Selective Activation of Pig Forearm Muscles using Thin-Film Intrafascicular Electrodes Implanted in the Median Nerve

The quality of functional electrical stimulation (FES) systems is limited by the recording quality and the stimulation selectivity of the neural interface it uses. Thus advances in the quality of the neural interface can directly improve what can be offered by the FES system. The objective of the present study was to investigate the stimulation selectivity of the thin-film longitudinal intrafascicular electrode (tfLIFE) in a large-nerve animal model. Two double sided 8-channel tfLIFE’s (top and bottom side each 4 contacts) were placed in the median nerve in pigs and stimulation was applied for 28 contact combinations (range: 20 μA 540 μA). Surface EMG responses were recorded from seven forelimb muscles and Vpp values were evaluated at a 2-12 ms post stimulation interval. A selectivity index (SI) was calculated to reflect the degree of evoked muscle activity of each individual muscle with respect to the whole set of muscles. Preliminary results show that selective activation of flexor and extensor muscles can be obtained. For example, for different contact combinations, the flexor carpi radialis muscle showed a SI = 68% (I=200 μA) and the bracialis muscle showed a SI = 79% (I=240 μA). As such, the tfLIFE electrode provides selective activation of muscles, which may be of paramount importance for advanced degree of freedom prosthetic limb control.