As many as 400,000 Americans are partially or totally paralyzed from spinal cord injuries, which interrupt the nerve cell signals relaying information between the brain and the body. Others lose the ability to move and communicate because of neurodegenerative disorders such as amyotrophic lateral sclerosis, or Lou Gehrig's disease, which causes the neurons controlling muscles to die. Still half a million more Americans suffer profound sensory deficits such as blindness or deafness. For more than a century, scientists have sought some type of electrical replacement for lost motor and perceptual functions to alleviate these conditions.