Chronotype and intellectual performance in the morning: the role of alertness, cortisol, and task stress

Abstract

ABSTRACT Existing studies report contradictory findings regarding the association between chronotype and intelligence, particularly for morning testing. This study aimed to shed more light on the association by employing a multivariate approach and considering variables that can potentially provide more insight into the nature of the relationship. A sample of university students (N = 123) completed Composite Scale of Morningness followed by an 8-day sleep diary and actigraphy recording. At the last morning of the recording, participants sampled their saliva five times for cortisol assays and took part in a testing session (8:30–10:15) consisting of completion of five intelligence tests, Dundee Stress State Questionnaire, and sleepiness-alertness scales at the beginning and at the end of the session. Results showed no association between general intelligence and chronotype, but eveningness was related to better word comprehension. The strongest predictor of general intelligence was task engagement, followed by task-related distress. Eveningness was related to lower absolute cortisol levels during 45 minutes since awakening, unrelated to cortisol awakening response, and linked to higher cortisol and lower subjective alertness during the testing session. It is concluded that eventual effects of chronotype on intellectual performance are very weak and can be outweighed by task engagement.