Changes in dry weight of pyramidal cell nuclei in the motor cortex during local motor-food conditioning.

The formation of a local motor-food conditioned reflex in rats, consisting of pressing on a level with the unpreferred paw, in one session led to a decrease in dry weight of the large pyramidal cell nuclei in the area of representation of that paw in the motor cortex. Frequent repetition of the local motor-food conditioned reflex consisting of pressing on the level with the preferred paw was not accompanied by any such changes. It is suggested that changes in dry weight of the large pyramidal cell nuclei in the area of representation of the unpreferred paw are due to involvement of these neurons in the formation of the new motor coordination (the local conditioned reflex).