During the day, the performance of the human being knows several fluctuations according to the level of awakening in its relation to the daytime. Therefore, the fluctuations of the same variable 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]. Therefore, 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]. This is said to 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 cognitive processes argues that the biological clock generates changes 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 performance of these tasks may be regulated primarily by three cognitive processes, including attention, working memory, and executive functions [8-10].

According to Kleitman [11], the 24-hour rhythm of metabolic activity modulates brain activity, resulting in fluctuations in cognitive function. The cerebellum and other subcortical brain structures such as the basal ganglia are involved in a variety of cognitive processes [12,13]. Attention, being one of these processes, refers to the ability to interact effectively with the environment. It involves processing and selecting incoming stimuli, responding to each stimulus, and maintaining a specific and effective response for minutes or hours [14]. According to the model by Posner and Rafal [15], attention consists of four components, including tonic vigilance, compatibility vigilance, selective attention, and sustained attention. Variations in these components are an independent manifestation of the circadian clock and not merely a passive response to changes in metabolism, including body temperature [16]. Therefore, the circadian fluctuations observed in tasks such as reaction time, memory, reading comprehension, and perceptual time can be explained by the variation of attention components [7]. From its peak during the day, the rhythm of inhibition process as one of the components of the executive functions drops at night and early in the morning [17], while that of working memory reaches a peak around 8 a.m. and decreases steadily until 1 p.m. in all chronotypes. After this period, its performance improves again in the intermediate and evening profiles [18]. Regardless of the circadian preferences of these profiles, females perform significantly better than males in visuo-motor coordination, hence the effect of gender on psychomotor performance [19].

The cognitive process rhythm varies depending on various factors, including gender, age, chronotype [20], personality traits [21], physical exercise [22], as well as experiences like the COVID-19 lockdown [23] or unique circumstances such as Ramadan fasting [24]. This raises our interest in some processes’ daily variation, notably inhibition, attention, working memory, and psychomotricity in students facing a university rhythm. Our first hypothesis suggests that the fluctuation of both chrono-cognitive and psychomotor performances of university students has two peaks: at 10 a.m. (the highest) and at 6 p.m.; and two bottoms at 2 p.m. (the deepest) and at 10 p.m. The second hypothesis assumes that chronotype has an influence on these performances according to the daytime variation.

Few studies in the literature have conducted research on the daily variation of cognitive processes in students at primary or secondary school, while no study has taken university students into consideration. Rhythms’ interactivity in the university environment might be the reason. Polyrhythms are imposed on university students, which can undoubtedly affect the daily variation of any psychomotor or cognitive characteristic that makes conducting such research difficult. Nonetheless, the current study involves the application of an experimental protocol that attempts to assess the effect of daytime on medical students’ attention, inhibition, working memory, and psychomotor fluctuations. These variations would help us determine the best time of day to study at university, taking both gender and chronotype of students into account, while also keeping in mind that other variables could have an impact on both cognitive and psychomotor performance.

The results showed that gathered data satisfy assumptions of normal distribution (all p>0.05) and homogeneity of variance (all p>0.05).

We remind that our study aims to investigate two initial hypotheses: the first is that the time of day has an effect on cognitive and psychomotor performances, and the second argues that chronotype is also correlated with these same performances among medical students. Before moving on to the analysis of the results obtained, we note that daily variation is an integral part of the circadian rhythm (24 hours). According to Valdez et al. [7], the circadian rhythm of cognitive processes for individuals with an intermediate chronotype who usually sleep from 11 p.m. to 7 a.m. is low in the morning between 7 a.m. and 10 a.m., improves around noon, reaches its first peak between 10 a.m. and 2 p.m., and decreases after lunch towards its first dip between 2 p.m. and 4 p.m. Its second peak is reached in the late afternoon and early evening between 4 p.m. and 10 p.m., and gradually decreases between 10 p.m. and 4 a.m. to reach its lowest levels (second dip) at dawn and early morning between 4 a.m. and 7 a.m.

The daily performance of individuals varies depending on the time of task execution. The different processes interacting in the human brain are related on the one hand to the type and conditions of the task, and on the other hand to the brain’s temporal ability to execute it [41]. Attention, as a cognitive process, was measured in this study by the Stroop test. Our sample demonstrated variations in the tasks to be performed in the Stroop test depending on the different periods of the day, so that the mean scores of the first task (RCFL mode) were significantly higher than those of the second task (RCFC mode). However, the mean errors for the second task exceed those of the first during all periods of the day. This shows a notable decrease in perception and inhibition in students in RCFC mode compared to RCFL mode, resulting in a reduction in selective attention and an increase in the difficulty of resisting interference. These results confirm the findings of two previous studies, one of which reported that weaker inhibition was observed in the early evening [42], and the other revealed that a decrease in inhibition was observed at 1 a.m. and 7 a.m., compared to 1 p.m. and 7 p.m. [43].

Moreover, following the observation of the daily variation in error scores, we note that those committed in the RCRL mode increase at 2 p.m. compared to 10 a.m., while those committed in the RCRC mode increase at 6 p.m. compared to 2 p.m., highlighting the increased perceptual difficulty, lack of attention, and weak resistance to interference among our students in the late afternoon (6 p.m.). These findings partially converge with the conclusions of Valdez [14] in his literature review (2019), which indicate that during the early morning hours, particularly between 4 a.m. and 7 a.m., and during late hours, productivity and job performance decline, with an increased risk of errors and accidents. Additionally, the decreased attention during these times of the day also has consequences on academic learning.

On the athletic front, research has shown that self-paced athletes, such as swimmers and runners, perform better on inhibition tasks [44]. Therefore, it is preferable to train at the time of day when inhibition reaches its peak, particularly at 10 a.m. according to our study.

On the other hand, our results show that in terms of scores on the FDM and FDMS, it can be suggested that simple attention among our students reaches its highest peak in the morning around 10 a.m., then decreases towards the lowest performance in the early afternoon (2 p.m.), and reaches its second peak towards the end of the afternoon (6 p.m.), before remarkably declining at night around 10 p.m. Our study also highlighted that the time of day has an impact on memory performance, due to significant differences in the performances measured by the WAIS subtests during different periods of the day (with 4-hour gaps). This reinforces the findings of Evansová et al. [45], who found differences in the declarative memory results of participants evaluated using the Rey Auditory Verbal Learning Test task (related to the time of evaluation with a half-hour gap).

Meanwhile, in the auditory modality of working memory represented by variations in scores of BDM, LDS, and LDSS among our students, the curve plotted throughout the day showed two peaks, with the highest at 10 a.m. and a single trough at 2 p.m. This finding supports the results of Folkard [46], who demonstrated a time-of-day effect on a working memory task under daynight conditions. However, studies conducted by Johnson et al. [47] and Monk and Carrier [48] suggest that performance differences in tasks observed during normal day-night conditions may be more influenced by the homeostatic drive of wake time than by the circadian timing system (CTS). The use of a forced desynchronization protocol in these studies allowed for the distinction of the two factors. Short-term memory, verbal reasoning, and serial search were found to systematically vary with wake time and follow the rhythm of body temperature, with the influence of wake time being at least as strong as that of the CTS on these specific tasks. These results underscore the importance of considering wake time and body temperature when studying performance in different tasks [47,49].

The daily variation of TRT in our study shows two troughs, the first of which represents the fastest reaction time at 10 a.m., and two peaks, the second of which represents the slowest reaction time at 10 p.m. However, MRTs are much faster than perception reaction times in comparison to all times of the day. This means that the motor movement takes less time than the information processing that precedes perception. The MRT also suggests that the two periods around 10 a.m. and 6 p.m. are the best times for physical activity, since the MRT reaches its peak performance during the day at these times in our students. This is further reinforced by the results of the CFF in our study, which confirm that the general arousal of students is much higher during these two time slots, particularly at 10 a.m. and 6 p.m., knowing that higher CFF scores indicate greater perceptual accuracy.

According to the correlation between chronotype and the RCC mode task among our students, we can understand that the more the chronotype score increases towards morning types, the more attention increases during the execution of the Stroop test tasks compared to all periods of the day. This explains the relationship between morningness and attention. In the same vein, Evansová et al. [45] demonstrated that chronotype has a significant effect on the Stroop subtest on color naming (i.e., RCC in our study) much more in extreme morning types than in extreme evening types, while no difference was observed between extreme morning types and intermediate types.

However, the correlation between chronotype and inhibition score in the afternoon demonstrates that the more the chronotype score increases towards morningness, the more inhibition increases in our students, particularly at 2 p.m., which explains why morning types are less efficient and attentive in the afternoon. Our study also validates the effect of chronotype on memory when it correlates with both the BDM at 10 a.m. and the LDS at 2 p.m.; this suggests that students who tend towards morningness perform better in terms of digit memory in the morning and LDS memory in the afternoon. Our study converges with the results of Schmidt et al. [50] who confirmed that chronotype and time of day interact with the working memory load. A more recent study has also revealed that morning chronotypes showed positive results in all measures of cognitive and physical performance compared to late chronotypes during the morning hours, particularly at 8 a.m. [51].

Following the correlations between chronotype and vigilance factors, namely RRT, MRT, and TRT, in our study, it turns out that the visual perception speed measured via RRT in our students has no relationship with their chronotype tendencies. On the other hand, the MRT showed to be faster in students with morning tendencies, particularly in the morning at 10 a.m. and in the late afternoon at 6 p.m., unlike 2 p.m. when their MRT is much slower. Furthermore, the correlation between chronotype and TRT in our study suggests that when the students’ chronotype score tends towards morningness, their TRT becomes slow in the early afternoon (2 p.m.) and fast in the late afternoon (6 p.m.). Therefore, morning types have better motor skills in the morning at 10 a.m. and in the afternoon at 6 p.m., and better vigilance at 6 p.m. Similarly, Facer-Childs et al. [51] also found a significant correlation between time of day and chronotype for psychomotor vigilance task performance. Early chronotypes performed better in the morning than in the afternoon and evening, whereas late chronotypes showed significant variation with poorer morning performance compared to evening. The performance variation was 3.5% for early chronotypes and 9.1% for late chronotypes. At 8 a.m., early chronotypes performed significantly better (8.4%) than late chronotypes. Furthermore, the correlation between the CFF and chronotype suggests that the wakefulness state of the students is more active at 10 a.m. and 10 p.m. (the frequency of the CFF is much closer to 25 Hz, the average at which humans must perceive flickering in a fixed light), when the chronotype score tends towards morningness.

However, it should be noted that throughout our experimentation, we ran across a number of challenges that endangered the favorable settings for our research. The fact that the tests must be completed in around 45 minutes every 4 hours, for four times a day, causes students to perceive the experiment as time-consuming and difficult. In order to comply with the experiment’s requirements, students had to almost stop performing their usual everyday activities. Additionally, as we noted in the paragraph “Research difficulties,” we have encountered many other issues such as students’ availability, and their level of readiness for the experiment. For this reason, further studies with bigger populations are required to get statistical results that are more conclusive for university students in general and medical students in particular.

The study confirms two hypotheses. The first is that the time of day affects cognitive and psychomotor performance, as shown by variations in performance on the Stroop test, forward and backward digit memory, and letter digit sequence at different times of the day. The second hypothesis is that a person’s chronotype is linked to cognitive and psychomotor performance. For example, students show the highest simple attention performance in the morning at around 10 a.m. before declining in the early afternoon (2 p.m.), as it was previously shown that self-paced athletes perform better when inhibition is at its peak. Overall, the study provides evidence that both time of day and chronotype are important factors that can impact cognitive and psychomotor performance.

We can conclude that medical students’ daily studies in the university are affected by their cognitive and psychomotor daily fluctuations. The study suggests that students’ cognitive and psychomotor abilities can vary throughout the day and may be influenced by factors such as sleep, diet, exercise, and stress. Given these fluctuations, it may be beneficial for medical students to schedule their study time and activities based on their individual rhythms and preferences. For example, some students may find it more effective to study in the morning when their cognitive abilities are at their peak, while others may prefer to study in the afternoon or evening. Additionally, students may want to incorporate activities such as exercise or meditation into their daily routines to help improve their cognitive function and reduce stress.

Overall, the article highlights the importance of understanding and accounting for individual cognitive and psychomotor fluctuations when planning and implementing daily study routines for Moroccan medical students. However, further research with larger sample sizes and more precise and adapted experimental protocols is warranted.