The effect of chronotype and time of assessment on cognitive performance

Standard cognitive measures are often applied at various times of the day to assess cognitive deficits in patients with neuropsychiatric and neurodegenerative disorders, irrespective of their chronotype. In this study, we aimed to determine whether the subjectively nonpreferred time of an assessment might be a crucial factor in persons with extreme chronotypes. We compared morning (08:00) and evening (20:00) cognitive performance in extreme morning, extreme evening, and intermediate chronotypes determined by the Morningness-Eveningness Questionnaire, supported by actigraphy and peripheral temperature measurement. The assessment sessions were performed in pseudorandom order over two consecutive weekend days. We administered the commonly used test battery for neurocognitive assessment comprised of tasks aimed mainly at attention, processing speed, working memory, and declarative memory. The time of assessment influenced the declarative memory measures, whereas the chronotype-specific differences occurred only in the Stroop colour-naming subtest aimed at processing speed. The observed effects should be considered in routine clinical practice because they might cause misrepresentation of the results obtained during improperly timed cognitive assessment. Our results also point towards similarity of doves and owls in contrast to larks in cognitive performance, suggesting that early morning assessments should also be considered in cases of intermediate chronotypes.