RECOVERY OF SKILLED MOTOR FUNCTIONS AFTER SMALL REPEATED LESIONS OF MOTOR CORTEX IN MACAQUE

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Abstract
Lesions made in the thumb area or other small parts of the motor cortex of Rhesus monkeys revealed that by the Marchi technic no definite area within the internal capsule can be assigned to the cortico-spinal fibers coming from a well defined division of area 4. It was also observed that fibers descended from the thumb area down to the lumbar region of the cord. The small lesions in the thumb area of the motor cortex produced con-tralateral transient paralysis. Both the paralysis itself and its gradual and almost complete recovery were measured quantitatively by the authors'' match box drawer technic and qualitatively by their problem box working with trained monkeys. When recovery had taken place the cortex was again exposed and areas adjacent to the previous lesion were found to yield thumb responses which were not obtainable at the first operation. Undercutting of these areas resulted in a recurrence of the paralysis, from which some recovery occurred, but the more delicate movements were lost. These findings suggest that the function of the injured motor cortex does not follow a mosaic like pattern as would be revealed if the permanent absence of particular functions followed circumscribed lesions. On the contrary, the tendency is to maintain a more or less complete functioning of the limb. This phenomenon may be explained by the inherent ability of "taking over" which is latent in uninjured parts of the motor cortex and for which anatomical pathways have been demonstrated.