Early adverse experiences such as abuse or neglect can influence brain development and consequently bring forth a predisposition toward mental and behavioral disorders. Many authors suggest that long-term changes in the functionality of the HPA axis might be involved in mediating this relationship. The direction of change and its consequences have not been clarified though: Do early adverse experiences yield a stable glucocorticoid hyperfunction or a long-term glucocorticoid hypofunction, and how is this change of functionality associated with mental or behavioral disorders? This review summarizes correlative findings and illustrates inconsistencies of current research literature. It focuses on the specific neurochemical milieu accompanying early adverse experiences and discusses possible interactions of the glucocorticoid system with oxytocin and components of the serotonergic system. On the basis of this physiological view, a novel two-pathway model is presented, according to which specific early experiences are associated with characteristic early changes in the functionality of these systems and result in a predisposition to distinct mental and behavioral disorders. (C) 2013 Elsevier Ltd. All rights reserved.