Concussions can have a lasting impact on the brain, as studies of the cognitive health of aging NFL players have shown. The brain changes that a concussion causes can last long after the symptoms have faded, a recent Canadian study finds.

The study followed 187 college athletes for over a year. Some had had concussions and some had not. Brain scans were used to track biomarkers indicating brain injury in participants' brains.

Twenty-five of the athletes in the study had a concussion during regular season play. The concussed athletes, who competed in the basketball, football, hockey, lacrosse, rugby, soccer and volleyball, were compared to 27 athletes without concussion and matched for factors such as participants' sex and sport.

The brain scans of concussed athletes still showed signs of brain injury when they were allowed to return to play and up to one year later.

All the athletes in the study completed pre-season testing for factors such as balance, thinking and memory. They also had a magnetic resonance imaging (MRI) brain scan before their seasons began.

The participating athletes who later had concussions had additional brain scans an average of five days after their concussions. They also had further scans when cleared to return to play, and again one to three months after returning to play, and finally one year after returning to play.

Those athletes in the study without concussion had brain scans during their next pre-season assessment.

Researchers compared the brain scans of the concussed to their own pre-injury brain scans, and these brain changes were further compared to those of healthy athletes.

Researchers found that the brain scans of concussed athletes still showed signs of brain injury when they were allowed to return to play and up to one year later. When they traced the way water molecules moved in the white matter of the brain, the researchers also noted that the brains of concussed athletes still showed possible signs of brain injury long after they had seemingly recovered, compared to their pre-injury brain scans.

The athletes who had suffered concussions had an average decrease in blood flow of nine milliliters (mL) per 100 grams of blood per minute compared to healthy athletes. At one year, they had an average decrease of 11 mL per 100 grams of blood per minute. These blood flow changes were also greater than those seen in uninjured athletes.

The brains of concussed athletes still showed possible signs of brain injury long after they had seemingly recovered.

“Our results provide strong evidence, suggesting incomplete recovery of brain function when returning to play and beyond,” said author, Nathan Churchill, PhD, of St. Michael's Hospital in Toronto, Canada. The researchers report that, compared to their pre-injury brain scans, concussed athletes who returned to play had significantly reduced blood flow in the brain in a part of the brain that helps control thinking and memory, emotional and social behavior, the fronto-insular cortex.

“The presence of significant, long-lasting brain changes after injury reinforces concerns about the consequences of repeated concussions,” explained Churchill “and to what extent these effects accumulate over time.” And it's not just concussions we need to be focused on. The repetitive jarring of the brain that happens in certain sports is a problem, too. Parents and coaches need to become more aware of the often subtle brain changes that can add up and interfere with mental processing.

The study is published in Neurology.