dissertationHands are so central to the human experience, yet we often take for granted the capacity to maneuver objects, to form a gesture, or to caress a loved-one’s hand. The effects of hand amputation can be severe, including functional disabilities, chronic phantom pain, and a profound sense of loss which can lead to depression and anxiety. In previous studies, peripheral-nerve interfaces, such as the Utah Slanted Electrode Array (USEA), have shown potential for restoring a sense of touch and prosthesis movement control. This dissertation represents a substantial step forward in the use of the USEAs for clinical careâ€"ultimately providing human amputees with widespread hand sensation that is functionally useful and psychologically meaningful. In completion of this ultimate objective, we report on three major advances. First, we performed the first dual-USEA implantations in human amputees; placing one USEA in the residual median nerve and another USEA in the residual ulnar nerve. Chapter 2 of this dissertation shows that USEAs provided full-hand sensory coverage, and that movement of the implant site to the upper arm in the second subject, proximal to nerve branch-points to extrinsic hand muscles, enabled activation of both proprioceptive sensory percepts and cutaneous percepts. Second, in Chapter 3, we report on successful use of USEA-evoked sensory percepts for functional discrimination tasks. We provide a comprehensive report of functional discrimination among USEA-evoked sensory percepts from three human subjects, including discrimination among multiple proprioceptive or cutaneous sensory percepts with different hand locations, sensory qualities, and/or intensities. Finally, in Chapter 4, we report on the psychological value of multiple degree of freedom prosthesis control, multisensor prosthesis sensation, and closed-loop control. This chapter represents the first report of prosthesis embodiment during closed-loop and open-loop prosthesis control by an amputee, as well as the most sophisticated closed-loop prosthesis control reported in literature to-date, including 5-degree-of-freedom motor control and sensory feedback from 4 hand locations. Ultimately, we expect that USEA-evoked hand sensations may be used as part of a take-home prosthesis system which will provide users with both advanced functional capabilities and a meaningful sense of embodiment and limb restoration
