Peripheral input pathways to the monkey motor cortex

We have shown (Asanuma et al., 1979c) that the monkey motor cortex receives peripheral somesthetic inputs directly from the thalamus. In the present experiments, we studied the pathways which mediated these inputs by stimulating superficial radial (SR) and deep radial (DR) nerves and recording evoked potentials from the motor and sensory cortices and the following results were obtained: 1. The focus for SR and DR evoked potentials in the sensory cortex was located in a circumscribed small area whereas in the motor cortex, the evoked potentials were distributed in a wide area along the central sulcus including the distal forelimb area. 2. Ablation of the sensory cortex reduced the size, but neither abolished nor changed the latency of the evoked potentials in the motor cortex. 3. Section of dorsal column nearly abolished the evoked potentials in the motor cortex, but only halved their size in the sensory cortex. 4. Section of ventrolateral cervical column including the spinothalamic tract halved the size of evoked potentials in the sensory cortex, but did not change the size in the motor cortex. 5. It is concluded that direct peripheral inputs to the motor cortex are mediated primarily through the dorsal column system whereas the peripheral inputs to the sensory cortex are mediated through both dorsal column and spinothalamic tract.