Magnetic resonance imaging (MRI) brain scans have revealed that playing a single season of high school football can cause significant microscopic changes in cortical and deep gray matter.
“It is becoming pretty clear that repetitive impacts to the head, even over a short period of time, can cause changes in the brain,” said study senior author Professor Chunlei Liu, a researcher in the Helen Wills Neuroscience Institute at the University of California, Berkeley.
“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.”
The brain is built 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 nestled in the interior of the brain.
Professor Liu and co-authors wanted to know if repetitive blows to the head could also affect the brain’s gray matter.
“Gray 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,” Professor Liu said.
The team used a new type of MRI called diffusion kurtosis imaging to take brain scans of 16 high school players (aged 15 to 17 years) before and after a season of football. All participants wore helmets, and none received head impacts severe enough to constitute a concussion.
They 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.
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.
“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,” Professor 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 brain microstructure of younger players is still rapidly developing, and that may counteract the alterations caused by repetitive head impacts,” said study first author Dr. Nan-Ji Gong, a postdoctoral researcher in the Department of Electrical Engineering and Computer Sciences at the University of California, Berkeley.
However, the researchers still urge caution — and frequent cognitive and brain monitoring — for youth and high schoolers engaged in impact sports.
“I think it would be reasonable to debate at what age it would be most critical for the brain to endure these sorts of consequences, especially given the popularity of youth football and other sports that cause impact to the brain,” Professor Liu said.
The results appear in the journal Neurobiology of Disease.