Even after a severe concussion, a brain can look normal and healthy on a traditional brain scan. But now a study co-authored by a Brigham Young University psychology professor, using a new kind of MRI technique, reveals brain changes that are subtle but significant.

The study, which appears in Tuesday's issue of the journal "Neurology," helps prove that concussions result in biological changes — and that long-lasting symptoms such as aggression and sleep problems are not just "psychological."

"We're just beginning to understand what is happening with concussions," said BYU psychology professor Erin Bigler, who conducted the study with colleagues at Baylor College of Medicine, including one of Bigler's former students, Elisabeth Wilde. "We're hoping this will lead to better and better ways to treat them."

"Even a seemingly mild 'ding' or a bump on the head can be serious," cautions the federal Centers for Disease Control on its Web site. The CDC describes a concussion as "caused by a bump, blow or jolt to either the head or the body that causes the brain to move rapidly inside the skull."

Concussions are the No. 1 neurological injury to soldiers in Iraq and Afghanistan, and the CDC estimates that there are between 1.6 and 3.8 million sports and recreation-related concussions a year in the United States. The number is an obvious guess, partly because many children and teenagers who suffer mild head injuries are never seen by a doctor.

Bigler himself experienced a concussion in the mid-1960s while playing football. He was knocked unconscious and spent a night in the hospital. And then, as often happened in those days, he was back at football practice on Monday and played in a game the next Friday. Nowadays, he said, doctors realize that an injury like his should sideline a player for a couple of weeks.

Most concussions, said Bigler, are mild, with no loss of consciousness. And most sufferers "recover and recover well," he said. But for others the effects linger. They can suffer problems with short-term memory, concentration and planning; fatigue, sleep disorders, headaches, vertigo, anxiety, depression, mood changes, apathy and aggressiveness with little or no provocation.

Bigler and Wilde's study used a new type of brain imaging technique — diffusion tensor imaging (DTI) — that enabled them to look at what he calls "the microenvironment" of the brain, an analysis not provided by traditional MRIs.