Role of subconcussion in repetitive mild traumatic brain injury

Short-term behavioral and histological findings following a single concussive and repeated subconcussive brain injury in a rodent model

PRIMARY OBJECTIVE

It is unclear of the correlation between a mild traumatic brain injury (mTBI) and repeated subconcussive (RSC) impacts with respect to injury biomechanics. Thus, the present study was designed to determine the behavioral and histological differences between a single mTBI impact and RSC impacts with subdivided cumulative kinetic energies of the single mTBI impact.

RESEARCH DESIGN

Adult male Sprague-Dawley rats were randomly assigned to a single mTBI impact, RSC impact, sham, or repeated sham groups.

METHODS AND PROCEDURES

Following a weight drop injury, anxiety-like behavior and general locomotive activity and were assessed using the open field test, while motor coordination was evaluated using a rotarod unit. Neuronal loss, astrogliosis, and microgliosis were assessed using NeuN, GFAP and Iba-1 immunohistochemistry. All assessments were undertaken at 3- and 7-days post impact.

MAIN OUTCOMES AND RESULTS

No behavioral disturbances were observed in injury groups, however, both injury groups did lead to microgliosis following 3-days post-impact.

CONCLUSIONS

No pathophysiological differences were observed between a single mTBI impact and RSC impacts of the same energy input. Even though a cumulative injury threshold for RSC impacts was not determined, a threshold still may exist where no pathodynamic shift occurs.

Cognitive and Salience Network Connectivity Changes following a Single Season of Repetitive Head Impact Exposure in High School Football

BACKGROUND AND PURPOSE

During a season of high school football, adolescents with actively developing brains experience a considerable number of head impacts. Our aim was to determine whether repetitive head impacts in the absence of a clinically diagnosed concussion during a season of high school football produce changes in cognitive performance or functional connectivity of the salience network and its central hub, the dorsal anterior cingulate cortex.

MATERIALS AND METHODS

Football players were instrumented with the Head Impact Telemetry System during all practices and games, and the helmet sensor data were used to compute a risk-weighted exposure metric (RWEcp), accounting for the cumulative risk during the season. Participants underwent MRI and a cognitive battery (ImPACT) before and shortly after the football season. A control group of noncontact/limited-contact-sport athletes was formed from 2 cohorts: one from the same school and protocol and another from a separate, nearly identical study.

RESULTS

Sixty-three football players and 34 control athletes were included in the cognitive performance analysis. Preseason, the control group scored significantly higher on the ImPACT Visual Motor (P = .04) and Reaction Time composites (P = .006). These differences increased postseason (P = .003, P < .001, respectively). Additionally, the control group had significantly higher postseason scores on the Visual Memory composite (P = .001). Compared with controls, football players showed significantly less improvement in the Verbal (P = .04) and Visual Memory composites (P = .01). A significantly greater percentage of contact athletes had lower-than-expected scores on the Verbal Memory (27% versus 6%), Visual Motor (21% versus 3%), and Reaction Time composites (24% versus 6%). Among football players, a higher RWEcp was significantly associated with greater increments in ImPACT Reaction Time (P = .03) and Total Symptom Scores postseason (P = .006). Fifty-seven football players and 13 control athletes were included in the imaging analyses. Postseason, football players showed significant decreases in interhemispheric connectivity of the dorsal anterior cingulate cortex (P = .026) and within-network connectivity of the salience network (P = .018). These decreases in dorsal anterior cingulate cortex interhemispheric connectivity and within-network connectivity of the salience network were significantly correlated with deteriorating ImPACT Total Symptom (P = .03) and Verbal Memory scores (P = .04).

CONCLUSIONS

Head impact exposure during a single season of high school football is negatively associated with cognitive performance and brain network connectivity. Future studies should further characterize these short-term effects and examine their relationship with long-term sequelae.

Assessing the Incidence of Head Trauma in Australian Mixed Martial Arts: A Retrospective Analysis of Fight Outcomes

BACKGROUND

Mixed martial arts (MMA) is experiencing a surge in popularity in Australia. Previous research has suggested knockout (KO) and technical knockout (TKO) are frequent outcomes during competition, raising concern about the brain health of athletes. This study aims to describe fight outcomes in Australian MMA and to explore differences in fight-ending outcomes between male and female athletes, amateur and professional competition, and different weight classes.

HYPOTHESIS

There is no difference in the incidence of KO/TKO between level of competition, sex, and weight class.

STUDY DESIGN

Descriptive epidemiology study.

LEVEL OF EVIDENCE

Level 3.

METHODS

Retrospective analysis of 143 Australian MMA events from 2020 to 2023 was conducted using video replay to assess fight outcomes between sex and level of competition. Binary logistic regression analysis was used to determine relationships between weight class and KO/TKO fight outcomes.

RESULTS

Male competition (34%) had a significantly greater number of KO/TKO secondary to head strikes fight outcomes compared with female competition (23%) (P = 0.01). The KO/TKO rate secondary to head strikes for amateur and professional male competition was 16.6 and 18.7 per 100 athlete-exposures (AEs), respectively. The amateur and professional female rate was 12.6 and 7.4 per 100 AEs, respectively. Amateur male light heavyweight and heavyweight, and professional male heavyweight were at greater odds of a KO or TKO compared with other weight classes in their equivalent level of competition.

CONCLUSION

There is a sex and professional level disparity in the incidence of fight-ending head trauma in Australian MMA. The study findings highlight the urgent need for targeted safety protocols and medical oversight, particularly for men in heavier weight classes.

CLINICAL RELEVANCE

This study highlights the need for enhanced safety protocols and medical oversight in Australian MMA, particularly for male athletes in heavier weight divisions.

Between-Session Reliability of Field-Based Assessments of Isometric Neck Strength

The reliability of the fixed-frame dynamometer for measuring isometric neck strength is established, but with limited field-based applications. This study aimed to establish the inter- and intra-session reliability of the peak force for neck flexors, extensors, and side flexors using the VALD ForceFrame and DynaMo and the force-time characteristics in the quadruped position (ForceFrame). Twenty-seven recreationally active males performed three repetitions of isometric neck flexion, extension, and side flexion over two sessions in random order using the VALD ForceFrame and DynaMo. Both devices demonstrated acceptable reliability, with the Forceframe ICC > 0.8 and CV% < 13.8% and the DynaMo ICC > 0.76 and CV% < 13.8%. No systematic or proportional differences were found using the Passing-Bablock procedure, and Bland-Altman analysis confirmed agreement across measures. Reliability was shown for right-side (ICC > 0.76) and left-side (ICC > 0.79) flexion and flexion (ICC > 0.75) across 50, 100, 150, and 200 ms. Statistical parametric mapping indicated no differences in ForceFrame-generated isometric force-time curves between sessions, though the CV was highest in the force development phase. The findings suggest that both tools can reliably assess neck strength, supporting their use in sports and clinical settings. However, assessment methods are not interchangeable, emphasising the need for standardised neck strength assessment approaches.

American Football On-Field Head Impact Kinematics: Influence of Acceleration Signal Characteristics on Peak Maximal Principal Strain

Recorded head kinematics from head-impact measurement devices (HIMd) are pivotal for evaluating brain stress and strain through head finite element models (hFEM). The variability in kinematic recording windows across HIMd presents challenges as they yield inconsistent hFEM responses. Despite establishing an ideal recording window for maximum principal strain (MPS) in brain tissue, uncertainties persist about the impact characteristics influencing vulnerability when this window is shortened. This study aimed to scrutinize factors within impact kinematics affecting the reliability of different recording windows on whole-brain peak MPS using a validated hFEM. Utilizing 53 on-field head impacts recorded via an instrumented mouthguard during a Canadian varsity football game, 10 recording windows were investigated with varying pre- and post-impact-trigger durations. Tukey pair-wise comparisons revealed no statistically significant differences in MPS responses for the different recording windows. However, specific impacts showed marked variability up to 40%. It was found, through correlation analyses, that impacts with lower peak linear acceleration exhibited greater response variability across different pre-trigger durations. Signal shape, analyzed through spectral analysis, influenced the time required for MPS development, resulting in specific impacts requiring a prolonged post-trigger duration. This study adds to the existing consensus on standardizing HIMd acquisition time windows and sheds light on impact characteristics leading to peak MPS variation across different head impact kinematic recording windows. Considering impact characteristics in research assessments is crucial, as certain impacts, affected by recording duration, may lead to significant errors in peak MPS responses during cumulative longitudinal exposure assessments.

Repetitive Subconcussive Head Impacts in Sports and Their Impact on Brain Anatomy and Function: A Systematic Review

Repetitive subconcussive head impacts occur regularly in sports. However, the exact relationship between their biomechanical properties and their consequences on brain structure and function has not been clarified yet. We therefore reviewed prospective cohort studies that objectively reported the biomechanical characteristics of repetitive subconcussive head impacts and their impact on brain anatomy and function. Only studies with a pre- to post-measurement design were included. Twenty-four studies met the inclusion criteria. Structural white matter alterations, such as reduced fractional anisotropy and an increase in mean diffusivity values, seem to be evident in athletes exposed to repetitive subconcussive head impacts exceeding 10 g. Such changes are observable after only one season of play. Furthermore, a dose-response relationship exists between white matter abnormalities and the total number of subconcussive head impacts. However, functional changes after repetitive subconcussive head impacts remain inconclusive. We therefore conclude that repetitive subconcussive head impacts induce structural changes, but thus far without overt functional changes.

Protective effects of early exercise on neuroinflammation, and neurotoxicity associated by traumatic brain injury: a behavioral and neurochemical approach

OBJECTIVE

The benefits of exercise in TBI have been proven. However, the time-dependent effects of exercise initiation and the involved mechanisms are controversial. We investigated the effects of preconditioning, continuous, early, and delayed treadmill exercise on motor behavior, brain edema, inflammation, and oxidative stress in experimental traumatic brain injury (TBI).

MATERIALS AND METHODS

48 male rats were assigned into two groups: sedentary control (Sham and TBI) and exercise groups: 1MB (preconditioning, initiation beginning at 1 month before trauma), 1MBA (continuous, initiation beginning at 1 month before and continuing 1 month after trauma), 24hA (early, initiation beginning at 24 h after trauma), and 1WA (delay, initiation beginning at 1 week after trauma). The rats in exercise groups were forced to run on a treadmill five days a week for 30 min per day. Rotarod and open file were used to assess motor behavior. ELISA was also used to measure total antioxidant capacity (TAC), tumor necrosis factor-alpha (TNF-α), and malondialdehyde (MDA) in serum and CSF.

RESULTS

Exercise significantly decreased neurological impairments, motor deficits, and apoptosis compared with the sedentary group. Early (within 24 h) and ongoing (1 MBA) exercise significantly improved motor behavior after TBI. In addition, these exercise programs inhibited brain edema and the number of apoptotic cells. MDA and TNF-α levels increased in all exercise groups, but the effects were greater after early exercise than after delayed exercise, resulting in a significant decrease in TAC levels in serum and CSF. We discovered a positive correlation between MDA, TAC, and TNF-α concentration in serum and CSF.

CONCLUSION

Our finding suggests that early exercise (24hA) and 1MBA groups afford neuroprotection and reduce the second injury consequence, probably by reducing neuronal apoptosis and oxidative stress.

Head Kinematics and Injury Analysis in Elite Bobsleigh Athletes Throughout a World Cup Tour

CONTEXT

The neurocognitive health effects of repetitive head impacts have been examined in many sports. However, characterizations of head impacts for sliding-sport athletes are lacking.

OBJECTIVE

To describe head impact kinematics and injury epidemiology in elite athletes during the 2021-2022 Bobsleigh World Cup season.

DESIGN

Cross-sectional study.

SETTING

On-track training and competitions during the Bobsleigh World Cup season.

PATIENTS OR OTHER PARTICIPANTS

Twelve elite bobsleigh athletes (3 pilots [1 female], 9 push athletes [5 females]; age = 30 ± 5 years; female height and weight = 173 ± 8 cm and 75 ± 5 kg, respectively; male height and weight = 183 ± 5 cm and 101 ± 5 kg, respectively).

MAIN OUTCOME MEASURE(S)

Athletes wore an accelerometer-enabled mouthguard to quantify 6-degrees-of-freedom head impact kinematics. Isometric absolute and relative neck strength, number of head acceleration events (HAEs), workload (J), peak linear velocity (m·s-1), peak angular velocity (rad·s-1), peak linear acceleration (g), and peak angular acceleration (rad·s-2) were derived from mouthguard manufacturer algorithms. Linear mixed-effect models tested the effects of sex (male versus female), setting (training versus competition), and position (pilot versus push athlete) on the kinematic variables.

RESULTS

A total of 1900 HAEs were recorded over 48 training and 53 competition days. No differences were found between the number of HAEs per run per athlete by sex (incidence rate ratio [IRR] = 0.82, P = .741), setting (IRR = 0.94, P = .325), or position (IRR = 1.64, P = .463). No sex differences were observed for workload (mean ± SD: males = 3.3 ± 2.2 J, females = 3.1 ± 1.9 J; P = .646), peak linear velocity (males = 1.1 ± 0.3 m·s-1, females = 1.1 ± 0.3 m·s-1; P = .706), peak angular velocity (males = 4.2 ± 2.1 rad·s-1, females = 4.7 ± 2.5 rad·s-1; P = .220), peak linear acceleration (male = 12.4 ± 3.9g, females = 11.9 ± 3.5g; P = .772), or peak angular acceleration (males = 610 ± 353 rad·s-2, females = 680 ± 423 rad·s-2; P = .547). Also, no effects of setting or position on any kinematic variables were seen. Male athletes had greater peak neck strength than female athletes for all neck movements, aside from right-side flexion (P = .085), but no sex differences were noted in relative neck strength.

CONCLUSIONS

We provide a foundational understanding of the repetitive HAEs that occur in bobsleigh athletes. Future authors should determine the effects of repetitive head impacts on neurocognitive function and mental health.

Association of Auditory Interference and Ocular-Motor Response with Subconcussive Head Impacts in Adolescent Football Players

The aim of this study was to examine whether neuro-ophthalmological function, as assessed by the King-Devick test (KDT), alters during a high school football season and to explore the role of auditory interference on the sensitivity of KDT. During the 2021 and 2022 high school football seasons, football players' neuro-ophthalmological function was assessed at five time points (preseason, three in-season, postseason), whereas control athletes were assessed at preseason and postseason. Two-hundred ten football players and 80 control athletes participated in the study. The year 1 cohort (n = 94 football, n = 10 control) was tested with a conventional KDT, whereas the year 2 cohort (n = 116 football, n = 70 control) was tested with KDT while listening to loud traffic sounds to induce auditory interference. There were improvements in KDT during a season among football players, regardless of conventional KDT (preseason 53.4 ± 9.3 vs. postseason 46.4 ± 8.5 sec; β = -1.7, SE = 0.12, p < 0.01) or KDT with auditory interference (preseason 52.3 ± 11.5 vs. postseason 45.1 ± 9.5 sec; β = -1.7, SE = 0.11, p < 0.001). The degree of improvement was similar between the tests, with no significant group-by-time interaction (β = -0.08, SE = 0.17, p = 0.65). The control athletes also improved KDT performance at a similar degree as the football cohorts in both KDT conditions. Our data suggest that KDT performance improves during a season, regardless of auditory interference or head impact exposure. KDT performance was not impacted by a noisy environment, supporting its sideline utility for screening more severe forms of injury.

Associations between repetitive head impact exposure and midlife mental health wellbeing in former amateur athletes

Introduction

Repetitive head impacts (RHI) have been suggested to increase the risk of developing a neurodegenerative disease, and many of these individuals develop a preceding mental health diagnosis. Given the lack of studies among amateur athletes, this study aimed to examine mental health outcomes in middle-aged amateur athletes who have been exposed to RHI through contact sport participation.

Methods

This is a single site, cohort study involving former amateur athletes aged between 30 and 60 with at least 10 years of organized contact or non-contact sport participation. All participants completed demographic and mental health questionnaires. Mental health outcomes included symptoms related to depression, anxiety, post-traumatic stress disorder (PTSD), attention deficit hyperactive disorder (ADHD), and aggression. Self-reported data on mental health diagnoses and associated prescription were elicited and used to estimate odds ratios (OR).

Results

Data from 41 contact athletes and 22 age/sex-matched non-contact athletes were available for analysis. The contact group exhibited a 2.25-fold higher likelihood of being diagnosed with mental health disorders and 1.29-fold higher likelihood of using associated medications compared to the non-contact group. The contact group reported significantly higher PTSD-related symptoms [4.61 (0.03,9.2), p=0.05] compared to the non-contact control group. While not statistically significant, the contact group showed increased depressive [2.37 (0.05, 4.79), p=0.07] and ADHD symptoms [4.53 (0.51, 9.57), p=0.08] compared to controls. In a secondary analysis, a distinct trend emerged within the contact group, revealing pronounced elevations in mental health symptoms among individuals with lower socioeconomic status (<$50,000/year) compared to higher income subgroups, and these symptoms decreased as income levels rose [depression: -3.08 (-4.47, -1.7), p<0.001; anxiety: -1.95 (-3.15, -0.76), p=0.002; ADHD: -4.99 (-8.28, -1.69), p=0.004; PTSD: -4.42 (-7.28, -1.57), p=0.003; aggression: -6.19 (-11.02, -1.36), p=0.01]. This trend was absent in the non-contact control group.

Discussion

Our data suggest that even individuals at the amateur level of contact sports have an increased likelihood of being diagnosed with mental health disorders or experiencing mental health symptoms compared to non-contact athletes. Our findings indicate that socioeconomic status may have an interactive effect on individuals' mental health, particularly among those with a long history of RHI exposure.

A comparison of sub-concussive impact attenuating capabilities of ice hockey helmets with and without XRD foam

OBJECTIVES

To compare the impact attenuating capabilities between ice hockey helmets manufactured with and without XRD impact protection foam, worn with and without a XRD skullcap, at reducing sub-concussive head accelerations.

DESIGN

Quasi-experimental laboratory.

METHODS

Ice hockey helmets were fit onto a Hybrid III 50th Head Form Head and dropped 25 times onto the left temporal side for each condition: XRD foam helmet, XRD foam helmet with XRD skullcap adjunct, non-XRD foam helmet, and non-XRD foam helmet with XRD skullcap adjunct. The helmets were dropped from a height that resulted in sub-concussive linear accelerations (25-80 g's). Using a tri-axial accelerometer, peak linear accelerations (g) were measured, and the average was used to compare impact attenuation properties across the four conditions.

RESULTS

The highest linear accelerations were observed in the XRD foam helmet without skullcap (32.97 ± 0.61 g) and were significantly greater (p < 0.001) than the XRD helmet with skullcap (21.38 ± 0.76 g). The helmet without XRD foam elicited the lowest peak linear accelerations (16.10 ± 0.73 g) which were significantly lower than the XRD foam helmet regardless of whether the skullcap was added (p < 0.001).

CONCLUSIONS

Although sub-concussive loads are potentially just as dangerous, much of the research regarding helmet and skullcap efficacy appears to be at high concussive impacts; <70 g's. The findings suggest that helmets with incorporated XRD foam, either within the design or added as an adjunct, are less effective at attenuating linear accelerations at sub-concussive levels than the low-density foam helmet.

Effect of Repetitive Head Impacts on Saccade Performance in Canadian University Football Players

OBJECTIVE

Investigate the effect of cumulative head impacts on saccade latency and errors, measured across two successive football seasons.

DESIGN

Participants were acquired from a sample of convenience-one Canadian university football team. Head impacts were collected during training camp, practices, eight regular season games, and four playoff games in each season. Saccade measurements were collected at five time points-before and after training camp, at midseason, after regular season, and after playoffs.

SETTING

Two seasons following players from a single USports football team during practices and games.

PARTICIPANTS

Players who completed a baseline saccade measurement and a minimum of one follow-up measurement were included in the study. A total of 127 players were monitored across two competitive seasons, including 61 players who participated in both seasons.

INDEPENDENT VARIABLES

Head impact measurements were collected using helmet-mounted sensors.

MAIN OUTCOME MEASURES

Saccade latency and number of errors were measured using high-speed video or electro-oculography.

RESULTS

On average, each head impact increased prosaccade latency by 5.16 × 10 -3 ms (95% confidence interval [CI], 2.26 × 10 -4 -1.00 × 10 -2 , P = 0.03) and antisaccade latency by 5.74 × 10 -3 ms (95% CI, 7.18 × 10 -4 -1.06 × 10 -2 , P = 0.02). These latency increases did not decrease between the two seasons; in fact, prosaccade latencies were 23.20 ms longer (95% CI, 19.40-27.14, P < 0.001) at the second season's baseline measurement than the first. The number of saccade errors was not affected by cumulative head impacts.

CONCLUSIONS

Repetitive head impacts in Canadian university football result in cumulative declines in brain function as measured by saccade performance.

CLINICAL RELEVANCE

Football organizations should consider implementing policies focused on reducing head impacts to improve player safety.

Sex-specific antioxidant biomarker depletion in patients with a history of mild traumatic brain injury

Individuals with a history of mild traumatic brain injury (mTBI) are at an increased risk for neurodegenerative disease, suggesting that intrinsic neuroprotective mechanisms, such as the endogenous antioxidant reservoir, may be depleted long-term after mTBI. Here, we retrospectively analyzed symptoms and blood antioxidants in patients with a history of mTBI who presented to Resilience Code, a sports medicine clinic in Colorado. Significant decreases in alpha-tocopherol, selenium, linoleic acid, taurine, docosahexaenoic acid, and total omega-3 were measured in the total mTBI population versus controls. Male mTBI patients showed depletion of a larger array of antioxidants than females. Patients with a history of mTBI also reported significantly worsened emotional, energy, head, and cognitive symptoms, with males displaying more extensive symptomology. Multiple or chronic mTBI patients had worsened symptoms than single or acute/subchronic mTBI patients, respectively. Finally, male mTBI patients with the largest reductions in polyunsaturated fatty acids (PUFAs) displayed worse symptomology than male mTBI patients with less depletion of this antioxidant reservoir. These results demonstrate that antioxidant depletion persists in patients with a history of mTBI and these deficits are sex-specific and associated with worsened symptomology. Furthermore, supplementation with specific antioxidants, like PUFAs, may diminish symptom severity in patients suffering from chronic effects of mTBI.

Investigation of Head Kinematics and Brain Strain Response During Soccer Heading Using a Custom-Fit Instrumented Mouthguard

Association football, also known as soccer in some regions, is unique in encouraging its participants to intentionally use their head to gain a competitive advantage, including scoring a goal. Repetitive head impacts are now being increasingly linked to an inflated risk of developing long-term neurodegenerative disease. This study investigated the effect of heading passes from different distances, using head acceleration data and finite element modelling to estimate brain injury risk. Seven university-level participants wore a custom-fitted instrumented mouthguard to capture linear and angular acceleration-time data. They performed 10 headers within a laboratory environment, from a combination of short, medium, and long passes. Kinematic data was then used to calculate peak linear acceleration, peak angular velocity, and peak angular acceleration as well as two brain injury metrics: head injury criterion and rotational injury criterion. Six degrees of freedom acceleration-time data were also inputted into a widely accepted finite element brain model to estimate strain-response using mean peak strain and cumulative strain damage measure values. Five headers were considered to have a 25% concussion risk. Mean peak linear acceleration equalled 26 ± 7.9 g, mean peak angular velocity 7.20 ± 2.18 rad/s, mean peak angular acceleration 1730 ± 611 rad/s2, and 95th percentile mean peak strain 0.0962 ± 0.252. Some of these data were similar to brain injury metrics reported from American football, which supports the need for further investigation into soccer heading.

A Novel Experimental Approach for the Measurement of Vibration-Induced Changes in the Rheological Properties of Ex Vivo Ovine Brain Tissue

Increased incidence of traumatic brain injury (TBI) imposes a growing need to understand the pathology of brain trauma. A correlation between the incidence of multiple brain traumas and rates of behavioural and cognitive deficiencies has been identified amongst people that experienced multiple TBI events. Mechanically, repetitive TBIs may affect brain tissue in a similar way to cyclic loading. Hence, the potential susceptibility of brain tissue to mechanical fatigue is of interest. Although temporal changes in ovine brain tissue viscoelasticity and biological fatigue of other tissues such as tendons and arteries have been investigated, no methodology currently exists to cyclically load ex vivo brain tissue. A novel rheology-based approach found a consistent, initial stiffening response of the brain tissue before a notable softening when subjected to a subsequential cyclic rotational shear. History dependence of the mechanical properties of brain tissue indicates susceptibility to mechanical fatigue. Results from this investigation increase understanding of the fatigue properties of brain tissue and could be used to strengthen therapy and prevention of TBI, or computational models of repetitive head injuries.

Neurobehavioral Symptoms in Spanish-Speaking Individuals With Subconcussive Injuries

OBJECTIVE

To examine whether exposure to high-risk events causing injury to the head or neck has an effect on neurobehavioral symptoms in the absence of an alteration of consciousness in Spanish-speakers.

SETTING

Web-based survey.

PARTICIPANTS

Seven hundred forty-eight individuals from Spain and Latin America, aged 18 to 65 years, with 10 years or more of education. Thirty-nine participants failed quality checks and were excluded. Seven hundred nine participants were included in the analyses.

DESIGN

Cross-sectional study. Subconcussive exposure was defined as endorsing exposure to one or more high-risk scenarios in the absence of any alteration of consciousness. Three injury groups were derived: No Head Injury, Subconcussive Exposure, and traumatic brain injury (TBI). The Subconcussive Exposure group was further divided into Single and Multiple Exposures. Two analyses were conducted: the effect of lifetime exposure to injury (No Head Injury, Subconcussive Exposure, TBI) on neurobehavioral symptoms; the effect of Subconcussive Exposure Frequency (No Head Injury, Single Exposure, Multiple Exposures) on neurobehavioral symptoms.

MAIN MEASURES

Spanish Ohio State University Traumatic Brain Injury Identification Method Self-Administered-Brief (OSU TBI-ID SAB); Neurobehavioral Symptom Inventory (NSI).

RESULTS

There was a significant effect for Injury group on the NSI partial eta-squared (ηp2 = 0.053) and a significant effect of Exposure Frequency group on the NSI (ηp2 = 0.40). Individuals with subconcussive exposures reported significantly more neurobehavioral symptoms than those with no history of head injury and significantly less symptoms than those with TBI. Individuals with multiple subconcussive exposures reported significantly more neurobehavioral symptoms than those with single and no exposure.

CONCLUSION

This research expands the utility of the OSU-TBI-ID SAB as a lifetime TBI history assessment tool to one capable of evaluating subconcussive exposure dosing effects in Spanish-speakers. Such an index may facilitate establishment of subconcussive exposure prevalence rates worldwide, leading to improved understanding of the chronic effects of high-risk exposures.

Lateral fluid percussion injury: A rat model of experimental traumatic brain injury

Traumatic brain injury (TBI) represents one of the leading causes of disability and death worldwide. The annual economic impact of TBI-including direct and indirect costs-is high, particularly impacting low- and middle-income countries. Despite extensive research, a comprehensive understanding of the primary and secondary TBI pathophysiology, followed by the development of promising therapeutic approaches, remains limited. These fundamental caveats in knowledge have motivated the development of various experimental models to explore the molecular mechanisms underpinning the pathogenesis of TBI. In this context, the Lateral Fluid Percussion Injury (LFPI) model produces a brain injury that mimics most of the neurological and systemic aspects observed in human TBI. Moreover, its high reproducibility makes the LFPI model one of the most widely used rodent-based TBI models. In this chapter, we provide a detailed surgical protocol of the LFPI model used to induce TBI in adult Wistar rats. We further highlight the neuroscore test as a valuable tool for the evaluation of TBI-induced sensorimotor consequences and their severity in rats. Lastly, we briefly summarize the current knowledge on the pathological aspects and functional outcomes observed in the LFPI-induced TBI model in rodents.

A prospective investigation of the effects of soccer heading on cognitive and sensorimotor performances in semi-professional female players

Introduction

Repetitive head impacts (RHI) from routine soccer (football) heading have been suggested to contribute to the long-term development of neurodegenerative disorders. However, scientific evidence concerning the actual risk of these RHI on brain health remains inconclusive. Moreover, female athletes-despite a presumably increased vulnerability toward the effects of RHI-are largely underrepresented in previous approaches. Therefore, our aim was to prospectively investigate the effects of heading on cognitive and sensorimotor performances, health perception, and concussion symptoms in semi-professional female soccer players.

Methods

An extensive test battery was used to assess cognitive and sensorimotor performances as well as health status (SF-36) and concussion symptoms (SCAT3) of a total of 27 female soccer players (22.2 ± 4.2 years) and 15 control subjects (23.2 ± 3.0 years) before and after one-and-a-half years. Throughout this period, soccer players' heading exposure was determined using video analysis.

Results

Subgroup comparisons (control [n = 12], low exposure [n = 7], high exposure [n = 8]) showed no time-dependent differences in SF-36 or SCAT3 scores. Similarly, across most behavioral tests, soccer players' performances evolved equally or more favorably as compared to the control subjects. However, there were significant effects pointing toward slightly negative consequences of heading on aspects of fine motor control (p = 0.001), which were confirmed by correlation and multiple regression analyses. The latter, further, yielded indications for a relationship between heading exposure and negative alterations in postural control (p = 0.002).

Discussion

Our findings do not provide evidence for negative effects of soccer heading on female players' health perception, concussion symptoms, and cognitive performances over the course of one-and-a-half years. However, we found subtle negative alterations in fine motor and postural control that could be attributed to heading exposure. Other factors, like the number of previous head injuries, were not linked to the observed changes. Given the reduction of our initial sample size due to player fluctuation, the results need to be interpreted with caution and validated in larger-scale studies. These should not only focus on cognitive outcomes but also consider sensorimotor changes as a result of RHI from soccer heading.

Sport Type and Risk of Subsequent Injury in Collegiate Athletes Following Concussion: a LIMBIC MATARS Consortium Investigation

OBJECTIVE

To investigate the association between sport type (collision, contact, non-contact) and subsequent injury risk following concussion in collegiate athletes.

MATERIALS AND METHODS

This retrospective chart review of 248 collegiate athletes with diagnosed concussions (age: 20.0 ± 1.4 years; height: 179.6 ± 10.9 cm; mass: 79.0 ± 13.6 kg, 63% male) from NCAA athletic programs (n = 11) occurred between the 2015-2020 athletic seasons. Acute injuries that occurred within six months following concussion were evaluated. Subsequent injuries were grouped by lower extremity, upper extremity, trunk, or concussion. The independent variable was sport type: collision, contact, non-contact. A Cox proportional hazard model was used to assess the risk of subsequent injury between sport types.

RESULTS

Approximately 28% (70/248) of athletes sustained a subsequent acute injury within six months post-concussion. Collision sport athletes had a significantly higher risk of sustaining any injury (HR: 0.41, p < 0.001, 95% CI: 0.28, 0.62), lower extremity (HR: 0.55, p = 0.04, 95% CI: 0.32, 0.97), and upper extremity (HR: 0.41, p = 0.01, 95% CI: 0.20, 0.81) injuries following concussion. No differences between sport types were observed for other injuries.

CONCLUSION

Collision sport athletes had a higher rate of any subsequent injury, lower, and upper extremity injuries following concussion. Future research should focus on sport-specific secondary injury prevention efforts.

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.

Musculoskeletal injury or Sports-Related Concussion (SRC) in a season of rugby union does not affect performance on concussion battery testing in university-aged student-athletes

BACKGROUND

Sub-concussive and concussive impacts sustained during contact sports such as rugby may affect neurocognitive performance, vestibular-ocular-motor function, symptom burden and academic ability.

METHOD

Student-athletes (n = 146) participating in rugby union British Universities or domestic competitions were assessed on the Immediate Post-Concussion and Cognitive Test, Post-Concussion Symptom Scale, vestibular-oculo-motor screening tool and revised perceived academic impact tool. Individual change from pre-season (July-September 2021) to 2-weeks following last exposure to contact (April-July 2022) was analysed.

RESULTS

Symptom burden significantly worsened (p=0.016) over the season. Significant improvements on verbal memory (p=0.016), visual memory (p=0.008) and motor processing speed (p=0.001) suggest a possible learning effect. Surprisingly, the number of days lost to concussion significantly and positively affected performance on verbal memory (p = 0.018) and reaction time (p = 0.027). Previous concussive events significantly predicted a worsening in symptom burden (p < 0.028), as did in-season concussive events, predicting improved verbal memory (p = 0.033) and symptom burden change (p = 0.047). Baseline performance significantly affected change on several neurocognitive tests, with low-scorers showing more improvement over the season.

CONCLUSION

Participation in rugby union was not associated with deleterious effects on brain function. Previous concussive events and in-season factors, possibly related to learning effects, may explain improvement in cognitive function across the season.

Head acceleration event exposure and cognitive and functional outcomes: a comparison of multiple football seasons

Athletes in contact sports are exposed to repetitive impacts as an inherent part of sport. There is concern over the accumulative effect; however, much is still unknown regarding their short-term effects. This study investigated impact accumulation and outcomes over three seasons (2015, 2017, 2019) in NCAA Football Bowl Subdivision players. Impacts were recorded using helmet accelerometers, and virtual reality testing (VR) was done across the season. Incidence rates for impacts (total; ≥25 G to <80 G; ≥80 G) all significantly differed by season (p < 0.05). VR scores changed across the seasons, specifically significant decreases in spatial memory (p < 0.05) in 2015, significant changes in balance and spatial memory (p < 0.05) in 2017, and no significant changes in 2019. Linear regressions predicting VR change score by impact incidence rate were nonsignificant. Monitoring exposure to impacts and changes in outcomes is useful; however, results are fluid, and many factors could indirectly have protective effects on athletes.

Blood-Brain Barrier Dysfunction and Exposure to Head Impacts in University Football Players

OBJECTIVE

To investigate the link between dysfunction of the blood-brain barrier (BBB) and exposure to head impacts in concussed football athletes.

DESIGN

This was a prospective, observational pilot study.

SETTING

Canadian university football.

PARTICIPANTS

The study population consisted of 60 university football players, aged 18 to 25. Athletes who sustained a clinically diagnosed concussion over the course of a single football season were invited to undergo an assessment of BBB leakage.

INDEPENDENT VARIABLES

Head impacts detected using impact-sensing helmets were the measured variables.

MAIN OUTCOME MEASURES

Clinical diagnosis of concussion and BBB leakage assessed using dynamic contrast-enhanced MRI (DCE-MRI) within 1 week of concussion were the outcome measures.

RESULTS

Eight athletes were diagnosed with a concussion throughout the season. These athletes sustained a significantly higher number of head impacts than nonconcussed athletes. Athletes playing in the defensive back position were significantly more likely to sustain a concussion than remain concussion free. Five of the concussed athletes underwent an assessment of BBB leakage. Logistic regression analysis indicated that region-specific BBB leakage in these 5 athletes was best predicted by impacts sustained in all games and practices leading up to the concussion-as opposed to the last preconcussion impact or the impacts sustained during the game when concussion occurred.

CONCLUSIONS

These preliminary findings raise the potential for the hypothesis that repeated exposure to head impacts may contribute to the development of BBB pathology. Further research is needed to validate this hypothesis and to test whether BBB pathology plays a role in the sequela of repeated head trauma.

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.

Evolving brain and behaviour changes in rats following repetitive subconcussive head impacts

There is growing concern that repetitive subconcussive head impacts, independent of concussion, alter brain structure and function, and may disproportionately affect the developing brain. Animal studies of repetitive subconcussive head impacts are needed to begin to characterize the pathological basis and mechanisms underlying imaging and functional effects of repetitive subconcussive head impacts seen in humans. Since repetitive subconcussive head impacts have been largely unexplored in animals, we aimed to characterize the evolution of imaging, behavioural and pathological effects of repetitive subconcussive head impacts in awake adolescent rodents. Awake male and female Sprague Dawley rats (postnatal Day 35) received 140 closed-head impacts over the course of a week. Impacted and sham-impacted animals were restrained in a plastic cone, and unrestrained control animals were included to account for effects of restraint and normal development. Animals (n = 43) underwent repeated diffusion tensor imaging prior to and over 1 month following the final impact. A separate cohort (n = 53) was assessed behaviourally for fine motor control, emotional-affective behaviour and memory at acute and chronic time points. Histological and immunohistochemical analyses, which were exploratory in nature due to smaller sample sizes, were completed at 1 month following the final impact. All animals tolerated the protocol with no overt changes in behaviour or stigmata of traumatic brain injury, such as alteration of consciousness, intracranial haemorrhage or skull fracture. We detected longitudinal, sex-dependent diffusion tensor imaging changes (fractional anisotropy and axial diffusivity decline) in corpus callosum and external capsule of repetitive subconcussive head impact animals, which diverged from both sham and control. Compared to sham animals, repetitive subconcussive head impact animals exhibited acute but transient mild motor deficits. Repetitive subconcussive head impact animals also exhibited chronic anxiety and spatial memory impairment that differed from the control animals, but these effects were not different from those seen in the sham condition. We observed trends in the data for thinning of the corpus callosum as well as regions with elevated Iba-1 in the corpus callosum and cerebral white matter among repetitive subconcussive head impact animals. While replication with larger study samples is needed, our findings suggest that subconcussive head impacts cause microstructural tissue changes in the developing rat brain, which are detectable with diffusion tensor imaging, with suggestion of correlates in tissue pathology and behaviour. The results point to potential mechanisms underpinning consequences of subconcussive head impacts that have been described in humans. The congruence of our imaging findings with human subconcussive head impacts suggests that neuroimaging could serve as a translational bridge to advance study of injury mechanisms and development of interventions.

Relaxed Alert Electroencephalography Screening for Mild Traumatic Brain Injury in Athletes

Due to the mildness of initial injury, many athletes with recurrent mild traumatic brain injury (mTBI) are misdiagnosed with other neuropsychiatric illnesses. This study was designed as a proof-of-principle feasibility trial for athletic trainers at a sports facility to generate electroencephalograms (EEGs) from student athletes for discriminating (mTBI) associated EEGs from uninjured ones. A total of 47 EEGs were generated, with 30 athletes recruited at baseline (BL) pre-season, after a concussive injury (IN), and post-season (PS). Outcomes included: 1) visual analyses of EEGs by a neurologist; 2) support vector machine (SVM) classification for inferences about whether particular groups belonged to the three subgroups of BL, IN, or PS; and 3) analyses of EEG synchronies including phase locking value (PLV) computed between pairs of distinct electrodes. All EEGs were visually interpreted as normal. SVM classification showed that BL and IN could be discriminated with 81% accuracy using features of EEG synchronies combined. Frontal inter-hemispheric phase synchronization measured by PLV was significantly lower in the IN group. It is feasible for athletic trainers to record high quality EEGs from student athletes. Also, spatially localized metrics of EEG synchrony can discriminate mTBI associated EEGs from control EEGs.

Characterizing Head Acceleration Events in Law Enforcement Cadets During Subject Control Technique Training

Law enforcement cadets (LECs) complete weeks of subject control technique training. Similar sport-related combat training has been shown to expose participants to head acceleration events (HAEs) that have potential to result in short- and long-term impairments. The purpose of this study was to describe the number and magnitude of HAEs in LECs throughout their training. 37 LECs (7 females; age = 30.6 ± 8.8 years; BMI = 30.0 ± 6.0) were recruited from a law enforcement organization. Participants wore instrumented mouthguards, which recorded all HAEs exceeding a resultant 5 g threshold for training sessions with the potential for HAEs. Participants completed three defensive tactics (DT) training sessions, a DT skill assessment (DTA), and three boxing sessions. Outcome measures included the number of HAEs, peak linear acceleration (PLA), and peak rotational velocity (PRV). There were 2758 true-positive HAEs recorded across the duration of the study. Boxing sessions accounted for 63.7% of all true-positive HAEs, while DT accounted for 31.4% and DTA accounted for 4.9%. Boxing sessions resulted in a higher number of HAEs per session (F2,28 = 48.588, p < 0.001, ηp2 = 0.776), and higher median PLA (F2,28 = 8.609, p = 0.001, ηp2 = 0.381) and median PRV (F2,28 = 11.297, p < 0.001, ηp2 = 0.447) than DT and DTA. The LECs experience a high number of HAEs, particularly during boxing sessions. Although this training is necessary for job duties, HAE monitoring may lead to modifications in training structure to improve participant safety and enhance recovery.

Magnetic Resonance Elastography-Based Technique to Assess the Biomechanics of the Skull-Brain Interface: Repeatability and Age-Sex Characteristics

Increasing concerns have been raised about the long-term negative effects of subconcussive repeated head impact (RHI). To elucidate RHI injury mechanisms, many efforts have studied how head impacts affect the skull-brain biomechanics and have found that mechanical interactions at the skull-brain interface dampen and isolate brain motions by decoupling the brain from the skull. Despite intense interest, in vivo quantification of the functional state of the skull-brain interface remains difficult. This study developed a magnetic resonance elastography (MRE) based technique to non-invasively assess skull-brain mechanical interactions (i.e., motion transmission and isolation function) under dynamic loading. The full MRE displacement data were separated into rigid body motion and wave motion. The rigid body motion was used to calculate the brain-to-skull rotational motion transmission ratio (Rtr) to quantify skull-brain motion transmissibility, and the wave motion was used to calculate the cortical normalized octahedral shear strain (NOSS) (calculated based on a partial derivative computing neural network) to evaluate the isolation capability of the skull-brain interface. Forty-seven healthy volunteers were recruited to investigate the effects of age/sex on Rtr and cortical NOSS, and 17 of 47 volunteers received multiple scans to test the repeatability of the proposed techniques under different strain conditions. The results showed that both Rtr and NOSS were robust to MRE driver variations and had good repeatability, with intraclass correlation coefficient (ICC) values between 0.68 and 0.97 (fair to excellent). No age or sex dependence were observed with Rtr, whereas a significant positive correlation between age and NOSS was found in the cerebrum, frontal, temporal, and parietal lobes (all p < 0.05), but not in the occipital lobe (p = 0.99). The greatest change in NOSS with age was found in the frontal lobe, one of the most frequent locations of traumatic brain injury (TBI). Except for the temporal lobe (p = 0.0087), there was no significant difference in NOSS between men and women. This work provides motivation for utilizing MRE as a non-invasive tool for quantifying the biomechanics of the skull-brain interface. It evaluated the age and sex dependence and may lead to a better understanding of the protective role and mechanisms of the skull-brain interface in RHI and TBI, as well as improve the accuracy of computational models in simulating the skull-brain interface.

The Effect of Ball Heading and Subclinical Concussion On the Neuromuscular Control Of The Lower Limb: A Systematic Review

Background

Soccer is unique among sports because it is the only sport that involves purposeful use of the head to control, pass, or shoot the ball. Over the previous five years, a relationship between lower extremity (LE) injury and sports related concussion (SRC) has been established in various sporting populations. Athletes at the high school, collegiate, and professional levels have demonstrated a greater risk for sustaining a LE injury post SRC. The purpose of this systematic review was to examine the relationship of the SRC with the incidence of LE injuries.

Methods

Ten databases were searched with the following keywords: Lower limb, ball heading, neuromuscular control, concussion, MEDLINE, Ovid MEDLINE(R) Daily, and Ovid MEDLINE(R), EMBASE, and Scopus. The search was limited to English-language and peer-reviewed publications, until 15/12/2022. The PEDro scale was used for the assessment of the risk of bias among the included studies. All included papers were qualitatively analyzed.

Results

A total of 834 studies were identified and 10 articles (four concussion-MSK biomechanics, six concussion-MSK injury) were included in the qualitative analyses. Included papers ranged from low to high quality. Due to the heterogeneous nature of the included study designs, quantitative meta-analysis was unable to be performed. All four of the included concussion-MSK biomechanics studies demonstrated, to some degree, that worse cognitive performance was associated with lower extremity MSK biomechanical patterns suggestive of greater risk for MSK injury. Among the six injury related studies, two investigations failed to determine group differences in cognitive performance between subsequently injured and non-injured athletes.

Conclusion

More research is needed to better understand the relationship of SRC and lower extremity injuries and the extent to which they are related to concussions and/or repetitive neurotrauma after ball heading sustained in soccer.

Level of Evidence

2.

Assessing the association between on-field heading technique and head impact kinematics in a cohort of female youth soccer players

There is concern that exposure to soccer headers may be associated with neurological sequelae. Training proper heading technique represents a coachable intervention that may reduce head acceleration exposure. The objective was to assess relationships between heading technique and head kinematics in female youth soccer players. Fourteen players (mean age = 14.4 years) wore instrumented mouthpieces during practices and games. Headers were reviewed by three raters to assign a technique score. Mixed models and LASSO regression evaluated associations of technique with peak linear acceleration (PLA), rotational acceleration (PRA), rotational velocity (PRV), and head impact power ratio (HIP Ratio) while adjusting for session type and ball delivery. Two hundred eighty-nine headers (n = 212 standing, n = 77 jumping) were analyzed. Technique score (p = 0.043) and the technique score - session type interaction (p = 0.004) were associated with PRA of standing headers, whereby each 10-unit increase in technique score was associated with an 8.6% decrease in PRA during games but a 5.1% increase in PRA during practices. Technique was not significantly associated with any other kinematic metrics; however, peak kinematics tended to decrease as technique score increased. LASSO regression identified back extension and shoulder/hip alignment as important predictors of peak kinematics. Additional research on heading technique and head acceleration is recommended.

Hyper-acute effects of sub-concussive soccer headers on brain function and hemodynamics

Introduction

Sub-concussive head impacts in soccer are drawing increasing research attention regarding their acute and long-term effects as players may experience thousands of headers in a single season. During these impacts, the head experiences rapid acceleration similar to what occurs during a concussion, but without the clinical implications. The physical mechanism and response to repetitive impacts are not completely understood. The objective of this work was to examine the immediate functional outcomes of sub-concussive level impacts from soccer heading in a natural, non-laboratory environment.

Methods

Twenty university level soccer athletes were instrumented with sensor-mounted bite bars to record impacts from 10 consecutive soccer headers. Pre- and post-header measurements were collected to determine hyper-acute changes, i.e., within minutes after exposure. This included measuring blood flow velocity using transcranial Doppler (TCD) ultrasound, oxyhemoglobin concentration using functional near infrared spectroscopy imaging (fNIRS), and upper extremity dual-task (UEF) neurocognitive testing.

Results

On average, the athletes experienced 30.7 ± 8.9 g peak linear acceleration and 7.2 ± 3.1 rad/s peak angular velocity, respectively. Results from fNIRS measurements showed an increase in the brain oxygenation for the left prefrontal cortex (PC) (p = 0.002), and the left motor cortex (MC) (p = 0.007) following the soccer headers. Additional analysis of the fNIRS time series demonstrates increased sample entropy of the signal after the headers in the right PC (p = 0.02), right MC (p = 0.004), and left MC (p = 0.04).

Discussion

These combined results reveal some variations in brain oxygenation immediately detected after repetitive headers. Significant changes in balance and neurocognitive function were not observed in this study, indicating a mild level of head impacts. This is the first study to observe hemodynamic changes immediately after sub-concussive impacts using non-invasive portable imaging technology. In combination with head kinematic measurements, this information can give new insights and a framework for immediate monitoring of sub-concussive impacts on the head.

Longitudinal, prospective study of head impacts in male high school football players

INTRODUCTION

Repetitive, subconcussive events may adversely affect the brain and cognition during sensitive periods of development. Prevention of neurocognitive consequences of concussion in high school football is therefore an important public health priority. We aimed to identify the player positions and demographic, behavioral, cognitive, and impact characteristics that predict the frequency and acceleration of head impacts in high school football players.

METHODS

In this prospective study, three cohorts of adolescent male athletes (N = 53, 28.3% Hispanic) were recruited over three successive seasons in a high school American football program. Demographic and cognitive functioning were assessed at baseline prior to participating in football. Helmet sensors recorded impact frequency and acceleration. Each head impact was captured on film from five different angles. Research staff verified and characterized on-field impacts. Player-level Poisson regressions and year-level and impact-level linear mixed-effect models were used to determine demographic, behavioral, cognitive, and impact characteristics as predictors of impact frequency and acceleration.

RESULTS

4,678 valid impacts were recorded. Impact frequency positively associated with baseline symptoms of hyperactivity-impulsivity [β(SE) = 1.05 impacts per year per unit of symptom severity (1.00), p = 0.01] and inattentiveness [β(SE) = 1.003 impacts per year per T-score unit (1.001), p = 0.01]. Compared to quarterbacks, the highest acceleration impacts were sustained by kickers/punters [β(SE) = 21.5 g's higher (7.1), p = 0.002], kick/punt returners [β(SE) = 9.3 g's higher (4.4), p = 0.03], and defensive backs [β(SE) = 4.9 g's higher (2.5), p = 0.05]. Impacts were more frequent in the second [β(SE) = 33.4 impacts (14.2), p = 0.02)] and third [β(SE) = 50.9 impacts (20.1), p = 0.01] year of play. Acceleration was highest in top-of-the-head impacts [β(SE) = 4.4 g's higher (0.8), p<0.001].

CONCLUSION

Including screening questions for Attention-Deficit/Hyperactivity Disorder in pre-participation evaluations can help identify a subset of prospective football players who may be at risk for increased head impacts. Position-specific strategies to modify kickoffs and correct tackling and blocking may also reduce impact burden.

Head Impact in Blind Football During the Tokyo Paralympics: Video-Based Observational Study

ABSTRACT

Head impacts during blind football are common and have high injury rates; however, their characteristics and impact are still underreported. We compared head impact characteristics in blind football players with and without falls on all 18 official blind football match videos from the Tokyo 2020 Paralympic games. The rate of head impacts with falls was significantly higher in the preliminary phase, offense phase, and during dribbling. Significant differences in the region of the head impacted were also observed among the impact subjects/objects. The findings in this study would contribute to the development of injury prevention measures to minimize head injuries from head impact in blind football.

Longitudinal Alterations of Cerebral Blood Flow in High-Contact Sports

OBJECTIVE

Repetitive head trauma is common in high-contact sports. Cerebral blood flow (CBF) can measure changes in brain perfusion that could indicate injury. Longitudinal studies with a control group are necessary to account for interindividual and developmental effects. We investigated whether exposure to head impacts causes longitudinal CBF changes.

METHODS

We prospectively studied 63 American football (high-contact cohort) and 34 volleyball (low-contact controls) male collegiate athletes, tracking CBF using 3D pseudocontinuous arterial spin labeling magnetic resonance imaging for up to 4 years. Regional relative CBF (rCBF, normalized to cerebellar CBF) was computed after co-registering to T1-weighted images. A linear mixed effects model assessed the relationship of rCBF to sport, time, and their interaction. Within football players, we modeled rCBF against position-based head impact risk and baseline Standardized Concussion Assessment Tool score. Additionally, we evaluated early (1-5 days) and delayed (3-6 months) post-concussion rCBF changes (in-study concussion).

RESULTS

Supratentorial gray matter rCBF declined in football compared with volleyball (sport-time interaction p = 0.012), with a strong effect in the parietal lobe (p = 0.002). Football players with higher position-based impact-risk had lower occipital rCBF over time (interaction p = 0.005), whereas players with lower baseline Standardized Concussion Assessment Tool score (worse performance) had relatively decreased rCBF in the cingulate-insula over time (interaction effect p = 0.007). Both cohorts showed a left-right rCBF asymmetry that decreased over time. Football players with an in-study concussion showed an early increase in occipital lobe rCBF (p = 0.0166).

INTERPRETATION

These results suggest head impacts may result in an early increase in rCBF, but cumulatively a long-term decrease in rCBF. ANN NEUROL 2023;94:457-469.

Heading Frequency and Risk of Cognitive Impairment in Retired Male Professional Soccer Players

Importance

Although professional soccer players appear to be at higher risk of neurodegenerative disease, the reason remains unknown.

Objective

To examine whether heading frequency is associated with risk of cognitive impairment in retired professional soccer players.

Design, Setting, and Participants

A UK nationwide cross-sectional study was conducted between August 15, 2020, and December 31, 2021, in 459 retired male professional soccer players older than 45 years and registered with the Professional Footballers' Association or a League Club Players' Association.

Exposure

Data on heading frequency in 3 bands-0 to 5, 6 to 15, and more than 15 times per match or training session and other soccer-specific risk factors, such as player position and concussion-were collected through a self-reported questionnaire.

Main Outcomes and Measures

Cognitive impairment was defined using the Telephone Interview for Cognitive Status-modified as scores of less than or equal to 21. Hopkins Verbal Learning Test, verbal fluency, and independent activities of daily living were also assessed. Test Your Memory and physician-diagnosed dementia/Alzheimer disease were self-reported via the questionnaire. Adjusted odds ratios (AORs) with 95% CIs were calculated.

Results

Of 468 retired male professional soccer players who completed questionnaires (mean [SD] age, 63.68 [10.48]; body mass index, 27.22 [2.89]), 459 reported heading frequency: 114 headed 0 to 5 times, 185 headed 6 to 15 times, 160 headed more than 15 times per match, and 125 headed 0 to 5 times, 174 headed 6 to 15 times, and 160 headed more than 15 times per training session during their careers. The prevalence of cognitive impairment was 9.78% (0-5 times), 14.78% (6-15 times), and 15.20% (>15 times) per match (P = .51). Compared with players reporting 0 to 5 headers per match, the AORs were 2.71 (95% CI, 0.89-8.25) for players reporting 6 to 15 headers per match and 3.53 (95% CI, 1.13-11.04) for players reporting more than 15 headers per match (P = .03 for trend). Corresponding AORs for heading frequency per training session were 2.38 (95% CI, 0.82-6.95) for those reporting 6 to 15, and 3.40 (95% CI, 1.13-10.23) for those reporting more than 15 in comparison with those who reported 0 to 5 (P = .03 for trend). Concussion involving memory loss was also associated with a greater risk of cognitive impairment (AOR, 3.16; 95% CI, 1.08-9.22). Similar results were observed with other cognitive tests and self-reported physician-diagnosed dementia/Alzheimer disease.

Conclusions and Relevance

The findings of this study suggest that repetitive heading during a professional soccer career is associated with an increased risk of cognitive impairment in later life. Further study is needed to establish the upper threshold for heading frequency to mitigate this risk.

Subconcussion revealed by sound processing in the brain

Introduction/Purpose

We tested the hypothesis that an objective measure of auditory processing reveals a history of head trauma that does not meet the clinical definition of concussion.

Methods

Division I collegiate student-athletes (n = 709) across 19 sports were divided into groups, based on their sport, using prevailing classifications of "contact" (317 males, 212 females) and "noncontact" (58 males, 122 females). Participants were evaluated using the frequency-following response (FFR) to speech. The amplitude of FFR activity in a frequency band corresponding to the fundamental frequency (F0)-the voice pitch-of the speech stimulus, an outcome reduced in individuals with concussions, was critically examined.

Results

We found main effects of contact level and sex. The FFR-F0 was smaller in contact athletes than noncontact athletes and larger in females than males. There was a contact by sex interaction, with the FFR-F0 of males in the contact group being smaller than the three other groups. Secondary analyses found a correlation between FFR-F0 and length of participation in contact sports in male athletes.

Conclusion

These findings suggest that the disruption of sensory processing in the brain can be observed in individuals without a concussion but whose sport features regular physical contact. This evidence identifies sound processing in the brain as an objective marker of subconcussion in athletes.

Cranial Bone Changes Induced by Mild Traumatic Brain Injuries: A Neglected Player in Concussion Outcomes?

Mild traumatic brain injuries (TBIs), particularly when repetitive in nature, are increasingly recognized to have a range of significant negative implications for brain health. Much of the ongoing research in the field is focused on the neurological consequences of these injuries and the relationship between TBIs and long-term neurodegenerative conditions such as chronic traumatic encephalopathy and Alzheimer's disease. However, our understanding of the complex relationship between applied mechanical force at impact, brain pathophysiology, and neurological function remains incomplete. Past research has shown that mild TBIs, even below the threshold that results in cranial fracture, induce changes in cranial bone structure and morphology. These structural and physiological changes likely have implications for the transmission of mechanical force into the underlying brain parenchyma. Here, we review this evidence in the context of the current understanding of bone mechanosensitivity and the consequences of TBIs or concussions. We postulate that heterogeneity of the calvarium, including differing bone thickness attributable to past impacts, age, or individual variability, may be a modulator of outcomes after subsequent TBIs. We advocate for greater consideration of cranial responses to TBI in both experimental and computer modeling of impact biomechanics, and raise the hypothesis that calvarial bone thickness represents a novel biomarker of brain injury vulnerability post-TBI.

The modulatory role of cannabis use in subconcussive neural injury

Cannabis use has become popular among athletes, many of whom are exposed to repetitive subconcussive head impacts. We aimed to test whether chronic cannabis use would be neuroprotective or exacerbating against acute subconcussive head impacts. This trial included 43 adult soccer players (Cannabis group using cannabis at least once a week for the past 6 months, n = 24; non-cannabis control group, n = 19). Twenty soccer headings, induced by our controlled heading model, significantly impaired ocular-motor function, but the degrees of impairments were less in the cannabis group compared to controls. The control group significantly increased its serum S100B level after heading, whereas no change was observed in the cannabis group. There was no group difference in serum neurofilament light levels at any time point. Our data suggest that chronic cannabis use may be associated with an enhancement of oculomotor functional resiliency and suppression of the neuroinflammatory response following 20 soccer headings.

Immunocal® limits gliosis in mouse models of repetitive mild-moderate traumatic brain injury

Successive traumatic brain injuries (TBIs) exacerbate neuroinflammation and oxidative stress. No therapeutics exist for populations at high risk of repetitive mild TBIs (rmTBIs). We explored the preventative therapeutic effects of Immunocal®, a cysteine-rich whey protein supplement and glutathione (GSH) precursor, following rmTBI and repetitive mild-moderate TBI (rmmTBI). Populations that suffer rmTBIs largely go undiagnosed and untreated; therefore, we first examined the potential therapeutic effect of Immunocal® long-term following rmTBI. Mice were treated with Immunocal® prior to, during, and following rmTBI induced by controlled cortical impact until analysis at 2 weeks, 2 months, and 6 months following the last rmTBI. Astrogliosis and microgliosis were measured in cortex at each time point and edema and macrophage infiltration by MRI were analyzed at 2 months post-rmTBI. Immunocal® significantly reduced astrogliosis at 2 weeks and 2 months post-rmTBI. Macrophage activation was observed at 2 months post-rmTBI but Immunocal® had no significant effect on this endpoint. We did not observe significant microgliosis or edema after rmTBI. The dosing regimen was repeated in mice subjected to rmmTBI; however, using this experimental paradigm, we examined the preventative therapeutic effects of Immunocal® at a much earlier timepoint because populations that suffer more severe rmmTBIs are more likely to receive acute diagnosis and treatment. Increases in astrogliosis, microgliosis, and serum neurofilament light (NfL), as well as reductions in the GSH:GSSG ratio, were observed 72 h post-rmmTBI. Immunocal® only significantly reduced microgliosis after rmmTBI. In summary, we report that astrogliosis persists for 2 months post-rmTBI and that inflammation, neuronal damage, and altered redox homeostasis present acutely following rmmTBI. Immunocal® significantly limited gliosis in these models; however, its neuroprotection was partially overwhelmed by repetitive injury. Treatments that modulate distinct aspects of TBI pathophysiology, used in combination with GSH precursors like Immunocal®, may show more protection in these repetitive TBI models.

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.

Examining later-in-life health risks associated with sport-related concussion and repetitive head impacts: a systematic review of case-control and cohort studies

OBJECTIVE

Concern exists about possible problems with later-in-life brain health, such as cognitive impairment, mental health problems and neurological diseases, in former athletes. We examined the future risk for adverse health effects associated with sport-related concussion, or exposure to repetitive head impacts, in former athletes.

DESIGN

Systematic review.

DATA SOURCES

Search of MEDLINE, Embase, Cochrane, CINAHL Plus and SPORTDiscus in October 2019 and updated in March 2022.

ELIGIBILITY CRITERIA

Studies measuring future risk (cohort studies) or approximating that risk (case-control studies).

RESULTS

Ten studies of former amateur athletes and 18 studies of former professional athletes were included. No postmortem neuropathology studies or neuroimaging studies met criteria for inclusion. Depression was examined in five studies in former amateur athletes, none identifying an increased risk. Nine studies examined suicidality or suicide as a manner of death, and none found an association with increased risk. Some studies comparing professional athletes with the general population reported associations between sports participation and dementia or amyotrophic lateral sclerosis (ALS) as a cause of death. Most did not control for potential confounding factors (eg, genetic, demographic, health-related or environmental), were ecological in design and had high risk of bias.

CONCLUSION

Evidence does not support an increased risk of mental health or neurological diseases in former amateur athletes with exposure to repetitive head impacts. Some studies in former professional athletes suggest an increased risk of neurological disorders such as ALS and dementia; these findings need to be confirmed in higher quality studies with better control of confounding factors.

PROSPERO REGISTRATION NUMBER

CRD42022159486.

How low can you go? Measuring human event-related brain potentials from a two-channel EEG system

Over the past ten years, there has been a rapid increase in the availability and use of mobile electroencephalography (mEEG) in research. Indeed, researchers using mEEG have recorded EEG and event-related brain potentials in a wide range of environments - for example, while walking (Debener et al., 2012), riding a bike (Scanlon et al., 2020), or even in a shopping mall (Krigolson et al., 2021). However, given that low-cost, ease-of-use, and setup speed provide the primary advantages of an mEEG system over large array traditional EEG systems, an important and unresolved question is just how many electrodes does an mEEG system need to collect research-quality EEG data? Here, we tested whether or not a two-channel forehead-mounted mEEG system - the "Patch" - could measure event-related brain potentials within their established amplitude and latency characteristics (Luck, 2014). In the present study, participants performed a visual oddball task while we recorded EEG data from the Patch. Our results demonstrated that we could capture and quantify the N200 and P300 event-related brain potential components using a minimal electrode array forehead-mounted EEG system. Our data further support the idea that mEEG can be used for quick and rapid EEG-based assessments, such as measuring the impact of concussions on the sports field (Fickling et al., 2021) or assessing the impact of stroke severity in a hospital (Wilkinson et al., 2020).

Effects of contact/collision sport history on gait in early- to mid-adulthood

BACKGROUND

To determine the effect of contact/collision sport participation on measures of single-task (ST) and dual-task (DT) gait among early- to middle-aged adults.

METHODS

The study recruited 113 adults (34.88 ± 11.80 years, (mean ± SD); 53.0% female) representing 4 groups. Groups included (a) former non-contact/collision athletes and non-athletes who are not physically active (n = 28); (b) former non-contact/collision athletes who are physically active (n = 29); (c) former contact/collision sport athletes who participated in high-risk sports and are physically active (n = 29); and (d) former rugby players with prolonged repetitive head impact exposure history who are physically active (n = 27). Gait parameters were collected using inertial measurement units during ST and DT gait. DT cost was calculated for all gait parameters (double support, gait speed, and stride length). Groups were compared first using one-way analysis of covariance. Then a multiple regression was performed for participants in the high-risk sport athletes and repetitive head impact exposure athletes groups only to predict gait outcomes from contact/collision sport career duration.

RESULTS

There were no significant differences between groups on any ST, DT, or DT cost outcomes (p > 0.05). Contact/collision sport duration did not predict any ST, DT, or DT cost gait outcomes.

CONCLUSION

Years and history of contact/collision sport participation does not appear to negatively affect or predict neurobehavioral function in early- to mid-adulthood among physically active individuals.

Longitudinal Associations of Clinical and Biochemical Head Injury Biomarkers With Head Impact Exposure in Adolescent Football Players

Importance

Consequences of subconcussive head impacts have been recognized, yet most studies to date have included small samples from a single site, used a unimodal approach, and lacked repeated testing.

Objective

To examine time-course changes in clinical (near point of convergence [NPC]) and brain-injury blood biomarkers (glial fibrillary acidic protein [GFAP], ubiquitin C-terminal hydrolase-L1 [UCH-L1], and neurofilament light [NF-L]) in adolescent football players and to test whether changes in the outcomes were associated with playing position, impact kinematics, and/or brain tissue strain.

Design, Setting, and Participants

This multisite, prospective cohort study included male high school football players aged 13 to 18 years at 4 high schools in the Midwest during the 2021 high school football season (preseason [July] and August 2 to November 19).

Exposure

A single football season.

Main Outcomes and Measures

The main outcomes were NPC (a clinical oculomotor test) and serum levels of GFAP, UCH-L1, and NF-L. Participants' head impact exposure (frequency and peak linear and rotational accelerations) was tracked using instrumented mouthguards, and maximum principal strain was computed to reflect brain tissue strain. Players' neurological function was assessed at 5 time points (preseason, post-training camp, 2 in season, and postseason).

Results

Ninety-nine male players contributed to the time-course analysis (mean [SD] age, 15.8 [1.1] years), but data from 6 players (6.1%) were excluded from the association analysis due to issues related to mouthguards. Thus, 93 players yielded 9498 head impacts in a season (mean [SD], 102 [113] impacts per player). There were time-course elevations in NPC and GFAP, UCH-L1, and NF-L levels. Compared with baseline, the NPC exhibited a significant elevation over time and peaked at postseason (2.21 cm; 95% CI, 1.80-2.63 cm; P < .001). Levels of GFAP and UCH-L1 increased by 25.6 pg/mL (95% CI, 17.6-33.6 pg/mL; P < .001) and 188.5 pg/mL (95% CI, 145.6-231.4 pg/mL; P < .001), respectively, later in the season. Levels of NF-L were elevated after the training camp (0.78 pg/mL; 95% CI, 0.14-1.41 pg/mL; P = .011) and midseason (0.55 pg/mL; 95% CI, 0.13-0.99 pg/mL; P = .006) but normalized by the end of the season. Changes in UCH-L1 levels were associated with maximum principal strain later in the season (0.052 pg/mL; 95% CI, 0.015-0.088 pg/mL; P = .007) and postseason (0.069 pg/mL; 95% CI, 0.031-0.106 pg/mL; P < .001).

Conclusions and Relevance

The study data suggest that adolescent football players exhibited impairments in oculomotor function and elevations in blood biomarker levels associated with astrocyte activation and neuronal injury throughout a season. Several years of follow-up are needed to examine the long-term effects of subconcussive head impacts in adolescent football players.

Repetitive Low-level Blast Exposure and Neurocognitive Effects in Army Ranger Mortarmen

INTRODUCTION

Occupational exposure to repetitive, low-level blasts in military training and combat has been tied to subconcussive injury and poor health outcomes for service members. Most low-level blast studies to date have focused on explosive breaching and firing heavy weapon systems; however, there is limited research on the repetitive blast exposure and physiological effects that mortarmen experience when firing mortar weapon systems. Motivated by anecdotal symptoms of mortarmen, the purpose of this paper is to characterize this exposure and its resulting neurocognitive effects in order to provide preliminary findings and actionable recommendations to safeguard the health of mortarmen.

MATERIALS AND METHODS

In collaboration with the U.S. Army Rangers at Fort Benning, blast exposure, symptoms, and pupillary light reflex were measured during 3 days of firing 81 mm and 120 mm mortars in training. Blast exposure analysis included the examination of the blast overpressure (BOP) and cumulative exposure by mortarman position, as well as comparison to the 4 psi safety threshold. Pupillary light reflex responses were analyzed with linear mixed effects modeling. All neurocognitive results were compared between mortarmen (n = 11) and controls (n = 4) and cross-compared with blast exposure and blast history.

RESULTS

Nearly 500 rounds were fired during the study, resulting in a high cumulative blast exposure for all mortarmen. While two mortarmen had average BOPs exceeding the 4 psi safety limit (Fig. 2), there was a high prevalence of mTBI-like symptoms among all mortarmen, with over 70% experiencing headaches, ringing in the ears, forgetfulness/poor memory, and taking longer to think during the training week (n ≥ 8/11). Mortarmen also had smaller and slower pupillary light reflex responses relative to controls, with significantly slower dilation velocity (P < 0.05) and constriction velocity (P < 0.10).

CONCLUSION

Mortarmen experienced high cumulative blast exposure coinciding with altered neurocognition that is suggestive of blast-related subconcussive injury. These neurocognitive effects occurred even in mortarmen with average BOP below the 4 psi safety threshold. While this study was limited by a small sample size, its results demonstrate a concerning health risk for mortarmen that requires additional study and immediate action. Behavioral changes like ducking and standing farther from the mortar when firing can generally help reduce mortarmen BOP exposure, but we recommend the establishment of daily cumulative safety thresholds and daily firing limits in training to reduce cumulative blast exposure, and ultimately, improve mortarmen's quality of life and longevity in service.

The brain's weakness in the face of trauma: How head trauma causes the destruction of the brain

Of all our organs, the brain is perhaps the best protected from trauma. The skull has evolved to enclose it and, within the skull, the brain floats in a protective bath of cerebrospinal fluid. It is becoming evident, however, that head trauma experienced in young adult life can cause a dementia that appears decades later. The level of trauma that induces such destruction is still being assessed but includes levels well below that which cracks the skull or causes unconsciousness or concussion. Clinically this damage appears as dementia, in people who played body-contact sports in their youth or have survived accidents or the blasts of combat; and appears also, we argue, in old age, without a history of head trauma. The dementias have been given different names, including dementia pugilistica (affecting boxers), chronic traumatic encephalopathy (following certain sports, particularly football), traumatic brain injury (following accidents, combat) and Alzheimer's (following decades of life). They share common features of clinical presentation and neuropathology, and this conceptual analysis seeks to identify features common to these forms of brain injury and to identify where in the brain the damage common to them occurs; and how it occurs, despite the protection provided by the skull and cerebrospinal fluid. The analysis suggests that the brain's weak point in the face of trauma is its capillary bed, which is torn by the shock of trauma. This identification in turn allows discussion of ways of delaying, avoiding and even treating these trauma-induced degenerations.

Repeat subconcussion in the adult rat gives rise to behavioral deficits similar to a single concussion but different depending upon sex

Although concussions are a popular focus of neurotrauma research, subconcussions occur with higher frequency but are less well-studied. A subconcussion is an impact to the head that does not result in immediately diagnosable concussion but can result in later neurological consequences. Repeat subconcussions can produce behavioral impairments and neuropathology that is similar to or worse than those seen following a single concussion. The current study modified a previously established closed head injury model of concussion to create a subconcussion model and examines sex differences in behavioral responses to repeated subconcussion in the adult rat. Rats received a single concussion, single or repeat subconcussions, or no impact and behavior was monitored from 2 h through 31 days post-injury. A single concussion or repeat subconcussion resulted in deficits in locomotion, righting reflexes, and recognition memory. The degree of deficit induced by repeat subconcussions were either similar (righting reflexes) or greater/more persistent (locomotor deficits and recognition memory) than that of a concussion. Single subconcussion resulted in acute deficits that were mild and limited to righting reflexes and locomotion. Sex differences were observed in responses to repeat subconcussion: females showed greater deficits in righting reflexes, locomotion, and vestibular function, while males showed greater alterations in anxiety and depressive-like behavior. This study established a model of subconcussive impact where a single subconcussive impact resulted in minimal behavioral deficits but repeat subconcussions resulted in deficits similar to or worse than a single concussion. Our data also suggest sex differences in behavioral responses to both concussive and subconcussive impacts.

Challenges in the pharmacological treatment of patients under suspicion of chronic traumatic encephalopathy: A review

Chronic traumatic encephalopathy (CTE) is caused by progressive neurodegeneration associated with repetitive head impacts. This disease is more common in professionals who practice contact sports, resulting in a concussion and subconcussive trauma. CTE is characterized by the accumulation of hyperphosphorylated tau protein in neurons, astrocytes, and frontotemporal lobe degeneration. Symptoms are usually nonspecific and overlap with other neurodegenerative diseases, such as Alzheimer's disease and frontotemporal dementia, making it difficult to provide drug treatment for patients with this comorbidity. Therefore, the objective of this article is to present an updated review of the pharmacological treatment of chronic traumatic encephalopathy and its challenges.

The Effects of Attention-Deficit/Hyperactivity Disorder Symptoms on the Association between Head Impacts and Post-Season Neurocognitive and Behavioral Outcomes

OBJECTIVE

Having attention-deficit/hyperactivity disorder (ADHD) is a risk factor for concussion that impacts concussion diagnosis and recovery. The relationship between ADHD and repetitive subconcussive head impacts on neurocognitive and behavioral outcomes is less well known. This study evaluated the role of ADHD as a moderator of the association between repetitive head impacts on neurocognitive test performance and behavioral concussion symptoms over the course of an athletic season.

METHOD

Study participants included 284 male athletes aged 13-18 years who participated in high school football. Parents completed the Strengths and Weaknesses of ADHD Symptoms and Normal Behavior (SWAN) ratings about their teen athlete before the season began. Head impacts were measured using an accelerometer worn during all practices and games. Athletes and parents completed behavioral ratings of concussion symptoms and the Attention Network Task (ANT), Digital Trail Making Task (dTMT), and Cued Task Switching Task at pre- and post-season.

RESULTS

Mixed model analyses indicated that neither head impacts nor ADHD symptoms were associated with post-season athlete- or parent-reported concussion symptom ratings or neurocognitive task performance. Moreover, no relationships between head impact exposure and neurocognitive or behavioral outcomes emerged when severity of pre-season ADHD symptoms was included as a moderator.

CONCLUSION

Athletes' pre-season ADHD symptoms do not appear to influence behavioral or neurocognitive outcomes following a single season of competitive football competition. Results are interpreted in light of several study limitations (e.g., single season, assessment of constructs) that may have impacted this study's pattern of largely null results.

Methodology of the INVestigating traIning assoCiated blasT pAthology (INVICTA) study

BACKGROUND

Subconcussive blast exposure during military training has been the subject of both anecdotal concerns and reports in the medical literature, but prior studies have often been small and have used inconsistent methods.

METHODS

This paper presents the methodology employed in INVestigating traIning assoCiated blasT pAthology (INVICTA) to assess a wide range of aspects of brain function, including immediate and delayed recall, gait and balance, audiologic and oculomotor function, cerebral blood flow, brain electrical activity and neuroimaging and blood biomarkers.

RESULTS

A number of the methods employed in INVICTA are relatively easy to reproducibly utilize, and can be completed efficiently, while other measures require greater technical expertise, take longer to complete, or may have logistical challenges.

CONCLUSIONS

This presentation of methods used to assess the impact of blast exposure on the brain is intended to facilitate greater uniformity of data collection in this setting, which would enable comparison between different types of blast exposure and environmental circumstances, as well as to facilitate meta-analyses and syntheses across studies.