Abstract: Besides the physiological state, circadian variations have also been found in subjective feelings and neurobehavioral functions crucial for the execution of our daily tasks. However, few studies investigated the effect of daily rhythm based on Chinese native groups, and whether there is a discrepancy in the daily fluctuations of different cognitive functions remains unknown. To reveal effect of daily rhythms on performance in Chinese individuals comprehensively, the present study measured the changes of physiological state (body temperature, cardiac activity and arterial pressure), subjective feelings (self-report sleepiness) and objective performances (vigilance, inhibition control, working memory) in Chinese adults every two hours during a day (9:00-21:00) under laboratory control. To be specific, a single factor (time of day: 9:00,11:00.13:00,15:00,17:00,21:00) within-subject design was employed in the current study, and a total of 27 healthy young adults (11 males, 16 females) were selected as our subjects according to rigorous criteria. At each time point, we firstly used KSS and a seven-point Likert Scale to measure the participants’ subjective sleepiness and mood, respectively. Then, participants were tested on a psychomotor vigilance task, a go/no go task and two working memory tasks under different cognitive loads (one-back and two-back) sequentially. Additionally, participants’ oral temperature, heart rate and arterial pressure were measured as indicators of their physiological state every hour throughout the experiment. In general, the results revealed that participants were at their highest level of cognitive performance in the morning (09:00–11:00), but there was a post-noon dip at 13:00–15:00, suggesting beneficial effect as a short nap on performance. Performance improves again during the evening (17:00–21:00), which is in line with previous research. Moreover, in this study, differences in daily variations have also been found not only between self-assessments and objective measurements but also in the performance of different neurobehavioral functions. Specifically, while the participants showed a stable performance of vigilance during daytime, there was an obvious fluctuation in their self-report sleepiness in the afternoon. At 15:00, subjective sleepiness reached its highest level in the daytime, whereas the objective performance of neurobehavioral functions (vigilance, inhibition control, and working memory) had improved. At 17:00, associated with diminished subjective sleepiness, vigilance and working memory performance were relatively optimal at that time, but the execution in the go/no go task decreased and reached its lowest level, reflecting that inhibition control is worst in the evening independent of other executive functions. Moreover, while the performance of inhibition control improved at 19:00, the performance of vigilance and working memory showed a post-dinner dip at the same time, suggesting a non-optimal time for study and examinations specific to Chinese individuals. Additionally, when the participants performed the working memory tasks under different memory loads, their performance also demonstrated different daily variations at 9:00-13:00. This discrepancy suggests that the impact of daily rhythms on the same neurobehavior function may vary under different cognitive loads and further research is needed to understanding the underlying neural mechanism. Taken together, the present study shows that daily rhythm modifies our subjective feelings and basic neurobehavior functions (attention, inhibition control and working memory) differently, which may explain oscillations in the performance of different tasks during the day. The findings provide valuable insights into planning daily schedules, optimizing working arrangements, and ensuring safety based on human rhythm, providing preliminary evidence for illuminating the relationship between daily rhythms and behavioral performance in the future.

Key words: Daily rhythm, Neurobehavioral functions, Vigilance, Inhibition control, Working memory

摘要： 本研究在实验室条件下，综合主观感受及客观行为表现考察我国大学生群体在一天内的节律变化。总体上，大学生的日间节律呈现出“上午（9:00-11:00）最佳，午后（13:00-15:00）下降，晚间（19:00-21:00）回升”的变化规律，但主客观指标反映的日间节律与不同神经行为功能的节律表现存在差异：客观警觉性注意在日间表现基本稳定，而主观困倦感午后波动明显，个体在15时的主观困倦感升至日间最高水平，而客观行为表现均已好转；17时，个体的主观感受、客观警觉性和工作记忆表现较好而抑制控制表现变差；19时，个体主观感受、工作记忆表现不佳而抑制控制表现好转。此外，上午至午后（9:00-13:00），个体在不同认知负荷下的工作记忆表现也存在节律差异。本研究为合理规划日常活动、优化工作安排、提升生产安全等提供数据支持，也为进一步探究我国个体的日间节律和心理行为之间的关系提供初步证据。

关键词: 日间节律, 神经行为功能, 警觉性注意, 抑制控制, 工作记忆