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 discharge in the temporal lobe. It has been proposed that these visual hallucinations result from an electrical interference with the ventral visual processing stream in the lateral temporal lobe and the memory system in medial temporal structures, which explains their frequent visual and mnestic features. Even though recent studies have demonstrated visual and memory functions in the prefrontal cortex, up to now epileptic discharge or electrical stimulation of prefrontal structures has only rarely been reported to induce visual phenomena. We report on two patients undergoing invasive presurgical epilepsy evaluation in which electrical cortical stimulation of the left prefrontal cortex repeatedly induced complex visual hallucinations. Interestingly, the induced visual responses differed with respect to their spatial organization: whereas those evoked on the inferior frontal gyrus were perceived in the whole visual field, complex visual responses on the middle frontal gyrus were restricted to the contralateral hemispace. 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 cortex might contain separate visual and mnemonic processing mechanisms.