The effect of changing stimulus intensities on median nerve somatosensory-evoked potentials.

We investigated median nerve somatosensory-evoked potentials (SEP) in 31 healthy volunteers to test the hypothesis that 1) increasing stimulus intensity influences SEP components in both amplitude and latency 2) SEP components respond differently to changing intensities. Cluster analysis and analysis of variance were used for statistical testing. Three groups of components could be found according to latency changes in response to increasing stimulus intensities: N13, and P15, the primary cortical response (N19, P22) and the components over 30 ms. In general, SEP components below 30 ms significantly shortened in latency and increased in amplitude with subsequent saturation. In contrast, in components over 30 ms latencies decreased linearly and amplitudes changed inhomogeneously. The clear effect of stimulus intensity on most median nerve SEP components makes it necessary to maintain comparable stimulus intensities when comparing intra- and interindividual registrations.