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Objectives. The goal of this study was to test some hypotheses from the model of sleepiness proposed by De Valk and Cluydts (2003). Therefore, we examined the effects of trait and state measures of activation and sleepiness on subjective and objective measures of daytime sleepiness after partial sleep deprivation. Methods. 28 healthy adults, aged 18-26 years (14 males), spent one night and the following morning in the aboratory. During the night the participants had opportunity to sleep half of their usual sleep time, which was accomplished by delaying their usual bedtime. In the morning they participated in two experimental situations, which differed in the level of activation. The level of activation was manipulated by two laboratory tasks: a simple reaction time task (SRT), and a combined speech and mental arithmetic task (CT). The order of the tasks was balanced between the subjects. Heart rate and electrodermal activity (EDA) were measured before and during each task, and subjective activation and anxiety were estimated before and after the tasks. After each task sleepiness was measured by the Karolinska Sleepiness Scale (KSS) and a single Sleep Latency Test (SLT) based on the MSLT rules. EDA lability during rest was used as a trait measure of activation, and the results on the Epworth Sleepiness Scale (ESS) as a measure of trait sleepiness. Additionally, trait anxiety was measured by the STAI-T Inventory. Results. Repeated measures ANOVAs and paired t-tests were performed. All objective and subjective measures of activation and anxiety indicated that higher levels of activation and tension were evoked by the CT compared to the SRT. The results on the KSS were lower after performing CT than after SRT (Mct=5.9, sd=1.76 ; Msrt=6.6 ; sd=1.91). It took longer to fall asleep in the SLT after performing CT than after SRT (Mct=9.6 ; sd=6.94 ; Msrt=6.2 ; sd=6.34). None of the trait measures of activation or sleepiness had a significant effect on sleepiness measures. Conclusion. Increased level of sympathetic activation and subjective tension can decrease subjective sleepiness and linger sleep onset after partial sleep deprivation. These results support the hypothesis about the importance of state activation as one of the determinants of daytime sleepiness, proposed in the model by de Valk and Cluydts. On the other had, the results of this experimental study do not support inclusion of trait aspects of activation or sleepiness in the proposed model. |
