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

Uncovering the hidden effects of repetitive subconcussive head impact exposure: A mega-analytic approach characterizing seasonal brain microstructural changes in contact and collision sports athletes

Repetitive subconcussive head impacts (RSHI) are believed to induce sub-clinical brain injuries, potentially resulting in cumulative, long-term brain alterations. This study explores patterns of longitudinal brain white matter changes across sports with RSHI-exposure. A systematic literature search identified 22 datasets with longitudinal diffusion magnetic resonance imaging data. Four datasets were centrally pooled to perform uniform quality control and data preprocessing. A total of 131 non-concussed active athletes (American football, rugby, ice hockey; mean age: 20.06 ± 2.06 years) with baseline and post-season data were included. Nonparametric permutation inference (one-sample t tests, one-sided) was applied to analyze the difference maps of multiple diffusion parameters. The analyses revealed widespread lateralized patterns of sports-season-related increases and decreases in mean diffusivity (MD), radial diffusivity (RD), and axial diffusivity (AD) across spatially distinct white matter regions. Increases were shown across one MD-cluster (3195 voxels; mean change: 2.34%), one AD-cluster (5740 voxels; mean change: 1.75%), and three RD-clusters (817 total voxels; mean change: 3.11 to 4.70%). Decreases were shown across two MD-clusters (1637 total voxels; mean change: -1.43 to -1.48%), two RD-clusters (1240 total voxels; mean change: -1.92 to -1.93%), and one AD-cluster (724 voxels; mean change: -1.28%). The resulting pattern implies the presence of strain-induced injuries in central and brainstem regions, with comparatively milder physical exercise-induced effects across frontal and superior regions of the left hemisphere, which need further investigation. This article highlights key considerations that need to be addressed in future work to enhance our understanding of the nature of observed white matter changes, improve the comparability of findings across studies, and promote data pooling initiatives to allow more detailed investigations (e.g., exploring sex- and sport-specific effects).

Changes in the central nervous system in football players: an MRI study

BACKGROUND

Football (soccer) is the world's most popular team sport.

PURPOSE

To comprehensively examine the brain in football (soccer) players, with the use of magnetic resonance imaging (MRI) techniques.

MATERIAL AND METHODS

The study involved 65 football players and 62 controls. The MR examinations were performed using MR 1.5-T system (Optima MR 360; GE Medical Systems). The examinations were carried out in the 3D Bravo, CUBE, FSEpropeller, and diffusion-weighted imaging (DWI) sequences. The 1HMRS signal was obtained from the volume of interest in the frontal and occipital lobes on both sides.

RESULTS

The present study, based on structural MRI, shows some changes in the brains of the group of football players. The findings show asymmetry of the ventricular system in four football players, arachnoid cysts in the parieto-occipital region, and pineal cysts. NAA/Cr concentration in the right frontal lobe was lower in the football players than in the controls, and the Glx/Cr concentration in the right occipital lobe was higher. The apparent diffusion coefficient value is lower in football players in the occipital lobes.

CONCLUSION

Playing football can cause measurable changes in the brain, known to occur in patients diagnosed with traumatic brain injury. The present findings fill the gap in the literature by contributing evidence showing that playing football may lead to changes in the brain, without clinical symptoms of concussion.

Mitigating Traumatic Brain Injury: A Narrative Review of Supplementation and Dietary Protocols

Traumatic brain injuries (TBIs) constitute a significant public health issue and a major source of disability and death in the United States and worldwide. TBIs are strongly associated with high morbidity and mortality rates, resulting in a host of negative health outcomes and long-term complications and placing a heavy financial burden on healthcare systems. One promising avenue for the prevention and treatment of brain injuries is the design of TBI-specific supplementation and dietary protocols centred around nutraceuticals and biochemical compounds whose mechanisms of action have been shown to interfere with, and potentially alleviate, some of the neurophysiological processes triggered by TBI. For example, evidence suggests that creatine monohydrate and omega-3 fatty acids (DHA and EPA) help decrease inflammation, reduce neural damage and maintain adequate energy supply to the brain following injury. Similarly, melatonin supplementation may improve some of the sleep disturbances often experienced post-TBI. The scope of this narrative review is to summarise the available literature on the neuroprotective effects of selected nutrients in the context of TBI-related outcomes and provide an evidence-based overview of supplementation and dietary protocols that may be considered in individuals affected by-or at high risk for-concussion and more severe head traumas. Prophylactic and/or therapeutic compounds under investigation include creatine monohydrate, omega-3 fatty acids, BCAAs, riboflavin, choline, magnesium, berry anthocyanins, Boswellia serrata, enzogenol, N-Acetylcysteine and melatonin. Results from this analysis are also placed in the context of assessing and addressing important health-related and physiological parameters in the peri-impact period such as premorbid nutrient and metabolic health status, blood glucose regulation and thermoregulation following injury, caffeine consumption and sleep behaviours. As clinical evidence in this research field is rapidly emerging, a comprehensive approach including appropriate nutritional interventions has the potential to mitigate some of the physical, neurological, and emotional damage inflicted by TBIs, promote timely and effective recovery, and inform policymakers in the development of prevention strategies.

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.

The effect of contact/collision sport participation without concussion on neurometabolites: A systematic review and meta-analysis of magnetic resonance spectroscopy studies

The aim of this study was to systematically review prior research investigating the effects of contact/collision sport participation on neurometabolite levels in the absence of concussion. Four online databases were searched to identify studies that measured neurometabolite levels in contact/collision sport athletes (without concussion) using proton (1 H) or phosphorus (31 P) magnetic resonance spectroscopy (MRS). All study designs were acceptable for inclusion. Meta-analytic procedures were used to quantify the effect of contact/collision sport participation on neurometabolite levels and explore the impact of specific moderating factors (where sufficient data were available). Narrative synthesis was used to describe outcomes that could not be meta-analysed. Nine observational studies involving 300 contact/collision sport athletes were identified. Six studies (providing 112 effect estimates) employed longitudinal (cohort) designs and three (that could not be meta-analysed) employed case-control designs. N-acetylaspartate (NAA; g = -0.331, p = 0.013) and total creatine (tCr; creatine + phosphocreatine; g = -0.524, p = 0.029), but not glutamate-glutamine (Glx), myo-inositol (mI) or total choline (tCho; choline-containing compounds; p's > 0.05), decreased between the pre-season and mid-/post-season period. Several moderators were statistically significant, including: sex (Glx: 6 female/23 male, g = -0.549, p = 0.013), sport played (Glx: 22 American football/4 association football [soccer], g = 0.724, p = 0.031), brain region (mI: 2 corpus callosum/9 motor cortex, g = -0.804, p = 0.015), and the MRS quantification approach (mI: 18 absolute/3 tCr-referenced, g = 0.619, p = 0.003; and tCho: 18 absolute/3 tCr-referenced, g = 0.554, p = 0.005). In case-control studies, contact/collision sport athletes had higher levels of mI, but not NAA or tCr compared to non-contact sport athletes and non-athlete controls. Overall, this review suggests that contact/collision sport participation has the potential to alter neurometabolites measured via 1 H MRS in the absence of concussion. However, further research employing more rigorous and consistent methodologies (e.g. interventional studies with consistent 1 H MRS pulse sequences and quantifications) is required to confirm and better understand the clinical relevance of observed effects.

Design Considerations for the Attenuation of Translational and Rotational Accelerations in American Football Helmets

Participants in American football experience repetitive head impacts that induce negative changes in neurocognitive function over the course of a single season. This study aimed to quantify the transfer function connecting the force input to the measured output acceleration of the helmet system to provide a comparison of the impact attenuation of various modern American football helmets. Impact mitigation varied considerably between helmet models and with location for each helmet model. The current data indicate that helmet mass is a key variable driving force attenuation, however flexible helmet shells, helmet shell cutouts, and more compliant padding can improve energy absorption.

Diagnostic Prospectives with Tau Protein and Imaging Techniques to Detect Development of Chronic Traumatic Encephalopathy

Brain damage sustained from repeated blows in boxing, wrestling, and other combat sports has serious physical and mental health consequences. The degenerative brain disease, chronic traumatic encephalopathy (CTE), presents clinically with memory loss, aggression, difficulty in rational thinking and other cognitive problems. This spectrum, which mimics Alzheimer's disease, is diagnosed post-mortem through a brain biopsy in many professional athletes. However, little is known about the process of development and how to identify vulnerable individuals who may be on course for developing CTE. Boxing is a sport that has a severe toll on athletes' health, primarily on their brain health and function. This review addresses the concerns of brain injury, describes the pathologies that manifest in multiple scales, e.g., molecular and cognitive, and also proposes possible diagnostic and prognostic markers to characterize the early onset of CTE along with the aim to identify a starting point for future precautions and interventions.

Magnetic resonance spectroscopy of traumatic brain injury and subconcussive hits: A systematic review and meta-analysis

Magnetic resonance spectroscopy (MRS) is a non-invasive technique used to study metabolites in the brain. MRS findings in traumatic brain injury (TBI) and subconcussive hit literature have been mixed. The most common observation is a decrease in N-acetyl-aspartate (NAA), traditionally considered a marker of neuronal integrity. Other metabolites, however, such as creatine (Cr), choline (Cho), glutamate+glutamine (Glx) and myo-inositol (mI) have shown inconsistent changes in these populations. The objective of this systematic review and meta-analysis was to synthesize MRS literature in head injury and explore factors (brain region, injury severity, time since injury, demographic, technical imaging factors, etc.) that may contribute to differential findings. One hundred and thirty-eight studies met inclusion criteria for the systematic review and of those, 62 NAA, 24 Cr, 49 Cho, 18 Glx and 21 mI studies met inclusion criteria for meta-analysis. A random effects model was used for meta-analyses with brain region as a subgroup for each of the five metabolites studied. Meta-regression was used to examine the influence of potential moderators including injury severity, time since injury, age, sex, tissue composition and methodological factors. In this analysis of 1428 unique head-injured subjects and 1132 controls, the corpus callosum was identified as a brain region highly susceptible to metabolite alteration. NAA was consistently decreased in TBI of all severity, but not in subconcussive hits. Cho and mI were found to be increased in moderate-to-severe TBI but not mild TBI. Glx and Cr were largely unaffected, however did show alterations in certain conditions.

American football position-specific neurometabolic changes in high school athletes - a magnetic resonance spectroscopic study

Reports estimate between 1.6-3.8 million sports-related concussions occur annually, with 30% occurring in youth male American football athletes. Many studies report neurophysiological changes in these athletes, but the exact reasons for these changes remain elusive. Investigation of injury mechanics highlights a need to address how player position might impact these changes. Here, 55 high school American football athletes (20 linemen; 35 non-linemen) underwent magnetic resonance spectroscopy four times over the course of a football season (once prior to the season (Pre), twice during (In1, In2), and once following (Post)) to quantify metabolites (N-acetyl aspartate, choline, creatine, myo-inositol, and glutamate/glutamine) in the dorsolateral prefrontal cortex (DLPFC) and primary motor cortex (M1). Head acceleration events (HAEs) were monitored at each practice and game. Spectroscopic and HAE data were analyzed by imaging session and player position. Linear regression analyses were conducted between metabolite levels and HAEs, and metabolite levels in football athletes were compared to age-and gender-matched non-contact athletes. Across-season (i.e., between Pre and In1, In2, Post), different DLPFC and M1 metabolites decreased (p<0.05) according to player position (i.e., linemen vs. non-linemen). The majority of regression results involved DLPFC metabolites in linemen, where metabolite levels were higher, from Pre to Post, with increasing HAE load. Comparisons with control athletes revealed higher metabolite levels in football athletes both before and after the season. This study highlights the importance of player position when conducting analyses on American football athletes and demonstrates elevated DLPFC and M1 brain metabolites in football athletes compared to control athletes at both Pre and Post, suggesting potential HAE-related neurocompensatory mechanisms.

Metabolomic response to collegiate football participation: Pre- and Post-season analysis

Contact sports participation has been shown to have both beneficial and detrimental effects on health, however little is known about the metabolic sequelae of these effects. We aimed to identify metabolite alterations across a collegiate American football season. Serum was collected from 23 male collegiate football athletes before the athletic season (Pre) and after the last game (Post). Samples underwent nontargeted metabolomic profiling and 1131 metabolites were included for univariate, pathway enrichment, and multivariate analyses. Significant metabolites were assessed against head acceleration events (HAEs). 200 metabolites changed from Pre to Post (P < 0.05 and Q < 0.05); 160 had known identity and mapped to one of 57 pre-defined biological pathways. There was significant enrichment of metabolites belonging to five pathways (P < 0.05): xanthine, fatty acid (acyl choline), medium chain fatty acid, primary bile acid, and glycolysis, gluconeogenesis, and pyruvate metabolism. A set of 12 metabolites was sufficient to discriminate Pre from Post status, and changes in 64 of the 200 metabolites were also associated with HAEs (P < 0.05). In summary, the identified metabolites, and candidate pathways, argue there are metabolic consequences of both physical training and head impacts with football participation. These findings additionally identify a potential set of objective biomarkers of repetitive head injury.

Effects of combat sports on cerebellar function in adolescents: a resting-state fMRI study

OBJECTIVES

To evaluate the effects of combat sports on cerebellar function in adolescents based on resting-state functional MRI (rs-fMRI).

METHODS

Rs-fMRI data were acquired from the combat sports (CS) group (n = 32, aged 14.2 ± 1.1 years) and non-athlete healthy control (HC) group (n = 29, aged 14.8 ± 0.9 years). The amplitude of low-frequency fluctuation (ALFF), regional homogeneity (ReHo), and functional connectivity (FC) within the cerebellum was calculated and then compared between the two groups.

RESULTS

None of these participants displayed intracranial lesions on conventional MRI and microhemorrhages on SWI. Compared with the HC group, the CS group showed decreased ALFF and ReHo in the bilateral cerebellum, mainly located in the inferior regions of the cerebellum (Cerebellum_8, Cerebellum_9, Cerebellum_7b, and Cerebellum_Crus2). While increased FC was found within the cerebellar network, mainly located in the superior regions near the midline (bilateral Cerebellum_6, Cerebellum_Crus1_R, and Vermis_6). There is no internetwork FC change between the CEN and other networks.

CONCLUSION

This study confirmed extensive effects of combat sports on cerebellar rs-fMRI in adolescents, which could enhance the understanding of cerebellar regulatory mechanism under combat conditions, and provide additional information about cerebellar protective inhibition and compensatory adaptation.

ADVANCES IN KNOWLEDGE

Adolescent combat participants are an ideal model to study training-induced brain plasticity and vulnerability. Relative to task-related fMRI, rs-fMRI can bring more information about cerebellar regulation and explain the Central Governor Model more comprehensively.

Career Head Impact Exposure Profile of Canadian University Football Players

This study quantified head impact exposures for Canadian university football players over their varsity career. Participants included 63 players from one team that participated in a minimum of 3 seasons between 2013 and 2018. A total of 127,192 head impacts were recorded from 258 practices and 65 games. The mean (SD) number of career impacts across all positions was 2023.1 (1296.4), with an average of 37.1 (20.3) impacts per game and 7.4 (4.4) impacts per practice. The number of head impacts that players experienced during their careers increased proportionally to the number of athletic exposures (P < .001, r = .57). Linebackers and defensive and offensive linemen experienced significantly more head impacts than defensive backs, quarterbacks, and wide receivers (P ≤ .014). Seniority did not significantly affect the number of head impacts a player experienced. Mean linear acceleration increased with years of seniority within defensive backs and offensive linemen (P ≤ .01). Rotational velocity increased with years of seniority within defensive backs, defensive and offensive linemen, running backs, and wide receivers (P < .05). These data characterize career metrics of head impact exposure for Canadian university football players and provide insights to reduce head impacts through rule modifications and contact regulations.

Normalized Brain Tissue–Level Evaluation of Volumetric Changes of Youth Athletes Participating in Collision Sports

Observations of short-term changes in the neural health of youth athletes participating in collision sports (e.g., football and soccer) have highlighted a need to explore potential structural alterations in brain tissue volumes for these persons. Studies have shown biochemical, vascular, functional connectivity, and white matter diffusivity changes in the brain physiology of these athletes that are strongly correlated with repetitive head acceleration exposure. Here, research is presented that highlights regional anatomical volumetric measures that change longitudinally with accrued subconcussive trauma. A novel pipeline is introduced that provides simplified data analysis on standard-space template to quantify group-level longitudinal volumetric changes within these populations. For both sports, results highlight incremental relative regional volumetric changes in the subcortical cerebrospinal fluid that are strongly correlated with head exposure events greater than a 50-G threshold at the short-term post-season assessment. Moreover, longitudinal regional gray matter volumes are observed to decrease with time, only returning to baseline/pre-participation levels after sufficient (5–6 months) rest from collision-based exposure. These temporal structural volumetric alterations are significantly different from normal aging observed in sex- and age-matched controls participating in non-collision sports. Future work involves modeling repetitive head exposure thresholds with multi-modal image analysis and understanding the underlying physiological reason. A possible pathophysiological pathway is presented, highlighting the probable metabolic regulatory mechanisms. Continual participation in collision-based activities may represent a risk wherein recovery cannot occur. Even when present, the degree of the eventual recovery remains to be explored, but has strong implications for the well-being of collision-sport participants.

Brain trauma exposure for American tackle football players 5 to 9 and 9 to 14 years of age

American football helmets used by youth players are currently designed and tested to the same standards as professionals. The National Operating Committee on Standard and Safety requested research aiming at understanding the differences in brain trauma in youth American football for players aged five to nine and nine to fourteen years old to inform a youth specific American football standard. Video analysis and laboratory reconstructions of head impacts were undertaken to measure differences in head impact frequency, event types, and magnitudes of maximum principal strain (MPS) for the two age groups. Overall frequencies and frequencies for five categories of MPS representing different magnitudes of risk were tabulated. The MPS categories were very low (<0.08), low (0.08-0.169), medium (0.17-0.259), high (0.26-0.349) and very high (>0.35). Both cohorts experienced a majority of head impacts (>56%) at very low magnitude of MPS. Youth American football players aged 9-14 yrs. sustained a greater frequency of head impacts at MPS between 0.08 and 0.169 % associated with changes in brain structure and function. There were no differences in overall frequency, or in frequency of head impacts in other categories of MPS. The proportion of impacts considered injurious (MPS > 0.08) was greater in the 5-9 group (44%), than the 9-14 group (39%), and impacts above 0.35 % were only reported for the younger age group. The larger helmet-to-shoulder ratio in the younger age groups may have contributed to this finding suggesting that youth American football players under the age of nine would benefit from a child-specific football helmet.

The clinical utility of proton magnetic resonance spectroscopy in traumatic brain injury: recommendations from the ENIGMA MRS working group

Proton (1H) magnetic resonance spectroscopy provides a non-invasive and quantitative measure of brain metabolites. Traumatic brain injury impacts cerebral metabolism and a number of research groups have successfully used this technique as a biomarker of injury and/or outcome in both pediatric and adult TBI populations. However, this technique is underutilized, with studies being performed primarily at centers with access to MR research support. In this paper we present a technical introduction to the acquisition and analysis of in vivo 1H magnetic resonance spectroscopy and review 1H magnetic resonance spectroscopy findings in different injury populations. In addition, we propose a basic 1H magnetic resonance spectroscopy data acquisition scheme (Supplemental Information) that can be added to any imaging protocol, regardless of clinical magnetic resonance platform. We outline a number of considerations for study design as a way of encouraging the use of 1H magnetic resonance spectroscopy in the study of traumatic brain injury, as well as recommendations to improve data harmonization across groups already using this technique.

Brain Metabolite Levels in Sedentary Women and Non-contact Athletes Differ From Contact Athletes

White matter tracts are known to be susceptible to injury following concussion. The objective of this study was to determine whether contact play in sport could alter white matter metabolite levels in female varsity athletes independent of changes induced by long-term exercise. Metabolite levels were measured by single voxel proton magnetic resonance spectroscopy (MRS) in the prefrontal white matter at the beginning (In-Season) and end (Off-Season) of season in contact (N = 54, rugby players) and non-contact (N = 23, swimmers and rowers) varsity athletes. Sedentary women (N = 23) were scanned once, at a time equivalent to the Off-Season time point. Metabolite levels in non-contact athletes did not change over a season of play, or differ from age matched sedentary women except that non-contact athletes had a slightly lower myo-inositol level. The contact athletes had lower levels of myo-inositol and glutamate, and higher levels of glutamine compared to both sedentary women and non-contact athletes. Lower levels of myo-inositol in non-contact athletes compared to sedentary women indicates long-term exercise may alter glial cell profiles in these athletes. The metabolite differences observed between contact and non-contact athletes suggest that non-contact athletes should not be used as controls in studies of concussion in high-impact sports because repetitive impacts from physical contact can alter white matter metabolite level profiles. It is imperative to use athletes engaged in the same contact sport as controls to ensure a matched metabolite profile at baseline.

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.

Association of Professional Football Cumulative Head Impact Index Scores With All-Cause Mortality Among National Football League Players

Importance

Long-term adverse health outcomes, particularly those associated with repetitive head impacts, are of growing concern among US-style football players in the US and Canada.

Objective

To assess whether exposure to repetitive head impacts during a professional football career is associated with an increase in the risk of all-cause mortality.

Design, Setting, and Participants

This retrospective cohort study included 13 912 players in the 1969 to 2017 National Football League (NFL) seasons. All cause-mortality up until July 1, 2018, was included. Data collection was performed from July 13, 2017, to July 1, 2018, as reported in the Pro Football Reference.

Exposures

The main exposure was a professional football cumulative head impact index (pfCHII). The pfCHII was measured by combining cumulative padded practice time and games played summed during seasons of play reported in the Pro Football Reference and a player position risk adjustment from helmet accelerometer studies.

Main Outcomes and Measures

Demographic characteristics except for the pfCHII were calculated for 14 366 players with complete follow-up. The pfCHII was calculated for 13 912 players (eliminating the 454 specials teams players). Cox proportional hazards regression was used to compare hazard ratios (HRs) of death by repetitive head impacts. Analyses were unadjusted and adjusted for birth year, body mass index, and height.

Results

Among 14 366 NFL players who had follow-up for analysis, the mean (SD) age was 47.3 (14.8) years, the mean (SD) body mass index was 29.6 (3.9), and 763 of 14 366 players (5.3%) had died. Among 13 912 players in the pfCHII analysis, the median pfCHII was 32.63 (interquartile range, 13.71-66.12). A 1-log increase in pfCHII was significantly associated with an increased hazard of death for the 1969 to 2017 seasons (HR, 2.02; 95% CI, 1.21-3.37; P = .01) after adjustment. The quadratic pfCHII was also statistically significant (HR, 0.91; 95% CI, 0.85-0.98; P = .01), indicating that the hazard of death increased at a decreasing rate, whereas the pfCHII increased.

Conclusions and Relevance

The findings suggest that an increase in repetitive head impacts is associated with an increased hazard of death among NFL players. Reduction in repetitive head impacts from playing football or other activities through additional rule and equipment changes may be associated with reduced mortality.

Mitigating the Consequences of Subconcussive Head Injuries

Subconcussive head injury represents a pathophysiology that spans the expertise of both clinical neurology and biomechanical engineering. From both viewpoints, the terms injury and damage, presented without qualifiers, are synonymously taken to mean a tissue alteration that may be recoverable. For clinicians, concussion is evolving from a purely clinical diagnosis to one that requires objective measurement, to be achieved by biomedical engineers. Subconcussive injury is defined as subclinical pathophysiology in which underlying cellular- or tissue-level damage (here, to the brain) is not severe enough to present readily observable symptoms. Our concern is not whether an individual has a (clinically diagnosed) concussion, but rather, how much accumulative damage an individual can tolerate before they will experience long-term deficit(s) in neurological health. This concern leads us to look for the history of damage-inducing events, while evaluating multiple approaches for avoiding injury through reduction or prevention of the associated mechanically induced damage.

Neuroimaging in the Diagnosis of Chronic Traumatic Encephalopathy: A Systematic Review

OBJECTIVE

Chronic traumatic encephalopathy (CTE) is a neurodegenerative tauopathy associated with repeated subconcussive and concussive head injury. Clinical features include cognitive, behavioral, mood, and motor impairments. Definitive diagnosis is only possible at postmortem. Here, the utility of neuroimaging in the diagnosis of CTE is evaluated by systematically reviewing recent evidence for changes in neuroimaging biomarkers in suspected cases of CTE compared with controls.

DATA SOURCES

Providing an update on a previous systematic review of articles published until December 2014, we searched for articles published between December 2014 and July 2016. We searched PubMed for studies assessing neuroimaging changes in symptomatic suspected cases of CTE with a history of repeated subconcussive or concussive head injury or participation in contact sports involving direct impact to the head. Exclusion criteria were case studies, review articles, and articles focusing on repetitive head trauma from military service, head banging, epilepsy, physical abuse, or animal models.

MAIN RESULTS

Seven articles met the review criteria, almost all of which studied professional athletes. The range of modalities were categorized into structural magnetic resonance imaging (MRI), diffusion MRI, and radionuclide studies. Biomarkers which differed significantly between suspected CTE and controls were Evans index (P = 0.05), cavum septum pellucidum (CSP) rate (P < 0.0006), length (P < 0.03) and ratio of CSP length to septum length (P < 0.03), regional differences in axial diffusivity (P < 0.05) and free/intracellular water fractions (P < 0.005), single-photon emission computed tomography perfusion abnormalities (P < 0.01), positron emission tomography (PET) signals from tau-binding, glucose-binding, and GABA receptor-binding radionuclides (P < 0.0001, P < 0.005, and P < 0.005, respectively). Important limitations include low specificity in identification of suspected cases of CTE across studies, the need for postmortem validation, and a lack of generalizability to nonprofessional athletes.

CONCLUSIONS

The most promising biomarker is tau-binding radionuclide PET signal because it is most specific to the underlying neuropathology and differentiated CTE from both controls and patients with Alzheimer disease (P < 0.0001). Multimodal imaging will improve specificity further. Future research should minimize variability in identification of suspected cases of CTE using published clinical criteria.

A Prospective Transcranial Doppler Ultrasound-Based Evaluation of the Effects of Repetitive Subconcussive Head Trauma on Neurovascular Coupling Dynamics

OBJECTIVE

To determine the effects of repetitive subconcussive head trauma on neurovascular coupling (NVC) responses.

DESIGN

Prospective cohort study collected between September 2013 and December 2016.

SETTING

University laboratory.

PARTICIPANTS

One hundred seventy-nine elite, junior-level (age, 19.6 ± 1.5 years) contact sport (ice hockey, American football) athletes recruited for preseason testing. Fifty-two nonconcussed athletes returned for postseason testing. Fifteen noncontact sport athletes (age, 20.4 ± 2.2 years) also completed preseason and postseason testing.

EXPOSURE(S)

Subconcussive sport-related head trauma.

MAIN OUTCOME MEASURES

Dynamics of NVC were estimated during cycles of 20 seconds eyes closed and 40 seconds eyes open to a visual stimulus (reading) by measuring cerebral blood flow (CBF) velocity in the posterior (PCA) and middle (MCA) cerebral arteries via transcranial Doppler ultrasound.

RESULTS

Both athlete groups demonstrated no significant differences in PCA or MCA NVC dynamics between preseason and postseason, despite exposure to a median of 353.5 (range, 295.0-587.3) head impacts (>2g) over the course of the season for contact sport athletes.

CONCLUSIONS

Within the context of growing concern over detrimental effects of repetitive subconcussive trauma, the current results encouragingly suggest that the dynamics of NVC responses are not affected by 1 season of participation in junior-level ice hockey or American football. This is an important finding because it indicates an appropriate postseason CBF response to elevated metabolic demand with increases in neural activity.

A novel repetitive head impact exposure measurement tool differentiates player position in National Football League

American-style football participation poses a high risk of repetitive head impact (RHI) exposure leading to acute and chronic brain injury. The complex nature of symptom expression, human predisposition, and neurological consequences of RHI limits our understanding of what constitutes as an injurious impact affecting the integrity of brain tissue. Video footage of professional football games was reviewed and documentation made of all head contact. Frequency of impact, tissue strain magnitude, and time interval between impacts was used to quantify RHI exposure, specific to player field position. Differences in exposure characteristics were found between eight different positions; where three unique profiles can be observed. Exposure profiles provide interpretation of the relationship between the traumatic event(s) and how tissue injury is manifested and expressed. This study illustrates and captures an objective measurement of RHI on the field, a critical component in guiding public policy and guidelines for managing exposure.

Dependence on subconcussive impacts of brain metabolism in collision sport athletes: an MR spectroscopic study

Long term neurological impairments due to repetitive head trauma are a growing concern for collision sport athletes. American Football has the highest rate of reported concussions among male high school athletes, a position held by soccer for female high school athletes. Recent research has shown that subconcussive events experienced by collision sport athletes can be a further significant source of accrued damage. Collision sport athletes experience hundreds of subconcussive events in a single season, and these largely go uninvestigated as they produce no overt clinical symptoms. Continued participation by these seemingly uninjured athletes is hypothesized to increase susceptibility to diagnoseable brain injury. This study paired magnetic resonance spectroscopy with head impact monitoring to quantify the relationship between metabolic changes and head acceleration event characteristics in high school-aged male football and female soccer collision sport athletes. During the period of exposure to subconcussive events, asymptomatic male (football) collision sport athletes exhibited statistically significant changes in concentrations of glutamate+glutamine (Glx) and total choline containing compounds (tCho) in dorsolateral prefrontal cortex, and female (soccer) collision sport athletes exhibited changes in glutamate+glutamine (Glx) in primary motor cortex. Neurometabolic alterations observed in football athletes during the second half of the season were found to be significantly associated with the average acceleration per head acceleration events, being best predicted by the accumulation of events exceeding 50 g. These marked deviations in neurometabolism, in the absence of overt symptoms, raise concern about the neural health of adolescent collision-sport athletes and suggest limiting exposure to head acceleration events may help to ameliorate the risk of subsequent cognitive impairment.

Effect of Routine Sport Participation on Short-Term Clinical Neurological Outcomes: A Comparison of Non-Contact, Contact, and Collision Sport Athletes

OBJECTIVES

To compare pre-season to post-season changes on a battery of clinical neurological outcome measures between non-contact, contact, and collision sport athletes over multiple seasons of play.

METHODS

244 high school and collegiate athletes participating in multiple non-contact, contact, and collision sports completed standardized annual pre-season and post-season assessments over 1-4 years. Pre/post-season changes in 10 outcome measures assessing concussion symptoms, neurocognitive performance, and balance were compared between the groups using linear mixed models.

RESULTS

Small, but statistically significant overall pre/post-season change differences were present between the groups for Axon computerized neurocognitive test processing speed, attention, and working memory speed scores (Axon-PS, Axon-Att, Axon-WMS), as well as Balance Error Scoring System (BESS) total score. Small seasonal declines not exceeding reliable-change thresholds were observed in the collision sport group relative to the contact and non-contact groups for Axon-PS and Axon-Att scores. The collision and contact sport groups demonstrated less pre-/post-season improvement than the non-contact sport group for Axon-WMA and BESS, with less BESS improvement also observed in the collision sport group relative to the contact sport group. Overall, longitudinal performance on all 10 outcome measures remained stable in all 3 groups over 4 years.

CONCLUSION

Our findings do not necessarily support the notion that participation in sports associated with exposure to repetitive head impacts has clinically meaningful cumulative effects over the course of a season, nor over four consecutive seasons in high school and collegiate athletes.

Statistical Characterization of Human Brain Deformation During Mild Angular Acceleration Measured In Vivo by Tagged Magnetic Resonance Imaging

Understanding of in vivo brain biomechanical behavior is critical in the study of traumatic brain injury (TBI) mechanisms and prevention. Using tagged magnetic resonance imaging, we measured spatiotemporal brain deformations in 34 healthy human volunteers under mild angular accelerations of the head. Two-dimensional (2D) Lagrangian strains were examined throughout the brain in each subject. Strain metrics peaked shortly after contact with a padded stop, corresponding to the inertial response of the brain after head deceleration. Maximum shear strain of at least 3% was experienced at peak deformation by an area fraction (median±standard error) of 23.5±1.8% of cortical gray matter, 15.9±1.4% of white matter, and 4.0±1.5% of deep gray matter. Cortical gray matter strains were greater in the temporal cortex on the side of the initial contact with the padded stop and also in the contralateral temporal, frontal, and parietal cortex. These tissue-level deformations from a population of healthy volunteers provide the first in vivo measurements of full-volume brain deformation in response to known kinematics. Although strains differed in different tissue type and cortical lobes, no significant differences between male and female head accelerations or strain metrics were found. These cumulative results highlight important kinematic features of the brain's mechanical response and can be used to facilitate the evaluation of computational simulations of TBI.

Emerging advances of in vivo detection of chronic traumatic encephalopathy and traumatic brain injury

Chronic traumatic encephalopathy (CTE) is a neurodegenerative disorder that is of epidemic proportions in contact sports athletes and is linked to subconcussive and concussive repetitive head impacts (RHI). Although postmortem analysis is currently the only confirmatory method to diagnose CTE, there has been progress in early detection techniques of fluid biomarkers as well as in advanced neuroimaging techniques. Specifically, promising new methods of diffusion MRI and radionucleotide PET scans could aid in the early detection of CTE.The authors examine early detection methods focusing on various neuroimaging techniques. Advances in structural and diffusion MRI have demonstrated the ability to measure volumetric and white matter abnormalities associated with CTE. Recent studies using radionucleotides such as flortaucipir and 18F-FDDNP have shown binding patterns that are consistent with the four stages of neurofibrillary tangle (NFT) distribution postmortem. Additional research undertakings focusing on fMRI, MR spectroscopy, susceptibility-weighted imaging, and singlephoton emission CT are also discussed as are advanced MRI methods such as diffusiontensor imaging and arterial spin labeled. Neuroimaging is fast becoming a key instrument in early detection and could prove essential for CTE quantification. This review explores a global approach to in vivo early detection.Limited data of in vivo CTE biomarkers with postmortem confirmation are available. While some data exist, they are limited by selection bias. It is unlikely that a single test will be sufficient to properly diagnosis and distinguish CTE from other neurodegenerative diseases such as Alzheimer disease or Frontotemporal Dementia. However, with a combination of fluid biomarkers, neuroimaging, and genetic testing, early detection may become possible.

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.

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Brain volumes evidencing injury are larger in football athletes than controls.

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Spatial extent of decreased FA correlates with head acceleration event exposure.

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Spatial extent of increased MD correlates with head acceleration event exposure.

Acute neurocognitive deficits in active duty service members following subconcussive blast exposure

Military service members are frequently subjected to subconcussive blast events during training and deployment. Emerging evidence suggests blast exposures of these magnitudes may have long-term consequences for dimensions of cognitive function. Less is known about cognitive sequelae acutely following deployment-related subconcussive blast events. The current study addressed this knowledge gap by assessing the extent to which subconcussive blast exposure affected performance on the Automated Neuropsychological Assessment Metrics 4 TBI-MIL (ANAM). Baseline-referenced and normative comparisons of archival ANAM data were analyzed for a cohort of personnel who were exposed to blast (blast group; n = 27) and personnel who were not exposed to blast (no-blast group; n = 36) that were otherwise asymptomatic for a concussion. The blast group exhibited statistically significant lower scores compared to the no-blast group (between-subjects), baseline assessments (within-subjects), and an age-matched normative population. Normative comparisons revealed that the scores for the reaction time subtests (i.e., procedural and both simple reaction time tasks) were outside the range of normal functioning (1 SD) and reliable change indices revealed clinically meaningful change only for simple reaction time. The results highlight covert effects of subconcussive blast exposure that may warrant further monitoring in the immediate aftermath of a blast event.

Head impact magnitudes that occur from purposeful soccer heading depend on the game scenario and head impact location

PURPOSE

This study quantified the linear and angular kinematics that result from purposeful heading during youth soccer games, and the influence of game scenario and head impact location on these magnitudes.

METHOD

This observational study recruited thirty-six female soccer players (13.4 ± 0.9 years old) from three elite youth soccer teams (U13, U14, U15) and followed for an entire soccer season. Players wore wireless sensors during each game to quantify head impact magnitudes. A total of 60 regular season games (20 games per team) were video recorded, and purposeful heading events were categorized by game scenario (e.g. throw in), and head impact location (e.g. front of head).

RESULTS

Game scenario had a statistically significant effect on the linear head acceleration, and rotational head velocity, that resulted from purposeful headers. Rotational velocity from purposeful headers varied significantly between head impact locations, with impacts to the top of the head (improper technique) resulting in larger peak rotational velocities than impacts to the front of the head (proper technique); this was also the case for the linear acceleration for punts.

CONCLUSION

Our findings suggest that the magnitude for both linear and angular head impact kinematics depend on the game scenario and head impact location. Headers performed with the top of the head (improper technique) result in larger rotational velocities compared to the front of the head (proper technique). Accordingly, youth players should be educated on how to execute proper heading technique to reduce head impact accelerations.

The neurobiological effects of repetitive head impacts in collision sports

It is now recognized that repetitive head impacts (RHI) in sport have the potential for long-term neurological impairments. In order to identify targets for intervention and/or pharmacological treatment, it is necessary to characterize the neurobiological mechanisms associated with RHI. This review aims to summarize animal and human studies that specifically address Blood Brain Barrier (BBB) dysfunction, abnormal neuro-metabolic and neuro-inflammatory processes as well as Tau aggregation associated with RHI in collision sports. Additionally, we examine the influence of physical activity and genetics on outcomes of RHI, discuss methodological considerations, and provide suggestions for future directions of this burgeoning area of research.

Unifying Pathophysiological Explanations for Sports-Related Concussion and Concussion Protocol Management: Literature Review

Objective

There is a plethora of theories about the pathophysiology behind a sport-related concussion. In this review of the literature, the authors evaluated studies on the pathophysiology of sport-related concussion and professional athlete return-to-play guidelines. The goal of this article is to summarize the most common hypotheses for sport-related concussion, evaluate if there are common underlying mechanisms, and determine if correlations are seen between published mechanisms and the most current return-to-play recommendations.

Methods

Two authors selected papers from the past 5 years for literature review involving discussion of sport-related concussion and pathophysiology, pathology, or physiology of concussion using mutually agreed-upon search criteria. After the articles were filtered based on search criteria, pathophysiological explanations for concussion were organized into tables. Following analysis of pathophysiology, concussion protocols and return-to-play guidelines were obtained via a Google search for the major professional sports leagues and synthesized into a summary table.

Results

Out of 1112 initially identified publications, 53 met our criteria for qualitative analysis. The 53 studies revealed 5 primary neuropathological explanations for sport-related concussion, regardless of the many theories talked about in the different papers. These 5 explanations, in order of predominance in the articles analyzed, were (1) tauopathy, (2) white matter changes, (3) neural connectivity alterations, (4) reduction in cerebral perfusion, and (5) gray matter atrophy. Pathology may be sport specific: white matter changes are seen in 47% of football reports, tauopathy is seen in 50% of hockey reports, and soccer reports 50% tauopathy as well as 50% neural connectivity alterations. Analysis of the return-to-play guidelines across professional sports indicated commonalities in concussion management despite individual policies.

Conclusions

Current evidence on pathophysiology for sport-related concussion does not yet support one unifying mechanism, but published hypotheses may potentially be simplified into 5 primary groups. The unification of the complex, likely multifactorial mechanisms for sport-related concussion to a few common explanations, combined with unique findings within individual sports presented in this report, may help filter and link concussion pathophysiology in sport. By doing so, the authors hope that this review will help guide future concussion research, treatment, and management.

Cerebral Autoregulation Is Disrupted Following a Season of Contact Sports Participation

Repetitive subconcussive head impacts across a season of contact sports participation are associated with a number of deficits in brain function. To date, no research has investigated the effect of such head impact exposure on dynamic cerebral autoregulation (dCA). To address this issue, 179 elite, junior-level (age 19.6 ± 1.5 years) contact sport (ice hockey, American football) athletes were recruited for pre-season testing. Fifty-two non-concussed athletes returned for post-season testing. Fifteen non-contact sport athletes (age 20.4 ± 2.2) also completed pre- and postseason testing. dCA was assessed via recordings of beat-by-beat mean arterial pressure (MAP) and middle cerebral artery blood velocity (MCAv) using finger photoplethysmography and transcranial Doppler ultrasound, respectively, during repetitive squat-stand maneuvers at 0.05 and 0.10 Hz. Transfer function analysis was used to determine Coherence (correlation), Gain (response amplitude), and Phase (response latency) of the MAP-MCAv relationship. Results showed that in contact sport athletes, Phase was reduced (p = 0.027) and Gain increased (p < 0.001) at post-season compared to pre-season during the 0.10 Hz squat-stand maneuvers, indicating cerebral autoregulatory impairment in both the latency and magnitude of the response. Changes in Phase were greater in athletes experiencing higher numbers and severity of head impacts. By contrast, no changes in dCA were observed in non-contact sport controls. Taken together, these results demonstrate that repetitive subconcussive head impacts occurring across a season of contact sports participation are associated with exposure-dependent impairments in the cerebrovascular pressure-buffering system capacity. It is unknown how long these deficits persist or if they accumulate year-over-year.

Neuro-Metabolite Changes in a Single Season of University Ice Hockey Using Magnetic Resonance Spectroscopy

Background: Previous research has shown evidence for transient neuronal loss after repetitive head impacts (RHI) as demonstrated by a decrease in N-acetylaspartate (NAA). However, few studies have investigated other neuro-metabolites that may be altered in the presence of RHI; furthermore, the relationship of neuro-metabolite changes to neurocognitive outcome and potential sex differences remain largely unknown.

Objective: The aim of this study was to identify alterations in brain metabolites and their potential association with neurocognitive performance over time as well as to characterize sex-specific differences in response to RHI.

Methods: 33 collegiate ice hockey players (17 males and 16 females) underwent 3T magnetic resonance spectroscopy (MRS) and neurocognitive evaluation before and after the Canadian Interuniversity Sports (CIS) ice hockey season 2011–2012. The MRS voxel was placed in the corpus callosum. Pre- and postseason neurocognitive performances were assessed using the Immediate Post-Concussion Assessment and Cognitive Test (ImPACT). Absolute neuro-metabolite concentrations were then compared between pre- and postseason MRS were (level of statistical significance after correction for multiple comparisons: p < 0.007) and correlated to ImPACT scores for both sexes.

Results: A significant decrease in NAA was observed from preseason to postseason (p = 0.001). Furthermore, a trend toward a decrease in total choline (Cho) was observed (p = 0.044). Although no overall effect was observed for glutamate (Glu) over the season, a difference was observed with females showing a decrease in Glu and males showing an increase in Glu, though this was not statistically significant (p = 0.039). In both males and females, a negative correlation was observed between changes in Glu and changes in verbal memory (p = 0.008).

Conclusion: The results of this study demonstrate changes in absolute concentrations of neuro-metabolites following exposure to RHI. Results suggest that changes in Glu are correlated with changes in verbal memory. Future studies need to investigate further the association between brain metabolites and clinical outcome as well as sex-specific differences in the brain's response to RHI.

A Mild Traumatic Brain Injury in Mice Produces Lasting Deficits in Brain Metabolism

Metabolic uncoupling has been well-characterized during the first minutes-to-days after a traumatic brain injury (TBI), yet mitochondrial bioenergetics during the weeks-to-months after a brain injury is poorly defined, particularly after a mild TBI. We hypothesized that a closed head injury (CHI) would be associated with deficits in mitochondrial bioenergetics at one month after the injury. A significant decrease in state-III (adenosine triphosphate production) and state-V (complex-I) driven mitochondrial respiration was found at one month post-injury in adult C57Bl/6J mice. Isolation of synaptic mitochondria demonstrated that the deficit in state-III and state-V was primarily neuronal. Injured mice had a temporally consistent deficit in memory recall at one month post-injury. Using proton magnetic resonance spectroscopy (¹H MRS) at 7-Tesla, we found significant decreases in phosphocreatine, N-Acetylaspartic acid, and total choline. We also found regional variations in cerebral blood flow, including both hypo- and hyperperfusion, as measured by a pseudocontinuous arterial spin labeling MR sequence. Our results highlight a chronic deficit in mitochondrial bioenergetics associated with a CHI that may lead toward a novel approach for neurorestoration after a mild TBI. MRS provides a potential biomarker for assessing the efficacy of candidate treatments targeted at improving mitochondrial bioenergetics.

A systematic review of neuroimaging findings in children and adolescents with sports-related concussion

BACKGROUND

Sport-related concussion (SRC) generally does not result in structural anomalies revealed through clinical imaging techniques such as MRI and CT. While advanced neuroimaging techniques offer another avenue to investigate the subtle alterations following SRC, the current pediatric literature in this area has yet to be reviewed. The aim of this review is to systematically explore the literature on magnetic resonance spectroscopy (MRS), diffusion tensor imaging (DTI), functional magnetic resonance imaging (fMRI), and cortical thickness following SRC in children and adolescents.

METHODS

A systematic Pubmed search using the preferred reporting items for systematic reviews and meta-analysis guidelines was conducted independently for each neuroimaging method. Studies were screened for inclusion based on pre-determined criteria.

RESULTS

A total of 26 studies were included (MRS = 4, DTI = 10, fMRI = 11, cortical thickness = 1). A total of 16 studies were conducted solely with male athletes, while 10 studies recruited an unequal number of male and female athletes.

CONCLUSIONS

While MRI and CT are generally unrevealing, advanced neuroimaging techniques demonstrated neurometabolic, microstructural, and functional alterations following SRC in athletes younger than 19 years of age in the acute, subacute, and chronic phases of recovery. However, more studies are needed to fully understand the impact of SRC on the developing brain in children and adolescents.

Subconcussive trauma

Even impacts that do not immediately elicit symptoms of a concussion can induce changes in neural integrity. Because these so-called "subconcussive" head acceleration events, or head impact exposures, do not elicit identifiable symptoms, athletes continue to participate with unclear consequences. Neuroimaging studies reveal that neurologic changes, including inflammation, are associated with repetitive head impact exposures. Given that brain changes have been observed in athletes following repetitive head impact exposure, it is important to understand better and mitigate against this phenomenon. It is important to transition from the metric of concussion alone to one that includes repetitive head impact exposure, including the development of models that address why brain integrity may be compromised, who is at risk, and how to mitigate the risk of such exposure. Future work can include a health-monitoring framework to effect change and promote athlete safety.

Multiparametric MRI changes persist beyond recovery in concussed adolescent hockey players

OBJECTIVE

To determine whether multiparametric MRI data can provide insight into the acute and long-lasting neuronal sequelae after a concussion in adolescent athletes.

METHODS

Players were recruited from Bantam hockey leagues in which body checking is first introduced (male, age 11-14 years). Clinical measures, diffusion metrics, resting-state network and region-to-region functional connectivity patterns, and magnetic resonance spectroscopy absolute metabolite concentrations were analyzed from an independent, age-matched control group of hockey players (n = 26) and longitudinally in concussed athletes within 24 to 72 hours (n = 17) and 3 months (n = 14) after a diagnosed concussion.

RESULTS

There were diffusion abnormalities within multiple white matter tracts, functional hyperconnectivity, and decreases in choline 3 months after concussion. Tract-specific spatial statistics revealed a large region along the superior longitudinal fasciculus with the largest decreases in diffusivity measures, which significantly correlated with clinical deficits. This region also spatially intersected with probabilistic tracts connecting cortical regions where we found acute functional connectivity changes. Hyperconnectivity patterns at 3 months after concussion were present only in players with relatively less severe clinical outcomes, higher choline concentrations, and diffusivity indicative of relatively less axonal disruption.

CONCLUSIONS

Changes persisted well after players' clinical scores had returned to normal and they had been cleared to return to play. Ongoing white matter maturation may make adolescent athletes particularly vulnerable to brain injury, and they may require extended recovery periods. The consequences of early brain injury for ongoing brain development and risk of more serious conditions such as second impact syndrome or neural degenerative processes need to be elucidated.

Age of first exposure to American football and long-term neuropsychiatric and cognitive outcomes

Previous research suggests that age of first exposure (AFE) to football before age 12 may have long-term clinical implications; however, this relationship has only been examined in small samples of former professional football players. We examined the association between AFE to football and behavior, mood and cognition in a large cohort of former amateur and professional football players. The sample included 214 former football players without other contact sport history. Participants completed the Brief Test of Adult Cognition by Telephone (BTACT), and self-reported measures of executive function and behavioral regulation (Behavior Rating Inventory of Executive Function-Adult Version Metacognition Index (MI), Behavioral Regulation Index (BRI)), depression (Center for Epidemiologic Studies Depression Scale (CES-D)) and apathy (Apathy Evaluation Scale (AES)). Outcomes were continuous and dichotomized as clinically impaired. AFE was dichotomized into <12 and ⩾12, and examined continuously. Multivariate mixed-effect regressions controlling for age, education and duration of play showed AFE to football before age 12 corresponded with >2 × increased odds for clinically impaired scores on all measures but BTACT: (odds ratio (OR), 95% confidence interval (CI): BRI, 2.16,1.19-3.91; MI, 2.10,1.17-3.76; CES-D, 3.08,1.65-5.76; AES, 2.39,1.32-4.32). Younger AFE predicted increased odds for clinical impairment on the AES (OR, 95% CI: 0.86, 0.76-0.97) and CES-D (OR, 95% CI: 0.85, 0.74-0.97). There was no interaction between AFE and highest level of play. Younger AFE to football, before age 12 in particular, was associated with increased odds for impairment in self-reported neuropsychiatric and executive function in 214 former American football players. Longitudinal studies will inform youth football policy and safety decisions.

The effect of repetitive subconcussive collisions on brain integrity in collegiate football players over a single football season: A multi-modal neuroimaging study

The cumulative effect of repetitive subconcussive collisions on the structural and functional integrity of the brain remains largely unknown. Athletes in collision sports, like football, experience a large number of impacts across a single season of play. The majority of these impacts, however, are generally overlooked, and their long-term consequences remain poorly understood. This study sought to examine the effects of repetitive collisions across a single competitive season in NCAA Football Bowl Subdivision athletes using advanced neuroimaging approaches. Players were evaluated before and after the season using multiple MRI sequences, including T₁-weighted imaging, diffusion tensor imaging (DTI), arterial spin labeling (ASL), resting-state functional MRI (rs-fMRI), and susceptibility weighted imaging (SWI). While no significant differences were found between pre- and post-season for DTI metrics or cortical volumes, seed-based analysis of rs-fMRI revealed significant (p < 0.05) changes in functional connections to right isthmus of the cingulate cortex (ICC), left ICC, and left hippocampus. ASL data revealed significant (p < 0.05) increases in global cerebral blood flow (CBF), with a specific regional increase in right postcentral gyrus. SWI data revealed that 44% of the players exhibited outlier rates (p < 0.05) of regional decreases in SWI signal. Of key interest, athletes in whom changes in rs-fMRI, CBF and SWI were observed were more likely to have experienced high G impacts on a daily basis. These findings are indicative of potential pathophysiological changes in brain integrity arising from only a single season of participation in the NCAA Football Bowl Subdivision, even in the absence of clinical symptoms or a diagnosis of concussion. Whether these changes reflect compensatory adaptation to cumulative head impacts or more lasting alteration of brain integrity remains to be further explored.

Potential for use of creatine supplementation following mild traumatic brain injury

There is significant overlap between the neuropathology of mild traumatic brain injury (mTBI) and the cellular role of creatine, as well as evidence of neural creatine alterations after mTBI. Creatine supplementation has not been researched in mTBI, but shows some potential as a neuroprotective when administered prior to or after TBI. Consistent with creatine’s cellular role, supplementation reduced neuronal damage, protected against the effects of cellular energy crisis and improved cognitive and somatic symptoms. A variety of factors influencing the efficacy of creatine supplementation are highlighted, as well as avenues for future research into the potential of supplementation as an intervention for mTBI. In particular, the slow neural uptake of creatine may mean that greater effects are achieved by pre-emptive supplementation in at-risk groups.

Long-Term Anesthetic-Dependent Hypoactivity after Repetitive Mild Traumatic Brain Injuries in Adolescent Mice

Recent evidence supports the hypothesis that repetitive mild traumatic brain injuries (rmTBIs) culminate in neurological impairments and chronic neurodegeneration, which have wide-ranging implications for patient management and return-to-play decisions for athletes. Adolescents show a high prevalence of sports-related head injuries and may be particularly vulnerable to rmTBIs due to ongoing brain maturation. However, it remains unclear whether rmTBIs, below the threshold for acute neuronal injury or symptomology, influence long-term outcomes. To address this issue, we first defined a very mild injury in adolescent mice (postnatal day 35) as evidenced by an increase in Iba-1- labeled microglia in white matter in the acutely injured brain, in the absence of indices of cell death, axonal injury, and vasogenic edema. Using this level of injury severity and Avertin (2,2,2-tribromoethanol) as the anesthetic, we compared mice subjected to either a single mTBI or 2 rmTBIs, each separated by 48 h. Neurobehavioral assessments were conducted at 1 week and at 1 and 3 months postimpact. Mice subjected to rmTBIs showed transient anxiety and persistent and pronounced hypoactivity compared to sham control mice, alongside normal sensorimotor, cognitive, social, and emotional function. As isoflurane is more commonly used than Avertin in animal models of TBI, we next examined long-term outcomes after rmTBIs in mice that were anesthetized with this agent. However, there was no evidence of abnormal behaviors even with the addition of a third rmTBI. To determine whether isoflurane may be neuroprotective, we compared the acute pathology after a single mTBI in mice anesthetized with either Avertin or isoflurane. Pathological findings were more pronounced in the group exposed to Avertin compared to the isoflurane group. These collective findings reveal distinct behavioral phenotypes (transient anxiety and prolonged hypoactivity) that emerge in response to rmTBIs. Our findings further suggest that selected anesthetics may confer early neuroprotection after rmTBIs, and as such mask long-term abnormal phenotypes that may otherwise emerge as a consequence of acute pathogenesis.