Even in the absence of a concussion, blows to the head during a single season of football or ice hockey may affect memory and thinking abilities.
White matter is brain tissue that plays an important role in the speed of nerve signals, according to background information in the study, which was published Dec. 11 on the website of the journal Neurology.
We found differences in the white matter of the brain in these college contact sport athletes compared to non-contact sport varsity athletes, Thomas W. McAllister, MD, of Indiana University School of Medicine in Indianapolis, said in a news release.
The degree of white matter change in the contact sport athletes was greater in those who performed more poorly than expected on tests of memory and learning, suggesting a possible link in some athletes between how hard or often they are hit, white matter changes and cognition.
McAllister, who was with the Geisel School of Medicine at Dartmouth College in Hanover, N.H., at the time of the study, and colleagues examined 80 concussion-free Dartmouth varsity football and ice hockey players who wore helmets that recorded the acceleration-time of the head following impact. They were compared with 79 non-contact sport athletes in activities such as track, crew and Nordic skiing. The players were assessed before and shortly after the season with brain scans and learning and memory tests.
The study found that a subgroup of both types of athletes performed worse than predicted on a test of verbal learning and memory at the end of the season. A total of 20% of the contact players and 11% of the non-contact athletes scored more than 1.5 standard deviations below the predicted score. McAllister said a decline this large would have been expected in less than 7% of a normal population.
This subgroup showed more change in the corpus callosum region, a bundle of nerves that connects the right and left sides of the brain, than the athletes who scored as predicted on the test.
This group of athletes with different susceptibility to repetitive head impacts raises the question of what underlying factors might account for the changes in learning and memory, and whether those effects are long-term or short-lived, McAllister said.
Neurology is the official journal of the American Academy of Neurology. Study abstract: www.neurology.org/content/early/2013/12/11/01.wnl.0000438220.16190.42