REPRESENTATION OF REACHING AND GRASPING IN THE MONKEY POSTCENTRAL GYRUS

In area 2 and further caudal part of the alert monkey's postcentral gy rus, we found neurons which were activated preferentially or only by m onkey's self-initiated hand actions to reach or grasp objects. Among t hem we studied those neurons which were selective to either (1) projec ting the arm and stretching digits toward an object (reaching); (2) gr asping with the first and the second digit (radial grasp, precision gr ip); (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 t he lateral part of the digit region while all other types of neurons w ere 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.