Repeated blows to the head are never a good idea, so it is not surprising that new research suggests that even when they do not cause concussion, blows may affect the brain’s white matter and impact cognition, memory and thinking abilities.

Head impacts may lead to worrying consequences, including increased susceptibility to concussion, long-term cognitive decline and chronic traumatic encephalopathy – a degenerative disease associated with people who have suffered multiple head injuries.

The Centers for Disease Control and Prevention (CDC) estimates that 173,285 children and adolescents aged up to 19 will visit an emergency department with sports and recreation-related traumatic brain injuries (TBI), including concussion.

For this study, published in the journal Neurology, researchers compared 80 concussion-free Division 1 NCAA Dartmouth College varsity football and ice hockey players, all of whom wore helmets that recorded the acceleration time of the head following impact, with 79 athletes competing in non-contact activities, such as track, crew and Nordic skiing.

Participants were assessed with learning and memory tests, and they had brain scans before and shortly after the season finished.

Study author Dr. Thomas W. McAllister, of Indiana University School of Medicine in Indianapolis, explains:

We found differences in the white matter of the brain in these college contact sport athletes compared to non-contact sport varsity athletes. 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/often they are hit, white matter changes, and cognition, or memory and thinking abilities.”

He says that white matter plays an important role in the speed of nerve signals in the brain tissue and allows different parts of the brain to communicate with each other.

The study shows that some brain regions in some athletes were altered by repetitive impacts over the course of a season, and that these changes may be related to verbal learning and memory.

The study also identified a subgroup of athletes who performed worse than expected on verbal learning and memory tests at the end of the season. These athletes came from both the contact and non-contact groups – 20% of the contact players and 11% of the non-contact players.

These figures are much higher than predicted, and Dr. McAllister says that such a discrepancy in the figures would be expected in less than 7% of a normal population.

Brain scans revealed that this subgroup showed more changes in the corpus callosum region of the brain. This region is a bundle of nerves that connects the right and left hemispheres and is the largest collection of white matter within the brain.

Dr. McAllister says:

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.”

The researchers call for more studies to investigate the underlying factors that may influence the different susceptibility to repeated impacts as displayed by the subgroup.