Descending control of reflex pathways in the production of voluntary isolated movements in man.

Transmission in Ib inhibitory spinal pathways from a contracting muscle was studied during a selective voluntary contraction in man. Whereas Ib inhibition to those motoneurons (MNs) responsible for the contraction was depressed, Ib inhibition to those synergistic MNs not directly involved in the contraction was increased. This differential control, supraspinal in origin, helps limit activation to the former MNs and could be important in ensuring the selectivity of skilled movements.