Who is most at risk for PTSD after trauma? Lessons from the Boston Marathon bombings

PTSD risk in adolescents after Boston Marathon bombingsDaniel Busso, MSc, is a doctoral student at the Harvard Graduate School of Education and a researcher in the Sheridan Laboratory at Boston Children’s Hospital.

More than 60 percent of teenagers have experienced a traumatic event in their lifetime, but only a minority will develop post-traumatic stress disorder (PTSD). For both researchers and clinicians, this raises an important question: Why are some youth at greater risk for mental health problems after trauma? As our lab reports in two recent studies, conducted after the 2013 Boston Marathon bombings, the answer may lie in our neurobiology.

PTSD, which includes intrusive memories, increased anxiety and difficulty concentrating or sleeping, has been linked to a variety of psychosocial and biological risk factors, such as prior experiences of trauma or a history of mental health problems. Other studies suggest that disruptions to the body’s stress response system, or in patterns of brain activity when responding to threat, may predispose people to the disorder.

However, a common problem in this research is that biological and mental health data are collected only once, usually long after the traumatic event itself, making it hard to tell whether what we found are risk factors for PTSD or the results of it. We found ourselves in a unique place to disentangle these associations.

Daniel Busso of Margaret Sheridan lab
About one year before the Marathon bombings, as part of another study of the effects of early childhood adversity, we had measured adolescents’ responses to negative and stressful events. In the MRI scanner, we measured their brain response to distressing images such as those depicting war, death or violence. In an overlapping group of adolescents, we also looked at activation of the autonomic nervous system (involved in the “fight or flight” response) while they experienced a social stressor such as giving a speech.

After the terrorist attack, we were able to follow up with study participants who were in Boston at the time of the bombings—asking whether their reactions to our laboratory stressors predicted the likelihood they would display PTSD symptoms more than a year later. In one paper, we show that activity in the amygdala in response to distressing images did indeed predict the severity of PTSD symptoms after the bombings. (The amygdala is a primitive part of the brain often associated with fear learning and threat perception.) In another paper, we showed that activation of the sympathetic nervous system (a branch of the autonomic nervous system) in response to giving a speech similarly predicted the likelihood of PTSD symptoms a year later.

Together, these studies suggest that activation of the fight or flight response and the amygdala are neurobiological markers of risk for PTSD that precede the experience of the trauma itself.

The body’s stress response to experimental stimuli was not the only thing to predict increased risk for PTSD symptoms. We also found that prior experience of violence, such as getting mugged or seeing someone else get mugged, was associated with an increased risk for PTSD symptoms after the Marathon attacks. This suggests that people can become physiologically attuned or “sensitized” to threat in their environments, making them more vulnerable to future stressors. Similarly, adolescents with prior histories of anxiety and depression were more likely to experience post-traumatic stress.

Finally, we observed that the more hours adolescents spent watching media coverage of the Marathon bombings, the more likely they were to experience symptoms such as intrusive memories, increased anxiety and difficulty concentrating or sleeping. This was true even in those who didn’t show an enhanced fight or flight response during our original studies.

These studies add to our growing understanding of why and how PTSD may emerge after exposure to traumatic events, and could help identify adolescents who are most vulnerable and in need of support. It is clear that clinicians and parents should work to protect children and adolescents who have been exposed to frightening and life-threatening events. This includes efforts to limit media exposure around the event and providing mental health supports. These steps are most important for the most vulnerable adolescents—those with a history of mental health problems or past violence exposure.