The effects of spinal cord injury on somatosensory evoked potentials produced by interactions between afferent...

The purpose of the present study was to determine the utility of somatosensory evoked potentials (SEPs) produced by interaction between afferent pathways for spinal cord injury evaluation. Interaction was measured as alterations in SEP configuration compared to controls. Monkeys anesthetized with N2O were used. Stimulus intensities were sufficient to excite all nerve fibers. The conditioning stimulus (CS) was applied to the left peroneal nerve and test stimulus (TS) to the left radial nerve. CS-TS intervals were 100 msec in duration. SEPs were recorded from primary cortical receiving area for the forelimb. Different surgical lesions were made at spinal cord level T3-T4. Amplitudes of TS-produced-SEPs remained unchanged postlesion. CS-produced-SEPs were found to be dependent upon the integrity of anterolateral column pathways. Accentuated interaction was observed following dorsal column ablation. Interaction was slightly enhanced after left hemisection but diminished after right hemisection or central cord lesion. Interaction between spatially separate afferent inputs as measured by SEP alteration was determined to be a sensitive indicator of spinal cord injury.