Amputation with median nerve redirection (targeted reinnervation) reactivates forepaw barrel subfield in rats

Prosthetic limbs are difficult to control and do not provide sensory feedback. Targeted reinnervation was developed as a neural-machine interface for amputees to address these issues. In targeted reinnervation, amputated nerves are redirected to proximal muscles and skin, creating nerve interfaces for prosthesis control and sensory feedback. Touching the reinnervated skin causes sensation to be projected to the missing limb. Here we use electrophysiological brain recording in the Sprague Dawley rat to investigate the changes to somatosensory cortex (S1) following amputation and nerve redirection with the intent to provide insight into the sensory phenomena observed in human targeted reinnervation amputees. Recordings revealed that redirected nerves established an expanded representation in S1, which may help to explain the projected sensations that encompass large areas of the hand in targeted reinnervation amputees. These results also provide evidence that the reinnervated target skin could serve as a line of communication from a prosthesis to cortical hand processing regions. S1 border regions were simultaneously responsive to reinnervated input and also vibrissae, lower lip, and hindfoot, suggesting competition for deactivated cortical territory. Electrically evoked potential latencies from reinnervated skin to cortex suggest direct connection of the redirected afferents to the forepaw processing region of S1. Latencies also provide evidence that the widespread reactivation of S1 cortex may arise from central anatomical interconnectivity. Targeted reinnervation offers the opportunity to examine the cortical plasticity effects when behaviorally important sensory afferents are redirected from their original location to a new skin surface on a different part of the body.