Evidence for context sensitivity of grasp representations in human parietal and premotor cortices

Grasp-related responses in neurons ofthe macaque rostral inferior parietal lobule [PF/PFG and the anteriorintraparietal area (AIP)] are modulated by task context. Event-relatedfunctional MRI was used to determine whether this is true in putativehomologs of the human cortex, the rostral inferior parietal lobule(rIPL) and the anterior intraparietal sulcus (aIPS). Fifteen healthy,right-handed adults were required to select prospectively the mostcomfortable way to grasp a horizontally oriented handle using thecued hand (left or right). In the “no-rotation” condition, the task wassimply to grasp the handle, whereas in the “rotation” condition, thegoal was to plan to grasp and rotate it into a vertical orientation withthe cued end (medial or lateral) pointing downward. In both conditions,participants remained still and indicated their grip preferencesby pressing foot pedals. As in overt grasping, participants’ grippreferences were significantly influenced by anticipation of the demandsassociated with handle rotation. Activity within the aIPS andrIPL increased bilaterally in both the rotation and no-rotation conditions.Importantly, these responses were significantly greater in therotation vs. no-rotation condition. Similar context effects were detectedin the presupplementary motor area, caudal intraparietal sulcus/superior parietal lobule, and bilateral dorsal and left ventral premotorcortices. Grasp representations within the rIPL and aIPS are sensitiveto predicted task demands and play a role in context-sensitive gripselection. Moreover, the findings provide additional evidence thatareas involved in the sensorimotor control of grasp also contribute tofeedforward planning.