World Neurosurg. (2020) 133:55.
Laughter has a major role in daily social interactions; consequently, its biologic bases have been previously studied. Nevertheless, its cerebral representation remains unclear. The most accepted hypothesis has postulated that laughter has 2 components: mirth, related to the temporal and frontal neocortical areas, and motor aspect, related to the limbic system and brainstem. Furthermore, in prior studies, laughter has been elicited during electric stimulation with depth electrodes in the supplementary motor area and the cingulum.
This Video 1 reports resection of a right superior frontal gyrus diffuse astrocytoma (isocitrate dehydrogenase mutant, World Health Organization grade II) with awake intraoperative electric cortical and subcortical stimulation mapping. Diffusion tensor imaging (DTI) tractography, including all the tracts in relation to the tumor, was obtained preoperatively and postoperatively. Stimulation of the cingulum medially and inferiorly to the tumor elicited a patient’s smile and laugh without mirth or merriment. Also, this point correlated with the reconstructed cingulum in the intraoperatively navigated DTI tractography.
In conclusion, these findings support the anatomic subdivision of the laughter’s mechanism and the role of the cingulum in its motor component. Furthermore, smiles and laughter could be useful functional landmarks to identify the cingulum during subcortical mapping. Although it remains unclear whether pursuing resection beyond this point would have caused permanent postoperative deficits, considering laughter’s role in social interaction and other emotion-processing functions associated with the cingulum, in the future it could be potentially considered a functional limit of the resection of intrinsic tumors.