NEURAL GENERATORS OF TIBIAL NERVE P-30 SOMATOSENSORY-EVOKED POTENTIALSTUDIED IN PATIENTS WITH A FOCAL LESION OF THE CERVICOMEDULLARY JUNCTION

The tibial nerve P30 potential was studied in 6 patients with focal le sions located in the vicinity of the cervicomedullary junction, P30 po tential was unaffected while cortical P39 was abnormal in the patients with a supramedullary lesion affecting the somatosensory pathway just above its decussation. Conversely, P30 was abnormal in the presence o f a lesion situated caudally to the cervicomedullary junction affectin g the lower limb sensory fibers just below their decussation, Median n erve P14 behaved similarly to the P30 potential in these cases, These clinical observations suggest that P30 potential, as P14 of median ner ve somatosensory evoked potentials, is generated in the lower brain st em probably before the decussation of the sensory fibers; nucleus grac ilis and medial lemniscus fibers in the lower brain stem are probably the anatomical structures generating P30 potential, This suggests that P30 potential may be used to study intraspinal and intracranial condu ction times separately in the afferent somatosensory pathways. (C) 199 6 John Wiley & Sons, Inc.