Does chronotype predict cognitive performance? A systematic review of morningness, eveningness, and cognitive outcomes in healthy individuals

Circadian variations are one of the fundamental organising principles of human functioning, influencing physiological, behavioural and cognitive processes throughout the 24-hour day. Among these variations, chronotype reflects individual differences in preference for specific periods of greater functional efficiency. The way these differences relate to cognitive functioning has attracted growing scientific interest, although questions remain to be clarified regarding the nature and consistency of this association. This Systematic Literature Review aimed to analyse the relationship between chronotype and cognitive performance in different domains, in samples of healthy participants of all ages. The existing literature has produced inconsistent and heterogeneous results, making it difficult to draw clear conclusions about the possible existence of cognitive advantages associated with certain chronotypes. In this context, we sought to examine the effects of chronotype, the effects of the time of assessment (time-of-day), and the possible interaction between the two, distinguishing these contributions conceptually and methodologically. The review focused on the following cognitive domains: attention, executive functions, memory, processing speed, general intelligence/abilities, and language/verbal abilities. Studies involving experimental sleep manipulations (e.g., sleep deprivation, extension, or restriction) were excluded, as were samples exposed to chronic circadian disturbances, such as shift workers, in order to isolate, as much as possible, the influence of chronotype under natural functioning conditions. Overall, the results revealed high methodological heterogeneity among the included studies, both in terms of experimental designs and cognitive assessment instruments and chronotype classification methods. Regarding chronotype effects, no strong and generalisable evidence was identified to support the existence of stable cognitive advantages associated with morning or evening chronotypes. When present, the effects tended to be small in magnitude and domain-specific. Therefore, the available evidence does not support conceptualising chronotype as a stable cognitive trait with a generalised impact on performance. As for time-of-day effects, the results were also dependent on the cognitive domain and inconsistent in terms of their direction and magnitude. Although some studies have reported better performance in the afternoon or evening, particularly in memory tasks, these patterns were not consistently observed. Such variability suggests that the effects of the time of assessment cannot be interpreted in isolation and should be framed within the interaction between circadian and homeostatic processes. The effects of synchrony, i.e., the alignment between an individual's chronotype and the time of assessment, showed the most consistent pattern, particularly in attention and executive control tasks. In several studies, performance was superior when the assessment took place at times aligned with the participant's circadian preference. Still, these effects were not universal and proved sensitive to methodological and contextual factors, such as age, task type, and control of relevant variables (e.g., time since waking or subjective alertness level). Overall, the results do not support a conceptualisation of chronotype as a direct determinant of cognitive performance. Conversely, they point to a dynamic model in which performance results from the interaction between individual characteristics (such as chronotype), contextual factors (such as time-of-day) and underlying physiological mechanisms. This framework suggests that the variations observed are better understood as situational effects modulated by multiple variables, rather than as cognitive differences between chronotypes. This review allowed us to integrate scattered evidence by organising the results by cognitive domains and excluding studies with artificial sleep manipulations, promoting greater conceptual homogeneity. The findings have relevant methodological implications, highlighting the importance of considering the timing of assessment in research and clinical practice contexts, as well as in educational settings. Future research should favour more controlled experimental designs, diverse samples, and the integration of physiological measures to clarify the mechanisms underlying the relationship between chronotype and cognitive functioning.