A. Branner et al., Selective stimulation of cat sciatic nerve using an array of varying-length microelectrodes, J NEUROPHYS, 85(4), 2001, pp. 1585-1594
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.