The 2015 film Concussion portrayed the turbulent journey of pathologist Dr Bennet Omalu as he uncovered how repeated trauma to the brain, as seen in American football players, could lead to devastating neurodegenerative disorders. It was seven years before the National Football League (NFL) would accept the association and a wealth of research has since followed in the wake of Omalu’s discovery. Now, new research is thought to have isolated a potential mechanism through which multiple concussions and traumatic brain injuries (TBI) can lead to neurodegenerative disorders as they disrupt the brain’s ability to cleanse itself of toxins and debris.

The study, published in the journal Nature Communications, used experimental mouse models to investigate the influence of TBI on brain function. They observed that even mild forms of brain trauma could significantly impair the brain’s glymphatic system, the functional pathway through which it clears itself of waste. The effects were seen within hours following injury and persisted for at least one month and are believed to be the result of increased intracranial pressure that commonly follows head trauma.

The researchers go on to show that pre-existing glymphatic dysfunction, be it from natural factors or a previous injury, can result in worse outcomes from injuries through the same mechanism, increasing the risk of negative cognitive outcomes for those sustaining repeated injuries. The study suggests this could also explain why some people are more severely affected by a blow to the head than others.

The results are of significance for athletes that participate in contact sports such as American football, as they indicate the importance of appropriate rest periods between injuries, which could constitute a devastating disruption to players’ careers. However, by taking the necessary breaks between traumas, they could be spared of impaired cognitive function later in life.

Glymphatic impairment is thought to lead to a host of debilitating mental impairments, including Alzheimer's disease, dementia, and chronic traumatic encephalopathy (CTE), the condition that Omalu identified in his research regarding NFL players. As such, understanding the mechanism through which concussions cause these illnesses and how to reduce their likelihood has the potential to protect athletes and members of the military from life-altering injury and disease.

"This provides some of the best evidence yet that if you haven't recovered from a brain injury and you get hit in the head again, you're going to have even more severe consequences," said John Lukens, from the University of Virginia's Department of Neuroscience and the Center for Brain Immunology and Glia, in a statement. "This reinforces the idea that you have to give people an opportunity to heal. And if you don't, you're putting yourself at a much higher risk for long-term consequences that you might not see in a year but could see in a couple of decades."