Selective stimulation of cat sciatic nerve using an array of varying-length microelectrodes

Restoration of motor function to individuals who have had spinal cord injur ies or stroke has been hampered by the lack of an interface to the peripher al nervous system. A suitable interface should provide selective stimulatio n of a large number of individual muscle groups with graded recruitment of force. We have developed a new neural interface, the Utah Slanted Electrode Array (USEA), that was designed to be implanted into peripheral nerves. It s goal is to provide such an interface that could be useful in rehabilitati on as well as neuroscience applications. In this study, the stimulation cap abilities of the USEA were evaluated in acute experiments in cat sciatic ne rve. The recruitment properties and the selectivity of stimulation were exa mined by determining the target muscles excited by stimulation via each of the 100 electrodes in the array and using force transducers to record the f orce produced in these muscles. It is shown in the results that groups of u p to 15 electrodes were inserted into individual fascicles. Stimulation sli ghtly above threshold was selective to one muscle group for most individual electrodes. At higher currents, co-activation of agonist but not antagonis t muscles was observed in some instances. Recruitment curves for the electr ode array were broader with twitch thresholds starting at much lower curren ts than for cuff electrodes. In these experiments, it is also shown that ce rtain combinations of electrode pairs, inserted into an individual fascicle , excite fiber populations with substantial overlap, whereas other pairs ap pear to address independent populations. We conclude that the USEA permits more selective stimulation at much lower current intensities with more grad ed recruitment of individual muscles than is achieved by conventional cuff electrodes.