Pyramidal influences in establishment of new motor coordinations in dogs

Abstract

Ablation of the motor cortex or section of the pyramidal tracts in dogs were studied for their effects on the performance of an alimentary instrumental reaction. The animal was required to keep its foreleg raised during feeding in order to gain access to food. The operated animals were capable of raising the leg in response to a signal and of holding it, but when snatching the food they immediately lower it. These dogs can, however, accomplish such a conditioned reflex if they do not have to lower the head during feeding. There may exist inborn reflexes from the cervical muscles or the vestibular apparatus ensuring the support on the forelegs when the head is lowered for feeding. When a new coordination including feeding with the leg raised, is elaborated, these inborn coordinations are inhibited. Evidently, inhibition of such inborn coordinations is effected through the pyramidal tract. The pyramidotomized animal is incapable of inhibiting the reation of lowering its leg when feeding with head down and cannot therefore keep its leg raised when feeding. However, there is no need of inhibiting inborn coordiantions when feeding with the head raised. For this reason pyramidotomized dogs are capable of keeping the leg raised in the latter condition.