Reaching and Grasping

According to a long standing idea, reaching movements are supported by the dorsomedial parietofrontal circuit consisting of the superior parietal lobule (SPL) and the dorsal premotor cortex (PMd), whereas grasping movements entail the dorsolateral pari- etofrontal network involving the inferior parietal lobule (IPL) and the ventral premotor cortex (PMv). Recently, however, this dichotomist organization has been put into question given that it does not mirror the anatomical and functional organization of reaching and grasping movements. It has been shown that the anatomical pathways linking the posterior parietal cortex to PMd and PMv partially overlap. Also SPL, PMd and PMv contain cells encoding reach direction as well as the orientation and shape of a target object, hand orientation and grip formation necessary for efficient grasping. Furthermore, both the dorsolateral and the dorsomedial networks are active during grasping in humans. Thus, the new evidence questions the existence of two sepa- rate circuits for reaching and grasping and suggests that they are likely to be involved in both actions.