05/16/2012 05:01 pm ET

Brain Injury Study: A Single Season Of Hits May Harm College Athletes' Ability To Learn

Just a single season of contact sports can take a toll on college athletes' ability to learn, according to a new study.

Overall, one season's worth of repetitive hits did not seriously harm players' thinking and memory skills, but when it came to learning, a small group of players was negatively affected.

"The good news is that we did not find that a season of essentially hitting your head over and over again was associated with widespread deterioration in cognitive performance," said Dr. Thomas McAllister, director of neuropsychiatry at the Dartmouth-Hitchcock Medical Center and an author on the study.

"Nevertheless," said McAllister, an author of the study published in Neurology Wednesday, "it does suggest the possibility that there's a subgroup playing their sport who end up performing worse than they should have at the end of the season."

Researchers compared more than 200 football and hockey players at Division I schools with 45 athletes participating in non-contact sports, such as track or crew. To test the effects of one season, researchers gave all of the athletes thinking and memory skills tests before the season started and after it came to an end.

They excluded students who were diagnosed with a concussion during the season because they wanted to look at head impacts in general, not just focus on the worst cases.

Few cognitive differences were found between the two groups of athletes in terms of pre- and post-season performance. But when researchers administered a test to measure new learning, 22 percent of the contact-sport athletes did worse than expected, compared to just 4 percent of the non-contact athletes.

"This study shows there's not a huge effect overall -- there's not a dramatic effect pre- and post-season," said Dr. Doug Smith, director of the Penn Center for Brain Injury and Repair, who was not involved in the new study.

"But there is a small effect in a subgroup of individuals. It raises the question, is there a selective vulnerability for certain individuals? For example, a genetic predisposition?"

McAllister said that the new study did not specifically address those issues. However, emerging evidence suggests that there may be genetic predictors of outcome after mild brain injury, he said, which might help explain why some athletes are more sensitive to the effects of hits than others.

"There is a lot of concern about whether people should play contact sports," McAllister said. "The question may not be 'Is it bad for everyone?'. Maybe the question should be, 'For whom might this be a bad idea?'."

Recently, head-impact injuries and concussions have become a concern in professional and college sports leagues in recent years, thrust back into the spotlight with the suicide of former NFL linebacker Junior Seau on May 2. On Wednesday, a former linebacker from The Ohio State University announced he was giving up on dreams of playing in the NFL and instead opting to go to law school because of his concerns about concussions, CNN reported.

A spokesman for the NCAA told The Huffington Post that while it had not yet reviewed the new findings, it "fully supports the continuing examination of the impact of head injuries and concussions in sports."

"The NCAA has taken significant proactive steps to protect student-athletes from head injuries in recent years by updating playing rules for multiple sports, including football and ice hockey," he added.

What is still unknown is whether there is a threshold for the hits a player can sustain before seeing a negative impact.

In an editorial accompanying the new study Dr. Ellen Deibert, a neurologist with Berkshire Brain Injury, and Richard Kryscio, a professor in the statistics department at the University of Kentucky, write that the number of impacts per athlete in a season can be "staggering." They estimate that during four years of high school and four years of college combined, a football player can sustain about 8,000 hits.

In the new study, the contact-sport athletes were exposed to an average of 469 separate impacts each over the course of a season including games and practices. "How many hits are too many, is as yet unknown," the report says.