LOCALIZATION OF GRASP REPRESENTATIONS IN HUMANS BY POSITRON EMISSION TOMOGRAPHY .2. OBSERVATION COMPARED WITH IMAGINATION

Positron emission tomography imaging of cerebral blood flow was used t o localize blain areas involved in the representation of hand grasping movements. Seven normal subjects were scanned under three conditions. In the first, they observed precision grasping of common objects perf ormed by the examiner. In the second, they imagined themselves graspin g the objects without actually moving the hand. These two tasks were c ompared with a control task of object viewing. Grasp observation activ ated the left rostral superior temporal sulcus, left inferior frontal cortex (area 45), left rostral inferior parietal cortex (area 40), the rostral part of left supplementary motor area (SMA-proper), and the r ight dorsal premotor cortex. Imagined grasping activated the left infe rior frontal (area 44) and middle frontal cortex, left caudal inferior parietal cortex (area 40), a more extensive response in left rostral SMA-proper. and left dorsal premotor cortex. The two conditions activa ted different areas of the right posterior cerebellar cortex. We propo se that the areas active during grasping observation may form a circui t for recognition of hand-object interactions, whereas the areas activ e during imagined grasping may be a putative human homologue of a circ uit for hand grasping movements recently defined in nonhuman primates. The location of responses in SMA-proper confirms the rostrocaudal seg regation of this area for imagined and real movement. A similar segreg ation is also present in the cerebellum, with imagined and observed gr asping movements activating different parts of the posterior lobe and real movements activating the anterior lobe.