Functional electrical stimulation--neural prosthesis for the disabled.

When the organ systems of the body are studied from an engineering point of view, electricity emerges as the essence of human life. In fact, life itself is now taken to exist only so long as the brain produces measurable electrical activity. It is not surprising, then, that medical practitioners have been fascinated by the effects of externally applied electricity since the beginning of medicine. New materials and increased understanding of their biological interface properties, both of the materials themselves and of living tissues in the presence of electrical current, now make it possible to influence minute natural electric currents in the body and to create substitute signals to reactivate lost functions or sensations. Many human beings throughout the world are finding relief from chronic pain through electrical stimulation, while surgical pain is prevented by means of electroanesthesia ; paralyzed patients breathe with their own muscles when the phrenic nerves are stimulated ; hypertension is relieved by stimulating the carotid sinus nerves ; skeletal muscles are stimulated from the skin and by means of implanted electrodes within the muscles or around or within peripheral nerves, to enable the disabled to regain function of their limbs ; patients' muscles are strengthened and their contractures relieved ; electrical stimulation can control the elimination of wastes ; and the peripheral nerves of the amputee have been stimulated to produce the sensation of touch. Bone and tissue growth can be enhanced by electrical currents. Even the brain of man has been electrically stimulated to excite primitive patterns of phosphenes to produce rudimentary vision .in the blind, and to suppress epileptic seizures as well as uncontrolled spasticity in cerebral palsy ; auditory nerves are stimulated to enable the deaf to "hear" simple sounds ; and what is