The role of traumatic brain injury — blamed for symptoms plaguing thousands of soldiers returning from Iraq — might be overstated, contends a military study that offers hope for successful treatment.

In many cases, post-traumatic stress and depression may be driving the symptoms, doctors reported Wednesday. And that’s good news because those are treatable.

Returning soldiers have struggled with memory loss, irritability, trouble sleeping and other problems. Many have suffered mild blast-related concussions, but there is no easy way to separate which symptoms are caused by physical damage and which are from mental problems caused by the traumatic stress of war.

The new study, based on a survey of 2,525 soldiers after they returned from deployment to Iraq, found that brain injury made traumatic stress more likely.

“We found that the symptoms and health concerns that we expected to be due to the concussion actually proved to be more strongly related to PTSD,” or post-traumatic stress disorder, and depression, said Dr. Charles Hoge, a colonel and psychiatry chief at Walter Reed Army Institute of Research who led the study. “There isn’t a clear delineation between a psychological and a physical problem.”

Other doctors were optimistic about treatment efforts.

“It gives us hope, because we’ve got good treatments for PTSD,” said Barbara Rothbaum, a psychologist who heads a trauma recovery program at Emory University in Atlanta.

Hoge reported on the survey Wednesday at a military health conference in Washington. Results also were published in today’s New England Journal of Medicine.

The vast majority of brain injuries, or concussions, are mild, but the military previously estimated that one-fifth cause symptoms lasting a year or more.

Fifteen percent of soldiers studied reported a mild brain injury — having been knocked unconscious or left confused or “seeing stars” after a blast. They were more likely than other soldiers to report health problems, missing work and symptoms such as trouble concentrating.

The worst symptoms were in soldiers who lost consciousness. About 44 percent of them met the criteria for post-traumatic stress, compared with 16 percent of soldiers with nonhead injuries, and only 9 percent of those with no injuries.

The military recently started screening all returning troops for concussions.