsof animals and, therefore, remains practically unchanged between humans and other animals.
The other laughs, voluntary, map onto a brain network linked to voluntary movements in humans, such as talking loudly. They play a fundamental role in strategic communication and social negotiation, which may explain the specific use of laughter in conversation as a form of spoken punctuation.
This neural system is primarily found in humans and is associated with complex vocal acts, such as speaking, singing, and beatboxing.
A 2022 studywhich analyzed the ways that our vocal tract takes when we laugh in this conversational manner, found that they resemble the ways that it takes when we speak. In contrast, the ways that our vocal tract takes when we laugh uncontrollably seem very different from speech, and its motor control is simpler, which is consistent with its ancestral origins.
This research shows that voluntary laughter requires a more complex and refined motor control than spontaneous laughter, occupying a middle ground betweenspontaneous laughter and spoken language– not only functionally, but also anatomically.
If a person suffers a stroke that damages this voluntary network, they may develop serious speech problems, although they are still able to laugh, cry, and swear. We would argue that this is because the older network remains intact.
The science of laughter may seem like a somewhat frivolous topic – and neuroscientists certainly have been dedicating more efforts to the study of negative emotions, such as fear, anxiety, anger, and disgust.
Research on human laughter is, however, proving to be a kind ofRosetta Stonefor understanding a surprising range of phenomena – including the origins of social cognition in mammals, the mechanisms of bonding and empathy, the modulation of pain, language in conversation, and emotional contagion.
The authors have no conflicts of interest, do not work for, own stock in, or receive funding from any company or organization that would benefit from this article, and have not disclosed any relevant relationships beyond their academic positions.