Longitudinal changes in resting state fMRI brain self-similarity of asymptomatic high school American football athletes.

American football has become the focus of numerous studies highlighting a growing concern that cumulative exposure to repetitive, sports-related head acceleration events (HAEs) may have negative consequences for brain health, even in the absence of a diagnosed concussion. In this longitudinal study, brain functional connectivity was analyzed in a cohort of high school American football athletes over a single play season and compared against participants in non-collision high school sports. Football athletes underwent four resting-state functional magnetic resonance imaging sessions: once before (pre-season), twice during (in-season), and once 34-80 days after the contact activities play season ended (post-season). For each imaging session, functional connectomes (FCs) were computed for each athlete and compared across sessions using a metric reflecting the (self) similarity between two FCs. HAEs were monitored during all practices and games throughout the season using head-mounted sensors. Relative to the pre-season scan session, football athletes exhibited decreased FC self-similarity at the later in-season session, with apparent recovery of self-similarity by the time of the post-season session. In addition, both within and post-season self-similarity was correlated with cumulative exposure to head acceleration events. These results suggest that repetitive exposure to HAEs produces alterations in functional brain connectivity and highlight the necessity of collision-free recovery periods for football athletes.

Development of brain atlases for early-to-middle adolescent collision-sport athletes.

Human brains develop across the life span and largely vary in morphology. Adolescent collision-sport athletes undergo repetitive head impacts over years of practices and competitions, and therefore may exhibit a neuroanatomical trajectory different from healthy adolescents in general. However, an unbiased brain atlas targeting these individuals does not exist. Although standardized brain atlases facilitate spatial normalization and voxel-wise analysis at the group level, when the underlying neuroanatomy does not represent the study population, greater biases and errors can be introduced during spatial normalization, confounding subsequent voxel-wise analysis and statistical findings. In this work, targeting early-to-middle adolescent (EMA, ages 13-19) collision-sport athletes, we developed population-specific brain atlases that include templates (T1-weighted and diffusion tensor magnetic resonance imaging) and semantic labels (cortical and white matter parcellations). Compared to standardized adult or age-appropriate templates, our templates better characterized the neuroanatomy of the EMA collision-sport athletes, reduced biases introduced during spatial normalization, and exhibited higher sensitivity in diffusion tensor imaging analysis. In summary, these results suggest the population-specific brain atlases are more appropriate towards reproducible and meaningful statistical results, which better clarify mechanisms of traumatic brain injury and monitor brain health for EMA collision-sport athletes.

Head acceleration event metrics in youth contact sports more dependent on sport than level of play.

The goal of the study was to evaluate how repetitive head traumas sustained by athletes in contact sports depend on sport and level of play. A total of 16 middle school football players, 107 high school football players, and 65 high school female soccer players participated. Players were separated into levels of play: middle school (MS), freshman (FR), junior varsity (JV), junior varsity-varsity (JV-V), and varsity (V). xPatch sensors were used to measure peak translational and angular accelerations (PTA and PAA, respectively) for each head acceleration event (HAE) during practice and game sessions. Data were analyzed using a custom MATLAB program to compare metrics that have been correlated with functional neurological changes: session metrics (median HAEs per contact session), season metrics (total HAEs, cumulative PTA/PAA), and regressions (cumulative PTA/PAA versus total HAEs, total HAEs versus median HAEs per contact session). Football players had greater session (p<.001) and season (p<.001) metrics than soccer players, but soccer players had a significantly greater player average PAA per HAE than football players (p<.001). Middle school football players had similar session and season metrics to high school level athletes. In conclusion, sport has a greater influence on HAE characteristics than level of play.

Factors affecting peak impact force during soccer headers and implications for the mitigation of head injuries.

It has been documented that up to 22% of all soccer injuries are concussions. This is in part due to players purposely using their head to direct the ball during play. To provide a more complete understanding of head trauma in soccer athletes, this study characterized the effects of four soccer ball characteristics (size, inflation pressure, mass, velocity) on the resulting peak impact force as it relates to the potential for incurring neurophysiological changes. A total of six hundred trials were performed on size 4 and 5 soccer balls as well as a novel lightweight soccer ball. Impact force was measured with a force plate and ball velocity was determined using motion capture. These data were used, in conjunction with dimensional analysis to relate impact force to ball size, mass, velocity, and pressure. Reasonable reductions in allowable ball parameters resulted in a 19.7% decrease in peak impact force. Adjustments to ball parameters could reduce a high cumulative peak translational acceleration soccer athlete down into a previously defined safer low loading range. In addition, it was noted that water absorption by soccer balls can result in masses that substantially increase impact force and quickly surpass the NCAA weight limit for game play. Additional research is required to determine whether varying soccer ball characteristics will enable soccer players to avoid persistent neurophysiological deficits or what additional interventions may be necessary and the legal implications of these data are discussed.

Accumulation of high magnitude acceleration events predicts cerebrovascular reactivity changes in female high school soccer athletes.

Mitigating the effects of repetitive exposure to head trauma has become a major concern for the general population, given the growing body of evidence that even asymptomatic exposure to head accelerations is linked with increased risk for negative life outcomes and that risk increases as exposure is prolonged over many years. Among women's sports, soccer currently exhibits the highest growth in participation and reports the largest number of mild traumatic brain injuries annually, making female soccer athletes a relevant population in assessing the effects of repetitive exposure to head trauma. Cerebrovascular biomarkers may be useful in assessing the effects of repetitive head trauma, as these are thought to contribute directly to neurocognitive symptoms associated with mild traumatic brain injury. Here we use fMRI paired with a hypercapnic breath hold task along with monitoring of head acceleration events, to assess the relationship between cerebrovascular brain changes and exposure to repetitive head trauma over a season of play in female high school soccer athletes. We identified longitudinal changes in cerebrovascular reactivity that were significantly associated with prolonged accumulation to high magnitude (> 75th percentile) head acceleration events. Findings argue for active monitoring of athletes during periods of exposure to head acceleration events, illustrate the importance of collecting baseline (i.e., pre-exposure) measurements, and suggest modeling as a means of guiding policy to mitigate the effects of repetitive head trauma.

Every hit matters: White matter diffusivity changes in high school football athletes are correlated with repetitive head acceleration event exposure.

Recent evidence of short-term alterations in brain physiology associated with repeated exposure to moderate intensity subconcussive head acceleration events (HAEs), prompts the question whether these alterations represent an underlying neural injury. A retrospective analysis combining counts of experienced HAEs and longitudinal diffusion-weighted imaging explored whether greater exposure to incident mechanical forces was associated with traditional diffusion-based measures of neural injury-reduced fractional anisotropy (FA) and increased mean diffusivity (MD). Brains of high school athletes (N = 61) participating in American football exhibited greater spatial extents (or volumes) experiencing substantial changes (increases and decreases) in both FA and MD than brains of peers who do not participate in collision-based sports (N = 15). Further, the spatial extents of the football athlete brain exhibiting traditional diffusion-based markers of neural injury were found to be significantly correlated with the cumulative exposure to HAEs having peak translational acceleration exceeding 20 g. This finding demonstrates that subconcussive HAEs induce low-level neurotrauma, with prolonged exposure producing greater accumulation of neural damage. The duration and extent of recovery associated with periods in which athletes do not experience subconcussive HAEs now represents a priority for future study, such that appropriate participation and training schedules may be developed to minimize the risk of long-term neurological dysfunction.

Impact attenuation of male and female lacrosse helmets using a modal impulse hammer.

It has been established that substantial negative changes in neurocognitive function can be observed in a large percentage of athletes who participate in contact sports such as soccer or football, motivating a need for improved safety systems. Head accelerations in men's lacrosse are similar to those in football and female lacrosse players experience high rates of concussions, necessitating better head protection in both sports. Previous studies have sought to evaluate the ability of modern football helmets to mitigate impacts both normal and oblique to the surface of the helmet using a system that quantifies both the input load and the resulting accelerations of a Hybrid III headform. This study quantifies the inputs and outputs of the helmet-Hybrid III headform system in order to compare the impact attenuation capability of two male and two female lacrosse helmets. Of those helmets tested, the better performing male helmet was the Schutt Stallion 650 and the better performing female helmet was the Hummingbird excepting device failure at the rear boss impact location, but football helmets still generally outperformed the lacrosse helmets tested here.

Cerebrovascular reactivity changes in asymptomatic female athletes attributable to high school soccer participation.

As participation in women's soccer continues to grow and the longevity of female athletes' careers continues to increase, prevention and care for mTBI in women's soccer has become a major concern for female athletes since the long-term risks associated with a history of mTBI are well documented. Among women's sports, soccer exhibits among the highest concussion rates, on par with those of men's football at the collegiate level. Head impact monitoring technology has revealed that "concussive hits" occurring directly before symptomatic injury are not predictive of mTBI, suggesting that the cumulative effect of repetitive head impacts experienced by collision sport athletes should be assessed. Neuroimaging biomarkers have proven to be valuable in detecting brain changes that occur before neurocognitive symptoms in collision sport athletes. Quantifying the relationship between changes in these biomarkers and head impacts experienced by female soccer athletes may prove valuable to developing preventative measures for mTBI. This study paired functional magnetic resonance imaging with head impact monitoring to track cerebrovascular reactivity changes throughout a season and to test whether the observed changes could be attributed to mechanical loading experienced by female athletes participating in high school soccer. Marked cerebrovascular reactivity changes were observed in female soccer athletes, relative both to non-collision sport control measures and pre-season measures and were localized to fronto-temporal aspects of the brain. These changes persisted 4-5 months after the season ended and recovered by 8 months after the season. Segregation of the total soccer cohort into cumulative loading groups revealed that population-level changes were driven by athletes experiencing high cumulative loads, although athletes experiencing lower cumulative loads still contributed to group changes. The results of this study imply a non-linear relationship between cumulative loading and cerebrovascular changes with a threshold, above which the risk, of injury likely increases significantly.

Collegiate women's soccer players suffer greater cumulative head impacts than their high school counterparts.

Soccer is the source of the highest concussion rates among female athletes and is associated with neurological deficits at many levels of play. Despite its importance to our understanding of head trauma in female athletes, little is known about the number and magnitude of head impacts experienced by female soccer players. Head impacts experienced by high school and collegiate athletes were quantified using xPatch sensors (X2 Biosystems) affixed behind the right ear of each player. The average peak translational acceleration (PTA) sustained by players at the high school level was significantly lower than that of the collegiate players, but the average peak angular accelerations (PAA) were not significantly different. Given that the collegiate players took many more impacts throughout the season, their mean cumulative exposure to translational (cPTA) and angular accelerations (cPAA) were significantly higher than those of the high school players. Additional research is required to determine whether the differences in cumulative exposure are responsible for the elevated risk of concussion in collegiate soccer players or if there are additional risk factors.

FMRI of visual working memory in high school football players.

Visual working memory deficits have been observed in at-risk athletes. This study uses a visual N-back working memory functional magnetic resonance imaging task to longitudinally assess asymptomatic football athletes for abnormal activity. Athletes were increasingly "flagged" as the season progressed. Flagging may provide early detection of injury.

The role of location of subconcussive head impacts in FMRI brain activation change.

Monte-Carlo permutation analysis was used to identify sets of head impacts most predictive of functional magnetic resonance imaging (fMRI) changes in football players. The relative distribution of impact location was found to be more predictive of brain activation changes than the number of impacts, suggesting that fMRI changes are related to systematic playing style.

Cerebrovascular reactivity alterations in asymptomatic high school football players.

Cerebrovascular reactivity (CVR) is impaired following brain injury, increasing susceptibility to subsequent injury. CVR was tracked in football and non-collision athletes throughout one season. CVR transiently decreased in football athletes during the first half of the season. Results indicate the brain adapts slowly to increases in loading, increasing risk for injury.

Post-Season Neurophysiological Deficits Assessed by ImPACT and fMRI in Athletes Competing in American Football.

Neurocognitive assessment, functional magnetic resonance imaging, and head impact monitoring were used to evaluate neurological changes in high school football players throughout competitive seasons. A substantial number of asymptomatic athletes exhibited neurophysiological changes that persisted post-season, with abnormal measures significantly more common in athletes receiving 50 or more hits per week during the season.

Sub-concussive hit characteristics predict deviant brain metabolism in football athletes.

Magnetic resonance spectroscopy and helmet telemetry were used to monitor the neural metabolic response to repetitive head collisions in 25 high school American football athletes. Specific hit characteristics were determined highly predictive of metabolic alterations, suggesting that sub-concussive blows can produce biochemical changes and potentially lead to neurological problems.

Effects of repetitive sub-concussive brain injury on the functional connectivity of Default Mode Network in high school football athletes.

Sub-concussive head impacts are identified as a source of accrued damage. Football athletes experience hundreds of such blows each season. Resting state functional magnetic resonance imaging was used to prospectively study changes in Default Mode Network connectivity for clinically asymptomatic high school football athletes. Athletes exhibited short-term changes relative to baseline and across sessions.

Alteration of default mode network in high school football athletes due to repetitive subconcussive mild traumatic brain injury: a resting-state functional magnetic resonance imaging study.

Long-term neurological damage as a result of head trauma while playing sports is a major concern for football athletes today. Repetitive concussions have been linked to many neurological disorders. Recently, it has been reported that repetitive subconcussive events can be a significant source of accrued damage. Since football athletes can experience hundreds of subconcussive hits during a single season, it is of utmost importance to understand their effect on brain health in the short and long term. In this study, resting-state functional magnetic resonance imaging (rs-fMRI) was used to study changes in the default mode network (DMN) after repetitive subconcussive mild traumatic brain injury. Twenty-two high school American football athletes, clinically asymptomatic, were scanned using the rs-fMRI for a single season. Baseline scans were acquired before the start of the season, and follow-up scans were obtained during and after the season to track the potential changes in the DMN as a result of experienced trauma. Ten noncollision-sport athletes were scanned over two sessions as controls. Overall, football athletes had significantly different functional connectivity measures than controls for most of the year. The presence of this deviation of football athletes from their healthy peers even before the start of the season suggests a neurological change that has accumulated over the years of playing the sport. Football athletes also demonstrate short-term changes relative to their own baseline at the start of the season. Football athletes exhibited hyperconnectivity in the DMN compared to controls for most of the sessions, which indicates that, despite the absence of symptoms typically associated with concussion, the repetitive trauma accrued produced long-term brain changes compared to their healthy peers.

The Role of Medical Imaging in the Recharacterization of Mild Traumatic Brain Injury Using Youth Sports as a Laboratory.

The short- and long-term impact of mild traumatic brain injury (TBI) is an increasingly vital concern for both military and civilian personnel. Such injuries produce significant social and financial burdens and necessitate improved diagnostic and treatment methods. Recent integration of neuroimaging and biomechanical studies in youth collision-sport athletes has revealed that significant alterations in brain structure and function occur even in the absence of traditional clinical markers of "concussion." While task performance is maintained, athletes exposed to repetitive head accelerations exhibit structural changes to the underlying white matter, altered glial cell metabolism, aberrant vascular response, and marked changes in functional network behavior. Moreover, these changes accumulate with accrued years of exposure, suggesting a cumulative trauma mechanism that may culminate in categorization as "concussion" and long-term neurological deficits. The goal of this review is to elucidate the role of medical imaging in recharacterizing TBI, as a whole, to better identify at-risk individuals and improve the development of preventative and interventional approaches.

MR spectroscopic evidence of brain injury in the non-diagnosed collision sport athlete.

With growing evidence of long-term neurological damage in individuals enduring repetitive head trauma, it is critical to detect lower-level damage accumulation for the early diagnosis of injury in at-risk populations. Proton magnetic resonance spectroscopic scans of the dorsolateral prefrontal cortex and primary motor cortex were collected from high school American (gridiron) football athletes, prior to and during their competition seasons. Although no concussions were diagnosed, significant metabolic deviations from baseline and non-collision sport controls were revealed. Overall the findings indicate underlying biochemical changes, consequential to repetitive hits, which have previously gone unnoticed due to a lack of traditional neurological symptoms.

Functionally-detected cognitive impairment in high school football players without clinically-diagnosed concussion.

Head trauma and concussion in football players have recently received considerable media attention. Postmortem evidence suggests that accrual of damage to the brain may occur with repeated blows to the head, even when the individual blows fail to produce clinical symptoms. There is an urgent need for improved detection and characterization of head trauma to reduce future injury risk and promote development of new therapies. In this study we examined neurological performance and health in the presence of head collision events in high school football players, using longitudinal measures of collision events (the HIT(™) System), neurocognitive testing (ImPACT(™)), and functional magnetic resonance imaging MRI (fMRI). Longitudinal assessment (including baseline) was conducted in 11 young men (ages 15-19 years) participating on the varsity and junior varsity football teams at a single high school. We expected and observed subjects in two previously described categories: (1) no clinically-diagnosed concussion and no changes in neurological behavior, and (2) clinically-diagnosed concussion with changes in neurological behavior. Additionally, we observed players in a previously undiscovered third category, who exhibited no clinically-observed symptoms associated with concussion, but who demonstrated measurable neurocognitive (primarily visual working memory) and neurophysiological (altered activation in the dorsolateral prefrontal cortex [DLPFC]) impairments. This new category was associated with significantly higher numbers of head collision events to the top-front of the head, directly above the DLPFC. The discovery of this new category suggests that more players are suffering neurological injury than are currently being detected using traditional concussion-assessment tools. These individuals are unlikely to undergo clinical evaluation, and thus may continue to participate in football-related activities, even when changes in brain physiology (and potential brain damage) are present, which will increase the risk of future neurological injury.

Biomechanical correlates of symptomatic and asymptomatic neurophysiological impairment in high school football.

Concussion is a growing public health issue in the United States, and chronic traumatic encephalopathy (CTE) is the chief long-term concern linked to repeated concussions. Recently, attention has shifted toward subconcussive blows and the role they may play in the development of CTE. We recruited a cohort of high school football players for two seasons of observation. Acceleration sensors were placed in the helmets, and all contact activity was monitored. Pre-season computer-based neuropsychological tests and functional magnetic resonance imaging (fMRI) tests were also obtained in order to assess cognitive and neurophysiological health. In-season follow-up scans were then obtained both from individuals who had sustained a clinically-diagnosed concussion and those who had not. These changes were then related through stepwise regression to history of blows recorded throughout the football season up to the date of the scan. In addition to those subjects who had sustained a concussion, a substantial portion of our cohort who did not sustain concussions showed significant neurophysiological changes. Stepwise regression indicated significant relationships between the number of blows sustained by a subject and the ensuing neurophysiological change. Our findings reinforce the hypothesis that the effects of repetitive blows to the head are cumulative and that repeated exposure to subconcussive blows is connected to pathologically altered neurophysiology.