Posterior cervical N13 in median nerve SEP has two components

Somatosensory evoked potentials (SEPs) to median nerve stimulation were investigated in normal controls and patients with cervical lesions. Attention was paid primarily to the N13 and P13 components in the posterior and anterior cervical records with non-cephalic references. In normal subjects the CV2 and CV6 electrodes registered N13 with almost the same amplitude. Dissociation between N13 at the CV2 electrode (ucN13) and N13 at the CV6 electrode (lcN13) was observed in the patients. In 4 patients with cervical dorsal column lesions, lcN13 was preserved but ucN13 was almost completely absent. Anterior cervical P13 (acP13) was preserved. In a patient with syringomyelia, lcN13 and acP13 were greatly attenuated while ucN13 was relatively well preserved. These results suggested that the origins of ucN13 and lcN13 are different. The generator of lcN13-acP13 was assumed to be the postsynaptic potential of the dorsal horn interneurons. Upon comparison with previous animal studies and intraoperative studies, it was concluded that the generator of ucN13 is the postsynaptic potential of the cuneate nucleus.