Copyright © 2023 Korean Academy of Sleep Medicine 127 INTRODUCTION During the day, the performance of the human being knows several fluctuations according to the level of awakening in its re- lation to the daytime. erefore, the fluctuations of the same vari- able or process present a sinusoidal rhythmicity. Many scientific studies show that behavioral vigilance in students has two main peaks and two troughs, the time period of which varies according to age [1-4]. erefore, the school rhythm is developed in such a way as to respect the rhythm of the student in relation to his or her own homeostatic and cognitive processes [5,6]. is is said to Circadian Fluctuations of Cognitive and Psychomotor Performance in Medical Students: e Role of Daytime and Chronotype Patterns Ikram Sabaoui 1 , Said Lotfi 2 , and Mohammed Talbi 1 1 Observatory of Research in Didactics and University Pedagogy (ORDIPU), Laboratory of Analytical and Molecular Chemistry, Faculty of Sciences Ben M’Scik, Hassan II University of Casablanca, Casablanca, Morocco 2 Multidisciplinary Laboratory In Education Sciences and Training Engineering (LMSEIF), Sport Science Assessment and Physical Activity Didactic, Normal Superior School (ENS), Hassan II University of Casablanca, Casablanca, Morocco Objective: Our research aimed to explore the impact of chronotype and time of day on the cognitive and psychomotor performance of medi- cal students around 25 years old. The study provides evidence that an individual’s circadian rhythm affects their daily performance and cogni- tive processes. Methods: To measure selective attention and inhibition, we utilized the Stroop test, while three subtests from the fourth edi- tion of Wechsler Adult Intelligence Scale (WAIS-IV) were employed to measure simple attention and working memory. In addition, the Leed psychomotor tester was utilized to measure perception and motor reaction time, and the morningness-eveningness questionnaire was ad- ministered to investigate students’ chronotype. Statistical analysis were based on many tests depending on the correlation types. We mainly used ANOVA repeated measures, Bonferroni post-hoc test, ANOVA I, chi-square, and Pearson correlation tests. Results: Our findings suggest that students exhibit decreased selective attention (F=128.842b, p<0.01, η 2 =0.868, 95% CI=2.744–16.998) and weakened inhibition during the late afternoon (6 p.m.) when the largest margin of error was committed (1.56±2.90) compared to 10 a.m. (0.82±1.72), leading to in- creased difficulty resisting interference; except that the size effect was small (η 2 >0.13). Simple attention reaches its peak in the morning around 10 a.m., while memory performance and auditory modality of working memory reach their peaks at 10 a.m. and the end of the afternoon (6 p.m.), respectively. Conclusion: Our study underscores the importance of taking wake time and body temperature into account when exam- ining task performance. Overall, the study highlights the importance of considering circadian rhythm and chronotype when designing aca- demic and athletic schedules. Keywords: Daytime; Cognitive performance; Psychomotor performance; Chronotype; Medical students Received: July 20, 2023 Revised: August 26, 2023 Accepted: August 31, 2023 Corresponding author: Ikram Sabaoui, PhD, Observatory of Research in Didactics and University Pedagogy (ORDIPU), Laboratory of Analytical and Molecular Chemistry, Faculty of Sciences Ben M’Scik, Hassan II University of Casablanca, Ghandi 20100, Morocco. Tel: 212-707083100, E-mail: s_kella@hotmail.fr cc This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (https://creativecommons.org/licenses/by- nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. ORIGINAL ARTICLE eISSN 2635-9162 / https://chronobiologyinmedicine.org Chronobiol Med 2023;5(3):127-137 / https://doi.org/10.33069/cim.2023.0018 CIM investigate the daily rhythmicity of the latter in students, who also face the polyrhythm challenges. A study that examines circadian rhythms as they relate to cog- nitive processes argues that the biological clock generates chang- es in one or more specific brain systems that lead to changes in cognitive processes that modulate the performance of a variety of tasks [7]. It is suggested that circadian rhythms during the per- formance of these tasks may be regulated primarily by three cog- nitive processes, including attention, working memory, and ex- ecutive functions [8-10]. According to Kleitman [11], the 24-hour rhythm of metabolic