Brain activation related to the representations of external space and bodyscheme in visuomotor control

Regional cerebral blood flow was assessed during reaching movements with ei ther target or finger selection. Measurements were performed with positron emission tomography in normal subjects. We thus identified two patterns of cerebral activation representing parietal command functions based on either external space or body scheme information. Directing the right-hand index finger toward one target dot in an array of five was related to activations distributed over dorsal extrastriate visual cortex (putative area V3A), al ong the parieto-occipital sulcus (putative V6/V6A) and the posterior intrap arietal sulcus (IPS). Right-hemisphere dominance was present at the occipit al extension of posterior IPS. Positioning one right-hand finger of five on the middle target dot was related with anterior IPS activation, extending over the marginal gyrus of the left inferior parietal lobe. The latter indi cated a parietal role in prehension, independent of the shape of the target reached for. In both conditions of the reaching task, instructions for mov ement were auditorily given by random numbers 1 to 5, thus excluding visual cueing. The observed lateralization of movement-related parietal functions helps to explain neurological symptoms such as ideomotor apraxia and spati al hemineglect. (C) 2001 Academic Press.