Hypothalamus may be involved in generating laughter

Anecdotal evidence suggests that the hypothalamus, a structure lying deep within the brain may be involved in generating laughter. Gelastic epilepsy, a rare condition characterized by laughing seizures, is commonly the result of a congenital brain lesion (called hamartoma) within the hypothalamus. Researchers seeking to identify the specific site (nuclei) within the hypothalamus that might be involved in expressing laughter reported their findings today at the American Epilepsy Society's 65th annual meeting.

Josef Parvizi and colleagues at Stanford University and Barrow Neurological Institute reviewed clinical and neuroimaging data on 100 gelastic epilepsy cases and grouped the patients based on their symptoms: patients with gelastic seizures only, patients with mixed gelastic and other seizure types, and patients with the additional symptoms of cognitive impairment and those with precocious puberty. (Abstract 1.214)

Their analysis suggests that in all 100 cases, the hamartomas were centered at the level of the mammillary bodies in the posterior region of the hypothalamus, suggesting that the laughing seizures are due to the involvement of the mammillary bodies or the nearby nuclei in the posterior hypothalamus. The investigators also found that patients with mixed gelastic and other types of seizures had the same size of lesions, but significantly longer lifetime duration of epilepsy compared to patients solely having gelastic seizures, suggesting that the pattern of seizures will change with the duration of epilepsy even though the size of hammartoma remains the same with age.