Peripheral nerve stimulation in neurological rehabilitation

An injury to the central nervous system can result in a permanent loss of the voluntary motor function and sensation. However, the peripheral motor and sensory nerves below the level of lesion often remain intact, and so do the muscles. Functional Electrical Stimulation (FES) is a technique to restore motor and sensory functions after such injuries. The forces generated in muscles activated by FES can be graded by varying the stimulus pulses, but the relationship of the force to the stimulus pulse varies in a complex manner that depends on, for example, muscle length, electrode-nerve coupling, and activation history. Several studies have shown that the application of closed-loop control techniques can improve the regulation of the muscle activation. Natural sensors such as those found in the skin, muscles, tendons, and joints present an attractive alternative to artificial sensors for FES purposes because they are present throughout the body and contain information useful for feedback control. Moreover, the peripheral sensory apparatus is still viable after brain and spinal cord injuries. Electrical signals can be recorded using long-term implanted nerve cuff electrodes in the human peripheral nerves. Reliable detection of sensory nerve signals is essential if such signals are to be of use in sensory-based functional electrical stimulation neural prosthetics as a replacement for artificial sensory (switches, strain gauges, etc.) In this paper the signal characteristics of the sensors, the nerve interface, signal processing, and example of human applications to restore motor functions are described. In the second part of this presentation, stimulation of sensory nerves in CNS injured persons to improve their motor functions through neurorehabilitation will be addressed.