A single season of high school football may be enough to cause structural changes to a teen’s brain, even when the blows do not cause concussion, according to a new study published in the journal Neurobiology of Disease.
The study is one of the first to look at how impact sports affect the brains of children at this critical age. The findings raise concern over whether repeated hits to the head can cause brain damage in youth, and whether it is possible to detect these changes at an early age.
“There is a lot of emerging evidence that just playing impact sports actually changes the brain, and you can see these changes at the molecular level in the accumulations of different pathogenic proteins associated with neurodegenerative diseases like Parkinson’s and dementia,” study senior author Dr. Chunlei Liu, a professor of electrical engineering and computer sciences and a member of the Helen Wills Neuroscience Institute at University of California (UC) Berkeley.
“We wanted to know when this actually happens — how early does this occur?”
In general, the brain is composed of white matter, long neural wires that pass messages back and forth between different brain regions, and gray matter, tight nets of neurons that give the brain its characteristic wrinkles.
Recent MRI studies have shown that playing a season or two of high school football can weaken white matter, which is mostly found buried in the interior of the brain. Liu and his team wanted to know if repetitive blows to the head could also impact the brain’s gray matter.
To find out, the team of researchers from UC Berkeley, Duke University and the University of North Carolina at Chapel Hill used a new type of magnetic resonance imaging (MRI) called “diffusion kurtosis imaging” to take brain scans of 16 high school players, ages 15 to 17, before and after a season of football. This type of MRI is able to examine the intricate neural tangles that make up gray matter.
The researchers found that the organization of the gray matter in players’ brains changed after a season of football, and these changes correlated with the number and position of head impacts measured by accelerometers mounted inside players’ helmets.
Specifically, they found significant changes in the structure of the gray matter in the front and rear of the brain — where impacts are most likely to occur — as well as changes to structures deep inside the brain. The changes were concentrated in the front and rear of the cerebral cortex, which is responsible for higher-order functions like memory, attention and cognition, and in the centrally located thalamus and putamen, which relay sensory information and coordinate movement.
All the teens had worn helmets, and none received head impacts severe enough to constitute a concussion.
“Grey matter in the cortex area is located on the outside of the brain, so we would expect this area to be more directly connected to the impact itself,” Liu said. “It is becoming pretty clear that repetitive impacts to the head, even over a short period of time, can cause changes in the brain.”
“This is the period when the brain is still developing, when it is not mature yet, so there are many critical biological processes going on, and it is unknown how these changes that we observe can affect how the brain matures and develops.”
While one bump to the head may be nothing to worry about, mounting evidence has shown that repeated blows to the cranium — such as those racked up playing sports like hockey or football, or through blast injuries in military combat —may result in long-term cognitive decline and increased risk of neurological disorders, even when the impacts do not lead to concussion.
Recent research has also shown that an alarming number of retired soldiers and college and professional football players exhibit signs of a newly identified neurodegenerative disease called chronic traumatic encephalopathy (CTE), which is characterized by a buildup of pathogenic tau protein in the brain.
Though not well understood, CTE is linked to mood disorders, cognitive decline and eventually motor impairment as the affected person ages. Definitive diagnosis of CTE can only be made after death by examining the brain for tau protein during an autopsy.
“Although our study did not look into the consequences of the observed changes, there is emerging evidence suggesting that such changes would be harmful over the long term,” Liu said.
Tests revealed that students’ cognitive function did not change over the course of the season, and it is yet unclear whether these changes in the brain are permanent, the researchers say.
“The brain microstructure of younger players is still rapidly developing, and that may counteract the alterations caused by repetitive head impacts,” said first author Dr. Nan-Ji Gong, a postdoctoral researcher in the Department of Electrical Engineering and Computer Sciences at UC Berkeley.
However, the researchers still urge caution and suggest frequent cognitive and brain monitoring for youth involved in impact sports.