Mirroring other's laughter. Cingulate, opercular and temporal contributions to laughter expression and observation

Simulation theories predict that the observation of other's laughter modulates activity in the same centers controlling its production. Investigating this issue is particularly challenging, given the technical difficulties of studying laughter production. Previous observations from surgical patients reported laughter production following the electrical stimulation (ES) of the pregenual anterior cingulate (pACC), the frontal operculum (FO) and the temporal pole (TP), deemed to control emotional, communicative and cognitive aspects of laughter, respectively. Here we investigated which region is recruited during laughter observation and production, by adopting a twofold strategy which combines ES and intracranial recording in the same patients. We identified nine sites equally distributed in the pACC, FO and TP, where ES elicited laughter. Subsequently, we presented the patients with visual stimuli depicting dynamic (video) and static (pictures) expressions of laughter, along with emotional and neutral controls, while intracranially recording high-frequency gamma activity (50-150 Hz) from the same sites. pACC sites showed a selective activation during laughter observation, but only if laughter is presented in a dynamical fashion. FO and TP failed to respond during both dynamic and static expressions. We conclude that pACC host a mirror mechanism directly mapping other's laughter onto the neural substrate responsible for the production of emotional laughter.