Ph.D. Dissertation Defense
1:30 PM EST
Tuesday, April 1, 2025
Wolstein Research Building, Auditorium 1413
“Sensorimotor Integration of Electrically Elicited Plantar Sensations from a Sensory Neuroprosthesis: Neural Mechanisms and Functional”
by
Suzhou Li
Ph.D. Candidate
ǿմý
Department of Biomedical Engineering
Cleveland, OH
Thesis Advisors: Ronald J. Triolo, PhD, and Hamid Charkhkar, PhD
Ph.D. Dissertation Defense
1:30 PM EST
Tuesday, April 1, 2025
Wolstein Research Building, Auditorium 1413
Virtual Zoom Link:
https://cwru.zoom.us/j/95638143770?pwd=obQCBhFCi52uc3tjxRfCqXGiy0vUCr.1
“Sensorimotor Integration of Electrically Elicited Plantar Sensations from a Sensory Neuroprosthesis: Neural Mechanisms and Functional”
by
Suzhou Li
Ph.D. Candidate
ǿմý
Department of Biomedical Engineering
Cleveland, OH
Thesis Advisors: Ronald J. Triolo, PhD, and Hamid Charkhkar, PhD
ABSTRACT
Individuals with lower limb loss (LLL) face a higher risk of falls and subsequently avoid daily activities, partly due to the absence of plantar sensation from the missing foot. The lack of plantar sensation leads to impaired stability and ability to recover from unexpected perturbations. We have developed a sensory neuroprosthesis (SNP) that provides sensations from the missing foot for individuals with LLL. Nerve cuff electrodes are surgically installed around the remaining peripheral nerves in the residual limb. Direct electrical stimulation to the nerve through the electrode contacts elicits sensations perceived as originating from the missing foot. The intensity and location of these sensations can then be modulated based on foot-floor interactions detected by a force-sensing insole under the prosthetic foot. This elicited plantar sensation can improve gait and postural stability, navigation through challenging terrains, and perception of limb speed. However, the mechanisms by which the SNP integrates into the body’s sensorimotor control and spinal reflex pathways to produce these functional improvements are still unknown.
The H-reflex was used to probe how elicited plantar sensations from the SNP are integrated into the sensorimotor control system. While the SNP was inactive or active, the H-reflex was evoked while participants maintained static postures simulating early stance or mid-stance and during treadmill walking. Regardless of the SNP condition, the H-reflex was modulated between static postures and across gait cycle phases in a similar manner as able-bodied individuals. This indicated that the remaining sensory afferents and central control were sufficient to modulate the H-reflex even after amputation. During the static postures, the SNP did not disrupt spinal reflex pathways between either of the postures. The SNP did facilitate the H-reflex across the gait cycle, aligning the modulation of the H-reflex more accurately with the stance and swing phases. These results indicate that the SNP was appropriately processed by the spinal reflex pathways, which suggests that it enhanced the neural control of gait to improve stability and balance.
The role of the SNP in sensorimotor control was further explored in a functional assessment of stumble recovery. Participants walked on a treadmill while the SNP was inactive or active and received perturbations initiated in early stance randomly to the prosthetic and intact sides involving brief accelerations of the treadmill belts. With the SNP active, participants decreased trunk angular sway and peak trunk flexion angular velocity during recovery from both prosthetic and intact side perturbations. For prosthetic side perturbations, peak ground reaction force magnitudes, ||GRF||, decreased when the SNP was active. For intact side perturbations, the SNP increased the peak ||GRF|| on the prosthetic side’s first recovery step. This approached the peak ||GRF|| on the intact side’s first recovery step after a prosthetic side perturbation and resulted in a more symmetric stumble recovery. One participant with a knee disarticulation reduced their reliance on handrails when the SNP was active, indicating improved stability and confidence in recovering with the SNP. These findings suggest that the SNP was integrated into the sensorimotor control for maintaining stability, and participants were more confident in relying on their prosthetic limb during recovery.
The findings from these studies suggest that the electrically elicited plantar sensations from the SNP are integrated into the sensorimotor control of individuals with LLL as evidenced by its interaction with spinal reflex pathways and its enhancement of reactive balance recovery. The SNP provides more accurate feedback about body orientation and foot placement than the limited feedback from the residual limb interacting with the prosthesis socket.