| The overall goal of this thesis was to develop a proof-of-principle for a device that might eventually restore walking in people with paraplegia. The thesis consisted of three component technologies each working in conjunction with one another in adult cats. The first component was the state-based control algorithm, which provided a framework to implement more detailed control of locomotion in the future. The goal of this study was to develop a physiologically based algorithm capable of mimicking the biological system to control multiple joints in the lower extremities for producing over-ground walking. The biological central pattern generator (CPG) integrates open and closed loop control to produce over-ground walking. Similarly, the algorithm used combined open and closed loop control of a state-based model of the step cycle. Each state produced different electrical stimulation patterns and activated a different combination of muscles. This study verified that such a controller could generate closed loop bilateral overground walking. The second study implemented a novel type of functional electrical stimulation, intraspinal microstimulation (ISMS), that activated motor networks in the ventral horn of the spinal cord that would remain intact below the lesion level after a spinal cord injury. In addition to producing movements around single joints, ISMS through individual microwires can elicit coordinated multi-joint movements and the resulting contractions are fatigue-resistant. For the first time, we demonstrate sustainable, bilateral over-ground walking using ISMS. The walking proved to be extremely fatigue-resistant with some cats walking for a distance of over 800 m. The third study added natural sensory feedback of both the limb position in space and ground reaction force using recordings of neurons located in the dorsal root ganglia (DRG). The goal of this study was to decode sensory information from the DRG in real time for control of unilateral ISMS stepping. These predictions were successfully used to activate a closed loop rule that limited backward hyperextension. Each project resulted in a novel accomplishment and produced a deliverable that successfully worked in conjunction with previously developed components toward a neuroprosthetic device to restore walking. |
