Spontaneous and voluntary laughter come from different parts of brain: study

By Stephen Beech

Spontaneous and voluntary laughter come from two different regions of the brain, reveals new research.

Laughter is a universal social signal that connects us with other people.

But, until now, the brain regions underlying laughter were not well understood, in part because it's hard to elicit genuine laughter in the lab.

For the new study, published in the journal Trends in Neurosciences, researchers analyzed reports from medical procedures in which the brain is electrically stimulated in awake patients.

Laughter can be an unintentional byproduct of such stimulations, allowing scientists to pinpoint laughter-evoking brain areas.

By examining the reports and other clinical and animal studies, the research team were able to describe two distinct networks in the brain for laughter: one that elicits spontaneous outbursts, and another that produces voluntary, conversational laughter.

Study author Sophie Scott explained that researchers have long observed two types of laughter in healthy humans.

She said: "Think about the last time you were laughing and you could not stop.

"Something set off you and you are helpless with mirth."

That, she says, is spontaneous, involuntary, and sometimes uncontrollable laughter, which can be associated with certain types of seizure disorders, mood disorders, Alzheimer's disease, and schizophrenia.

She says the second kind is volitional laughter.

Scott, of University College London (UCL), said: "That's most of the laughter you encounter.

"It's timed incredibly precisely. If you look at people having a conversation, they will laugh together at the end of a sentence and then breathe together.

"When people are talking to each other, volitional laughter starts and stops really quickly."

She says that type of coordination points to a degree of control that is lacking in spontaneous laughter.

To tease apart the brain circuitry underlying the two types of laughter, the researchers turned to reports of pre-surgical brain stimulation in epilepsy patients.

During those procedures, doctors identify brain regions to target for surgery by electrically stimulating parts of the brain while patients are awake.

The probes often unintentionally evoke laughter, and patients are able to describe their feelings in real time.

The research team analyzed the reports, along with other clinical and animal studies, to propose two distinct networks underlying spontaneous and voluntary laughter.

The spontaneous network consists of brain regions involved in motor control and emotional regulation, including the pregenual anterior cingulate cortex, nucleus accumbens, and the temporal pole.

Stimulating those regions produces laughter accompanied by enhanced mood, euphoria, and mirth.

The voluntary network comprises areas involved purely in motor control of laughing and smiling, such as the rolandic operculum, globus pallidus, and presupplementary motor area.

Stimulation of those regions evokes laughter without positive emotions.

The researchers suggest that the spontaneous network is a more evolutionarily ancient pathway that arose in animal "rough-and-tumble" play, with laughter-like vocalizations serving as a signal to prevent aggression and promote social bonding.

The hypothesis is consistent with recent discoveries that several mammalian species produce laughter-like vocalizations during social interactions.

But the voluntary network overlaps with brain regions that produce speech, supporting the idea that it controls more purpose-driven, conversational laughter.

Study co-author Fausto Caruana says that, as well as shedding light on neurological and psychiatric disorders marked by altered laughter, the research team hope the findings can serve "as a kind of Rosetta stone for decoding multiple aspects of communication and the social use of vocalizations.

Caruana said: "The role of these circuits in pain modulation is also intriguing.

"Studies have shown that laughter can act as a natural analgesic.

"And the anterior cingulate, identified in this literature review as part of the spontaneous laughter network, is also an important player in the brain's own pain-dampening system."

Caruana, of the National Research Council of Italy, added: "We are interested in further investigating the analgesic role of laughter and the neural circuits that support it."