Severe stress and the development of the amygdala in youth: A theory and its statistical implications

An empirical understanding of normal developmental variation in the amygdala is emerging. However, studies examining volumetric differences in the amygdala among patient populations, particularly individuals with posttraumatic stress disorder (PTSD), have not produced a consistent pattern of findings. One reason for this may be the failure to effectively address age variation in study design and data analysis. Findings on age related variation in human amygdala volumes as well as the role of stress on amygdala development are reviewed. A theory is developed which posits that normal developmental variation in amygdala volumes may be altered under conditions of severe stress. Specifically, that stress may delay, accelerate, or prolong typical growth patterns. The theory highlights identifying the factors related to either delayed, accelerated, or a prolonged period of growth. The theory also points to systematically testing age as an interactive (moderator) variable in pediatric and psychiatric neuroimaging research. This is because the theory implies that disorder status/exposure to severe stress may influence the relationship between age and amygdala volumes.