Cortical representation of sensation elicited by peripheral nerve stimulation in an individual with incomplete spinal cord injury

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.