Physiological activation of the hind limb muscles of the anesthetized cat using the Utah slanted electrode array

The restoration of graceful, yet powerful movements in paralyzed regions of the body has not been achieved in humans. The problems are manifold and each is quite complex. Normal motions around a single joint are typically produced by coordinated activation of many muscles. Further, graded force generation in a single muscle is achieved by successively recruiting more and more motoneurons that innervate the target muscle. Finally, normal physiological movements are often achieved without excessive fatigue, a condition difficult to replicate with conventional cuff-type, epimysial, or surface electrodes. We have conducted experiments using intrafascicular multielectrodc stimulation (IFMS) in the cat sciatic nerve that address many of these problems by D. McDonnall, et al. (2004). We have implanted Utah slanted electrode arrays (USEA's) in the sciatic nerve of cat, and have been able to selectively stimulate small, independent subpopulations of motoneurons that innervate the muscles of the lower leg. The USEA consists of a 10 /spl times/ 10 grid of graded-length microelectrodes separated by 400 microns. We have shown that motoneuron stimulation via the USEA is highly selective and that stimulation via specific electrodes can evoke a maximal force in each of these muscles without producing substantive forces in the others. Further, because different electrodes excite different motoneurons innervating a particular muscle, we have been able to interleave low-frequency stimulation through these electrodes to produce ripple-free, fatigue-resistant forces over a large range of forces. These experiments demonstrate that IFMS can be achieved with high-count penetrating electrode arrays with a slanted architecture. Such arrays, when inserted into the nerves of the peripheral nervous system, could be used to recreate graceful, yet powerful, fatigue-resistant motions in the musculo-skeletal system of paralyzed subjects. The large number of muscles that can be activated via the 100 electrodes in a single USCA implantation, together with the relative ease of surgical implantation of these devices, offers a promising approach to reanimation of paralyzed limbs.