COMPARISON OF MOTOR CORTEX INFLUENCES UPON VARIOUS HIND-LIMB MOTONEURONS IN PYRAMIDAL CATS AND PRIMATES

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Abstract
The influences of descending volleys originating from the primary motor cortex were studied using knee and hip flexor and extensor motoneuron populations in the "pyramidal" cat and primate preparations. Descending volleys, which were evoked from the pericruciate motor area in the cat, produced facilitation of knee and hip flexor monosynaptic reflexes and inhibition of knee and hip extensor monosynaptic reflexes. In monkeys and baboons the initial effect of descending volleys originating from the precentral gyrus was direct facilitation. This initial facilitatory effect was followed by a period of reflex inhibition which, in turn, was followed by another period of facilitation. The cortically induced motoneuron inhibition was of brief duration and of small mangitude in all of the knee and hip flexor motoneuron populations. However, cortical inhibition was much longer in duration and nearly complete in degree in the knee and hip extensor motoneuron populations. The results of this and earlier studies suggest a correlation between posture and motor cortex effects on segmental motoneurons.