[Incidence of identification and configuration variants of the NSEP signal in relation to the recording site and measuring moment].

The component evaluation of the spinal and cortical recorded SEP-signals of thirty healthy volunteers after stimulation of the median nerve at the wrist gave information about variation of waveforms and frequency of peak identification with respect to the position of the active electrode and the repetition of the SEP recording. Basically one can distinguish three main groups of NSEP waveforms (Fig. 1). Firstly the "classical form" (i.e. N11 in the ascending part, N13 at the highest peak of the NSEP main component and N14 in the descending part of the curve). Secondly the "plateau-form" and thirdly the "polypeak form" (i.e. many peaks of the same amplitude). The latter two configurations were seen in more than a third of the evaluated NSEP maincomponents. Neither the position of the active electrode (C2 and C7) nor repetition of the SEP recording were found to have significant influence on the waveform. The position of the active electrode influenced the number of identificable peaks: the early components (N9 and N11) were more often recognisable when the recording was made over the lower neckregion (C7), N14 when the recording was made over the upper neckregion (C2). N13 was always identificable in both electrode positions. The repetition of the SEP recordings immediately after the first run is helpful if there was difficulty in identifying the peaks. The normal values of the SEP latency of the spinal and cortical recorded signals were evaluated taking above mentioned criteria into account.