Neural prostheses

Assuming that neural regeneration after spinal cord injury (CI) will eventu ally become a clinical reality, functional recovery will probably remain in complete. Assistive devices will therefore continue to play an important ro le in rehabilitation. Neural prostheses (NPs) are assistive devices that re store functions lost as a result of neural damage. NPs electrically stimula te nerves and are either external or implanted devices. Surface stimulators for muscle exercise are now commonplace in rehabilitation clinics and many homes. Regarding implantable NPs, since 1963 over 40000 have been implante d to restore hearing, bladder control and respiration. Epidural spinal cord stimulators and deep brain stimulators are routinely implanted to control pain, spasticity, tremor and rigidity. Implantable NPs have also been devel oped to restore limb movements using electrodes tunnelled under the skin to muscles and nerves. Spinal cord microstimulation (SC mu stim) is under stu dy as an alternative way of restoring movement and bladder control. Improve ment in bladder and bowel function is a high priority fur many SCI people. Sacral root stimulation to elicit bladder contraction is the current NP app roach, but this usually requires dorsal rhizotomies to reduce reflex contra ctions of the external urethral sphincter. It is possible that the spinal c entres coordinating the bladder-sphincter synergy could be activated with S C mu stim. Given the large and growing number of NPs in use or development, it is surprising how little is known about their long-term interactions wi th the nervous system. Physiological research will play an important role i n elucidating the mechanisms underlying these interactions.