Researchers analyzed 193 patients from the Vietnam Head Injury Study with penetrating traumatic brain injury to determine if the location of shrapnel damage to their brains influenced risk of developing PTSD. Damage to areas connected to the amygdala was associated with a lower chance of developing PTSD. The study suggests lesions that could protect against PTSD map to a specific brain circuit connected to the amygdala and the medial prefrontal cortex.