Fast, quantitative assay of nerve somatotopy via recording stimulus-evoked compound action potentials with the Utah slanted electrode array

Clinical uses for assaying nerve somatotopy or continuity could benefit from more detailed mappings than current methods offer. In the present study, the efficacy of using the Utah Slanted Electrode Array (USEA) to assay nerve resomatotopy in a fast, detailed, and quantitative manner was tested. Feline tibial nerve at the ankle (TNA) and superficial peroneal nerve (SPN) branches were stimulated with bipolar electrodes at the ankle. The resultant compound action potentials (CAPs) were recorded from a USEA implanted in the sciatic nerve. Results from eight preparations showed that somatotopy of the nerve could be distinguished using the recordings with the USEA. This approach was fast, monitoring 100 sites within the nerve simultaneously. The results were quantitative, with CAP amplitudes from one stimulus being twice the CAP amplitudes from the other stimulus in distinct areas. This method was also very eproducible, showing the same somatotopy both within a preparation and among preparations: TNA stimulation consistently evoked a larger response at the posterior side of the nerve, whereas SPN stimulation evoked a larger response at the anterior side of the nerve. The ability of the USEA to record from small groups of cutaneous afferents was examined by cutaneous, bipolar stimulation of skin innervated by the TNA and SPN branches. Cutaneous stimulation of the dorsal surface of the paw evoked a recorded response at the anterior side of the nerve, whereas stimulation of the plantar surface was recorded at the posterior side of the nerve. This result was expected, because the SPN innervates the dorsum of the paw and the TNA innervates the plantar surface of the paw. Musculotopy of the sciatic nerve was also examined by stimulation through the USEA of the sciatic nerve. The resultant musculotopy map showed activation of muscles innervated by the peroneal nerve by stimulation through electrodes implanted at the anterior of the nerve. Muscles innervated by the tibial nerve were activated by stimulation through electrodes implanted at the posterior of the nerve. This result showed that the somatotopy map was similar to the musculotopy map. The documented ability to record nerve CAPs with USEAs may provide novel opportunities for research investigations and clinical applications. v