Correlation analysis of somatosensory evoked potential waveforms.

Somatosensory evoked potential (SEP) waveforms were recorded over the spine and scalp in response to tibial nerve stimulation at the ankle for 28 subjects. The scalp data were analyzed with the correlation coefficient (CC) to determine the reproducibility of the signals and to identify side-to-side symmetry. The test for reproducibility uses the CC to verify validity, a low CC implying that the data are defective. The symmetry test uses the CC to obtain a measure of similarity of the responses to stimulation from opposite sides of the body. Statistics are presented showing the normal ranges of the CC values and their standard deviations. We conclude that the CC can provide objective and quantitative waveform information that complements latency and amplitude measurements in the clinical interpretation of tibial SEP waveforms.