Masking effect of motivation on ultradian rhythm

To test the masking effect of motivation on ultradian fluctuations in arousal, we examined the self-rating scores for sleepiness, fatigue, and motivation and the electroencephalographic data for 5 male university students (age range, 18 to 20 years). They watched either an animated video series (Animation condition) intended to enhance motivation or interest or a landscape video series (Landscape condition) intended to induce lack of interest due to boredom. Each subject watched the two series for more than one week in a 3.1 x 3.1 m isolation unit. Each series was presented for 12 min. every 20 min. from 0900 to 1800. Subjective sleepiness and fatigue increased, and motivation was decreased for Landscape condition, suggesting the validity of the experimental manipulation. Closed-eye Oz-EEG alpha and beta activities fluctuated in an ultradian manner for both conditions, although slower cycles were observed at an interval of the Animation condition. The coefficients of variation of time series data were also lower for the Animation condition. These data suggest that either high motivation or absence of sleepiness or fatigue mask ultradian arousal cycles by producing fewer or slower fluctuations.