Date of Award
Doctor of Philosophy (PhD)
Intuitive control of conventional prostheses is hampered by their inability to replicate the rich tactile and proprioceptive feedback afforded by natural sensory pathways. Electrical stimulation of residual nerve tissue is a promising means of reintroducing sensory feedback to the central nervous system. The macro-sieve electrode (MSE) is a candidate interface to amputees’ truncated peripheral nerves whose unique geometry enables selective control of the complete nerve cross-section. Unlike previously studied interfaces, the MSE’s implantation entails transection and subsequent regeneration of the target nerve. Therefore, a key determinant of the MSE’s suitability for this task is whether it can elicit sensations at low current levels in the face of altered axon morphology and caliber distribution inherent to nerve regeneration.
This dissertation describes a combined rat sciatic nerve and behavioral model that was developed to answer this question. Four rats learned a go/no-go detection task with auditory stimuli and then underwent surgery to implant the MSE in the sciatic nerve. After healing, they returned to behavioral training and transferred their attention to monopolar electrical stimuli presented in one multi-channel and eight single-channel stimulus configurations. Current amplitudes varied based on the method of constant stimuli (MCS). A subset of single-channel configurations was tested longitudinally at two timepoints spaced three weeks apart.
Psychometric curves generated for each dataset enabled the calculation of 50% detection thresholds and associated slopes. For a given rat, the multi-channel configuration’s per-channel current requirement for stimulus detection was lower than all corresponding single-channel thresholds. Single-channel thresholds for leads located near the nerve’s center were, on average, half those of leads located more peripherally. Of the five leads tested longitudinally, three had thresholds that decreased or remained stable over the three-week span. The remaining two leads’ thresholds showed a significant increase, possibly due to scarring or device failure. Overall, thresholds for stimulus detection were comparable with more traditional penetrative electrode implants, suggesting that the MSE is indeed viable as a sensory feedback interface.
These results represent an important first step in establishing the MSE’s suitability as a sensory feedback interface for integration with prosthetic systems. More broadly, it lays the groundwork for future experiments that will extend the described model to the study of other devices, stimulus parameters, and task paradigms.
Daniel W. Moran
Wilson Z. Ray