Intrastpinal microstimulation for restoring hand movement
This project will develop cervical intraspinal microstimulation (cISMS) for restoring movement to the paralyzed arm and hand. In spinally-injured patients with surviving cervical cord below the level of lesion, microampere current pulses delivered through electrodes implanted near upper-limb motor nuclei could compliment functional electrical stimulation (FES) of peripheral targets to restore individuated finger movements, regulate plasticity of spinal circuitry during rehabilitation and/or relieve spasticity. However, long-term stability of implanted electrodes will be essential if clinical applications are to be considered. We are developing several type of intraspinal electrode that designed to reduce movement of electrodes relative to the tissue, thus minimizing glial scarring around the contacts and extending the implant lifetime. The optimum design of electrode arrays, placement within the cord, surgical insertion techniques and stimulus protocols for cISMS will be determined in a series of experiments performed in macaque monkeys. The compound effect of simultaneous stimulation at multiple sites will be examined to test whether cISMS can produce coordinated, functional hand movements involving multiple muscles. Preliminary observations of widespread facilitatory interactions between spinal sites suggest that cISMS recruits local circuitry in addition to directly exciting motoneurons. This may increase the repertoire of motor effects that can be elicited from a limited number of spinal stimulating electrodes. Spinal circuitry may contribute to the generation of coordinated movements, as is suggested by the modulation of premotor interneurons with a task that required precise control of index finger and thumb. The firing rates of such cells during grasping will be used to develop cISMS protocols that mimic the natural activation of these circuits to restore realistic hand movements. Finally, the suitability of these stimulation protocols for restoring movement following spinal cord injury will be tested in monkeys with a chronic cervical transection.