Intraspinal microstimulation using cylindrical multielectrodes

Journal ArticleA cylindrical multielectrode system specifically designed for intraspinal microstimulation was mechanically and electrically evaluated in the ventral horn of the feline lumbo-sacral spinal cord. Electrode insertions proved to be straight as evaluated from radiographs. Impedances were measured in situ and force recruitment curves from quadriceps muscles were collected over a wide range of stimulus parameters. For a given charge, higher current amplitudes produced greater forces than proportionally longer pulse durations, indicating that charge is not the sole indicator of evoked force in applications utilizing electrical stimulation. Overlap measurements for calculating current-distance constants were collected at a variety of current amplitudes, electrode pair separations, and pair orientations in the spinal grey matter. Forces obtained in the majority of these trials demonstrated an order effect, presumably due to asymmetric neuronal connectivity within the spinal cord. In the cases showing no order effect, the dorso-ventral electrode pair orientation yielded a higher average current-distance constant (278 µA / mm 2) than either the medio-lateral or rostro-caudal electrode pair orientations (197 µA / mm 2). Specifications of an array of cylindrical multielectrodes for use in future intraspinal microstimulation prostheses were updated

Microfabricated cylindrical multielectrodes for neural stimulation

Journal ArticleThe effects of spinal cord injuries are likely to be ameliorated with the help of functional electrical stimulation of the spinal cord, a technique that may benefit from a new style of electrode: the cylindrical multielectrode. This paper describes the specifications for, fabrication techniques for, and in vitro evaluation of cylindrical multielectrodes. Four tip shapes were tested to determine which shape required the lowest peak force and would, therefore, be expected to minimize dimpling during implantation. The impedance of the electrode interface was monitored for changes due to insertion as well as repetitive delivery of current pulses. The charge delivery capacity was determined by testing with safe (0.8 mC cm2) of charge density. The results of these tests suggest that this electrode design could be used to stimulate neurons in the ventral horn of the spinal cord

Doctor of Philosophy

dissertationParalysis can be ameliorated through functional electrical stimulation (FES) of the intact peripheral nerves. The Utah Slanted Electrode Array (USEA) can improve FES systems by providing selective access to many independent motor unit populations.This dissertation includes three studies that expand the role of USEAs in FES applications. The fi rst study leverages the selectivity of the USEA to independently activate the hamstring muscles. Because the di fferent biarticular hamstring muscles can either ex or extend the limb (at the knee or hip), the ability to selectively activate each one independently is required to evoke functional movements such as stance and gait. USEAs implanted in the muscular branch of the sciatic nerve were able to selectively activate each muscle of the hamstring group. Activation of these muscles was graded with increasing stimulus strength, and provided ample dynamic range to allow for fine control of muscle force. The second study demonstrates the ability of the USEA to selectively block neural activity. Upper motor neuron damage can cause hyperre exia and spasticity as well as paralysis. By delivering high-frequency sinusoids through electrodes of the USEA, ber subsets in a nerve were blocked while allowing the remainder of the nerve to function normally. Sinusoids delivered through different electrodes allowed for deactivation of di fferent muscles. The ability to selectively interrupt activity in fiber subpopulations within a nerve will provide new therapeutic options for the positive symptoms of upper motor neuron damage. The fi nal study addresses the practical difficulty of choosing the appropriate stimulus parameters to evoke functional movements. In a USEA-based FES system, the electrodes and stimulus parameters that evoke the desired responses must be identifi ed empirically. USEAs were implanted into three diff erent hind limb nerves, and the response evoked by each electrode was measured noninvasively using 3-D endpoint force. Each electrode was classifi ed as evoking limb flexion or limb extension, and a range of stimulus intensities was identifi ed that evoked a graded force response. Excitation overlap between selected electrode pairs was quantifi ed using the refractory technique. This method will allow for electrode and stimulus parameter selection for use in an FES system using minimal, noninvasive instrumentation