A study from the University of California, Berkley, Duke University, and the University of North Carolina at Chapel Hill used a new form of MRI to examine the brains of young tackle football players. The players were between 15 to 17 years old and wore helmets outfitted with accelerometers during gameplay. The participants' brains were scanned before and after one season of high school football.

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. (Source: Nan-Jie Gong and Chunlei Liu, UC Berkeley)

The scans showed significant changes in the brain’s grey matter. The changes were apparent at the front and the back of the head in the cerebral cortex - the most common places that are hit when playing football. The cerebral cortex is responsible for memory, attention, cognition, movement and sensory information.

"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 Chunlei Liu, a professor of electrical engineering and computer sciences and a member of the Helen Wills Neuroscience Institute at UC 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."

In the last 10 years, research has shown the development of chronic traumatic encephalopathy (CTE) in retired college and professional football players. CTE is the buildup of pathogenic tau protein in the brain. Most doctors and researchers believe that CTE can cause mood disorders, cognitive decline and motor impairment with age. Currently, CTE can only be diagnosed with a brain autopsy, only possible after the patient's death.

"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," Liu said. "We wanted to know when this actually happens -- how early does this occur?"

The brain is made of white matter and grey matter. White matter is the neural wires that pass messages between the brain. Grey matter is the nets of neurons that create the brain’s wrinkles. Past studies have shown that one or two seasons of high school football weaken the white matter of the brain. The effect of head contact on the grey matter has not yet been fully explored.

"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.

The team used a new kind of MRI called diffusion kurtosis imaging and examined the neural tangles of the grey matter. The MRI found that the organization of grey matter can be changed after just one season of football. The changes correlated with the number and position of head impacts that the accelerometers in the player’s helmets measured.

The study also found that cognitive function is not affected by one season of football. Further research would need to be conducted to see the long-term effect of a football season has on the grey brain matter.

"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," Liu said.

The study was published in the journal Neurobiology of Disease.