[Scalp recorded P13 and spinal recorded N13 in short latency somatosensory evoked potentials]

Using non-cephalic reference and by median nerve stimulation, P 13 component and N 13 component are recorded on the scalp (scalp P 13) and the posterior neck (spinal N 13), respectively, in the short latency somatosensory evoked potentials (SSEP). The purpose of this study is to disclose the origin, characteristics and clinical significance of these two components. Ten healthy volunteers served for normal subjects. Ten patients with pontine lesion or brain death were studied. The effect of barbiturate was also studied in additional 5 patients during anesthesia for cranioplastic surgeries. Electrical stimuli of 0.2 msec square wave pulse were used in routine examination. To confirm the effects of stimulation frequency, 3, 6, 9, 12, 15, 18, 21, 24 and 27 Hz were also used in normal subjects. Recording electrodes were placed in the following sites. (1) Scalp electrode at the Shagass' point contralateral to the stimulated side (Par.). (2) Posterior neck electrode on the spinous process of the fifth cervical vertebrae (Cv5), (3) Anterior neck electrode on the thyroidal cartilage (Ant. C). (4) Erb's electrode just above the mid-clavicular point ipsilateral to the stimulation. Erb's electrode contra-lateral side of stimulation was used as a reference. Spinal N 13 on posterior neck reversed its polarity into P 13 (spinal P 13) on the anterior cervical electrode. A study with different stimulus rates revealed that the latency of scalp P 13 significantly prolonged at 24 Hz stimulation. On the other hand, the latency of spinal N 13-P 13 easily prolonged even at 18 Hz. This suggested that spinal N 13-P 13 were generated polysynaptically.(ABSTRACT TRUNCATED AT 250 WORDS)