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A clue found to seizures that cause helpless giggles

“Laughing seizures” have long been one of the mysteries surrounding epilepsy. During an event, an epileptic suffering a laughing seizure can guffaw, sometimes hysterically, but certainly not because he or she finds anything funny. Now a new study published in the journal Brain, from a team led by Josef Parvizi of Stanford University, has helped clear up some of the mystery.

Earlier research traced these events, more formally called gelastic seizures, to abnormal clumps of neurons in the hypothalamus called hamartomas. “The hamartomas start firing on their own and cause the seizures,” Parvizi explained.  

But exactly where in the hypothalamus are gelastic seizure-related hamartomas located? That answer’s important because the hypothalamus has several regions, or nuclei, that manage input and create output related to a variety of body functions like temperature regulation, sexual behavior and hormone release. Parvizi likens it to a college campus. “Just like a campus, you have different buildings and every department has its own students and own connections,” he said.  

In looking at 100 cases of children with gelastic seizures who’ve had their brains imaged, Parvizi and his colleagues were able to show that in every case the hamartoma lesions were located in a region known as the mammillary bodies. (They don’t have anything to do with breasts. They just sort of look like breasts and the neuroscientists who first described them were men, so there you go.)

These structures, located on the posterior part of the hypothalamus, are associated with memory functions. Alcoholics can wreck their mammillary bodies, and if they do, they can start to unconsciously fill in memory gaps with confabulations. 

Nobody knows exactly what that has to do with laughter, if anything, but, Parvizi says hopefully, “it gives us an anatomical clue. Next, we have to zoom in there and understand the cellular biology of that region and its connectivity.”

By cellular biology, he means what chemicals -- neurotransmitters -- cause the neurons to fire and what chemicals they, in turn, produce to communicate with other parts of the brain. “That way we can track and trace them,” he said.

In future studies, he hopes to figure why gelastic seizures don’t produce some other effect. “Why not screaming?” he asked rhetorically. “Why not coughing? Why is it laughing? That is a fascinating topic.”

Ultimately, he thinks the answer to those questions will lead to an explanation for why and how any of us laugh.

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