Human event-related potentials and circadian variations in arousal level.

Contingent negative variation (CNV) potentials were recorded from ten male subjects during a single session in divided- and focussed-attention conditions. Beside a strong dependency of CNV and N1 amplitudes and reaction time on task difficulty, the results of the present study show an effect of the subject types, classified by their peak performance times. The slight increase of CNV amplitude form morning to afternoon recording in evening-type subjects contrasted with a substantial decline in the morning-type subjects. Unexpectedly, both task conditions showed remarkably similar time courses of amplitudes. The attempt to model the individual amplitude curves from arousal levels led to inconclusive results. No final conclusions about the relationship of CNV and arousal levels over the course of a day can be drawn.