Young athletes show subtle brain changes after concussion
With the increasing awareness of chronic traumatic encephalopathy (CTE), many are beginning to recognize the long-term risks of playing football. However, two recent studies suggest we may be underestimating the short-term effects the game can have on the brain.
Two separate reports presented at the UT Southwestern Medical Center in Dallas at the annual meeting of the Radiological Society indicates that young football players who have experienced concussions and a history of high impact collisions may have observable brain changes after just one season of play.
Both studies examined the default mode network (DMN), which is associated with wakeful rest in the brain. Changes in this brain network have previously been identified in those with mental illnesses, and studies have indicated that traumatic brain injuries may cause decreased connectivity within the DMN.
“The DMN exists in the deep gray matter areas of the brain,” explained Elizabeth M. Davenport, Ph.D., a postdoctoral researcher in the Advanced NeuroScience Imaging Research (ANSIR) lab at UT Southwestern’s O’Donnell Brain Institute. “It includes structures that activate when we are awake and engaging in introspection or processing emotions, which are activities that are important for brain health.”
For the first study, researchers from ANSIR lab studied youth football players without a history of concussion to assess the effects of repeated subconcussive impacts on the DMN.
“Over a season of football, players are exposed to numerous head impacts. The vast majority of these do not result in concussion,” said lead researcher Gowtham Krishnan Murugesan, a Ph.D. student in biomedical engineering and member of the ANSIR lab. “This work adds to a growing body of literature indicating that subconcussive head impacts can have an effect on the brain. This is a highly understudied area at the youth and high school level.”
In the study, the team equipped 26 youth football players between the ages of 9 and 13 with the Head Impact Telemetry System (HITS) and recorded data on their impacts over an entire football season. The HITS system uses sensors and accelerometers within the football helmet to track the magnitude, location, and direction of impacts.
Using this data, the team divided the players into two groups based on their risk of concussion. Half were placed into a “high exposure group”, while the others were designated as “low concussion exposure”. Those who had experienced a concussion were excluded. The researchers also evaluated a third group of 13 participants who did not play contact sports.
All participants underwent pre- and post-season resting functional MRI (fMRI) scans to assess the connectivity within the DMN network. The data from these scans were then assessed using machine learning to predict which players were most at risk for concussions.
Based on the scans alone, the algorithm could identify those with high-impact exposure with 82% accuracy. It could also discern between the low-impact and non-contact groups with 70% accuracy.
The researchers say this suggests that repeated subconcussive hits can be tied to specific changes in the brain that can be observed after the season has ended.
“The brains of these youth and adolescent athletes are undergoing rapid maturation in this age range. This study demonstrates that playing a season of contact sports at the youth level can produce neuroimaging brain changes, particularly for the DMN,” Murugesan said.
For the second study, researchers led by Dr. Davenport had 20 high school football players wear helmets equipped with HITS for a season. Of those players, five experienced at least one concussion, while 15 had no reported history of concussion.
The participants all underwent an eight-minute magnetoencephalography (MEG) scan before and after the season, which evaluates the magnetic fields produced within the brain. The researchers then analyzed the MEG power associated with the eight brain regions of the DMN.
In post-season scans, all five players who had experienced a concussion showed significantly lower connectivity within the DMN regions, while players with no concussion history actually showed improvement in DMN connectivity.
These findings indicate that concussions that occurred in past seasons can potentially have effects that last through the current season, or potentially longer.
“The brain’s default mode network changes differently as a result of previous concussion,” Dr. Davenport said. “Previous concussion seems to prime the brain for additional changes. Concussion history may be affecting the brain’s ability to compensate for subconcussive impacts.”
Both studies were relatively small and need larger tests to verify their accuracy. The teams also hope to eventually combine both MEG and fMRI to provide a more comprehensive picture of the complex factors at play after a concussion.