Conditioning of the Cortisol Awakening Response

The hormone cortisol is involved in bodily functions varying from stress to metabolism and the circadian rhythm, and is therefore a relevant clinical target. Cortisol effects can be manipulated through medication, and theoretically these effects are subject to conditioning. However, existing studies show variable results of cortisol conditioning. We explored a novel paradigm, based on studies showing the circadian rhythm can be conditioned non-pharmacologically in animals and that learning is possible during sleep. The target of the conditioning procedure was the cortisol awakening response, part of naturally-occurring morning rise in cortisol. Participants (40 males) followed a two-week protocol, with baseline measures taking place in the first week and conditioning and evocation in the second. A scent was used as the conditioned stimulus, presented in the 30 minutes before awakening for three mornings. In the final night of the study, participants awoke 4 hours earlier than normal, after exposure to the conditioned stimulus (experimental group) or a different scent (control group) in the 30 minutes before awakening. Results showed no differences between the control and experimental groups in the 45 minutes after awakening in the final night on cortisol levels or self-report outcomes (positive and negative affect, vitality, fatigue). Heart rate variability also did not show differences in the period from 30 minutes before to 45 minutes after awakening. Therefore, it seems that our novel design did not lead to results that support conditioning of the cortisol awakening response. Future studies might instead focus on replications of previous effective designs.