Discharge of red nucleus neurons during voluntary muscle contraction: Activity patterns and correlations with isometric force

Discharges of red nucleus neurons were analyzed in the cat during voluntary muscle contractions performed under isometric and anisometric conditions. The observations established: that neurons of the red nucleus modulate their firing in advance of the motor output under both conditions; that increased activity of these neurons is specific to the direction of the force exerted; and that this increase is primarily related to the magnitude of the rate of force change generated by the animal.