On the functions of the cortical motor area in precise movement organization.

The effects of unilateral ablation of the cortical motor forelimb area on instrumental avoidance responses consisting of lifting the forelimb and holding it within a 4 cm wide "safety zone" were studied in dogs. It was found that the surgery irreversibly impaired the search for the safety zone, while the ability to maintain the limb at a certain height was not affected. The surgery also impaired the corrective movements, especially if their direction was opposite to the inborn unconditioned reaction. The ability to perform corrective movements of small amplitude was also transiently diminished Widening of the safety zone markedly improved the post-operative performance.