Effects of stress on neural processing of combat-related stimuli in deployed soldiers: an fMRI study

Severe trauma exposure may lead to symptoms of both posttraumatic stress disorder and depression. Neuroanatomical theories suggest that both disorders may share imbalances in fronto-limbic circuits. Longitudinal studies are necessary to better understand the impact of a stressful life situation on potential long-term fronto-limbic imbalances. Here we investigated soldiers neural processing of combat-related stimuli versus negative affective stimuli before and after the deployment in different war zones. In the final analysis we included 104 deployed soldiers (combat group) and 36 soldiers that were not deployed (control group). Behaviorally, we found a significant group by time interaction regarding depression symptom scores with an increase in the combat group. Depressive symptoms were subclinical. On the neural level, neither the whole brain analysis nor the region of interest (ROI) analyses including frontal and limbic ROIs revealed any significant results in the group by time interaction. However, extracted ROI values of the group by time interaction of amygdala and hippocampus were positively associated with the change in depression symptom scores in the combat group, but not in the control group. These results highlight the role of depression in individuals that experience stressful life situations. Future studies may need to investigate the role of depressive symptoms after trauma exposure with different tasks that may be particularly sensitive to changes due to depressive symptoms.