Studies on the feasibility of a penetrating microelectrode array as a peripheral nerve interface

The goal of functional electrical stimulation (FES) is to restore function to paralyzed limbs by replacing volitional activation of muscles with electrical stimulation of their nerves. Requirements to restore efficient motor function are a gradual recruitment of muscle fibers and selective activation of muscle groups. Further, it may be necessary to integrate sensory feedback information to stabilize motor performance. Peripheral nerves contain both sensory and motor fibers and hence offer a suitable location for the placement of a neural interface. A new type of peripheral nerve interface, a penetrating microelectrode array, was tested in acute and chronic experiments in cat. Additionally, an alternative site for recording sensory information using the array was explored, the dorsal root ganglia.; First, it was shown that the electrode array can be implanted intrafascicularly into peripheral nerve with minimal functional consequences. Single- and multiunit sensory responses were recorded and motor fibers were stimulated with currents in the microampere range. However, the Utah Electrode Array, having equal length electrodes, did not provide adequate stimulation and recording selectivity.; In response, a new array structure, the Utah Slanted Electrode Array (USEA), was developed and tested. This new structure allowed access to several fascicles in the nerve. Muscle recruitment was highly graded and specific to individual or synergistic muscle groups. Sensory information could be recorded selectively from several different skin and muscle sensory receptors.; Following these successful acute experiments, the devices were tested by chronic implantation for 4 to 6 months. The animals did not show functional deficits and the morphology of the nerve was normal. Stimulation selectivity was preserved over the duration of the implant and after an initial increase, stimulation thresholds remained constant in a majority of animals. However, the recorded sensory signals degraded with time.; As an alternative we investigated deriving the sensory signals from dorsal root ganglia. Short-term sensory recordings had excellent signal-to-noise ratios and could be obtained from a large percentage of electrodes. The representation of a large population of skin and muscle receptors was available with these recordings.; In summary, this research indicates that the USEA is a viable neural interface technology.