[Cortical and subcortical somatosensory evoked potentials to median nerve stimulation in man].

In order to define the precise locations of precentral and postcentral gyri during neurosurgical operations, somatosensory evoked potentials to contralateral median nerve stimulation were recorded from the cerebral cortex in 19 cases with organic cerebral lesions which located near the central sulcus. In addition to that, distribution patterns of early components of SEPs were displayed by Nihonkoden Atac 450 in 3 cases who had bone defects after wide decompressive craniectomy but were without any sensory disturbances In 4 cases, in whom deep electrodes were inserted for the stereotaxic operations or other reasons, frontal subcortical SEPs were recorded in order to know the origins of frontal components of SEPs. From the parietal cortex, N19, P22 and P23 were observed. And from the frontal cortex, P20 and N25 were obtained. Their average peak latencies were as follows; (table; see text) Because all subjects had organic lesion in the brain, the peak latencies were a little bit longer, and their standard deviations were larger than those in normal cases. Usually, clear-cut phase reversal could be observed between N19 and P20 across the central sulcus. So, the precentral and postcentral gyri were easily identified during the operations. N19 and P23 appeared over the wide areas of the parietal cortex. Also, P20 and N25 were recorded almost whole areas of the frontal cortex. On the other hand, P22 appeared from relatively restricted part of the postcentral gyrus where sensory hand area might have been located. Depth recording from the frontal subcortical area revealed that P20 could be recorded from the bilateral frontal subcortical areas and there observed no phase reversal between the cortical and subcortical SEPs.(ABSTRACT TRUNCATED AT 250 WORDS)