Search

The feasibility of implanting an array of penetrating electrodes into peripheral nerves is studied in acute experiments in the cat sciatic nerve. A novel, silicon-based array of microelectrodes, the Utah Electrode Array, was used, which contains 25 or 100 1-mm long electrodes that project out from a silicon substrate. Electrode arrays of this complexity, when inserted in the peripheral nerve, could cause significant compression of the nerve and block the conduction of action potentials. Using a high velocity insertion technique, the electrode array was implanted into the sciatic nerve. Compound action potentials were evoked by and recorded with cuff electrodes. Compound action potentials recorded 1 h after insertion were only slightly altered from those recorded before insertion. Single units were readily extracted from evoked multiunit neural recordings in response to cutaneous stimulation and limb rotation around joints. Current injections into the nerve through the electrodes evoked muscle twitches with currents in the 10 microA range. Recording and stimulation stability were demonstrated for periods of up to 60 h. We have shown that high density arrays of electrodes can be inserted into the peripheral nerve and can provide a stable recording and stimulating interface to individual peripheral nerve axons. Such an array may be useful in future neuroscience research and potential neuroprosthetic applications.

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.

We studied the consequences of long-term implantation of a penetrating microelectrode array in peripheral nerve over the time course of 4-6 mo. Electrode arrays without lead wires were implanted to test the ability of different containment systems to protect the array and nerve during contractions of surrounding muscles. Treadmill walking was monitored and the animals showed no functional deficits as a result of implantation. In a different set of experiments, electrodes with lead wires were implanted for up to 7 mo and the animals were tested at 2-4 week intervals at which time stimulation thresholds and recorded sensory activity were monitored for every electrode. It was shown that surgical technique highly affected the long-term stimulation results. Results between measurement sessions were compared, and in the best case, the stimulation properties stabilized in 80% of the electrodes over the course of the experiment (162 days). The recorded sensory signals, however, were not stable over time. A histological analysis performed on all implanted tissues indicated that the morphology and fiber density of the nerve around the electrodes were normal.

The authors have developed a neural interface, the Utah Slant Array (the USA), that provides unprecedented access to a large number of sensory and motor neurons. The array has been designed to be implanted into fascicles of peripheral nerves, and it provides up to 100 channels of neural communication. The authors are currently evaluating the recording and stimulation capabilities of the USA in acute experiments in cat sciatic nerve. Very high selectivity even for high forces can be reached by near simultaneous stimulation of two or more electrodes innervating the same muscles. The authors suspect that, using the same methods, fatigue resistant stimulation is also possible.

A practical interface to the peripheral nervous system (or to the spinal cord) that could be used in a neuroprosthetic application must have two features: it should be able to selectively stimulate a large number of individual muscle groups in a highly specific fashion; and it should also be able to stimulate these muscles in a broadly graded fashion in a manner similar to the way they are stimulated naturally. We have developed a new type of silicon based microelectrode array which consists of 100 penetrating needles that project out from a thin silicon substrate. We have developed such an electrode array and have evaluated it in a series of acute implantations in cat sciatic nerve. Using a high velocity insertion technique, the array can be inserted through the epineurium and perineurium with little damage to the propagation of neural activity through the implantation site. The array records single- and multi-unit sensory information. It is capable of generating muscle twitches with single, biphasic 200 usec current pulses in the 1-10 microampere range.

Restoration of motor function to individuals who have had spinal cord injuries or stroke has been hampered by the lack of an interface to the peripheral nervous system. A suitable interface should provide selective stimulation 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. Its goal is to provide such an interface that could be useful in rehabilitation as well as neuroscience applications. In this study, the stimulation capabilities of the USEA were evaluated in acute experiments in cat sciatic nerve. The recruitment properties and the selectivity of stimulation were examined by determining the target muscles excited by stimulation via each of the 100 electrodes in the array and using force transducers to record the force produced in these muscles. It is shown in the results that groups of up to 15 electrodes were inserted into individual fascicles. Stimulation slightly above threshold was selective to one muscle group for most individual electrodes. At higher currents, co-activation of agonist but not antagonist muscles was observed in some instances. Recruitment curves for the electrode array were broader with twitch thresholds starting at much lower currents than for cuff electrodes. In these experiments, it is also shown that certain combinations of electrode pairs, inserted into an individual fascicle, excite fiber populations with substantial overlap, whereas other pairs appear to address independent populations. We conclude that the USEA permits more selective stimulation at much lower current intensities with more graded recruitment of individual muscles than is achieved by conventional cuff electrodes.