Lower cervical origin of the P13-like potential in median SSEPs

The authors studied the origin of the scalp P13-like potential in median so matosensory evoked potentials, which have been reported to be preserved in patients with cervicomedullary lesions or in brain death. There were five p atients with high to middle cervical lesions (C2/3 or C3/4 level). Small P1 3-like potentials after P11 were identified for all patients with a nonceph alic reference but not with an ear reference. Their onset latencies were sl ightly earlier than the expected latency of the true P13/14 onset. In two p atients, delayed true P13/14s followed by N18s were identified with both no ncephalic and ear references. The authors argue that the P13-like potential observed in these patients is a different entity from scalp P13 in normal subjects. Because the C3/4 vertebral level corresponds to the C5 cord level , the origin of the P13-like potential must be below C5, contradicting the previous opinion that it is generated at the cervicomedullary junction or a t the high cervical dorsal column. The authors named this potential lower c ervical P13 (or lrP13). and present an opinion that it is generated by the beginning of the second spinal ascending volley, which has been described b y direct-recording studies in humans.