REORGANIZATION OF MOTOR FUNCTION IN THE CEREBRAL CORTEX OF MONKEYS DEPRIVED OF MOTOR AND PREMOTOR AREAS IN INFANCY

Abstract

Following bilateral ablation of areas 4 and 6 of Brodmann, recovery of motor function in adult monkeys is minimal. In contrast, the infant monkey operated at 3 wks. regains the motor power essential for eating, walking and climbing, although fine movements of the digits never develop the delicacy of coordination of the normal animal. This recovery is due in part to integration through other cortical regions, such as the frontal association areas (fields 9, 10, 11 and 12) and the postcentral region (fields 3-1-2 and 5). Motor performance of a monkey from which portions of the cortex were removed in infancy shows characteristic differences from that of a normal animal; after bilateral ablation of areas 4 and 6 hyperextension and walking on a broad base appear; addition of the postcentral gyrus to the above lesion produces adduction and a scissors gait; reflex grasping and a tendency to climb and cling persist although voluntary purposeful behavior is also present. The paresis of conjugate eye deviation following lesions of area 8 resembles in severity that caused by a similar lesion in the adult. This may be due to early myelinization and functional development of the shorter tracts. The concept that specific cortical foci have major functions in specific regions of the body, but that in addition, a minor influence is exerted over many other parts, would thus seem to be relatively of greater importance in the infant than in the adult monkey.