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Sleepiness is a major public health problem associated with motor vehicle crashes, occupational accidents, decreased productivity, and interpersonal problems. It can be influenced by many factors, including the individual's circadian rhythm. The objective of this study is to assess the correlation between the morningness/eveningness dimension and daytime sleepiness in medical school students. This is a cross-sectional study; 310 subjects (123 women and 187 men, M age 20.5 ± 1.9 yr.) completed a questionnaire on use of drugs, diagnostic diseases, sleeping habits, the Morningness/Eveningness Questionnaire and the Epworth Sleepiness Scale. The only variable related to daytime sleepiness was the morningness/eveningness dimension ( r = –.18, p = .002). Questions with higher coefficients of discrimination between the morning and the evening chronotype were “Lying down to rest in the afternoon when circumstances permit” (.61), “Sitting and reading” (.53), and “As a passenger in a car for an hour without a break” (.53). The implications of the findings are discussed.

Memory consists of several phases or processes that can be influenced by many factors, including the individual's circadian rhythm and the time of day at which tests are performed. The present objective was to evaluate the performance on memory tests of different chronotypes during the morning and the evening shifts. Subjects (21 men and 26 women, between the ages of 20 and 35 yr.) were evaluated for memory and metamemory differences in the morning and in the afternoon, using a battery of neuropsychological tests composed of the Word List with Emotional Content, Visual Memory, Scale–Semantic Memory, Digit Span, Word-Pairs Associated, Verbal Fluency Test, and Metamemory questionnaire. In the evening shift, there was a statistical difference among chronotypes on the Word List with Neutral Content and on the Verbal Fluency Test. In the morning, there were no statistically significant differences; however, the morning-type subjects had higher scores on the metamemory tests ( p < .01), while the evening-type subjects had higher scores in the afternoon ( p < .01). In spite of their perception, on Word-Pairs Associated and Word List with Emotional Content, the subjects, independently of their chronotype, showed better performance by the evening than by the morning shift. These results highlight the importance of controlling the shift of day and chronotype in studies with the objective of exploration of human performance.