In humans, at a molecular level, PTSD is strongly linked to the hyperactive HPA axis, and specifically to a high glucocorticoid-receptor (GR) sensitivity due to a low secretion of salivary and blood glucocorticoids (cortisol in humans and corticosterone in mice) during late night until early morning [14]–[19]. This evidence concerns the gene NR3C1 and post-traumatic stress disorder.