Concussions can have a lasting impact on the structure of the brain months after the initial injury, according to new research. These changes can linger long after clinical symptoms — such as dizziness and impaired balance — have disappeared. The study could help scientist better understand the long term effects of concussion on injured athletes. However, the link between these structural changes in the brain and any long-term effect on the individual’s behavior and cognition are still not known.

Scientists already knew that sport-related concussions can cause structural wear and tear on the brain. But this study, which is being presented as an abstract at the American Academy of Neurology’s Sports Concussion Conference tomorrow, gives a clearer time frame. It shows that changes to individuals’ white matter — bundles of nerve cells that connect different regions of the brain — can persist for at least six months.

"In other words, athletes may still experience long-term brain changes even after they feel they have recovered from the injury," study author Melissa Lancaster said in a statement. "These findings have important implications for managing concussions and determining recovery in athletes who have experienced a sports-related concussion."

To gauge these long-term effects on the brain, scientists from the Medical College of Wisconsin tracked 17 high school and college football players after they’d suffered a blow to the head. The athletes (with a mean age of 17) were tested for various clinical symptoms, including loss of balance, memory, and cognition. The researchers also scanned the patients’ brains using advanced neuroimaging techniques 24 hours, eight days, and six months after the injury.

These tests, which include diffusion tensor imaging (DTI) and diffusion kurtosis tensor imaging (DKTI), are more expensive than regular MRIs and less commonly applied to concussion patients. They detect the movement of water molecules in white matter to determine the health of the nerves. In normal white matter, water diffuses easily along the fiber, but damage to the brain reduces this flow.

The researchers, under principal investigator Michael McCrea, found that the athletes who had suffered concussion had reduced water movement in their white matter 24 hours, eight days, and even six months after their initial injury. Those individuals who had shown more extreme clinical symptoms at the time of their concussion were also more likely to show alterations to their brain’s white matter. Most notably, all the individuals who suffered a concussion stopped reporting any clinical symptoms at the six-month mark. However, their brains still showed structural damage.

The findings are "very important," says James Couch, a professor of neurology at the University of Oklahoma, who did not take part in the study. But more research is needed, he told The Verge. The adaptability of the brain makes it extremely difficult to link structural changes to behavioral ones — and that’s ultimately what scientists want to figure out. "To move this forward, we need more subjects and a follow-up of not just two years or five years but 15, 20, 30, or 40 years," says Couch. "This is only 17 patients and 18 controls: we need to keep going to see what the correlation actually is."

Couch adds that there’s also growing evidence for genetic factors playing a large role in the damage concussion can do, and environmental influences too. He says that the application of advanced brain scans like those used in the study will be the key tool to finding out more, but that only long-term studies will give us solid data. "Say you’ve got some guy that plays high school football and takes a lot of hits to his head," he says. "What happens to him, not when he’s 18, but when he’s 48? Is this a guy that might have become the CEO of a company or is he stuck working in the mail room? We need to follow that."