The cortisol awakening response after sleep deprivation: Is the cortisol awakening response a "response" to awakening or a circadian process?

This study tested whether the cortisol awakening response is dependent on the transition from sleep to awakening, or alternatively, a circadian-driven process that is independent of awakening. A total of 40 participants were randomly assigned to either a total sleep deprivation or a sleep condition. Salivary cortisol was also assessed. Participants in the sleep condition demonstrated a traditional cortisol awakening response, whereas participants in the total sleep deprivation condition showed no increases in morning cortisol. These results are consistent with the notion that if circadian-driven processes are related to the cortisol awakening response, they may only be activated when awakening occurs or is anticipated.