DYNAMIC AND HIERARCHICAL PROCESSING IN THE MONKEY SOMATOSENSORY CORTEX

Integration of somatic sensory information proceeds within the postcen tral gyrus in a hierarchical manner. In its caudal part, compared with the rostral part, are found more neurons with large receptive fields covering multi-fingers. Specific types of stimulation rather than simp le somatic stimulation are required to fully activate many of the caud al neurons. They fire more briskly by a particular mode of hand action s such as stretching an arm toward an object, scratching surface with finger tips, grasping an object with the thumb and radial fingers etc. Distribution of the stretching, scratching, or grasping neurons overl apped with that of proximal joints, that of the neurons with large rec eptive fields (functional surfaces) representing either finger tips or the radial half of the hand respectively. We postulate that active mo vement neurons represent one type of hand actions to manipulate object s, emerging as the results of integration of cutaneous and deep affere nt sources. In addition we found a group of neurons which had selectiv ity to either soft or hard objects. These neurons appeared to represen t specific features of objects contacted to the hand, rather than the hand action since they were activated also by passive contact of the s ame object to the hand.