The more hits the head took, the more change doctors said they saw.
"These are not changes you would be able to see with your naked eye," Whitlow said. "These are very, very subtle changes."
Whitlow said there are still many unanswered questions and parents shouldn't be alarmed.
"There's a lot of things we don't know," Whitlow said. "We don't know if they persist. We don't know if they go away after the season. We don't know if there are even more changes if people play multiple seasons."
Those answers could be years away. Researchers say more information is needed to understand whether the changes could lead to negative long-term health issues.