Lateralized parietal activity during decision and preparation of saccades.

The posterior parietal cortex is involved in numerous visuospatial tasks, but little is known about the lateralization of these functions. We used functional magnetic resonance imaging to map the posterior parietal areas involved in saccades. Cerebral activation was studied during three different steps of saccadic elaboration: internal Decision of where to direct a horizontal saccade, motor Preparation and saccade Execution. These steps activated distinct areas: Decision and Preparation selectively activated the left posterior parietal cortex (left deep posterior intraparietal sulcus and left medial posterior intraparietal sulcus), whereas Execution activated only the right posterior parietal cortex (right medial posterior intraparietal sulcus). In humans, left but not right posterior parietal cortex might be specifically related to decision making and preparation of forthcoming ocular saccades.