This paper describes a closed loop control system that uses afferent neural activity from muscle spindle fibers as feedback for controlling ankle position. The gastrocnemius muscle was stimulated through a dual channel intrafascicular electrode implanted in a fascicle of the tibial nerve. Dual channel intrafascicular electrodes were also used to record spindle fiber activity from the tibialis anterior and the lateral gastrocnemius muscles to estimate ankle joint angle. Experiments were conducted in neurally intact anesthetized cats and in unanesthetized decerebrate cats to demonstrate the feasibility of this control scheme.
