Abstracts

Laughter and smiling have been reported as ictal symptoms in epileptic patients and as inappropriate signs of affect in neurological disease. Cortical electric stimulation so far has failed to demonstrate a reproducible site responsible for the generation of laughter. We report the induction of laughter and smiling by cortical electrical stimulation in the frontal lobe in two patients. The subjects underwent presurgical epilepsy evaluation with subdural grid electrodes for identification of the epileptogenic zone and delineation of the adjacent functionally eloquent cortex. We applied biphasic, predominantly bipolar electrical stimulation at 0.3 msec, 50 Hz and 1-15 mAMP levels in patients undergoing grid subdural EEG for surgical candidacy (aged 18 months, with left frontal cortical lesion extending to the vertex and posteriorly to the motor area and 35 years, with a lesion in the right supplementary motor area, SMA; after resection, histology from both patients was classified as tuberal type cortical dysplasia). Stimulation of the prefrontal area induced reproducible laughter. The adult patient reported absence of emotional content. Slowing of speech occurred during the stimulation of electrodes in the upper and posterior vicinity. In this patient laughter was elicited under two electrodes in the cranial anterior part of the SMA. In the child, this response was induced by stimulation of the lateral prefrontal cortex near the falx cerebri. Neither of the stimulation tests that caused laughter were associated with afterdischarges. The anterior portion of the SMA/lateral premotor cortex in the dominant hemisphere is involved in generating the motor pattern of laughter. Whether other cortical areas are also involved in the generation of laughter is not certain, but there is one case published in biomedical literature (1) in which laughter could be elicited by cortical electric stimulation. Laughter response was evoked in this patient by stimulation in the posterior superior frontal gyrus, representing the anterior border of the lateral premotor cortex.
Reference: 1. Fried I, Wilson CL, MacDonald KA, Behnke EJ.: Electric current stimulates laughter. Nature. 1998 Feb 12;391(6668):650.