College football players : hits sustained from playing just one season cause structural changes to the brain

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New research led by Carnegie Mellon University and the University of Rochester Medical Center indicates that concussions aren’t the sole cause of damage to the brain in contact sports.

A study of college football players found that typical hits sustained from playing just one season cause structural changes to the brain.

The researchers studied 38 University of Rochester players, putting accelerometers—devices that measures accelerative force – in their helmets for every practice and game.

The players’ brains were scanned in an MRI machine before and after a season of play.

While only two players suffered clinically diagnosed concussions during the time they were followed in the study, the comparison of the post- and pre-season MRIs showed greater than two-thirds of the players experienced a decrease in the structural integrity of their brain.

Specifically, the researchers found reduced white matter integrity in the midbrain after the season compared to before the season.

Furthermore, and indicating the injury was specifically related to playing football, the researchers found the amount of white matter damage was correlated with the number of hits to the head players sustained.

The study is published in the journal Science Advances.

“Public perception is that the big hits are the only ones that matter. It’s what people talk about and what we often see being replayed on TV,” said senior study author Brad Mahon, an associate professor of psychology at Carnegie Mellon and scientific director of the Program for Translational Brain Mapping at the University of Rochester.

“The big hits are definitely bad, but with the focus on the big hits, the public is missing what’s likely causing the long-term damage in players’ brains. It’s not just the concussions. It’s everyday hits, too.”

The midbrain, located in the center of the head and just beneath the cerebral cortex, is part of a larger stalk-like rigid structure that includes the brain stem and the thalamus.

The relative rigidity of the midbrain means it absorbs forces differently than surrounding softer tissues, making it biomechanically susceptible to the forces caused by head hits.

The midbrain supports functions like eye movements, which are impacted by concussions and hits to the head.

While head hits are known to affect many parts of the brain simultaneously, the researchers decided to focus the study on the midbrain, hypothesizing that this structure would be the “canary in the coal mine” for sub-concussive hits.

“We hypothesized and found that the midbrain is a key structure that can serve as an index of injury in both clinically defined concussions and repetitive head hits,” said Adnan Hirad, an M.D./Ph.D. candidate at the University of Rochester’s Medical Scientist Training Program and lead author of the study.

“What we cataloged in our study are things that can’t be observed simply by looking at or behaviorally testing a player, on or off the field. These are ‘clinically silent’ brain injuries.”

Each player in the study received an MRI scan within two weeks of the start of each season and within one week at the end.

The helmet accelerometers measured linear and rotational acceleration during all practices and games, recording all contact that produced forces of 10 gs or greater.

Astronauts on the space shuttle experienced 3 gs during lift-off. Race car drivers feel the effects of 6 gs, and car crashes can produce brief forces of more than 100 gs.

The 38 NCAA Division III players experienced nearly 20,000 hits across all practices and games.

Of those hits, the median force was around 25 gs, with half of the hits exceeding that amount.

Only two of the nearly 20,000 hits resulted in concussions.

“We measured the linear acceleration, rotational acceleration and direction of impact of every hit the players sustained.

This allowed us to create a three-dimensional map of all of the forces their brains sustained,” Hirad said.

The MRI scans measured structural changes in the brain that took place over the course of each season.

They found that rotational acceleration (impact causing the head to twist) more so than linear acceleration (head-on impact) is correlated with the observed changes in the structural integrity of white matter in the midbrain.

“This study suggests that midbrain imaging using diffusion MRI might be a way in the future to diagnose injury from a single concussive head hit and/or from repetitive sub-concussive head hits,” said Dr. Jeffrey Bazarian, professor of Emergency Medicine, Neurology, Neurosurgery and Public Health Sciences at the University of Rochester Medical Center and a co-author of the study.

The second part of the study served as an independent means to validate the researchers’ approach to the football cohort.

This group included 29 athletes from various other contact sports who had a clinically defined concussion and 58 who didn’t.

The concussed participants underwent MRI scans and offered blood samples within 72 hours of injury. Like the football cohort, those players exhibited reduced structural integrity in the midbrain. In addition, they exhibited increased tau, a protein, in their blood. As structural integrity in the brain decreases, tau increases.

“Tau is an important marker of acute changes in the brain and is thought to be, in the long term, implicated in neurodegenerative diseases like chronic traumatic encephalopathy, also known as CTE,” Hirad said.

A 3D representation of a magnetic resonance imaging scan, showing areas in the front and rear of the brain lit up.
Magnetic resonance imaging (MRI) brain scans have revealed that playing a single season of high school football can cause microscopic changes in the grey matter in young players’ brains. These changes are located in the front and rear of the brain, where impacts are most likely to occur, as well as deep inside the brain. (Image by Nan-Jie Gong and Chunlei Liu, UC Berkeley)

Given this new insight on repetitive head hits, what should we do?

“Our research, in the context of prior research over the past several years, is beginning to indicate that the accumulation of many sub-concussive hits is instrumental in driving long-term damage in football players’ brains,” Mahon said.

“Future research will be required in order to translate our findings into concrete directives that are relevant to public health.

An important direction for future research will be to carry out larger-scale longitudinal studies of contact sports athletes in various ages groups.”

“We also need to re-evaluate how we make return-to-play decisions,” Hirad said. “Right now, those decisions are made based on whether or not a player is exhibiting symptoms of a concussion like dizziness or loss of consciousness.

Even without a concussion, the hits players are taking in practice and games appear to cause brain damage over time.”


A study published in the November issue of Neurobiology of Disease indicates that playing one season of high school football leads to significant microstructural changes in the human brain – even without being diagnosed with a concussion.

Using helmet accelerometers and MRI imaging, researchers from institutions including Duke, the University of California, Berkeley and University of North Carolina at Chapel Hill examined the structural changes in the brain that occurred during one season.

“We wanted to ask how long a person has to be in contact sports to see some sort of effect on the brain,” said Jeffrey Petrella, professor of radiology and one of the paper’s authors, said.

“We took high school athletes because high school is an age when the brain is still developing and particularly vulnerable to trauma.” 

Previous studies investigating football’s impact on the brain have focused on degenerative diseases those who have played football for extensive periods of time.

A year ago, a group of researchers, including Petrella, began focusing on high school football. 

In its first study in 2017, the team focused on the white matter of the brain – its wiring – and saw changes in a bundle of nerve fibers known as the fornix.

This most recent study builds upon that previous work to examine the gray matter structures. 

“We found that not only was the wiring of the brain affected, but also superficial parts of the brain – the gray matter – was as well,” Petrella said. 

The white matter affected, the fornix, has implications for memory effects.

The fornix is often vulnerable in high speed motor vehicle accidents, given its curved structure and the rotation of the head, Petrella said.  

According to Petrella, the gray matter changes found in this study were localized to the frontal lobe and thalamus, which are responsible for higher order cognitive function, inhibition, sensory perception and memory.

Petrella said this type of damage could lead to more impulsive behavior.

For both gray and white matter changes, researchers saw a positive correlation between the number of hits taken by a player and the damage to the brain. 

“Many NFL players describe changes in personality over time, characterized by more impulsivity,” Petrella explained.

“This could be contributing to the biological basis underlying that increased impulsivity and loss of inhibition.” 

Most of the high school students the researchers studied experienced only subconcussive hits. However, one student did experience a concussion near the end of the season. Petrella noted that the brain imaging results of this student allow for some optimism regarding structural changes caused by high school football. 

“In the fornix, when the player was injured, there was evidence of loss of integrity,” he said. “When we re-scanned the player after a couple of months of rest, these changes had completely disappeared.”

Although Petrella acknowledged that this repair could be influenced by the plasticity of a younger brain, he also stressed the importance of rest and recovery.

However, the reversibility of these changes may not extend to the lifetime of football experienced by professional players. 

Some prior studies of football players focused on correlating concussions with brain damage.

This study reflected the number of hits a player received, rather than the severity. Petrella described how the emphasis on subconcussive injuries in this study highlights the roles of an extensive range of player positions, including those who don’t experience high velocity hits. 

“We studied subconcussive injuries, and that’s a unique thing that we’re seeing here,” he said. “You have an uneventful season of high school football in which you don’t get a concussion, but you’re still seeing brain changes.”

Petrella said the researchers built on the experiences of co-author Samuel Kuzminski, who was a college football player himself.

The study indicated that hits directly to the crown of the head had greater effect on the frontal lobe. Petrella said modifications to the way athletes are trained—including training to minimize hits to the crown—will help protect younger players whose brains are still developing. 

“Even in high school football, which is not as violent a game as college or the pros, we need to be cognizant of safety,” he said. “We’re not saying high school football is unhealthy. It’s just a cautionary flag that coaches need to take more protective measures, teaching kids how to hit appropriately and not lead with the head.” 


More information: A.A. Hirad el al., “A common neural signature of brain injury in concussion and subconcussion,” Science Advances (2019). DOI: 10.1126/sciadv.aau3460 , advances.sciencemag.org/content/5/8/eaau3460

Journal information: Science Advances
Provided by Carnegie Mellon University

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