Pinpointing the Laughter Zone

Abnormal growths near the part of the
hypothalamus called the mammillary
bodies cause laughing seizures.

There's nothing funny about gelastic epilepsy. It hits young children, worsens with time, and can lead to several devastating seizure types as well as developmental and behavioral problems. But still, the kids who have this very rare epilepsy are laughing. They can't help it.

The part of the brain responsible for laughter appears to be located on the underside of the hypothalamus, a place disturbed by all of the growths, called hypothalmic hamartomas, known to cause laughing epilepsy. This discovery was one byproduct of research examining 100 cases of gelastic epilepsy to determine how the locations and sizes of hamartomas resulted in different symptoms and outcomes. The research, recently published in the journal BRAIN, and discussed by a panel of neuroscientists at the AES meeting in Baltimore on Sunday, showed that while variously sized tumors found in proximity to different parts of the hypothalamus had different expressions, all of those causing laughter were adjacent to the part of the hypothalamus known as the mammillary bodies.

"We've known for decades that hamartomas in the hypothalamus cause laughing seizures," said Stanford neurologists Josef Parvizi, lead author of the study. "But that's like saying the problem is coming from a city. We wanted to see exactly which district in that city were involved to help us understand the networks that underlie laughter. Just knowing it was in the hypothalamus was not enough."

Parvizi collaborated with John Kerrigan at the Barrow Neurological Institute in Phoenix, which Parvizi calls "the Mecca for hypothalmic hamartoma research." Their paper, which also examined the different outcomes of children with different sized tumors, and tumors adjacent to different parts of the hypothalamus, concluded that however large they are, and wherever they are located, quick diagnosis and removal of hamartomas is key to a good outcome. "If you let this condition linger," says Parvizi, "you are going to run into trouble." 

Because in many cases the first expression of the disease is laughing seizures, gelastic epilepsy often goes long undiagnosed. Especially, for some reason, in girls. The girls in the study had surgery, on average, about 60 months later than the boys. Why? Parvizi could only speculate: "Maybe because if a boy is laughing it is considered more abnormal than if a girl is. But I don't know."