Pathological laughter. A review of the literature.

Normal laughter is a unique human behavior with characteristic facial and respiratory patterns elicited by a variety of stimulus conditions. The neuroanatomy remains poorly defined but three levels seem likely: a) a cortical level; b) a bulbar, or effector, level; and 3) a synkinetic, or integrative, level probably at or near the hypothalamus. Pathological laughter occurs when laughter is inappropriate, unrestrained (forced), uncontrollable, or dissociated from any stimulus. Pathological laughter is found in three main conditions: a) pseudobulbar palsy; b) gelastic epilepsy; and c) psychiatric illnesses. It is also found in other pathological conditions. What brings these together is their clinical similarity and probable disinhibition at higher brainstem levels.