Amygdala and hippocampal subregions mediate outcomes following trauma during typical development: Evidence from high-resolution structural MRI.

The vast majority of individuals experience trauma within their lifetime. Yet, most people do not go on to develop clinical levels of psychopathology. Recently, studies have highlighted the potential protective effects of having larger amygdala and hippocampal volumes, such that larger volumes may promote adaptive functioning following trauma. However, research has not yet elucidated whether certain subregions of these stress-sensitive structures have specific protective effects. Herein, we examined the mediating effects of amygdala and hippocampal subregions on the relationship between traumatic exposure and concurrent or longitudinal changes in psychiatric symptom levels in typically developing youth (9-15 years of age). Using high-resolution T-and T-weighted structural MRI scans, we found that the volume of the right basolateral complex of the amygdala mediated associations between trauma exposure and internalizing symptoms. Specifically, greater levels of childhood trauma related to larger volumes, and larger volumes were associated with fewer internalizing symptoms. The volume of the right CA4/dentate gyrus (DG) of the hippocampus yielded similar mediation results, such that greater trauma was related to larger volumes, which in turn were associated with decreases in internalizing symptoms across time. These findings provide initial support for potentially protective effects of larger right amygdala and hippocampal subregion volumes against internalizing symptomology concurrently and longitudinally during adolescence.