Soccer heading has long been suspected of impacting brain health, but exactly where and how it leaves a mark has been a blind spot. Now, for the first time, scientists have a clear picture of the damage and why the zone of impact contributes to issues with learning and problem-solving over time.
Columbia University researchers have used new imaging techniques to identify that repeated heading of soccer balls affects the the junction between white and gray matter in the orbitofrontal cortex, the region just behind the forehead that helps with planning and strategy. Newly developed diffusion MRI analyses has revealed that more frequent heading is linked to subtle microstructural disruption in this region – and that this disruption explains the small but measurable drops in verbal learning performance among adult amateur players.
“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,” said study lead Michael Lipton, M.D., a professor of radiology and biomedical engineering at Columbia University’s Vagelos College of Physicians and Surgeons.
Soccer heading and the brain’s gray matter/white matter interface
Lipton and his team developed two new dMRI techniques to examine white matter in the cerebral cortex; one method focused on the microstructure of white matter where it meets the layer of gray matter. The other, developed by graduate student Joan Song, homed in on the microstructure inside the transition zone between gray and white matter. In the brain scans of heavy headers, the normally crisp gray-white boundary looked fuzzier in the orbitofrontal cortex – exactly where models predict the most shear – while there were no significant changes in other regions.
“In healthy individuals, there’s a sharp transition between these tissues,” Song said. “Here we studied if an attenuation of this transition may occur with minor impacts caused by heading.”
In one study of 352 New York–area amateurs aged 18 to 53 years, players reported how often they headed the ball over the prior year. Brain scans were then analyzed with one dMRI method that profiled how sharply tissue properties transition across the gray-white interface. Essentially, during impact, the head accelerates and then slows quickly. Gray and white matter have slightly different stiffness and density, so they don’t move together at the same velocity. That mismatch makes them slide against each other at their boundary, creating sideways stretching (shear force). And the gray-white junction – especially near the grooves (sulci) in the orbitofrontal cortex – is where that sliding stress is concentrated.
“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,” said Lipton. This leaves the white matter vulnerable to injury, especially adjacent to the sulci.”
In a second study, the team used a different, complementary dMRI method developed by Columbia researcher Bluyé DeMessie, focused on the same gray-white transition zone and compared the brain scans of the 352 players with scans of 77 non-contact athletes, in order to show the effect is specific to soccer heading exposure. Participants from both studies then undertook a simple memory test.
Ultimately, the researchers found that heading exposure was associated with lower scores on this standard learning task. This finding aligned with the brain scans of the heavy headers, and both dMRI methods produced consistent results. While the cognitive differences were small – nowhere near what would be considered clinical impairment – they were consistent across the cohort when age, sex and prior concussion history were taken into account.
“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 said.
Columbia University
What’s more, the brain area in question here overlaps with regions often affected in traumatic brain injury and, in some athletes with many years of head impacts, chronic traumatic encephalopathy (CTE). However, the authors caution that this isn’t proof of CTE – more research is needed, following these markers over time, to see if these scan abnormalities can predict future cognitive problems.
“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 said. “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.”
It’s also worth noting that these findings are more a cross-sectional snapshot, which can’t prove causation. Secondly, the exposure metric ranks players by how much they headed the ball in the past 12 months and don’t capture a lifetime of impacts.
What does this mean for players and parents? The authors stop short of providing concrete thresholds, but prior work – and the new analyses –suggest that low levels of heading (a couple of times per week) results in scans that look very similar to non-contact athletes, while the heaviest heading group shows the most significant differences. Because individual susceptibility likely varies with factors like genetics and concussion history, a one-size-fits-all “safe” number is unlikely to be decided on. Instead, these gray-white interface biomarkers could give clinicians a way to identify when a player’s exposure is starting to matter biologically, long before symptoms arise, and help inform changes to training and coaching in order to moderate contact.
“We don’t have enough information to make generalized recommendations,” said 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.
“The impact of heading is likely to vary from person to person, depending on genes, concussion history, and other factors,” he added. “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.”
These findings advance our knowledge of how sports-related brain impacts appear to be contributing to cognition deficits in amateur and professional players. It’s also seen researchers look to design better diagnostic and protective equipment – from mouth guards to helmets – that can both monitor and cushion the blows that are still a common occurrence in contact sports.
The research was published in two papers, in the journal Neurology and the journal JAMA Network Open.
Source: Columbia University
