Masking effect of motivation on ultradian rhythm

Bright light effects on ultradian rhythms in performance on hemisphere-specific tasks

Ultradian rhythms in indices of brain hemisphere activity and in cognitive performance have been found in numerous studies. Asymmetry of these rhythms with regard to phase and frequency have also been documented in some studies. There is some evidence that bright light can affect ultradian rhythms of arousal state and vigilance. A study on unilateral exposure to bright light has demonstrated more pronounced effects of bright light on the right hemisphere. The aim of this study was to examine whether daytime intermittent bright light could affect parameters of ultradian rhythms in performance speed on hemisphere-specific tasks, and whether the effect of bright light was symmetric for the rhythms in performance on hemisphere-specific tasks presented laterally. A counter-balanced, within-subject research design was applied. The performance of 15 participants on hemisphere-specific tasks exposed laterally was measured every 30 min starting at 08:00 h and ending at 20:30 h in intermittent bright light (IBL, pulses of 15 min of 4000 lux light regularly interspersed between 45 min of background light levels of 300 lux) and in ordinary room light (ORL) conditions (300 lux). Individual time series data were subjected to cosinor analysis. General linear model analyses (the factors were: level of processing, visual field, and the task) were performed on the rhythms' parameters. There was a substantial lengthening of the rhythms' periods in IBL conditions for performance speed on spatial tasks and an increase in amplitude of the rhythms of performance speed for spatial tasks in both visual fields and for verbal tasks in the left visual field in the IBL conditions when compared to the ORL conditions. The results showed that the schedule of light exposure affected ultradian rhythms of hemisphere-specific tasks differently and that the right hemisphere seems to be more "sensitive" to light than the left hemisphere.

Random number generation during sleep deprivation: effects of caffeine on response maintenance and stereotypy

Neurophysiological and functional imaging studies have demonstrated that frontal regions of the brain are particularly responsive to homeostatic sleep pressure. Previous neuropsychological studies indicate that sleep deprivation causes impairments in prefrontal cortical function. Random number generation (RNG) is thought to provide a sensitive index of executive functions that rely on the prefrontal cortex. The present study tested the hypothesis that sleep deprivation would impair RNG and that caffeine would mitigate this impairment. Healthy young men (n = 21) participated in two 40-h sleep deprivations 1 week apart. During each sleep deprivation period subjects received either caffeine or placebo according to a randomized, double-blind cross-over design, and they completed an oral RNG task at 3-h intervals. Comparison of test sessions at analogous times of day revealed that sleep deprivation was associated with significant drops in the number of responses, a threefold increase in the percentage of rule violations, 59% greater response redundancy and a 20% increase in stereotypy of adjacent response pairs. Sleep deprivation did not consistently alter counting tendency. Caffeine ameliorated the decrease in the number of responses but did not mitigate other deficits in RNG that arose during sleep deprivation. These findings are consistent with prior reports of diminished vigilance and increased perseveration during extended wakefulness. They support the conclusion that caffeine preserves simple aspects of cognitive performance during sleep deprivation, whereas caffeine may not prevent detrimental effects of sleep deprivation on some complex cognitive functions.

Effect of cognitive arousal on sleep latency, somatic and cortical arousal following partial sleep deprivation

Emerging research has shown that sleepiness, defined as the tendency to fall asleep, is not only determined by sleep pressure and time of day, but also by physiological and cognitive arousal. In this study we evaluated (i) the impact of experimentally induced cognitive arousal on electroencephalogram (EEG) defined sleep latency, and subjective, somatic and cortical arousal, and (ii) whether experimentally induced cognitive arousal enhances performance on a driving simulator test. Twelve healthy sleepers each spent three nights and the following day in the sleep laboratory: an adaptation, a cognitive arousal and a neutral testing day. In the cognitive arousal condition, a visit of a television camera crew took place and subjects were asked to be interviewed. On each testing day, a 5-min heart rate recording, subjective sleepiness and arousal scales, Multiple Sleep Latency Test and a 25-min driving simulator task were scheduled three times at 2-h intervals. Experimentally induced cognitive arousal resulted in significant increases in objective sleep latency. Significantly elevated levels of subjective and somatic arousal--as indexed by a subjective arousal scale and heart rate--were also evidenced following cognitive arousal induction. A marginally significant trend for increased cortical arousal, measured by EEG beta activity, was also found. No effects were found on driving simulator performance. These findings support the concept of cognitive arousal as a significant component in determining sleep latency. In addition, it was illustrated that cognitively induced arousal can provoke increases in somatic and possibly even cortical arousal in normal sleepers. However, this was not accompanied by an enhanced ability to perform adequately on a driving simulator test.