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: (1) that neurons of the red nucleus modulate their firing in advance of the motor output under both conditions; (2) that increased activity of these neurons is specific to the direction of the force exerted ; (3) that this increase is primarily related to the magnitude of the rate of force change generated by the animal.