ABSTRACT
A neural prosthesis is an assistive system that replaces or augments a function that was lost or diminished because of the injury or disease of the nervous system. The method most frequently applied in neural prostheses (NP) is the external electrical activation of the appropriate impaired sensory-motor systems, that is, use of functional electrical stimulation (FES). FES elicits desired neural activation by delivering the controlled amount of electrical charge patterned as bursts of electrical charge pulses. In principle, it is possible to apply a time varying magnetic field, thereby inducing electrical currents within the selected parts of the neural pathways; however, this technique is not yet efficient enough for functional activation of sensory-motor systems. A detailed presentation of most aspects of neural prosthesis can be found in
and Sinkjær (2000). Figure 28.1 shows the principle of FES-based neural prosthesis. After an injury or disease (e.g.,
stroke, spinal cord injury, Parkinson’s disease) of the central nervous system (CNS) or peripheral lesion some sensory-motor systems will be intact, yet other structures will be paralyzed or paretic. A lesion leads to paralysis with the muscles still being innervated, but sometimes also to denervation of muscles. The innervated muscles are often activated in an unpredicted manner, but they are not controllable volitionally. These muscles are the best candidates for the effective neural prosthesis application. In parallel, many sensory pathways preserve their connections to the CNS, yet their activity does not reach the appropriate centers within the CNS. NP can also restore some elements of the sensory systems. In other words, NP should be considered as a bypass of the damaged sensorymotor systems.
