TRANSMISSION OF THE CORTICAL COMMAND FOR HUMAN VOLUNTARY MOVEMENT THROUGH CERVICAL PROPRIOSPINAL PREMOTONEURONS

In man there is now strong evidence for the existence of a system of c ervical propriospinal premotoneurons interposed in the corticospinal p athway to upper limb motoneurons. The relevant neurons are located ros tral to upper limb motoneurons. They receive both weak excitation and strong inhibition from low threshold afferents in the upper limb. Ongo ing EMG activity recorded in wrist and elbow extensors during voluntar y movements of different types (tonic contraction, reaching) is suppre ssed by a cutaneous volley evoked by stimulation of the superficial ra dial nerve. There is evidence that this cutaneous-induced suppression is due to inhibition of transmission of the cortical command in the sy stem of cervical propriospinal premotoneurons; thus indicating that pa rt of the descending command for movement reaches the relevant motoneu rons via these premotoneurons. In patients with hemiplegia, the cutane ous-induced depression of ongoing EMG activity is significantly larger on the hemiplegic side. This suggests that the mechanisms underlying residual motricity after a lesion of the corticospinal tract involve t he system of propriospinal premotoneurons. Copyright (C) 1996 Elsevier Science Ltd