Objective: Sensory input in lower-limb amputees is critically important to maintaining balance, preventing falls, negotiating uneven terrain, responding to unexpected perturbations, and developing the confidence required for societal participation and public interactions in unfamiliar environments. Despite noteworthy advances in robotic prostheses for lower-limb amputees, such as microprocessor knees and powered ankles, natural somatosensory feedback from the lost limb has not yet been incorporated in current prosthetic technologies.
Approach: In this work, we report eliciting somatic sensation with neural stimulation delivered by chronically-implanted, non-penetrating nerve cuff electrodes in two transtibial amputees. High-density, flexible, 16-contact nerve cuff electrodes were surgically implanted for the selective activation of sensory fascicles in the nerves of the posterior thigh above the knee. Electrical pulses at safe levels were delivered to the nerves by an external stimulator via percutaneous leads attached to the cuff electrodes.
Main results: The neural stimulation was perceived by participants as sensation originating from the missing limb. We quantitatively and qualitatively ascertained the intensity, modality as well as the location and stability of the perceived sensations. Stimulation through individual contacts within the nerve cuffs evoked repeatable sensations of various modalities and at discrete locations projected to the missing toes, foot and ankle, as well as in the residual limb. In addition, we observed a high overlap in reported locations between distal versus proximal cuffs suggesting that the same sensory responses could be elicited from more proximal points on the nerve.
Significance: Based on these findings, the high-density cuff technology is suitable for restoring natural sensation to lower-limb amputees and could be utilized in developing a neuroprosthesis with natural sensory feedback. The overlap in reported locations between proximal and distal cuffs indicates that our approach might be applicable to transfemoral amputees where distal muscles and branches of sciatic nerve are not available.