There’s been much debate over the brain damage football can cause, and now a new study provides evidence that professional football players have brain abnormalities.

Brain scans of retired National Football League players revealed the athletes are more likely to suffer disruptions in executive brain function, which is high-level control of other brain activity. And players who suffered the most head injuries during their careers had the most abnormalities, researchers found.

“The NFL alumni showed some of the most pronounced abnormalities in brain activity that I have ever seen,” study leader Dr. Adam Hampshire, of Imperial College London, said in a statement.