Role of the motor cortex in the rearrangement of a natural movement coordination in dogs.

Chronic experiments on dogs were performed to study the activity of the shoulder muscles involved in elevating the forelimb used by the animal to lift a food-containing cup and keep it elevated during eating. At the early stage of acquisition of this operant reaction, limb-lifting occurred with an anticipatory upward head movement; lowering of the head to the feeder was associated with lowering of the lifted limb. The new coordination required for food to be obtained, i.e., maintaining the elevated limb in a posture with the head lowered, could only be achieved as a result of learning. In untrained dogs with the natural coordination, elevation of the limb occurred with activation of the deltoid and teres major muscles, teres minor being active on standing but ceasing its activity before limb elevation. During training the activity of the teres minor muscle changed to the opposite pattern. Limb elevation in the learned coordination was accompanied by activation of all three shoulder flexors. Lesioning of the motor cortex in the projection area of the "working" limb, but not in other areas, led to impairments of the acquired coordination and a new pattern of shoulder muscle activity. These data led to the conclusion that rearrangement of the initial coordination was linked with the formation of a new means of elevating the limb in which the muscle pattern was supported by the motor cortex.