SUBCORTICAL P-30 POTENTIAL FOLLOWING TIBIAL NERVE-STIMULATION - DETECTION AND NORMATIVE DATA

Stimulation of the tibial nerve evokes a P30 far-field potential over rite scalp which, like the median nerve P14, probably originates in th e vicinity of the cervico-medullary junction. Unlike the P14 potential , P30 recording has not been systematically performed in clinical prac tice, probably because of doubts about the generator of the potential and the possibility of consistently recording it on the scalp after th e unilateral stimulation of the tibial nerve. In this study, we tested the reliability of the tibial nerve scalp far-field P30 potential in 34 normal subjects using different montages, of which the Fpz-Cv6 deri vation gave the highest signal to noise ratio, making it possible to o btain a P30 potential peaking at 29.2 +/- 1.6 msec in all normal subje cts. This suggests that this component should to be included in the ro utine recording of tibial nerve SEPs in order to evaluate the spinal a nd intracranial conduction of the somatosensory pathway separately.