The study had three purposes: 1.) examine the temporal change in depression symptoms among collegiate student-athletes throughout a fall athletic season, 2.) identify the course of depression in student-athletes pre- and post-concussion injury, and 3.) examine the relationship between neurocognitive performance and depression at baseline and post-concussion injury. Depression symptoms were measured every two weeks, beginning at pre-season baseline, until the end of the athletic season using the Patient Health Questionnaire-9 (PHQ-9). The Immediate Post-Concussion Assessment and Cognitive Testing (ImPACT) exam was used to measure neurocognitive performance at baseline and post-concussion. A total of 593 (92.1%) participants were used in the depression analyses. On average, nearly a third of the athletes endorsed minimal levels of depression symptoms across the fall athletic season. Across the entire athletic season, 3.7% of student-athletes had their PHQ-9s red-flag for moderate to severe depression symptoms. Significant differences were found in depression symptoms across time, and by sex. At pre-season baseline, higher depression symptoms were significantly correlated with decreased scores on Visual Memory, Visual Motor Speed, and Total Symptom Score, and increased Reaction Time. A total of 27 concussed athletes were used in the concussion and depression analyses. No significant differences were found between depression symptoms pre-concussion and any of the post-concussion time intervals. At 1 week post-concussion, elevated depression symptoms were significantly correlated with slower Reaction Time and higher Total Symptom Scores at 1 week post-concussion, and increased Impulse Control and Total Symptom Scores at 3-5 months post-concussion. These results demonstrate the need to evaluate depression symptoms at pre-season baseline, across the athletic season, and post-concussion in collegiate student-athletes. / Kinesiology

Concussion, defined as a functional injury with complex symptomatology, affects millions annually and has been classified as a serious public health concern. Clinical tools currently available for concussion assessment fail to objectively measure cognitive function and thus, are inadequate for proper evaluation of the cognitive dysfunctions associated with the injury. As a result, investigation into the neurological consequences associated with concussion has become a prominent focus in neuroscience research. Traditionally, neuroimaging methods have been used primarily on concussion detection, while behavioural and neuropsychological assessments have been used for both concussion detection and cognitive-performance tracking. However, to date, minimal work has explored the use of neuroimaging to track the consequences of concussion at the neurophysiological level. Accordingly, the present thesis sought to investigate the clinical applicability of electroencephalography (EEG) as an effective neuroimaging tool capable of concussion detection, as well as its ability to objectively track neurophysiological changes over time. Event-related potentials (ERPs) were used to assess specific functions, or more accurately, dysfunctions of select cognitive processes as reflected by electrophysiological changes in the brain. Specifically, the Mismatch Negativity (MMN), N2b, and P300 were investigated to evaluate memory, attention, and executive control in concussed populations. The results of this thesis demonstrated alterations in each of the aforementioned ERPs, signifying cognitive dysfunctions linked to neurophysiological abnormalities in concussed populations. Of particular importance, Chapter 2 revealed the first instance of MMN abnormalities in a concussed population, Chapter 3 was the first to assess concussed adolescents at the acute stage of their injury, and Chapter 4 demonstrates the potential of ERPs to track neurophysiological changes from the acute to post-acute stages of the injury. Ultimately, the findings presented in this dissertation support the clinical viability of using ERPs to not only detect cognitive dysfunctions associated with concussion, but also to objectively track neurophysiological changes on the path to recovery. / Dissertation / Doctor of Philosophy (PhD)

The blood-brain barrier (BBB) is regulated by factors that can be secreted by multiple cell types, including astrocytes, that maintain the BBB in health and promote repair after injury. However, astrocyte contributions to the BBB are largely assumed from transplantation studies in which astrocyte progenitor grafts conferred BBB-like properties to tissues that normally lack a BBB. To determine if astrocytes contribute an essential and non-redundant function in maintaining the healthy BBB, I genetically ablated a small number of astrocytes using a conditional, tamoxifen-inducible mouse model. Within 2 hours after induction, I observed sparse astrocyte death in the cortex and leakage of the small molecule Cadaverine and large plasma protein fibrinogen, which are normally contained by a functional BBB. Vessels within regions of ablated astrocytes showed reduced expression of the tight junction protein zonula occludens-1, indicating impairment of the physical barrier formed between endothelial cells. Cadaverine leakage persisted for weeks, a feature I also found in mice after mild concussive traumatic brain injury (cTBI), thus highlighting the potential for revealing astrocyte roles in post-injury repair. Unlike the genetic ablation model, astrocytes within Cadaverine leakage areas did not undergo cell death after cTBI and instead downregulated homeostatic proteins. Our preliminary results show this atypical phenotype appearing 10 minutes after cTBI, along with severe vessel rupture, BBB leakage, and disruption of endfoot and basement membrane proteins. This damage persists for months, suggesting that the BBB fails to repair in these areas. Our results provide direct in-vivo evidence for essential astrocyte roles in the maintenance of the healthy BBB. Maintenance and/or repair fail after mild concussive cTBI, possibly contributing to irreversible progression to neurodegenerative diseases. / Doctor of Philosophy / The blood-brain barrier (BBB) is a unique property of blood vessels in the Central Nervous System (CNS) different from other vessels in the body. The physically tight barrier of the BBB is formed by tight junction proteins between endothelial cells and limits paracellular diffusion. The metabolic barrier is formed by concentrations of glucose transporters that promote transport of essential nutrients to the brain. Lastly, a transport barrier limits the passage of molecules and cells across the endothelial cell layer, preventing the entry of non-essential molecules, including pathogens and immune cells found in the blood. The BBB is thought to be induced and maintained by factors secreted by nearby cells in the brain. Among these cells are astrocytes, a type of glial cell that nearly completely cover blood vessels with their processes called endfeet. This strategic positioning led the field to assume that astrocytes are responsible for generating the unique properties of the BBB. Yet little direct evidence exists to support this conclusion, and newer evidence calls into question if astrocytes are even needed for BBB functions. To test this, I used a genetic mouse model to induce death of small numbers of astrocytes in adult mice. This caused leakage of blood contents of various sizes into the brain. In addition, the tight junction proteins responsible for forming the physical BBB were disrupted. These effects remained for weeks, a feature I also found after mild concussive traumatic brain injury (cTBI). This suggests that astrocytes may have an additional function in repairing the injured BBB. Our results demonstrate an essential role for astrocytes in the maintenance of the healthy adult BBB. Maintenance and/or its repair fail after cTBI, possibly contributing to the cascade into irreversible progression to neurodegenerative diseases.

Between 1.6 and 3.8 million sports-related concussions are sustained by persons living in the United States annually. While sports-related concussion was once considered to only result in immediate neurocognitive impairment and symptoms that are transient in nature, recent research has correlated long-term neurodegenerative effects with a history of sports-related concussion. Increased awareness and current media attention have contributed to concussions becoming a primary health concern. Although much research has been performed investigating the biomechanics of concussion, little is understood about the biomechanics that cause concussion in humans. The research presented in this dissertation investigates human tolerance to head acceleration using methods that pair biomechanical data collected from human volunteers with clinical data. Head impact exposure and injury risk are quantified and presented. In contrast to the publicly available data on the safety of automobiles, consumers have no analytical mechanism to evaluate the protective performance of football helmets. With this in mind, the Summation of Tests for the Analysis of Risk (STAR) evaluation system was developed to evaluate the impact performance of footballs helmets and provide consumers with information about helmet safety. The STAR evaluation system was designed using real world data that relate impact exposure to injury risk. / Ph. D.

As many as 3.8 million sports-related traumatic brain injuries (TBIs) occur each year, nearly all of which are mild or concussive. These injuries are especially concerning given recent evidence that repeated concussions can lead to long-term neurodegenerative processes. One way of reducing the number of injuries is through improvements in protective equipment design. Safety standards and relative performance ratings have led to advancements in helmet design that have reduced severe injuries and fatalities in sports as well as concussive injuries. These standards and evaluation methods frequently use laboratory methods and brain injury criteria that have been developed through decades of research dedicated to determining the human tolerance to brain injury. It is necessary to determine which methods are the most appropriate for evaluating the performance of helmets and other protective equipment. Therefore, the aims of this research were to evaluate the use of different brain injury criteria and apply them to laboratory evaluation of helmets. These aims were achieved through evaluating the predictive capability of different brain injury criteria and comparing laboratory impact systems commonly used to evaluate helmet performance. Laboratory methods were developed to evaluate the relative performance of hockey helmets given the high rate of concussions associated with the sport. The implementation of these methods provided previously unavailable data on the relative risk of concussion associated with different hockey helmet models. / Ph. D.

An estimated 3.8 million sports-related concussions occur every year. Little research has been collected on soccer players, despite women's soccer having the third highest rate of concussion among all popular collegiate sports. The objective of this work was to evaluate multiple interventions that have been introduced to address the high rate of concussions in this population. Wearable head impact sensors were evaluated on their ability to accurately count and measure head impacts during a collegiate women's soccer season. Head impact exposure was quantified using video analysis of this season as well. Sensors were unable to accurately count impacts and reported nonsensical head acceleration measurements, indicating that data reported from head impact sensors should be interpreted with caution. The ability of soccer headgear to reduce linear and rotational head accelerations during common soccer impacts was examined in the laboratory. Ball-to-head and head-to-head impacts were performed at a range of speeds and impact orientations. Headgear resulted in small reductions during ball-to-head tests, which are not likely to be clinically relevant. In head-to-head tests, use of headgear on the struck head provided an overall 35% reduction in linear head acceleration, and a 53% reduction when another headgear was added to the striking head. The ten headgear tested varied greatly in performance. These data suggest that the use of protective headgear could reduce concussion incidence significantly in this population. Research presented in this thesis will inform soccer organizations on best practices for player safety with regard to head impacts. / Master of Science

The information presented herein attempts to quantify the conditions surrounding concussive impacts from foul tips to the masks of catchers and umpires in baseball. Media reports of such occasions were researched on video and pitch speed data from the Pitch F/X system recorded to suggest speeds and locations at which impacts occur. To evaluate mask performance, a pneumatic-wheel, electric-motor driven pitching machine was utilized to shoot baseballs at the instrumented head of a Hybrid III dummy. Head accelerations were calculated from a 3-2-2-2 accelerometer array to allow for comparisons of linear and angular kinematics. 6 common masks (2-piece traditional-style and 1-piece hockey-style) were tested at 7 locations at 60 mph to determine the severity of each location. The center-eyebrow and chin locations were further tested at 84 mph. Speed and location data were used to evaluate a large sample of 25 masks to explore possible performance differences between manufacturer models, mask types and cage styles. The results of this study showed no significant difference between hockey-style and traditional-style mask performance. Titanium caged masks, although lighter than their steel counterparts, experienced higher linear accelerations. However, all masks experienced linear and angular accelerations well below commonly accepted injury thresholds. Yet, concussive injury has still occurred in the players and umpires that wear these masks. The work presented here can be used to help better understand these thresholds and influence the design, construction and evaluation of a new generation of masks that decrease the risk of concussions to the wearer. / Master of Science

With a rise in wearable sensor technology and the desire to investigate head impacts in previously unstudied groups, wearable head impact sensors have reached nation-wide popularity for their promising benefits to consumers and researchers. However, there are risks in relying on such technology before proper validation of its performance has been completed. Preliminary tests have found that current sensors vary widely in performance. The objective of this work was to develop and implement a test method for evaluation of wearable sensors in an ideal laboratory environment. A custom pendulum was used to impact a NOCSAE headform mounted on a Hybrid III neck. Sensors were tested under helmeted and unhelmeted conditions, according to their prescribed use. The headform was impacted at four locations, each at four impact energies ranging from 25 g to 100 g. Peak and time series headform kinematics output by each sensor were compared to accelerometers and angular rate sensors inside the headform. Average and standard deviations of peak sensor error and normalized RMS error were evaluated at each test condition to describe sensor performance. Requirements were set in the slope and coefficient of determination from linear regressions constrained through the origin to describe adequate sensor performance under ideal conditions. Sensors that met the requirement in at least one kinematic variable will be further evaluated in more realistic on-field and cadaver tests. The combination of all testing phases will be used to provide an overall sensor evaluation for both researchers and consumers. / Master of Science

Fit is often pointed to as the most important factor to consider when selecting a helmet. However, there is no published biomechanical evidence suggesting that of helmet fit effects concussion risk. The objectives of this study were to quantify helmet fit on a headform and to determine the effect fit has on helmet performance. An impact pendulum was used to strike a helmeted NOCSAE headform mounted on a Hybrid III neck. Helmets were impacted at 4 locations at 3 energies representing a range of concussive to sub-concussive impacts. The fit conditions evaluated in this study represent fitting scenarios in which an athlete is provided a helmet that is properly or improperly sized and cases in which a properly sized helmet is too loose, too tight, or properly adjusted. A custom pressure sensor was developed and used to characterize helmet fit in each condition with a quantitative fit metric representative of a variation from zero pressure on the headform. All helmets produced significant differences in both peak linear and peak angular acceleration due to fit. Differences were generally small with some exceptions. Furthermore, air bladder inflation generated significant differences in both peak linear and peak angular acceleration, but these were generally small in magnitude. While fit associated with size and air bladder inflation significantly affected linear and rotational head acceleration for most impact conditions, the best fit condition did not always generate the lowest accelerations. Differences can be attributed to varying helmet characteristics between and within helmet models. / Master of Science

Yes / ... Sustaining a sport-related concussion (SRC) has been associated with negative consequences to emotion and cognition in recent years,4,5 and head impacts are no different.1 Moreover, there is a consistent link reported with neurodegenerative diseases such as motor-neuron disease, Parkinson’s disease, and dementia. Although this is well-known within the scientific community, and becoming so in the general population, we still place children at risk. Promoting attitude change toward SRC and head impacts in sport is difficult enough with adults as many are accustomed to the way their contact sports are played and spectated. However, a redeeming feature for many researchers is that the evidence is there, and the rhetoric is being discussed in the mainstream media across the world.