Functionally selective peripheral nerve stimulation with a flat interface nerve electrode.

One of the important goals of peripheral nerve electrode development is to design an electrode for selective recruitment of the different functions of a common nerve trunk. A challenging task is gaining selective access to central axon populations. In this paper, a simple electrode that takes advantage of the neural plasticity to reshape the nerve is presented. The flat interface nerve electrode (FINE) reshapes the nerve into a flat geometry to increase the surface area and move central axon populations close to the surface. The electrode was implanted acutely on the sciatic nerve of eight cats. The FINE can significantly reshape the nerve and fascicles (p < 0.0001) while maintaining the same total nerve cross-sectional area. The stimulation thresholds were 2.89 nC for pulse amplitude modulation and 10.2 nC for pulse-width modulation. Monopolar, square-pulse stimulation with single contacts on the FINE selectively recruited each of the four main branches of the sciatic nerve. Simultaneous stimulation with two contacts produced moments about the ankle joint that were a combination of the moments produced by the individual contacts when stimulated separately.