Objective: Executive functions govern our ability to navigate complex and novel situations in day-to-day life. There is increased interest on environmental influences that may cause changes to executive functioning. The current thesis involves two studies examining the derivation and performance of an executive behaviour screener from the Behavioral Assessment System for Children (BASC-2-PRS; Reynolds & Kamphaus, 2004) on two different adolescent samples using a previously derived four-factor model of executive functioning (Garcia-Barrera et al., 2011, 2013). Participants and Methods: Study 1. BASC-2 PRS standardization data consisting of a demographically matched American sample of 2722 12-21 year olds was obtained. The screener was derived using 25 items assigned a priori to each executive factor. Confirmatory factor analysis (CFA), invariance testing, and multiple indicators multiple causes (MIMIC) models were used to evaluate the screener. Study 2. The screener was applied to a previously collected sample of 479 elite adolescent hockey players from Canada with or without a history of concussion, followed through a single season of play. CFA, invariance testing, and MIMIC models were used to evaluate the screener and the hockey sample was compared to the standardization sample. Results: Study 1. Acceptable-to-good reliability was obtained for all factors (α = .75-.89). The four-factor model was the best fit to the data (CFI = .990, TLI = .989, RMSEA = .037). Configural, metric, and scalar but not latent mean invariance was shown for sex. Age-related uniform differential item functioning (DIF) and SES-related uniform and non-uniform DIF were shown. Standardized norms for use in clinical settings were created. Study 2. Acceptable-to-good reliability was shown for 3 factors (α = .72-.85). Emotional Control showed poor reliability (α = .58). The four-factor model was the best fit to the data (CFI = .991, TLI = .990, RMSEA = .026). Configural, metric, and scalar but not latent mean invariance was shown between the two samples. Uniform and non-uniform DIF were not observed for those with an increasing number of past concussions. Conclusions: Findings support the four-factor model measured through the screener in adolescence. Females and hockey players demonstrate fewer executive behaviour problems overall. Sex, age, and SES may influence the interpretation of factor scores. Continued exploration and development of the screener is suggested. / Graduate / 2018-09-27

Concussions are debilitating injuries affecting the short and long-term health of those who suffer from them. While an increased awareness of the injury has helped lead to a better understanding of the importance of better monitoring and treatment protocols, concussive injuries continue to occur at an alarming rate. Current injury risk thresholds exist and are used in the development of better equipment to protect athletes in high impact sports, however much of this data is based on simulations and/or cadaveric and animal model data from falls. Thus, there is a lack of data from concussive injuries resulting from a multitude of injury events within different sports, including collisions, falls and punches. The purpose of this thesis was to use dynamic response characteristics and brain tissue response to compare four different injury events from reconstructions of real life concussive injury events. This research was designed to provide information related to brain trauma characteristics specific to four common concussive brain injury events. Seventy-two (72) injury reconstructions were used in this study involving four injury events; collisions, helmeted falls, unhelmeted falls and punches. The results from the first study revealed that while all injury events produced similar MPS and Von Mises stress values, the injury events produced different peak linear and rotational accelerations. In terms of risk for concussive injury, differences were also found between percent risk for concussion and the specific injury events, questioning the validity of current concussive thresholds’ applicability to across all types of concussive injury events. The second study aimed to characterize each concussive injury event by means of specific kinematic characteristics unique to that particular event. The results showed that dynamic response variables that accounted for the most variance changed dependant on the concussive producing event. The third study compared maximal principle strain and strain fields within the brain by the specific injury event. The results showed that global strain within specific regions of the brain were significantly different between the different injury events. Furthermore, unique strain fields within the cerebrum were found between the four concussive injury events. The three studies in this research program characterize four common concussive injury events found in sport. It aimed to describe the unique dynamic response characteristics for each injury event that may have significant influence on protective equipment development and standards testing. Finally, though the aim of this study was not to correlate location of strains within the brain with onset of concussive symptoms and duration, this study demonstrated that the concussive producing event can have an effect on location of peak strain and strain field within regions of the cerebrum associated with concussive symptoms.

Concussions are a problem in competitive sports with growing concern over the acute and long-term consequences of repetitive head trauma. Participation in sport increases risk of concussion, particularly contact sports including rugby, hockey and football (Harmon et al., 2013). In rugby league, there are between 8.0-17.5 concussions/1000 player hours, representing roughly 10-15% of all injuries in the sport (Gardner et al., 2015). Shoulder, head, hip and knee are reported to be the most common regions that impact the head and are responsible for the greatest number of concussive injuries in rugby (Cusimano et al., 2013; Fuller et al., 2010; Gardner et al., 2014; Toth, Mcneil, & Feasby, 2005). In each of the common injury events reported in elite men’s rugby, there are unique combinations of impact conditions which include effective mass, compliance, velocity and location of impact. The head-to-head event represents a low mass, low compliance event, whereby the hip and shoulder-to-head collisions represents high mass, high compliance events. Scientists have conducted research in an effort to describe incidence and mechanisms of concussive injury in rugby, however, little is known about the biomechanics of head injury in the sport (Fréchède & Mcintosh, 2009; Fréchède & McIntosh, 2007; McIntosh et al., 2000). The purpose of this thesis is to characterize dynamic response and brain tissue deformation for (1) hip-to-head, (2) shoulder-to-head, (3) knee-to-head, and (4) head-to-head concussion events in men’s rugby. Twenty-nine (29) impact videos of diagnosed concussive injuries associated with the four common injury events were reconstructed in the Neurotrauma Impact Science Lab. Head-to-head impacts were reconstructed in this study using a pendulum system, while hip, shoulder and knee to head impacts were reconstructed using the pneumatic linear impactor. Results of this study demonstrate that the common injury events resulting in concussion in elite men’s rugby have different dynamic response characteristics. Head-to-head events produced significantly greater peak linear and peak rotational acceleration, however no significant differences in maximum principal strain between the injury events. Results of this study can be useful in reducing rates and severity of concussive injury in rugby.

Traumatic brain injury (TBI) is becoming increasingly recognized as a global health issue. Each year over 160,000 Canadians experience some form of TBI, which can be caused by sport-related injuries, motor vehicle accidents, or assault. Adolescents are especially susceptible to repeat head injury and represent an at-risk population for sustaining sports-related concussions. The hippocampus, known for its role in learning and memory, is vulnerable to this injury. Although most TBI studies exclude females, there are important sex differences in outcomes and recovery following brain injury. A greater understanding of how sex differences contribute to the heterogeneity of this disease is critical for clinical care and potential treatments. Currently, few preclinical studies have assessed sex differences in adolescents following repeated mild traumatic brain injury (rmTBI). This study uses an awake closed head injury (ACHI) paradigm in male and female adolescent rats to investigate acute injury-induced changes to the hippocampus after rmTBI. A neurological assessment protocol (NAP) administered immediately after each impact showed that the ACHI acutely alters state of consciousness, and results in deficits after each impact. Following 8 ACHIs spaced 2 hours apart, adolescent rats were injected with the thymidine analogue BrdU and perfused 2 hours later on either post injury day (PID) 1 or 3. BrdU was used to identify cells undergoing DNA synthesis, and Ki-67 - expressed during all active phases of the cell cycle - was used as an endogenous marker for proliferation. Results indicate a robust and diffuse increase in cellular proliferation in male rmTBI animals that was not present to the same extent in female rmTBI animals. Triple labeling experiments revealed a higher proportion of microglia/macrophages in the subgranular zone of rmTBI animals, indicating an immediate inflammatory response in both sexes. This study shows sex differences in the pathophysiology of rmTBI in adolescent rats. Further investigation will reveal the detrimental versus neuroprotective contributions of this effect on learning and memory. / Graduate

Athletes participating in ice hockey are at a high risk of experiencing a concussion which can lead to impairments in cognitive functions. Deciding when a player can be returned to playing ice hockey is part of the concussion management called return to play (RTP). This can bebased on subjective or objective measures. Returning a concussed hockey player too soon can result in devastating consequences. This review aimed to investigate what objective measure could be used to assess a concussed player. It specifically focused on Immediate Post Concussion Assessment and Cognitive Test (ImPACT) and a cognitive motor integration (CMI) performance task. It was hypothesized that by combining the two could contribute to an optimal objective assessment and be used as accurate indicators in the RTP decision. This review involved searches from PubMed, Scopus and Web of Science which resulted in a total of four articles. The amount of articles was a big limitation. Main findings are that concussed participants showed decreased cognitive performance relative to baseline despite subjectively reporting being symptom free. Findings in this review suggest that adding a CMI performance task to the ImPACT test battery could be a way to objectively catch several composites incognitive recovery including tasks that require higher levels of cognitive functioning. Administering an assessment based on two objective measures could add accuracy and contribute to a safe RTP not risking a second impact syndrome or prolonged cognitive impairments.

Concussion is a popular clinical topic that has been the subject of unprecedented recent media coverage. As concerns about the potential short- and long-term implications of repetitive head injury in sports such as football continue to mount, the proper clinical management of concussion seems to increase in importance. The days of ignoring the ''ding'' on the sideline are definitely over. A series of updated clinical evaluation and management recommendations from international experts are highlighted in this review. The clinical presentation of an acute concussion, both the typical and more subtle variations, may be evaluated with new validated sideline evaluation tools (eg, Sports Concussion Assessment Tool 2). In addition, the role of computerized neuropsychological and balance testing in the acute and ongoing evaluation are discussed, along with how they contribute to the return-to-play decision. Same-day return to play is outdated, and the relative insensitivity of current neuroimaging modalities to demonstrate structural damage is highlighted. New therapeutic interventions such as amantadine and cognitive rest may improve recovery time. The appropriate management of concussion typically results in a normal functional and neurocognitive outcome. The recommendations in this article may guide clinicians, with varying degrees of prior experience managing concussion, to increase the likelihood of an excellent outcome.

In this paper, we investigate the potential for the development of a composite score investigating population-level phenotype changes in a mouse model of traumatic brain injury. Traumatic brain injuries (TBI) are a growing concern in the United States because the number of individuals impacted by TBI and associated symptoms is increasing, leading to a growing demand for research both in the clinical and preclinical setting. However, preclinical TBI modeling is complicated by the lack of inter and intra lab consistency in the assessment of behavioral and pathologic outcomes. Indeed, it remains unclear which behavior assessments are most useful in evaluating the effects of preclinical TBI. To investigate the relative contribution of various behavior tests in the assessment of preclinical TBI, three statistical models (simple linear regression, pairwise correlation, and factor analysis) were conducted on behavioral data from the Mannix-Meehan lab at Boston Children’s Hospital in Boston, Massachusetts, U.S.A. from 2012-2018. In this paper, a composite metric was created from the computation analysis of the three statistical methods. The score revealed MWM and EPM as the most potent behavioral tests. The Open Field and Rotarod test had a small impact on the outcome, but only in one of the three statistical models assessed. Thus, to effectively analyze treatment efficiencies, injury severity and long-term impairments, MWM and EPM are the best behavioral test for a mouse model. Furthermore, this method of analysis of entire populations of mice allows for more subtle phenotypic changes resultant from injury models to be revealed, and the generalizability of this model lends to widespread use.

Concussions are brain injuries--also called mild traumatic brain injuries--that affect the function of the brain temporarily or permanently. The purpose of this doctoral project was to develop an education module for staff at an urgent care center to address the lack of knowledge and low level of comfort regarding the care for patients with a head trauma. This project introduced and educated the clinical staff on an evidence-based protocol for the treatment and management of a patient with a concussion. The Rosswurm and Larrabee model for evidence-based change was used as a foundation for refining the practice question, gathering evidence, and translation of the protocol into the clinical setting. The Dreyfus model of the 5 stages of skill acquisition was used to measure the learners' level of achievement. A pretest and posttest were conducted to determine whether there was a gain in knowledge and confidence as a result of the project. There were 6 participants: 3 nonclinical staff and 3 nurses. Overall, there was a statistically significant improvement in confidence based on the Wilcoxon sign ranks test (z = -2.201; p = .028); however, a statistically significant increase in knowledge was not apparent, even though the scores did improve. All staff members were able to apply the practice guideline and make sound judgments using case studies. This project resulted in the translation of evidenced-based care into the urgent care setting, enhanced the confidence of the nursing staff, and has the potential to bring about positive social change by improving the quality of care that will be provided to patients with head injuries.

This thesis reports on a study to determine the viability of using a mobile tablet device as a brain concussion detection tool. The research builds upon the results of a prior method of collecting data for measuring motion sensitivity, where a user presses and releases a force sensor to balance a rising and falling line on a computer display. The motion sensitivity data collected using this force sensor device was shown to have less irregularity in persons with concussion. The MotionScan application, developed for this research, uses the accelerometer of a tablet device to record motor movement of a user while the user tries to control a free-moving ball on the tablet screen to trace a line. Data collection sessions were conducted with 20 participants, where researchers recorded motor performance data for similar tasks using both the MotionScan application and the force sensor device. Researchers analyzed the performance outcomes on the tablet application and force sensor device, and validated that they both record motor movements similarly. Participants were also asked for their feedback on the interface of MotionScan and the data collection process, which was used to improve the usability of MotionScan and data collection processes. The research demonstrates that a tablet device can measure the variability in a person’s motor sensitivity and with more research could be used as a concussion detection tool.

The majority of clinical impairments following a concussion resolve within 7-10 days. However, there is limited clarity as to long-term impact of this injury on neurocognitive function, motor control, and particularly integration of these domains. While repetitive head trauma is associated with numerous neurological disorders, the link is not well described. Visual-motor tracking tasks have been used to identify differences in visual processing, error detection, and fine motor control in aging and numerous pathologies. Examining the complexity of motor output from visual-motor tracking provides insight into multiple cognitive and motor function domains, and into fine motor control used for daily living, work, and sport. The purpose of this dissertation was, therefore, to: (1) use multiple regression to determine the extent to which concussion history and symptoms (loss of consciousness and amnesia) influence visual-motor task performance multiscale complexity, and (2) determine whether task performance complexity can distinguish, through logistic regression and prediction, between individuals with and without a history of concussion. In study 1, individuals with (n = 35) and without (n = 15) a history of concussion performed a visual-motor tracking task. Men and women exhibited linear decreases in task performance complexity, as well as midand high-frequency task performance components, with increasing numbers of concussions. However, men and women exhibited differing patterns, as did those with and without a history of concussion-related loss of consciousness. Finally, trial-to-trial complexity variability increased with increasing numbers of concussions. Findings indicate (1) a cumulative reduction in the way in which previously concussed individuals process and integrate visual information to guide behavior and (2) gender is an important consideration in concussion-related visual-motor outcomes. In Study 2, individuals with (n = 85) and without (n = 42) a history of concussion performed a visualmotor tracking task. Linear and nonlinear measures of task performance were used to build gender-specific logistic classification models using 10-fold cross-validation. When ensuring 80% sensitivity, the best models were 75-80% accurate in predicting a history of concussion. Such discrimination has clinical value in identifying individuals who merit further evaluation and observation over time for conditions related to repetitive head traumas.