This study examined 124 medical residents from Hospital General La Raza in Mexico City (50 males and 74 females; age 26.7 ± 3.48 years). All participants provided written informed consent. The human data were performed under the Declaration of Helsinki [11] and Mexican legislation on Bioethics. The ethical approval was awarded by the Academic Ethics Committee of the Division of Biological and Health Sciences of the Universidad Autónoma Metropolitana-Iztapalapa (CECBS20-05).

During a 6-week rotation period, we evaluated the participants in four different service units (emergency medicine, perinatology, neurosurgery, and pediatrics). The shift schedule included 36 continuous hours on duty, followed by 24 hours off duty and a normal diurnal working schedule (8 to 17 hours) on the next day. Participants were evaluated in two different conditions: 1) sleep deprivation (SD), in which participants were analyzed immediately after finishing their on-duty schedule, and 2) SR, in which participants were studied after five weeks of the shift schedule during the daytime. After the initial assessment, all the participants received a sleep hygiene orientation as an intervention, which consisted of four talks for two hours per day for one week. Then, all the participants completed the questionnaires again.

Residents completed a daily sleep/work log throughout the study. Sleep logs were used to collect data on sleep timing and duration, sleep quality, awakenings, and work schedules and were available for 20 nights. Additionally, they completed a range of sleep tests/questionnaires, including the Sleep Habits Questionnaire (SHQ), the Sleep Quality Scale (SQS), the Athens Insomnia Scale (AIS), the Pittsburgh Sleep Quality Index (PSQI), the Epworth Sleep Scale (ESS), and Karolinska Sleepiness Scale (KSS).

Residents completed the PVT on four occasions throughout the experiment. Participants were instructed to press a key as fast as possible whenever a red circle appeared in the middle of a computer screen. The test was performed at the start and end of each shift for each extended shift. The mean reaction time (RT), the mean of the 10% slowest responses, and the number of lapses (response times ≥ 500 ms) were used as measures of neurobehavioral performance. To normalize the data distribution, the mean RT was expressed as the log of the mean RT, and lapses were normalized.

Participants completed the Mayer-Salovey-Caruso Emotional Intelligence Test (MSCEIT), which is based on an ability model of emotional intelligence. The model’s two principal areas are experiential (CIEX) and strategic (CIES) areas and its four classes or branches of emotional abilities are perceiving emotions (CIEP), facilitating thought (CIEF), understanding emotions (CIEC), and managing emotions (CIEM). It has eight individual task scores: faces, pictures, facilitation, sensations, changes, blends, management, and relationships [12] . Raw test data are scored online according to the MSCEIT through https://www.teacorrige.com.

Personalized mitigation strategies were designed so that participants could increase their sleep and rest during their free time. General information on sleep hygiene was provided for the correct use of strategies and improvement of sleep habits. In addition, those who had a sleep disorder (apnea, insomnia, etc.) were independently evaluated and supported with consultations and sleep studies. The program included explanations and examples of relevant sleep factors (diet, exercise, substance use, light, noise, temperature, and bedding), which are personal and environmental determinants that can positively or negatively affect sleep. The goal of sleep hygiene was to avoid behaviors that interfere with a normal sleep pattern and to perform those that promote good sleep.

The intervention was provided in four sessions of two hours each for two weeks and started one week after finishing the tests in SD and SR conditions. In week one, at sessions one and two, a presentation of the sleep hygiene program was made to provide information to the participants for a correct understanding of sleep and recognition of the importance of sleep for daily activities. The topics that were given in the sessions were the following: What is sleep and why is it important for health? Why do we need sleep? What is normal sleep? What are the stages of sleep? Sleep and circadian rhythms: what they are and how they work. Sleep’s impact on the immune system. What influences the quality and length of sleep? Factors related to the quality of sleep among daytime workers. How much sleep do we need? What is sleep deprivation (negative impacts of sleep deprivation, the role of sleep deprivation in immune-related disease risk and outcomes)? What is shift worker syndrome? Sleep problems and mental disorders. Common sleep disorders. How does lack of sleep affect cognitive impairment? Sleep for cognitive enhancement. What can we do about it?

In week two, at sessions three and four, the sleep hygiene program was presented to provide information about good sleep habits (myths and facts). We implemented strategies for the correct use of free time and provided information for the correct use of electronic devices and stimulus control. The topics of the sessions were the following: What is sleep hygiene? The importance of sleep hygiene for shift workers. What are the signs of poor sleep hygiene? How do you practice good sleep hygiene? How to reset your sleep routine. How to build a better bedtime routine. Tips for having a good night’s sleep. How to build healthy daily habits. Ways to optimize your bedroom for better sleep. Healthy sleep hygiene habits for shift workers. Sleep myths debunked fascinating facts about sleep. How long should a nap be? All about naps. General recommendations (what you eat and drink can influence your sleep, your bedroom could be keeping you awake, planning meals around shifts, using light to your advantage, transitioning between shifts, the relationship between sleep and routine, napping and the body clock, shift work can affect your health and insomnia). Most used techniques for sleep hygiene and insomnia. Strategies to solve noise and light problems when sleeping during the day. Cognitive behavioral treatment for insomnia. Finally, participants were instructed on relaxation techniques.

Data were analyzed by a repeated-measures two-way analysis of variance (2W RM ANOVA), which considered the condition (SR vs. SD) and intervention (before vs. after sleep hygiene instruction) as the repeated measure. To analyze changes in the RT distribution for cognitive and perceptual processing speed, the 95th percentiles were assessed for the PVT. Data obtained with sleep tests and questionnaires (KSS, ESS, PSQI, AIS, SQS, SHQ,) were analyzed using 2W RM ANOVA with the condition (SR vs. SD) as a factor and the intervention (before vs. after sleep hygiene instruction) as the repeated measure. Significant ANOVA results were followed by Sidak multiple comparisons tests (correction for multiple comparisons). The significance of statistical differences was established at the 0.05 level. The data that support the findings of this study are available from the corresponding author upon reasonable request.

Pittsburgh sleep quality index showed a significant improvement in both SR and SD groups after intervention (F_(1,246) = 7421; p < 0.001) (Figure 1(a)). The Gray area in the graph indicates the values in which this index is in the normal range. No significant differences were observed between groups, indicating that quality of sleep is affected in both groups. PSQI global score > 6 indicates that subjects present severe difficulties and are considered poor sleepers (Buysse et al., 1989).

No significant differences were observed between groups, indicating that the quality of sleep is affected in both groups. Similarly, the Epworth Sleepiness Scale indicated that after the intervention, both SR and SD groups displayed normal somnolence values after the intervention (F_(1,246) = 7188; p < 0.001) (Figure 1(b)). The gray area inside the graph indicates the normal range of somnolence.

We did not find significant differences between the SR and SD groups. However, the Karolinska scale showed a significant increase after the intervention in both SR and SD groups (F_(1,246) = 225; p < 0.001), but no significant differences were detected when groups were compared (SR vs. SD, Figure 1(c)).

Sleep habits (SHQ) improved significantly after the intervention in both SR and SD groups (F_(1,246) = 11303; p < 0.001) (Figure 2(a)). Low scores on the global SHQ indicate that a participant has better sleep habits. Sleep quality measured by SQS revealed that this parameter was severely affected in SR and SD groups, and the sleep hygiene intervention significantly improved sleep quality (F_(1,246) = 4998; p < 0.001) (Figure 2(b)). Higher scores on the global SQS indicate that a participant has better sleep quality. Finally, the intervention improved

the participants’ scores on the AIS in both the SR and SR groups (Figure 2(c)). The severity criteria of the AIS include three levels of insomnia: absence of insomnia (0 - 5), mild insomnia (6 - 9), moderate insomnia (10 - 15), and severe insomnia (16 - 24) (Mayer and Salovey, 1997). The differences in SHQ, SQS, and AIS scores between groups did not reach statistical significance (SR vs. SD).

RT in the PVT was significantly slower in the SD group than in the SR group (F_(1,246) = 187.7; p < 0.001). After the intervention, the SD group improved significantly, but values remained far from the normal range (Figure 3(a)). Concerning lapses, the SD group showed significant differences from the SR group and had a modest but significant improvement after the intervention (F_(1,246) = 10.16; p = 0.002). This suggests that the test is more sensitive to total sleep deprivation (Figure 3(b)).

Before conducting the comparisons, a missing-value analysis was performed to confirm the validity of the participant’s responses. According to criteria from Mayer et al. [13] , the responses in this study were complete and valid. The sample had low scores in the emotional intelligence quotient of the MSCEIT, reflecting affected social cognition in both SR and SD groups before the intervention (F_(1,246) = 11; p < 0.001). Nevertheless, after the intervention, the EIQ of the participants significantly improved in both groups. In some cases, participants obtained scores described as proficient after the intervention (Figure 4).

Experiential (CIEX) and strategic areas (CIES) of the MSCEIT were subnormal before the sleep hygiene course and improved after the intervention (F_(1,246) = 686, p < 0.001, F_(1,246) = 927; p < 0.001, respectively) (Figure 5). Results were similar for emotional abilities (perceiving emotions, CIEP; facilitating thought, CIEF; understanding emotions, CIEC; and managing emotions, CIEM) (F_(1,246) =

1010; p < 0.001; F_(1,246) = 1149; p < 0.001; F_(1,246) = 527; p < 0.001; F_(1,246) = 1192; p < 0.001; respectively) (Figure 6). Table 1 shows the improvement of individual tasks scores (faces, pictures, facilitation, sensations, changes, blends, management, and relationships) after the intervention (F_(1,246) = 1199; p < 0.001, F_(1,246) = 1221; p < 0.001, F_(1,246) = 1149; p < 0.001, F_(1,246) = 1229; p < 0.001, F_(1,246) = 1060;

*p < 0.001.

p < 0.001, F_(1,246) = 1933; p < 0.001, F_(1,246) = 725; p < 0.001, F_(1,246) = 956; p < 0.001. Finally, collected data from the logs allowed us to identify that the intervention increased sleep duration in the SR group, while this parameter remained unaffected in the SD group. Bedtime decreased significantly after the intervention in both groups (F_(1,246) = 122.5; p < 0.001; Table 2).