Junction between white and grey matter—in the outermost brain layer just behind the forehead—sustains the most damage from heading
For those of us who winced every time a waterlogged leather ball struck our heads during soccer practice, it’s 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 grey matter—in the outermost brain layer just behind the forehead—sustains the most damage from heading, and this damage leads to cognitive deficits.
The results were reported in two papers, published in the journals Neurology(link is external and opens in a new window) and JAMA Network Open(link is external and opens in a new window).
“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 the brain imaging tools they need to detect these injuries in individuals, learn more about how repetitive head impacts affect the brain, and develop effective 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 modelling studies suggest that minor, repetitive head impacts may alter the microstructure of the brain’s white matter, which plays a crucial role in learning and memory.
Diffusion MRI brain imaging can assess white matter microstructure, but due to technical limitations, it is only possible 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 centred.
DeMessie’s method characterises the microstructure of white matter where it meets a layer of grey matter.
A different method developed by another graduate student, Joan Song, characterises the microstructure inside the transition zone between grey and white matter.
“In healthy individuals, there’s a sharp transition between these tissues,” Song says. “Here, we studied whether 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 age-matched athletes who were not involved in collision sports. All participants took a simple memory test.
Findings
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 areas of the brain.
Similarly, the most frequent headers also exhibited significantly fuzzier transitions between grey and white matter in the orbitofrontal region, but not in the other areas located farther back in the brain.
The interface of the brain’s grey and white matter layers is particularly vulnerable to impacts, Lipton says.
Grey 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 minor).
“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.
Is Any Amount of Heading Safe?
Lipton says the studies confirm his team’s earlier findings that some amount of heading is likely safe for most soccer players.
“We don’t have enough information to make generalised recommendations,” says Lipton.
“But when we divided the players into four groups according to their heading frequency, we found that the players who only headed the ball about twice a week looked similar to the non-contact athletes in our study.”
But Lipton warns that the threshold of heading needed to cause harm is unknown.
“The impact of heading is likely to vary from person to person, depending on genes, concussion history, and other factors,” he says.
“For example, a person who only occasionally heads the ball, but carries a genetic risk, may experience comparatively large effects, while a person without the genetic risk could head the ball dozens of times a week, but experience few effects.”
