Most traumatized people don’t develop the vivid flashbacks and relentless thoughts of the incident that are hallmarks of posttraumatic stress disorder (PTSD). But researchers know little about how trauma changes the brain—and whether some people's brains are more susceptible to PTSD to begin with. Now, neuroscientists in Japan who are working with survivors of the 2011 earthquake and tsunami have identified one brain region whose size seems to predict susceptibility to PTSD symptoms and another brain region that shrank slightly in people with the highest number of symptoms.
Previous imaging studies have found that in PTSD sufferers, parts of the brain involved in memory, fear, and mood control are smaller compared with the brains of people who come through their trauma more-or-less unscathed. But it has been difficult to tell whether these differences were always there or appeared after the trauma. For cognitive neuroscientist Atsushi Sekiguchi, who was studying the neural underpinnings of stress at Tohoku University in Sendai, the earthquake was a rare opportunity to tease apart cause and effect. "We had a lot of brain imaging data for university students before the earthquake," he says. The coastal region of Tohoku was one of the hardest hit, with tsunami waves as high as 40 meters sending floods up to 10 kilometers inland. In Sendai, the largest city, waves flooded the streets and the airport, sending cars and even planes swirling through the city while black smoke billowed from the burning Nippon Oil refinery.
To investigate the effects of the disaster on residents, the researchers recruited 42 of their earlier subjects for magnetic resonance imaging scans 3 to 4 months after the quake. The subjects also rated the frequency and intensity of their PTSD symptoms, such as intrusive memories, avoiding people or places associated with the trauma, heightened startle response, and feelings of reexperiencing the event.
None of the subjects had full-blown PTSD at the time of the test; the highest score on the symptom scale, 39, was just below the cutoff for a PTSD diagnosis. But the MRI scans showed that even 3 months after the trauma, some of the students' brains were already changing in a way that tallied with PTSD symptoms.
Even before the earthquake, a brain region called the pregenual anterior cingulate cortex  was smaller in subjects with higher scores than in subjects with few or no symptoms. Previous research has revealed that this region, which plays a key role in monitoring and controlling emotions, is smaller in PTSD sufferers. According to Sekiguchi, the new finding suggests that the reduced size is a “vulnerability factor” for the disorder. Another area, called the orbitofrontal cortex, seemed to be affected by the trauma itself. Students who showed a decrease in volume in this area, compared with their earlier scans, had higher PTSD scores, the team reports online today in Molecular Psychiatry. Because this region is involved in eliminating fear-related memories, the fact that it proved to be smaller in subjects with more intense symptoms makes sense, Sekiguchi explains.
Psychiatrist Roger Pitman of Harvard Medical School in Boston calls the findings tantalizing. "The study shows how sensitive the brain is even at comparatively low levels of symptoms," he says. The ability to identify the brain areas affected by the condition—as well as those that set the stage for it—adds to our knowledge but doesn’t have immediate implications for treatment, Pitman believes. He adds that future strategies might include scanning people in advance who are expected to be involved in trauma—soldiers, for instance—to spot those at risk for the disorder. Researchers might also develop neuroprotective drugs for specific brain areas. "But we aren’t there yet," Pitm an says.