In 2009 a regiment of Danish soldiers, the Guard Hussars, was deployed for a six-month tour in Afghanistan's arid Helmand province, a Taliban stronghold. They were stationed along with British soldiers—270 in all—at a forward operating base called Armadillo. Although none of the Guard Hussars were killed during the tour of duty, they nonetheless experienced many horrors of battle. A commander was seriously injured by a roadside bomb, and a night patrol ended in a firefight that killed and dismembered several Taliban combatants.

The Guard Hussars' war experience is graphically depicted in the award-winning documentary film Armadillo, which debuted in 2010. It follows the soldiers from their emotional farewells in Denmark through their months in combat and, finally, back to joyous homecomings and family reunions. The film is a study of the inner lives of young men as they experience the excitement and camaraderie, the tedium and—mostly—the terror and trauma of war.

Coincidentally, these same soldiers were also the subject of another, very different kind of study. At the same time that the film was being shot, the men were part of a larger group of Danish soldiers who were being scientifically observed and tested for emerging symptoms of post-traumatic stress disorder, or PTSD. A large team of Danish and American psychological scientists, led by Dorthe Berntsen of Aarhus University, wanted to do what had never been done before in this field of research: instead of studying soldiers who were already suffering from PTSD, they decided to assess young recruits before they were sent off to war, when they were still relatively unscathed, then to record them during the war experience, and finally to follow them back home and through several months of readjustment. In this way, the scientists hoped to see why some soldiers develop PTSD and others do not and how the symptoms of the disorder progress.

As in the film, the scientists first encountered the soldiers at home in Denmark, where they were readying for deployment to Afghanistan. Psychologists met with their 746 subjects five or six weeks before they were scheduled to be deployed and administered a battery of psychological tests. These included a PTSD inventory, a test for depression, and a questionnaire about traumatic life events, including childhood experiences of family violence, physical punishment and spousal abuse. Additional tests were administered during the soldiers' service, related to the direct experience of war: perceptions of war zone stress, actual life-threatening war experiences, battlefield wounds and the experience of killing an enemy combatant. The scientists continued to assess the soldiers when they were sent home, at a couple of weeks, at three months, and finally at least seven months after their return.

Cumulative Cause

The study revealed some surprising findings. The current and widely held view of PTSD is that its main cause is exposure to combat and other war atrocities—and that more trauma boosts the likelihood of experiencing the disorder. Moreover, experts believe that for those who develop PTSD, the typical pattern is for symptoms to emerge soon after a particularly traumatic experience and to persist over time. For unknown reasons, some soldiers appear resilient in the face of war trauma, never developing symptoms or else rapidly recovering.

These expectations did not match up with what the scientists found. Indeed, the consensus view of the disorder may be fundamentally wrong in at least two ways. As reported in a forthcoming issue of the journal Psychological Science, PTSD does not appear to be triggered by a traumatic battle experience, nor does there appear to be any typical trajectory for PTSD symptoms.

What Berntsen and her colleagues found instead is wide variation in both the causes and development of PTSD. The vast majority of Danish soldiers were resilient—recovering quickly from mild symptoms—or altogether impervious to psychological harm. The rest fell into distinct and unexpected patterns. The first group showed no symptoms before deployment or even during their tour of duty, but symptoms spiked after they returned home. For these soldiers, symptoms did not appear to follow any specific traumatic event, but by seven months after the men had returned, their stress symptoms had worsened to the point where they were diagnosed with PTSD. [For more on the potential cumulative causes of PTSD, see “Does Post-Traumatic Stress Disorder Require Trauma?” by Hal Arkowitz and Scott O. Lilienfeld; Scientific American Mind, May/June 2012.]

Problems at Home

Even more interesting were the remaining soldiers, about 13 percent of the subjects in the study, whose stress seemed to ease during deployment. That is, they had significant stress symptoms, such as major anxiety and frequent nightmares, after signing up for service but before deploying—symptoms that eased in the first months of war, only to spike again later, when they were safely at home. This pattern has never been observed before, and it seems puzzling: Why would shipping off to a dangerous and unfamiliar war zone ameliorate stress symptoms?

The scientists have a theory, and it has to do with the root causes of PTSD, previously undocumented. As compared with the resilient Danish soldiers, all those who developed PTSD were much more likely to have suffered emotional problems and traumatic events prior to deployment. In fact, the onset of PTSD was not predicted by traumatic war experiences but rather by childhood experiences of violence, especially punishment severe enough to cause bruises, cuts, burns and broken bones. PTSD sufferers were also more likely to have witnessed family violence and to have experienced physical attacks, stalking or death threats by a spouse. They also more often had past experiences that they could not, or would not, talk about.

These previously overlooked PTSD sufferers whose stress actually diminished in the war zone were also much less educated than the resilient soldiers. This disadvantage, combined with their pronounced mental health problems before going to war, suggests that they may in reality have been escaping a different war zone: the family. In other words, they showed improvement as soldiers only because they were in such poor psychological condition in civilian life. Army life—even combat—offered them more in the way of social support and life satisfaction than they had ever had at home. These soldiers were probably benefiting emotionally from being valued as individuals for the first time ever and from their first authentic camaraderie—mental health benefits that diminished after they once again returned to civilian life.