Peripheral nerve stimulation (PNS) is a promising technique for restoring touch to people with neurological injuries. However, its application remains limited because past studies solely focused on people with limb loss and because the optimal paradigm for encoding touch information is still unclear. This study investigated PNS as a modality to restore touch in an individual with sensory-incomplete spinal cord injury (SCI) and quantified intracortical activity in primary somatosensory cortex (S1) resulting from PNS. S1 activity serves as an objective measure to compare and refine PNS paradigms to ultimately improve the effectiveness of PNS as sensory feedback in bidirectional neuroprostheses. We found that PNS delivered to the median and ulnar nerves via chronically-implanted, multi-contact cuff electrodes consistently evoked hand sensations with intensities that reliably scaled with stimulation pulse width (PW). In S1, increasing PNS PW recruited larger cortical populations, increased multi-unit firing rates, and shortened latencies between PNS onset and peak S1 activation. Interestingly, most S1 responses to PNS had strong onset transients, like those previously observed in response to mechanical indentation. Because our PNS paradigm was designed to recruit a population of peripheral afferents synchronously at a fixed frequency, our results suggest that central mechanisms play a role in producing cortical onset transients. This study supports PNS as a viable sensory feedback approach for individuals with incomplete SCI and reveals the representation of electrically-evoked sensory percepts in human cortex for the first time.

The authors have declared no competing interest.

NCT03898804

This study was funded by the Congressionally Directed Medical Research Program Spinal Cord Injury Research Program, Clinical Trial Award SC18038 and by the National Institutes of Health, National Institute of Neurological Disorders and Stroke, R01NS119160. Additional funds were provided as part of start up support from the Case Western Reserve University Department of Biomedical Engineering.

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The study is part of the Reconnecting the Hand and Arm to the Brain (ReHAB) clinical trial (ClinicalTrials.gov #NCT03898804). All procedures were reviewed and approved by the University Hospitals Cleveland Medical Center's Institutional Review Board. The U. S. Food and Drug Administration also approved the devices and procedures for this study under an Investigational Device Exemption.

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All data produced in the present study are available upon reasonable request to the authors.