[Origin of components P 11 and P 13 in short latency somato-sensory evoked potentials (SSEP): correlative study of SSEP and intraoperative evoked potentials].

In 15 patients with cervical or posterior fossa lesion, SSEPs were recorded between the skull and the non-cephalic reference electrodes during the surgical operation and compared with the evoked potentials directly recorded at the same time from the surface of the cervical spinal cord and the brain stem. The directly recorded evoked potential consisted of three main components appeared within about 25 ms., they were a small negative spike wave, a large positive spike wave and a subsequent slow potential. The positive spike wave of the evoked potentials recorded from the surface of the dorsal column was not only coincided in latency with component P 11 of SSEP, but also showed the greatest amplitude at the lower cervical level. Moreover, the positive spike wave gradually delayed in latency and reduced in amplitude from lower to upper cervical segments. The amplitude of the positive spike wave was greater at the surface of the dorsal column ipsilateral to the stimulated median nerve than that of contra-lateral recording. No polarity change was observed between the anterior and posterior surface of the spinal cord. Similarly, the positive spike wave of the evoked potentials, recorded from the surface of the brain stem, showed fairly same latency with P 13 and a maximal amplitude at the surface of the cuneate tuberculum ipsilateral to the median nerve stimulated, and those positive spike wave traveled to contra-lateral ventral surface of the pons, presumably from ipsilateral cuneate nucleus to the contra-lateral medial lemniscus.(ABSTRACT TRUNCATED AT 250 WORDS)