Representation of reaching and grasping in the monkey postcentral gyrus

In area 2 and further caudal part of the alert monkey's postcentral gyrus, we found neurons which were activated preferentially or only by monkey's self-initiated hand actions to reach or grasp objects. Among them we studied those neurons which were selective to either (1) projecting the arm and stretching digits toward an object (reaching); (2) grasping with the first and the second digit (radial grasp, precision grip); (3) grasping with the ulnar digits and palmar skin (ulnar grasp, whole hand grip); or (4) scratching or touching an object with distal digit pads and nails. Neurons of the radial grasp type were found in the lateral part of the digit region while all other types of neurons were found in the medial part. Each of hand action neurons was found in a cluster of neurons which had common receptive fields corresponding to effective sites for the particular type of grasping.