Encoding of motor parameters by corticomotoneuronal (CM) and rubromotoneuronal (RM) cells producing postspike facilitation of forelimb muscles in the behaving monkey.

This paper compares the properties of corticomotoneuronal (CM) and rubromotoneuronal (RM) cells identified by postspike facilitation (PSF) of rectified EMG activity in the awake monkey. The postspike effects of CM and RM cells in flexors and extensors of the wrist and fingers have been determined, as have the discharge properties of these cells in relation to alternating ramp-and-hold wrist movements. The characteristics of postspike facilitation and postspike suppression (PSS) were similar for RM and CM cells. The magnitude of RM-PSF was weaker than CM-PSF and RM cells showed a stronger preference for facilitation of extensor muscles than CM cells. As with CM cells, the onset of discharge in RM cells preceded the onset of EMG activity in their target muscles. Tonic discharge related to static torque was more prominent in CM cells, whereas phasic discharge was more prominent in RM cells; however, many RM cells showed some tonic activity weakly related to static torque. We conclude that CM and RM cells share many common features; however, RM cells are concerned primarily with the dynamics of muscle contraction.