Their youthful brains were developing normally, with no signs of developmental, psychological or neurological problems. None had ever had a concussion. But by the end of a single football season, 24 children between the ages of 9 and 18 who had more frequent impacts to the head showed signs of damage to brain development, new research says.
"Repetitive head impact exposure may have a cumulative effect in the rapidly developing brains of youth and high school football players," said study co-author Gowtham Krishnan Murugesan, a radiology research assistant at UT Southwestern Medical Center in Dallas, adding that the results mirror other recent findings.
The study outfitted 60 youth and high school football players who had no history of head trauma or developmental issues with a head impact telemetry system that measures the magnitude, location and direction of impacts to the head. The researchers were not looking at whether the impact resulted in a concussion, only that impact occurred.
The children were sorted into two categories: high cumulative head impact players (24) and low cumulative head impact players (36).
Before beginning to play, each child had a resting state functional scan, known as an fMRI; the scans were repeated at the end of football season. The researchers were trying to see how exposure to repetitive hits affects the normal "pruning" process in the brain that occurs during adolescence.
"Pruning is an essential part of brain development," Murugesan said, comparing the process to how a tree needs to have dead or unneeded branches cut to keep it healthy and allow it to grow.
"Disruption in normal pruning has been shown to be related to weaker connections between different parts of the brain," he said.
After comparing the functional MRI results to the player's level of impact, the researchers found that youth in the high-impact group had damage to their brains' pruning process after one season.
"Our study has found a significant decrease in gray matter pruning in the frontal default mode network, which is involved in higher cognitive functions, such as the planning and controlling of social behaviors, " Murugesan said.
Although the "teenage years are a critical time for brain development, brain remodeling or synaptic pruning, this was a short-term study and did not follow the players longitudinally over several years. We don't really know the full application," said Dr. Julian Bailes, director of neurosurgery and co-director of the NorthShore University HealthSystem Neurological Institute, who was not involved in the research.
Weill Cornell neurologist Dr. Richard Isaacson, who was also not involved in the study, called the research "early" and said the results don't necessarily "translate to a clinical or cognitive outcome." More research is needed to see whether the decline in brain pruning permanently affected the child's cognitive function or whether the brain's natural plasticity allowed it to repair itself.
"I would call this a pilot study," Isaacson said. "The call to action would be that we need more robust longitudinal studies with a pre- and a post-assessment of more than brain imaging. The study should also measure cognitive and neurological function and look for changes."
As we learn more about the issue, Isaacson said, parents should do everything they can to limit contact in sports, "especially in practice before games, where studies show the majority of contact occurs."
Bailes pointed out that caution should be used in all sports, not just football.
"It's soccer; it's ice hockey; it's wrestling," he said. "It's any sport that has the potential for collision and head impact."