Background: The cortisol awakening response (CAR) is the glucocorticoid peak that occurs within the first hour of awakening. Existing evidence supports a relationship between the magnitude of the CAR and the neural mechanisms that underlie learning and memory, however functional behavioural evidence is lacking. The aim of this study, therefore, was to determine whether the CAR magnitude was associated with same-day cognitive performance.
Methods: Saliva was collected at 0, 15, 30 and 45 minutes after awakening in 31 healthy adults (18-37 years) on 2 consecutive test days. Participants completed the perceived stress scale and provided spot salivary samples at testing. Cognitive assessments included tests of memory, attention, reaction time and executive function using the CANTAB™ test battery.
Results: The magnitude of the CAR was not significantly different between the two days of testing, but was highly correlated (r=0.61, p=0.001). A larger CAR was associated with improved cognitive performance assessed later the same day. A larger CAR was associated with significantly fewer errors in working memory (r=-0.416, p=0.028), and improved performance on tasks of attention (r=0.513, p=0.005) and executive function (r=0.425, p=0.025). Reaction time, cognitive switching and pattern recognition were not associated with CAR magnitude. Perceived stress and spot cortisol samples were not associated with changes in cognitive performance.
Conclusion: These results suggest that the CAR magnitude influences cognitive performance, particularly executive function, throughout the day. These effects do not appear to be driven by changes in perceived stress or circulating cortisol at the time of testing. Whether this increase in cognitive performance is a direct or indirect effect of the CAR is currently unknown.