Thanks to an in-progress study of Boston-area teenagers, a group of researchers had the unexpected opportunity to study how emotional responses predicted PTSD symptoms in the wake of the Boston Marathon bombings. The study \u2014 a collaboration between the University of Washington, Boston Children\u2019s Hospital and Harvard Medical School \u2014 was in the process of examining the impact of childhood trauma in a large group of Boston-area adolescents. The researchers had already gathered baseline data from these young people in the form of brain scans. Then, on April 15, 2013, two pressure cooker bombs exploded during the Boston Marathon, killing three people and injuring more than 260 others. This devastating event gave the research team the opportunity to assess the appearance of symptoms related to post-traumatic stress disorder (PTSD) in these same teenagers. Online Surveys Assess PTSD Symptoms The Boston bombings were a frightening and emotionally stressful experience for most people in the Boston area, even those who were not in the vicinity of the attacks when they occurred. The proximity of the attacks and the tense nature of the citywide manhunt caused many people serious mental distress. One month after the terrorist attack, the researchers invited the teenage participants in their study to complete an online survey. The survey was designed to detect any symptoms of PTSD that may have arisen as a result of the bombings. The researchers then compared their existing brain scan data for each participant to see if they could discover patterns of brain activity that predicted the presence of PTSD symptoms. They published the results of this study in July 2014 in the journal Depression and Anxiety. Some Show Strong Amygdala Reaction to Negative Stimuli During the original phase of the study, the Boston-area students were given functional magnetic resonance imaging (fMRI) scans while experiencing neutral or negative emotional stimuli. The researchers showed the subjects neutral images of things like everyday inanimate objects, as well as negative images of people displaying sadness, hostility or violence. Some of the teenagers displayed increased blood flow to the amygdala and the hippocampus while viewing these images. The amygdala is a primitive part of the brain located deep in the temporal lobe. It is part of the limbic system that handles emotional and instinctive reactions to input, including the development of fear. Outer, more recently developed areas of the brain that are capable of higher-order functions usually moderate the strong emotional responses of the amygdala and the limbic system. When the researchers compared their brain-imaging results to their online survey results, they discovered that the heightened amygdala reaction in some of the subjects predicted those who reported symptoms of PTSD after the Boston terrorist attacks. In order to eliminate as many variables as possible from their study results, the researchers asked a variety of questions to determine the degree to which each subject was affected by the bombings. They were asked whether they were present at the Boston Marathon finishing line, whether they were in a neighborhood or school under lockdown during the manhunt, whether they followed media coverage of the attacks and whether they had personal connections to any of the victims. Even when accounting for the varied experiences of the participants, heightened amygdala activity remained a strong predictor of PTSD symptoms. Tragedy Provides an Unprecedented Opportunity Previous studies have looked at the brain activity of patients with PTSD and found heightened activation of the amygdala. However, researchers had no way of knowing whether the events leading to the development of PTSD caused this heightened activity, or whether it was already present in the brains of these individuals. The team of scientists who conducted this study could not have foreseen that a terrorist attack would create a new application for their data. However, they were quick to recognize the opportunity to increase our understanding of how and why PTSD affects certain people.