Assessing HPA feedback sensitivity without pharmacological interventions? On the distribution of cortisol concentrations in phases of varying secretory activity

Abstract

TheCortisolAwakeningResponse (CAR)has risen toprominence in recent years as a predictor of both physical and psychological health status. However, the role of the CAR within the healthy circadian rhythmremains speculative; previously described asproviding an unspecified ‘boost’ for the day ahead. Recent studies have demonstrated a positive relationship between the CAR and Executive Function (EF) in samples of older adults and in cases of abnormal cognitive function. The aim of the present research was to explore the relationship between the CAR and an attention switching index of EF in a healthy young adult. It was hypothesised that a larger CAR would predict better attention switching task (AST) performance on the same morning. This was assessed using a researcher-participant case-study of a healthy 24-year old male (RL) across 50 days. Cortisol sampling (nested within days) was at 15-min intervals across the post-awakening hour. AST performance was assessed at 45-min post-awakening. Mixed regression modelling of variation in cortisol concentrations confirmed that the greater the increase in cortisol concentrations from 0–30min post-awakening (CAR) the betterwas subsequent AST performance at 45min post-awakening (t=2.29, p= .024). This effect was independent of awakening time and other potential confounds. These findings suggest that state variation in the CAR predicts state variation in performance on this index of EF post-CAR, and if replicated in further samples of healthy adults, may indicate a mechanism by which the CARmodulates cognitive performance for the day ahead.