Animal research has shown that a host of early life stressors such as maternal separation are associated with disrupted diurnal HPA axis activity and increased HPA axis and autonomic excitability (3). This evidence is buttressed by limited human research showing that day care (a putative proxy for maternal separation) is associated with similar, albeit less pronounced, differences (38). Moreover, animal models have linked early stressors with increased dendritic branching, the expression of corticotropin-releasing hormone, and neuronal excitability in the amygdala, which are correlated with HPA axis activity and anxiety (3). Consistent with these findings, elevated endogenous cortisol is associated with potentiated amygdala reactivity to emotional facial expressions like those used in the present study (9, 10).
