Collegiate contact sport athletes were more likely to score lower on learning and memory tests at the end of the season compared to their test scores at season's start, compared to those who participated in non-contact sports. In addition, those who had score declines had more changes in their white matter, a part of the central nervous system responsible for conducting the speed of the nerve signals, CBS News reports.

The researchers tested 80 football and ice hockey players who did not have a history of concussions, as well as 79 non-contact sport athletes who competed in non-contact sports like track, crew and Nordic skiing.

The athletes were all asked to take the California Verbal Learning Test II, which looked at verbal learning and memory, at both the beginning and end of the season. They also underwent an MRI brain scan that specifically looked at white matter.

Out of the athletes had a 1.5 standard deviation decline in test scores at the end of the season, 20 percent were in contact sports. Only 11 percent participated in non-contact activities. 

Researchers are particularly concerned about head injures, due to the mounting evidence that shows that athletes who have experienced repeated blows to the head may develop a condition known as chronic traumatic encephalopathy (CTE). CTE is a Alzheimer's-like neurodegenerative brain disease that causes memory loss, confusion, impaired judgment, impulse control problems, aggression, depression and progressive dementia at younger ages than typical.