Assessment of peripheral nerve crush injury with cortical somatosensory evoked potentials in the cat.

Somatosensory evoked potentials (SEPs) were recorded from anesthetized cats to assess regeneration of the superficial radial nerve after crush injury. SEPs were recorded by epidural electrodes chronically implanted over the primary somatosensory cortex (SI) and elicited by electrical stimulation of the dorsal surface of the contralateral forepaw. The stimulation intensity and impedances measured across the skin-stimulating electrodes were maintained constant for each animal throughout the experimental period. SEPs which disappeared after the radial nerve crush were elicited within the first week by stimulation applied to skin nearest the nerve crush site. Radial nerve crush also affected the SEP elicited by stimulating the intact ulnar side of the forepaw. In all animals examined, the SEP amplitude evoked by stimulation of the skin supplied by the ulnar nerve increased immediately after radial nerve crush. As early as 4 days after nerve crush, SEPs were elicited by stimulating the distal region of the digits that had been denervated. This phenomenon might be accounted for by peripheral collateral sprouting of intact neighboring nerves and/or by central unmasking of ulnar median input from the denervated radial skin area. Within 117 days, SEPs were elicited by stimulation applied anywhere in the previously denervated forepaw area. The topographical amplitude distribution of SEPs after reinnervation was not identical to that obtained under baseline conditions. The use of SEPs for chronic recording is an effective means to monitor reinnervation of skin after peripheral nerve injury.