There is a moment, as Sophie Scott remembers it, when laughter becomes inescapable. Something sets you off — a joke, a memory, a look shared across a room — and suddenly you are helpless with mirth. You cannot control it. You do not want to. For decades, neuroscientists have known that humans produce two distinct kinds of laughter, but they never understood why until now.
A sweeping review published in Trends in Neurosciences reveals that spontaneous, involuntary laughter and voluntary, conversational laughter arise from two separate brain networks — a discovery with implications for understanding everything from seizure disorders to the nature of human connection itself.
Scott, a neuroscientist at University College London, and Fausto Caruana of the National Research Council of Italy in Parma led the team that parsed hundreds of clinical reports to reach this conclusion. Their key evidence came from an unexpected source: epilepsy patients undergoing presurgical brain stimulation. During these procedures, clinicians probe the brain while patients are awake, and sometimes — unintentionally — the electrical current triggers laughter. The patients can then describe exactly what they felt.
By analyzing these reports alongside other clinical and animal studies, the researchers mapped two distinct circuits. The spontaneous network, which produces the uncontrollable, mirthful kind, centers on the pregenual anterior cingulate cortex, nucleus accumbens, and temporal pole. Stimulating these regions generates laughter accompanied by genuine euphoria — an elevated mood and a sense of joy. This pathway appears to be an evolutionary holdover from the rough-and-tumble play of our mammalian ancestors, where laughter-like vocalizations signaled playfulness and prevented aggression. Recent discoveries confirm that many mammals, from rats to apes, produce laughter during social play.
The voluntary network, by contrast, lives in brain regions tied to motor control and speech: the rolandic operculum, globus pallidus, and presupplementary motor area. Stimulation here produces laughter without any positive emotion — a mechanical response without the soul. "That's most of the laughter you encounter," says Scott. "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." This coordination, she explains, requires a degree of executive control that spontaneous laughter simply lacks.
The findings offer a kind of Rosetta stone for understanding how humans communicate, and they may also illuminate the role of laughter in pain relief. The anterior cingulate cortex, part of the spontaneous network, is a known player in the brain's own analgesic system. Caruana says his team is now investigating whether the same circuitry that makes us laugh when we are joyful might also ease our suffering when we are in pain.
For Scott, the research points to something deeper than neuroscience. Laughter, she suggests, is not merely a response to humor. It is a bridge — an ancient, embodied signal that has quietly organized human connection for millions of years.