Cortical topography of human anterior intraparietal cortex active during visually guided grasping.

Dexterous manual prehension requires successfully transforming sensory representations of an object's intrinsic spatial properties (e.g., shape) into motor plans for configuring the opposition space of the hand. In macaques, these sensorimotor transformations are accomplished in a circuit connecting the anterior intraparietal sulcus (area AIP) with inferior frontal cortex (area F5ab). Activation in the human anterior intraparietal sulcus (aIPS) during visually guided grasping suggests a homologue of macaque area AIP. If true, then despite individual variation in cortical topography, visually guided grasping should be consistently associated with focal activation at the junction of the IPS and postcentral sulcus. FMRI was used to test this hypothesis in 14 right-handed adults. Despite substantial variability in IPS topography, a contrast between pincer grasping vs. reaching to complex asymmetrical shapes revealed activation foci at the junction of the IPS and postcentral gyrus in all 14 individuals. This site is likely within the most superior, rostral aspect of Brodmann's area 40, corresponding to area PF or PDE as defined by von Economo and Koskinas, and area 86 as defined by Vogt and colleagues. In both humans and macaques this region appears to play a key role in visually guided grasping.