ARTICLE IN BRIEF
In a preliminary study comparing the brains of 50 college football players and 25 matched controls, researchers found that playing football was associated with reduced hippocampal volume on magnetic resonance imaging.
College football players tend to have smaller hippocampal volumes than do non-playing students and the difference is especially pronounced in football players with a history of concussion, according to a new study.
Researchers used high-resolution anatomic magnetic resonance imaging (MRI) to measure hippocampal volume in 50 college football players — half with a history of concussion, half without — and 25 matched controls.
In a report in the May 14 edition of the Journal of the American Medical Association (JAMA), the researchers reported that the longer the football players played the sport, the more likely they were to have smaller hippocampal volume, regardless of whether they had a documented history of concussion. The study also found a relationship between years of football played and slower reaction time as measured by cognitive testing.
“Volume changes have been shown in older, retired athletes, but we're showing it can happen in younger athletes,” said study coauthor Patrick Bellgowan, PhD, a neuroscientist and faculty member at the Laureate Institute for Brain Research in Tulsa, OK, and the University of Tulsa.
“Emerging evidence suggests that the hippocampus is also vulnerable to mild TBI [traumatic brain injury], as indicated by volume reduction and postconcussion disruptions of hippocampal function and disconnectivity,” the researchers wrote. “Even in the absence of concussion, compromised white matter integrity has been documented in the hippocampus of collegiate contact-athletes.”
The study was carried out from June 2011 to August 2013 and involved 50 Division I football players, including 25 who had at least one clinician-diagnosed concussion that involved imaging. The players were matched with 25 controls by sex, age, and education level.
The football players underwent cognitive testing at the start of their first football season on campus. The testing was conducted using the Immediate Post-Concussion Assessment and Cognitive Testing battery (ImPACT). The percentile scores for three composite measures — verbal memory, visual memory, and reaction time — and the raw impulsivity score were used for analysis. The football players also provided information on the number of years they had played
“The hippocampal volume difference was pretty dramatic,” Dr. Bellgowan told Neurology Today. “We were surprised how big the difference was.”
In the left hemisphere, hippocampal volume was 14.1 percent smaller for football players with no history of concussion and 23.8 percent smaller for athletes with a concussion history when compared to the controls. In the right hemisphere, hippocampal volume was 16.7 percent smaller for football players with no history of concussion and 25.6 percent for the players with a concussion history.
Also, the “number of years of football-playing experience was inversely associated with both left hemispheric hippocampal volume and baseline reaction time,” the researchers reported.
The findings, while preliminary, suggest that even sub-concussive hits may have a deleterious effect on the brains of young athletes.
“These results extend existing literature showing slowed reaction time associated with a history of concussion by demonstrating slowed reaction times related to exposure to tackle football regardless of concussion history,” they reported. “Further longitudinal research is needed to establish the temporal relationships of these findings.”
Dr. Bellgowan said his team is now planning a similar study of 8th grade football players to determine whether there is any evidence of brain effects even at that early age. He said that despite a growing body of literature on the potential consequences of concussions, some parents and coaches feel as though the concerns have been exaggerated.
“These data suggest that we may be looking at long-term effects that could have life-long meaning,” Dr. Bellgowan said. And while many concussion studies have focused on football, “it's not just about football. It's about all contact sports.”
The research team acknowledged that the study had limitations: it was cross-sectional in design, had a small sample size, and relied on self-reports. Athletes often underreport concussion, which could have blurred the distinction between the two groups of athletes. The findings were also not clear-cut. For instance, “Unlike prior studies of sports-related concussion, and despite differences in hippocampal volume, the athlete groups showed no significant differences in baseline cognitive performance, possibly because of the relatively small sample size in the present study.”
THE IMPACT OF STRESS
It is not clear what could be causing the smaller hippocampal volume. The researchers noted that exposure to high levels of stress-related hormones has been associated with smaller hippocampal volume — a factor that could be at work with top-notch athletes who practice and perform with intensity.
“Collegiate athletes have been exposed to both physical and psychological stressors throughout their careers,” they wrote. “These stressors could produce an excess of glucocorticoid secretion that may act to suppress neurogenesis and decrease dendritic arborization within the hippocampus.”
The issue of concussion — both immediate and long term — has focused in large part on professional athletes, particularly retired National Football League (NFL) players. Research suggests that football players are at risk for chronic traumatic encephalopathy, which has been linked to memory loss, confusion, depression, dementia, and other symptoms.
Frank Conidi, MD, DO, director of the Florida Center for Headache and Sports Neurology in South Florida, where he evaluates and studies athletes with sports-related concussions, told Neurology Today that the latest study on college football players was interesting, but “...it isn't something you can translate clinically or draw clinical conclusions from.” He said the findings raise some important questions that need to be further explored.
For example, he continued, “Is hippocampal volume a measure of long-term neurocognitive deficit?” Dr. Conidi, an assistant clinical professor of neurology at Florida State University College of Medicine, said some information can be gleaned from computerized neurocognitive assessment tools such as the ImPACT system that was used to provide baseline readings on the football players in the study. But he said that conducting a thorough battery of standardized neuropsychological tests on the players would have been a more validated measure and yielded more information from a research perspective.
Another question: “Is there a specific part of the hippocampus that is vulnerable to injury?” Dr. Conidi asked.
Erin Bigler, PhD, a professor of psychology and neuroscience and director of the Magnetic Resonance Imaging (MRI) Research Facility at Brigham Young University, said the JAMA study “is an important next step in understanding the role the hippocampus plays in traumatic brain injury and in particular what it means in the case of concussion.
“The hippocampus is a critical structure for short-term memory and it is also located in a vulnerable position in the brain,” he told Neurology Today.
Dr. Bigler said that a fuller picture is emerging on “the cumulative effects these multiple impacts are having.” While much attention has been focused on professional players, he said, repeated hits to the head might be particularly problematic for the still developing brains of children and young adults. He noted that today's high school and collegiate football players tend to have a lot of heft and speed, making the game very physical.
“At 20, you don't have a fully mature brain,” he pointed out. “The brain is likely not developmentally mature until the mid 20s.”
He said the hypothesis that hormonal stressors could play a role in hippocampal volume made sense. Even at the high school level, he said, the level of practice and play is intense and expectations are high.
“You've got competition; the football stadium is packed for every game,” he said.
Anthony Alessi, MD, FAAN, a neurologist at Neuro Diagnostics, LLC, in Norwich, CT, and a consultant to the NFL Players Association, said there needs to be more focus on both the immediate and long-term repercussions of head hits and concussions on younger athletes.
“Athletes and their families need to get all the information they can and be counseled appropriately,” he said. Dr. Alessi, an associate clinical professor at the University of Connecticut, said that while the NFL, in the wake of legal and union pressure, limits the amount of full-contact practice, colleges have not yet followed suit.
No matter the rules, he said that parents of high school and youth-league athletes of all sports need to “instill in their children the importance of preventing head injury and reporting head injuries.
“The bottom line is that hitting your head, no matter how you do it, is not a healthy thing,” he said.
EXPERTS COMMENT ON STUDY OF BRAIN CHANGES IN COLLEGE FOOTBALL PLAYERS