Recruitment Selectivity of Single and Pairs of Transverse, Intrafascicular, Multi-channel Electrodes (TIME) in the Pig Median Nerve

Abstract : When applied in the rat model the Transverse Intrafascicular Multi-channel Electrode (TIME) showed selective nerve fascicle recruitment. But results from the larger and poly-fasicular median nerves in pigs indicated that a single TIME could not reach the entire nerve and could only selectively recruit a subset of the nerve fascicles. The use of multiple TIME structures could offer a means to achieve highly selective fascicular stimulation while reaching a larger percentage of the fascicles in the nerve. This work investigates this approach using pairs of TIMEs implanted in the median nerves of anesthesized pigs (n=6). TIME structures were implanted at different angles relative to each other or in parallel with one another. Electrical stimuli was passed through each contact of each TIME and the resulting electromyograms were recorded from seven muscles innervated by the median nerve. The ability to recruit these muscles was used to assess the stimulation selectivity of each contact using a selectivity index comparing the root-mean-square of the the evoked EMG of individual muscles. Results showed a significant increase in the selectivity index, when using two TIMEs compared to one. The optimal improvement was observed when TIMEs were placed in parallel to each other in such a way that they interfaced non-overlapping nerve regions.