Peripheral input pathways projecting to the motor cortex in the cat.

The possibility that the motor cortex receives peripheral input directly from the thalamus was examined using the evoked potential method and the following results were obtained. Potentials in the motor cortex evoked by stimulation of superficial radial (SR) or group II deep radial (DR) nerve were neither abolished nor delayed by ablation of the sensory cortex. Potentials in the motor cortex evoked by stimulation of group II DR nerve were most severely reduced by interruption of the spinocervcial tract. Potentials evoked by stimulation of SR nerve were more severely reduced in the sensory cortex than in the motor cortex by section of the dorsal funiculus or cooling of the cuneate nucleus. The size of evoked potentials in the motor cortex increased rapidly when stimulus intensity to DR nerve exceeded the threshold to group II fibers. The results suggest that some inputs from the SR and group II DR nerves reach the motor cortex without a relay through the sensory cortex.