Gelastic seizures: video-EEG and scintigraphic analysis of a case with a frontal focus; review of the literature and pathophysiological hypotheses.

We report scalp EEG and SPECT findings in a young patient who experienced gelastic seizures; clinical, EEG and scintigraphic data strongly suggested a frontal focus in a context of cryptogenic epilepsy. Few cases of gelastic seizures originating in the frontal lobe have been reported in the literature, most of them involving a diencephalic hamartoma or a temporal focus although, no clinical pattern has been found to be specific for each of these three anatomical regions. The ictal laughter is of variable nature, unmotivated or associated with feelings of mirth, forced or natural, except in the case of a frontal focus where the laughter seems consistently described as forced and unmotivated. However, mirth and laughter are two dissociable clinical elements; their genesis probably involves distinct mechanisms. Anatomical considerations lead to several hypotheses concerning laughter generation: it could be a simple reactional behavior in response to a modified cognitive process, an automatic behavior or a forced action. In a few cases with a temporal focus, laughter seems directly related to a disorganization of the associative temporal cortex and may be considered as a reactional behavior. In cases with frontal focus, anterior cingulate and orbital structures would be particularly implicated in laughter genesis, although with possible different pathophysiological routes: in the first case by disconnection within the premotor mesial system or by an imbalance between premotor mesial and premotor lateral systems, and in the second case by activation of a previously conditioned orbital region.