[Bilateral motor cortex effects on interneurons of the ventral horn of the lumbar segments]

The ventral horn interneurons in the spinal cord L6-7 segments were recorded in anesthetized cats during stimulation of the pericruciate cortex of both cerebral hemispheres. The majority of ventral interneurons are activated by volleys from the contralateral motor cortex and nearly half of them--by volleys from the ipsilateral cortex as well. Two kinds of firing patterns occurred: separate spikes and bursts of spikes. The latency of the 1st type firing was significantly greater than that of the 2nd one. There was a close relation of convergence of the afferent and corticospinal volleys on ventral horn interneurons: neurons activated by ipsilateral afferents only received synaptic influence only from the contralateral motor cortex whereas neurons with ipsilateral as well as contralateral inputs were activated by corticospinal volleys from both hemispheres. The interneurons with bilateral segmental and supraspinal connections seem to be involved in integrative action as important elements of the neuronal mechanism of bilateral motor coordination.