(Undated) -- New research shows repetitive hits to the head cause changes to brain matter. Doctor Damir Janigro says there are different levels of head impact. The study shows the part of the brain in charge of learning and functioning does not heal as quickly when the head impact is consistent. College football players participating in the study still showed damage six-months after their season ended. The non-athletes taking part in the study did not show signs of brain damage.