The cortisol awakening response: more than a measure of HPA axis function.
In most healthy people morning awakening is associated with a burst of cortisol secretion: the cortisol awakening response (CAR). It is argued that the CAR is subject to a range physiological regulatory influences that facilitate this rapid increase in cortisol secretion. Evidence is presented for reduced adrenal sensitivity to rising levels of ACTH in the pre-awakening period, mediated by an extra-pituitary pathway to the adrenal from the suprachiasmatic nucleus (SCN). A role for the hippocampus in this pre-awakening regulation of cortisol secretion is considered. Attainment of consciousness is associated with 'flip-flop' switching of regional brain activation, which, it is argued, initiates a combination of processes: (1) activation of the hypothalamic pituitary adrenal (HPA) axis; (2) release of pre-awakening reduced adrenal sensitivity to ACTH; (3) increased post-awakening adrenal sensitivity to ACTH in response to light, mediated by a SCN extra-pituitary pathway. An association between the CAR and the ending of sleep inertia is discussed.
Clow
Angela
A
Psychophysiology and Stress Research Group, Department of Psychology, University of Westminster, London, UK. clowa@wmin.ac.uk
Hucklebridge
Frank
F
Stalder
Tobias
T
Evans
Phil
P
Thorn
Lisa
L
D000818:Animals; D006801:Humans; D006854:Hydrocortisone / Q000502:physiology*; D007030:Hypothalamo-Hypophyseal System / Q000502:physiology*; D010913:Pituitary-Adrenal System / Q000502:physiology*; D012890:Sleep / Q000502:physiology; D014851:Wakefulness / Q000502:physiology*
D006854:Hydrocortisone