Journal of Vision - Visually-guided grasping produces fMRI activation in dorsal but not ventral stream brain areas, by Culham, DeSouza, Woodward, Kourtzi, Gati, Menon, & Goodale

Jody C. Culham	Department of Psychology, University of Western Ontario, ON, Canada
J. F. X. DeSouza	Dept of Physiology, University of Western Ontario, ON, Canada
S. Woodward	Department of Psychology, University of Western Ontario, ON, Canada
Z. Kourtzi	Max Planck Institute for Biological Cybernetics, Tuebingen, Germany
J. S. Gati	Robarts Research Institute, ON, Canada
R. S. Menon	Robarts Research Institute, ON, Canada
M. A. Goodale	Department of Psychology, University of Western Ontario, ON, Canada

Purpose: Visual processing is dissociated between a dorsal (occipitoparietal) stream for action and a ventral (occipitotemporal) stream for perceptual recognition. Visually guided grasping requires processing of object shape, but for the purposes of action rather than perceptual recognition. By comparison, visually-guided reaching requires transporting the hand to the target location but not shape processing. We used functional magnetic resonance imaging (fMRI; 4 Tesla) to determine whether grasping (compared to reaching) produced activation in dorsal areas, ventral areas, or both. Methods: Rectangular objects of varying length and orientation were mounted on a rotating drum that subjects viewed directly without mirrors. On each trial, one of the objects was illuminated and the subject grasped the rectangle along the long axis using a precision grip (with the finger and thumb). In a control condition, subjects reached and touched, but did not grasp, the target object. Event-related single trials took advantage of the hemodynamic delay to dissociate true grasping-related activation from potential motion artifacts. Results: In each of six subjects, grasping produced greater activation than reaching in the anterior intraparietal (AIP) cortex. Negligible grasp-specific activation was observed in ventral stream object areas. Conclusions: These results suggest that the processing of shape required to form a grasp involves dorsal but not ventral stream regions. The dorsal stream area that was activated is a likely human homologue of monkey AIP, an area containing neurons that code object shape and fire during grasping.