Diameter-dependent excitation of peripheral nerve fibers by multipolar electrodes during electrical stimulation.

Neural prostheses are technical devices that interface the nervous system to restore lost body functions by means of electrical stimulation, and to increase the activities of daily living of disabled persons--at least to some extent. One of the major reasons for the limited performance of neural prostheses is caused by the inverse recruitment of axons via excitation, by means of electrical stimulation. Due to their biophysical properties, electrical stimulation excites axons according to their diameter, starting with large-diameter fibers. This is the inverse order with respect to physiologic recruitment. It causes muscle fatigue, dyssynergia and limited muscle force control, respectively. A new electrode arrangement, with longitudinal multipolar stimulation, allows the selection of fiber diameters by its design with rectangular stimulation pulses and a reasonable amount of charge per phase. This report discusses the impact of the new approach in comparison with other stimulation paradigms to obtain fiber-selective nerve activation and its opportunities for neural prostheses in context with miniaturization trends in implant technology.