Stimulus intensity and inter-stimulus interval effects on pain-related cerebral potentials.

The inter-relationship between stimulus intensity and inter-stimulus interval (ISI) on pain-related evoked vertex potentials was studied. Sixteen subjects were tested with 4 stimulus intensities at 4 different ISIs forming 16 averaged event-related potentials for each subject. Data were analyzed in 2 ways: first by multiple regression analysis of peak-to-peak amplitudes and secondly by single-trial analysis for each subject based on a linear model employing principal component loadings as basis functions, from which were derived separate time-dependent functions describing the contributions of intensity and ISI. Peak-to-peak amplitudes of the averaged waves increased with increases in either intensity of ISI. There were no significant interactions. However, single-trial analysis revealed subtle, but consistent, differences in the peak latencies between stimulus and ISI components, suggesting that the components arise from distinct sources.