Dynamics of a long-latency reflex pathway in the monkey.

Angular wrist displacements in the monkey result in a short-latency (20--25 ms) "reflex" response of motor cortical cells in area 4 and separate peaks of activity in the gross EMG of the stretched muscles. Frequency domain analysis was carried out between (1) wrist position as input and motor cortical neuron response as output, (2) position as input and EMG response as output, and (3) motor cortical neuron response as input and EMG response as output. The results show that the dynamics of primary spindle afferents characterize the dynamics of the pathway to the motor cortex and that of the reflex loop. Results are discussed in terms of "long-loop" reflexes.