CASE REPORT Electrical Cortical Stimulation of the Human Prefrontal Cortex Evokes Complex Visual Hallucinations

Complex visual hallucinations are a well-known feature of electrical stimulation or epileptic dischargein the temporal lobe. It has been proposed that these visual hallucinations result from an electricalinterference with the ventral visual processing stream in the lateral temporal lobe and the memorysystem in medial temporal structures, which explains their frequent visual and mnestic features. Eventhough recent studies have demonstrated visual and memory functions in the prefrontal cortex, up tonow epileptic discharge or electrical stimulation of prefrontal structures has only rarely been reportedto induce visual phenomena. We report on two patients undergoing invasive presurgical epilepsyevaluation in which electrical cortical stimulation of the left prefrontal cortex repeatedly inducedcomplex visual hallucinations. Interestingly, the induced visual responses differed with respect to theirspatial organization: whereas those evoked on the inferior frontal gyrus were perceived in the wholevisual field, complex visual responses on the middle frontal gyrus were restricted to the contralateralhemispace. Based on the spatial organization of the visual experiences in our patients, animal work,and neuroimaging data it might be suggested that specific subregions of the human prefrontal cortexmight contain separate visual and mnemonic processing mechanisms.