It would be unethical to intentionally subject people to extreme psychological duress in the name of science. But ongoing military operations offer opportunities to see what happens to people exposed to stressful situations.
Researchers in the Netherlands found the brains of soldiers who go into combat show impairment in function and structure upon returning, but that these effects largely go away over time.
A new study published in the journal Proceedings of the National Academy of Sciences looked at 33 healthy Dutch soldiers deployed to Afghanistan for four months. It was the first military deployment for all of them, part of a NATO peacekeeping operation.
Researchers compared these participants to 26 soldiers who were never deployed.
The soldiers who were deployed experienced armed combat and exposure to enemy fire, as well as other common combat stressors. But this did not appear to aggravate stress symptoms; researchers did not find significant differences in post-traumatic stress disorder, anxiety and mood scores between the deployed and non-deployed groups.
But despite no apparent trends in psychological symptoms, the two groups of participants did display marked brain differences.
The combat group showed reduced functioning in the midbrain, as well as structural differences in that area. These soldiers who had gone to Afghanistan tended to perform worse on cognitive tests than those who were not deployed.
Those effects were seen less than two months after the soldiers returned from combat.
But a year and a half later, researchers found that the soldiers who had been deployed had, on average, returned to normal with respect to both brain structure and cognitive performance.
The combat group still showed some brain impairment: Imaging tests showed that there was less connectivity between particular brain regions among these soldiers than those who had not been deployed.
"Although there are some subtle changes, it doesn't really directly translate into impaired performance," said Guido van Wingen of the Brain Imaging Center in Amsterdam, who was the lead author of the study.
Although cognitive performance may suffer, a different brain function may be enhanced in soldiers with recent combat experience: vigilance. Previous research from van Wingen's group shows that the amygdala, a part of the brain important for detecting potential danger, has heightened activity in soldiers who have returned recently from combat. That effect also normalizes over time.
The sample size of the study began small, and got smaller over time. Nine people from the combat group and nine people from the non-deployed group did not complete the long-term follow-up.
Also, this study deals only with people from the Netherlands.
The research is too preliminary to make recommendations, van Wingen said.
But it makes sense that soldiers would benefit from time to recuperate in between deployments, so that the brain can re-adapt to a non-combat situation, he said.
"What the results collectively show is the brain is able to restore (itself) from the adverse effects of stress, if you give it at least enough time," van Wingen said.