There’s the laugh that you can’t control at the worst possible moment, and there’s the one you manufacture to keep the peace. Most people know the difference from the inside. New research confirms the brain has known all along—and has been running two completely separate systems to manage them without you even knowing.

A review published in Trends in Neurosciences, led by researchers from the National Research Council of Italy and University College London, has confirmed what most people have suspected since their first performance review: the brain operates two entirely separate laughter systems. One is ancient and emotional. The other is deliberate and social—a tool the brain borrowed from its speech circuitry to keep things running smoothly in polite company.

According to StudyFinds, most people can reliably tell the two apart even when they can’t explain why, because the brain produces something physically distinct each time.

The Brain Knows the Difference Between Real and Fake Laughter

The two types sound different because their underlying biomechanics are completely different. Spontaneous laughter barely uses the mouth—lower tongue, longer vocal tract, almost no deliberate input. The manufactured kind recruits the same hardware as speech, with the tongue, lips, and mouth moving in coordinated ways that mirror talking. People pick up on the difference without knowing they’re doing it. Research shows they’re far better at identifying who produced a voluntary laugh than a spontaneous one. The vocal signature gives it away every time.

The less expected angle is how spontaneous laughter affects pain. The circuit driving it runs through the anterior cingulate cortex, a region associated with emotion and pain regulation, and research from the University of Oxford has found that it raises pain thresholds by triggering endorphin release. “We think it is the bonding effects of the endorphin rush that explain why laughter plays such an important role in our social lives,” said Robin Dunbar of Oxford. Nitrous oxide—laughing gas—works through some of the same circuits.

When these systems break down, the consequences are serious enough to inspire a comic book villain. Pathological laughing and crying syndrome—the condition reportedly behind Joaquin Phoenix’s portrayal of the Joker—causes involuntary outbursts that are unrelated to how the person actually feels. Gelastic seizures are epileptic episodes triggered by sudden laughter. Cataplexy can cause sudden muscle paralysis from strong emotion. All are linked to damage within these two circuits, per StudyFinds.

The authors admit that spontaneous laughter is nearly impossible to reliably trigger in a lab, which limits how far the research can go right now. But the two-circuit model gives neurologists something they didn’t have before—a clearer picture of what’s actually breaking down in conditions where laughter has gone completely wrong.