FUNCTIONAL RECOVERY OF FORELIMB RESPONSE CAPACITY AFTER FORELIMB PRIMARY MOTOR CORTEX DAMAGE IN THE RAT IS DUE TO THE REORGANIZATION OF ADJACENT AREAS OF CORTEX

Functional recovery after brain damage has been described frequently a nd different mechanisms have been proposed to account for the observed recovery. One possible mechanism involves the capacity of one part of the brain to take over the function of another. A possible area for t his to take place is in the cerebral cortex, where a variety of reorga nizational processes have been described after different manipulations . We show in the present study that the forelimb force and response ca pacity of the rat, which becomes highly impaired after the bilateral a blation of the forelimb primary motor cortex, is recovered when the an imals receive an electrical stimulation in the ventral tegmental nucle us contingent to each forelimb response in the task. Microstimulation mapping of the cortical areas adjacent to the forelimb primary motor c ortex revealed the appearance of an area located caudolaterally to the forelimb primary motor cortex, where forelimb movements could be evok ed in recovered animals but to a lesser extent in non-recovered animal s. A positive and significant correlation was observed between the siz e of the reorganized forelimb area and the behavioral performance of t he animals. Ablation of the forelimb reorganized area in recovered ani mals reinstated the forelimb behavioral impairment, while the same les ion in normal animals had no effect on the behavioral performance. The results indicate that recovery after bilateral forelimb primary motor cortex ablation may be due to the reorganization of specific adjacent areas in the cortex.