For those of us who winced every time a water-logged leather ball struck our heads during soccer practice, it's perhaps no surprise that frequent heading of the ball has been linked to cognitive performance.
Even with today's lighter balls, heading still jars the brain and is associated with learning and memory deficits, though the impacts do not cause concussions. But until recently, no studies had identified which part of the brain is most affected by heading and responsible for its cognitive effects.
Imaging analyses developed by Columbia researchers have now found that the junction between white and gray matter-in the outermost brain layer just behind the forehead-sustains the most the damage from heading, and this damage leads to cognitive deficits. The results were reported in two papers, published in the journals Neurology and JAMA Network Open.
"What's important about our studies is that they show, really for the first time, that exposure to repeated head impacts causes specific changes in the brain that, in turn, impair cognitive function," says study leader Michael Lipton, MD, PhD, professor of radiology and biomedical engineering at Columbia University Vagelos College of Physicians and Surgeons.
The studies also provide researchers with brain imaging tools they need to detect these injuries in individuals, learn more about the ways repetitive head impacts affect the brain, and develop treatments. "We're especially interested in looking at the potential relationship between these biomarkers and the later development of chronic traumatic encephalopathy (CTE), a neurodegenerative disease that has been diagnosed in athletes who experienced many head impacts over their playing careers," Lipton says.
"The location of the abnormalities we report is remarkably similar to CTE pathology, though we don't yet know if they are linked to CTE or if any of these currently healthy athletes will develop CTE."
New techniques developed to find damage
Biomechanical modeling studies suggest that minor, repetitive head impacts could change the microstructure of the brain's white matter, which plays a critical role in learning and memory. Diffusion MRI brain imaging can assess white matter microstructure, but due to technical hurdles, only in areas deep within the brain.
"As a result, researchers have avoided looking at the outer layers of white matter-the very areas that may be the most susceptible to injury from heading," says Bluyé DeMessie, a graduate student in Lipton's lab.
Lipton's team developed two new dMRI techniques to examine white matter in the cerebral cortex, the brain's outermost layer, where learning, problem-solving, and other functions are centered. DeMessie's method characterizes the microstructure of white matter where it meets a layer of gray matter. A different method developed by another graduate student, Joan Song, characterizes microstructure inside the transition zone between gray and white matter.
"In healthy individuals, there's a sharp transition between these tissues," Song says. "Here we studied if an attenuation of this transition may occur with minor impacts caused by heading."
Lipton's team ran these analyses on dMRI scans from 352 adult amateur soccer players, who reported varying levels of heading over the previous year, and on 77 aged-matched athletes who were not involved in collision sports. All participants took a simple memory test.
What the study found
The most fervent headers of the ball-reporting more than 1,000 headers each year-had significantly greater microstructural damage in white matter near the brain's cerebral sulci in the orbitofrontal cortex, just behind the forehead. Sulci are located in the valleys between folds of the cerebral cortex. Only minor changes in white matter regions were seen in deeper regions of the brain.
Similarly, the most frequent headers also had significantly fuzzier transitions between gray and white matter in the orbitofrontal region, but not in other regions toward the back of the brain.
The interface of the brain's gray and white matter layers is particularly vulnerable to impacts, Lipton says. "Gray and white matter have different densities and move at different rates in response to head impact, which creates shear forces between the two types of tissue. This leaves the white matter vulnerable to injury, especially adjacent to the sulci."
Greater damage in the sulci and the transition zone in general linked head impacts to worse cognitive performance on verbal learning and memory tests (though the differences in cognitive tests were small).
"The fact that both techniques, looking at two different features, find the same association strengthens our conclusion that these changes are mediating heading's cognitive effects," Lipton says.
References
More information
"Soccer Heading Exposure-Dependent Microstructural Injury at Depths of Sulci in Adult Amateur Players," was published Sept. 17 in Neurology.
All authors: Bluyé DeMessie (Albert Einstein College of Medicine and Columbia), Walter F. Stewart (Medcurio, Inc), Richard B. Lipton (Einstein), Mimi Kim (Einstein), Kenny Ye (Einstein), Molly E. Zimmerman (Fordham University), Thomas W. Kaminski (University of Delaware), Roman Fleysher (Columbia), and Michael Lipton (Columbia).
"Orbitofrontal Gray-White Interface Injury and the Association of Soccer Heading With Verbal Learning," was published Sept. 18 in JAMA Network Open.
All authors: Joan Y. Song, (Albert Einstein College of Medicine and Columbia), Roman Fleysher (Columbia), Kenny Ye (Einstein), Mimi Kim (Einstein), Walter F. Stewart (Medcurio Inc.), Molly E. Zimmerman (Fordham University), Richard B. Lipton (Einstein), Michael L. Lipton (Columbia).
The research was funded by grants from the Dana Foundation David Mahoney Neuroimaging Program and the National Institutes of Health (R01NS123374, R01NS123374, T32GM149364, and R01NS123374).
