Time of Day Effects in the Relationships Between Daytime Sleepiness, Current Arousal, and Cognitive Performance.

This article investigates how time of day moderates the relationships between self-reported daytime sleepiness, current arousal, and cognitive performance in older adults. Analyzing data from 133 community-dwelling adults aged 50 to 89, the study found that greater daytime sleepiness was associated with poorer immediate list learning in the afternoon but not in the morning, while lower current arousal predicted worse processing speed in the afternoon only. These findings suggest that time of cognitive testing should be considered when assessing sleepiness and cognition in older adults, as the impact of sleepiness and arousal on cognitive tasks varies by time of day. The study emphasizes the importance of distinguishing between trait-like sleepiness and state arousal measures and notes limitations including a predominantly non-Hispanic White, well-educated sample and reliance on subjective sleepiness assessments.