Responses of cat motor cortex neurons to cortico-cortical and somatosensory inputs.

Intracellular techniques were used to investigate a cortico-cortical path from sensory cortex to motor cortex of cats. Cortico-cortical epsps were evoked in motor cortex neurons by microstimulation of area 3a. Epsps with latencies between 1.2 and 2.4 ms were identified as monosynaptic. These short latency cortico-cortical effects were recorded in layers II through VI of the motor cortex. Neurons with monosynaptic cortico-cortical epsps also received excitatory inputs from forelimb nerves, usually from both muscle and cutaneous afferent fibers. The epsps evoked from forelimb nerves in motor cortex neurons were preceded by neural activity in somatosensory cortex. Time delays between arrival of inputs in sensory cortex and in motor cortex were compared to the latencies of cortico-cortical epsps in the same motor cortex neurons. It was apparent that the timing was appropriate for the identified cortico-cortical path to have relayed some sensory inputs to motor cortex.