Although there is an abundance of evidence linking the function of the hypothalamic-pituitary-adrenal (HPA) axis to adverse early-life experiences, the precise nature of the association remains unclear. Some evidence suggests early-life adversity leads to cortisol hyper-reactivity, while other evidence suggests adversity leads to cortisol hypo-reactivity. Here, we distinguish between trauma and adversity, and use p-curves to interrogate the conflicting literature. In Study 1, trauma was operationalized according to DSM-5 criteria; the p-curve analysis included 68 articles and revealed that the literature reporting associations between trauma and blunted cortisol reactivity contains evidential value. Study 2 examined the relationship between adversity and cortisol reactivity. Thirty articles were included in the analysis, and p-curve demonstrated that adversity is related to heightened cortisol reactivity. These results support an inverted U-shaped function relating severity of adversity and cortisol reactivity, and underscore the importance of distinguishing between “trauma” and “adversity”.
Maternal behavior and the neonatal HPA axis in the Wistar Audiogenic Rat (WAR) strain: Early-life implications for a genetic animal model in epilepsy
