Selective and independent activation of four motor fascicles using a four contact nerve-cuff electrode.

Any one of the four motor nerves in the cat sciatic nerve could be activated selectively and independently, from threshold to saturation, using a self-sizing spiral cuff electrode containing four radially placed monopolar contacts. These studies were carried out in nine adult cats with acute implants. Of the 36 possible fascicles, 23 fascicles could be activated selectively with current stimuli applied to a single contact and ten of the remaining fascicles could be activated selectively with current stimuli applied to two contacts, "field steering." In three experiments, time constraints precluded attempting selective activation through "field steering" techniques. In eight of the ten cases where "field steering" was used, a positive and a negative current source (anodic steering) were required to achieve the desired fascicle and in the remaining two cases, two negative current sources (cathodic steering) were required. The relative distance from the electrode contacts to each fascicle was well correlated to the order in which each fascicle was activated. In seven experiments, carried out in two animals, selective activation was verified by collision block techniques. The results of these experiments support the hypothesis that selective and independent activation of any of four motor fascicles in the cat sciatic nerve is possible using a four contact self-sizing spiral cuff electrode. Furthermore, in a more general case, these results support the concept of a "tunable" electrode that is capable of "steering" the excitation from an undesirable location to a preferred location.