Mild Traumatic Brain Injury (mTBI), often called concussion, has become a growing public health concern, prevalent in both athletic and military settings. In response, many researchers have explored cognitive outcomes post-mTBI, with a plethora of meta-analyses summarizing these findings; however, these meta-analyses examine solely mean performances on cognitive tasks, ignoring intra-individual variability (IIV) in cognitive performance that may elucidate neuropsychological impairment following mTBI. The current thesis involved two studies, responding to both the growing meta-analytic research and limited IIV findings. Study 1: Many meta-analyses have amalgamated individual study results on post-mTBI neuropsychological outcomes. With the abundance of meta-analyses, a systematic review of meta-analyses stands as the next logical step. Method: A systematic literature search yielded 11 meta-analyses meeting inclusion criteria (i.e., English-language systematic reviews/meta-analyses covering post-mTBI observational cognitive research on late adolescents/adults), with their findings qualitatively synthesized based on moderator variables (i.e., cognitive domain, time since injury, past head injury, participant characteristics, comparison group, assessment technique, and persistent symptoms). Results: The overall effect sizes ranged for both general (range: .07-.61) and sports-related mTBI (range: .40-.81) and differed both between and within cognitive domains, with executive functions appearing most sensitive to multiple mTBI. Cognitive domains varied in recovery rates, but overall recovery occurred by 90 days post-injury for most individuals and by seven days post-injury for athletes. Greater age/education and male gender produced smaller effects sizes, while high school athletes suffered the largest deficits post-mTBI. Control-group comparisons yielded larger effects than within-person designs, while assessment techniques had limited moderating effects. Conclusions: Overall, meta-analytic review quality remained low with few studies assessing publication or study quality bias. Meta-analyses consistently identified adverse acute mTBI-related effects and fairly rapid symptom resolution. Study 2: The long-term outcomes of executive functions and IIV following mTBI are unclear due to inconsistent and limited research, respectively. Further, the relationship between physical activity (PA) and cognitive performance at young adulthood remains almost fully unexplored. In turn, the current study aimed to (a) assess the diagnostic utility of both executive functions and IIV at predicting mTBI history and (b) evaluate the interaction between PA levels and mTBI on both of these cognitive metrics. Method: Altogether 138 self-identified athletes (Mage = 19.9 ± 1.91 years, 60.8% female, 19.6% 1 mTBI, 18.1% 2+ mTBIs) completed three executive-related cognitive tasks (i.e., N-Back, Go/No-go, Local-Global). Ordinal logistic regression analyses examined the joint effect of person-mean and IIV as predictors of mTBI status. Multi-level models examined mTBI and PA levels as predictors of trial-to-trial changes in performance. Results: Only mean response time (RT) for the Local-Global task predicted mTBI status, while no IIV variables reached unique significance. PA levels predicted subtle within-task decreases in RT across Local-Global trials. Conclusions: IIV research on mTBI remains limited; however, the preliminary results do not indicate any additional predictive value of IIV indices above mean performances. For executive functions, shifting appeared most affected, with past researchers identifying post-mTBI impairment in attentional processing. Higher PA levels minutely benefited within-task shifting and mean inhibitory performance, although these finding require cautious interpretation. / Graduate / 0622 / jkarr@uvic.ca

This thesis investigates head injuries (HIs) occurring in sports and recreation (SR) that presented to emergency departments (EDs) in Edmonton, Alberta, from April 1st, 1997 to March 31st, 2008. There were 4,950 SR HIs identified over the 11 years (5.13 HIs per 1,000 ED injury visits). Individuals less than 18 years old were 3.4 times more likely, and males were 1.25 times more likely to present with a head injury from SR (p < 0.0001). A history of one or two previous SR HIs increased the odds of subsequent HI by 2.62 and 5.94 times, respectively, while children aged 7 13 and 14 17 were more than four times more likely to sustain a HIs from SR (p < 0.001). The effects of multiple HIs occurring in children participating in SR activities needs to be addressed, due to the chronic neurobehavioral effects of HIs. / Epidemiology

Mild Traumatic Brain injury (mTBI) is one of the most common forms of acquired neurological damage. However, the term 'mild' TBI is misleading because the physical, cognitive and emotional impairments that can follow from mTBI can be significant. In order to provide objective, prognostic measures for diagnosing the severity of mTBI and identifying individuals who may be at risk for poor outcomes a battery of neuropsychological measures for detecting cognitive impairment was evaluated. The Rapid Screen of Concussion (RSC) is a collection of tests assessing verbal recall, orientation, processing speed and speed of language comprehension. Previous studies have demonstrated that the RSC has acceptable reliability, validity and sensitivity to cognitive impairment that arises during the acute stages of injury. However, no studies have investigated the predictive validity of this instrument. Moreover it is unclear what additional patient or post injury variables could assist in identifying those individuals who may be at risk of poor neuropsychological outcomes following mTBI. These were among the main issues that were addressed across the five empirical studies in this thesis. A pragmatic, prospective, longitudinal and cross-sectional study of the sequelae of mTBI in patients presenting to the Department of Emergency Medicine of the Royal Brisbane and Women's hospital was the basis of this project. The first empirical chapter (chapter 2), examined the psychometric properties of two measures of verbal learning and memory and investigated their potential for discriminating between mTBI and orthopaedic controls. The performance of 93 patients with mTBI and 68 participants with orthopaedic injuries was analysed to identify the number of individuals who performed at ceiling on the Hopkins Verbal Learning test (HVLT-R) versus a 5-word test of immediate and delayed recall. While both of these verbal recall measures were effective in separating the mTBI and orthopaedic groups, overall, the HVLT-R was shown to be a more suitable measure for screening for deficits in verbal learning and memory after mTBI. Given the superiority of the HVLT-R as a measure of verbal learning and memory, chapter 3 aimed to examine whether inclusion of this test could improve the sensitivity of the RSC in mTBI compared to orthopaedic and uninjured control samples. Results were generally within the direction predicted. Significant differences were found between groups on the majority of cognitive indices assessed. Both the orthopaedic and mTBI group performed more poorly than the uninjured group on all measures except the Hopkins delayed recognition. Additional performance decrements shown by the mTBI group compared to the orthopaedic group illustrate that factors beyond the general effects of trauma influence performance and may be related to cognitive impairment specific to sustaining mTBI. Overall it was concluded that the revised RSC is a sensitive instrument deserving investigation in assessing the more long term cognitive effects following mTBI. Chapter 4 applied this sensitive battery for investigation of group and individual recovery of neuropsychological test performance and post-concussive symptom reporting up to 3-months after mTBI. A sample of 30 mTBI participants and 30 uninjured controls were serially assessed on cognitive measures and symptom report scales immediately after injury and after 1-week, 1-month and 3-months. Symptom reporting on the Rivermead post-concussive inventory separated the mTBI and control groups after 1-week but diagnostic accuracy was no greater than chance at 1 and 3-months. In contrast the mTBI group performed more poorly than controls on measures on neuropsychological measures acutely, at 1-week and 1-month, with group differences still evident after 3-months. Nonethless, a trend of progressive recovery over time was seen in the mTBI group. In chapter 5, criteria utilising the concepts of reliable and statistically significant change were applied to the data. Overall, 73% of mTBI patients were impaired on one or more tests acutely. Significant recovery was demonstrated by 20% of mTBI participants by 3-months; however recovery remained incomplete for half of the mTBI participants by 3-months. These results highlighted the importance of an individual approach to the assessment of mTBI and support the notion that a proportion of mTBI cases may have protracted difficulties. Chapter 6 extended these findings by showing that the RSC has prognostic ability. It was found that acute neuropsychological performance on the RSC was a significant predictor of performance on an extended battery at 3-months. The final chapter provides a general discussion and synthesis of the findings. In summary, the present dissertation demonstrated that inclusion of a sensitive measure of verbal recall led to improved diagnostic validity of the RSC. Neuropsychological measures rather than symptom reporting were sensitive in detecting cognitive impairment at 3-months. Analysis of individuals showed that up to 50% of the group had failed to – demonstrate reliable recovery – that is, make improvements over and above practice effects after 3-months. Finally, acute neuropsychological performance was predictive of long term performance. Overall, the present thesis has identified a short battery of tests that is suitable for assessment of mTBI within 24 hours and may assist in identifying individuals at risk of poor cognitive outcomes after mTBI.

Mild Traumatic Brain injury (mTBI) is one of the most common forms of acquired neurological damage. However, the term 'mild' TBI is misleading because the physical, cognitive and emotional impairments that can follow from mTBI can be significant. In order to provide objective, prognostic measures for diagnosing the severity of mTBI and identifying individuals who may be at risk for poor outcomes a battery of neuropsychological measures for detecting cognitive impairment was evaluated. The Rapid Screen of Concussion (RSC) is a collection of tests assessing verbal recall, orientation, processing speed and speed of language comprehension. Previous studies have demonstrated that the RSC has acceptable reliability, validity and sensitivity to cognitive impairment that arises during the acute stages of injury. However, no studies have investigated the predictive validity of this instrument. Moreover it is unclear what additional patient or post injury variables could assist in identifying those individuals who may be at risk of poor neuropsychological outcomes following mTBI. These were among the main issues that were addressed across the five empirical studies in this thesis. A pragmatic, prospective, longitudinal and cross-sectional study of the sequelae of mTBI in patients presenting to the Department of Emergency Medicine of the Royal Brisbane and Women's hospital was the basis of this project. The first empirical chapter (chapter 2), examined the psychometric properties of two measures of verbal learning and memory and investigated their potential for discriminating between mTBI and orthopaedic controls. The performance of 93 patients with mTBI and 68 participants with orthopaedic injuries was analysed to identify the number of individuals who performed at ceiling on the Hopkins Verbal Learning test (HVLT-R) versus a 5-word test of immediate and delayed recall. While both of these verbal recall measures were effective in separating the mTBI and orthopaedic groups, overall, the HVLT-R was shown to be a more suitable measure for screening for deficits in verbal learning and memory after mTBI. Given the superiority of the HVLT-R as a measure of verbal learning and memory, chapter 3 aimed to examine whether inclusion of this test could improve the sensitivity of the RSC in mTBI compared to orthopaedic and uninjured control samples. Results were generally within the direction predicted. Significant differences were found between groups on the majority of cognitive indices assessed. Both the orthopaedic and mTBI group performed more poorly than the uninjured group on all measures except the Hopkins delayed recognition. Additional performance decrements shown by the mTBI group compared to the orthopaedic group illustrate that factors beyond the general effects of trauma influence performance and may be related to cognitive impairment specific to sustaining mTBI. Overall it was concluded that the revised RSC is a sensitive instrument deserving investigation in assessing the more long term cognitive effects following mTBI. Chapter 4 applied this sensitive battery for investigation of group and individual recovery of neuropsychological test performance and post-concussive symptom reporting up to 3-months after mTBI. A sample of 30 mTBI participants and 30 uninjured controls were serially assessed on cognitive measures and symptom report scales immediately after injury and after 1-week, 1-month and 3-months. Symptom reporting on the Rivermead post-concussive inventory separated the mTBI and control groups after 1-week but diagnostic accuracy was no greater than chance at 1 and 3-months. In contrast the mTBI group performed more poorly than controls on measures on neuropsychological measures acutely, at 1-week and 1-month, with group differences still evident after 3-months. Nonethless, a trend of progressive recovery over time was seen in the mTBI group. In chapter 5, criteria utilising the concepts of reliable and statistically significant change were applied to the data. Overall, 73% of mTBI patients were impaired on one or more tests acutely. Significant recovery was demonstrated by 20% of mTBI participants by 3-months; however recovery remained incomplete for half of the mTBI participants by 3-months. These results highlighted the importance of an individual approach to the assessment of mTBI and support the notion that a proportion of mTBI cases may have protracted difficulties. Chapter 6 extended these findings by showing that the RSC has prognostic ability. It was found that acute neuropsychological performance on the RSC was a significant predictor of performance on an extended battery at 3-months. The final chapter provides a general discussion and synthesis of the findings. In summary, the present dissertation demonstrated that inclusion of a sensitive measure of verbal recall led to improved diagnostic validity of the RSC. Neuropsychological measures rather than symptom reporting were sensitive in detecting cognitive impairment at 3-months. Analysis of individuals showed that up to 50% of the group had failed to – demonstrate reliable recovery – that is, make improvements over and above practice effects after 3-months. Finally, acute neuropsychological performance was predictive of long term performance. Overall, the present thesis has identified a short battery of tests that is suitable for assessment of mTBI within 24 hours and may assist in identifying individuals at risk of poor cognitive outcomes after mTBI.

Mild Traumatic Brain injury (mTBI) is one of the most common forms of acquired neurological damage. However, the term 'mild' TBI is misleading because the physical, cognitive and emotional impairments that can follow from mTBI can be significant. In order to provide objective, prognostic measures for diagnosing the severity of mTBI and identifying individuals who may be at risk for poor outcomes a battery of neuropsychological measures for detecting cognitive impairment was evaluated. The Rapid Screen of Concussion (RSC) is a collection of tests assessing verbal recall, orientation, processing speed and speed of language comprehension. Previous studies have demonstrated that the RSC has acceptable reliability, validity and sensitivity to cognitive impairment that arises during the acute stages of injury. However, no studies have investigated the predictive validity of this instrument. Moreover it is unclear what additional patient or post injury variables could assist in identifying those individuals who may be at risk of poor neuropsychological outcomes following mTBI. These were among the main issues that were addressed across the five empirical studies in this thesis. A pragmatic, prospective, longitudinal and cross-sectional study of the sequelae of mTBI in patients presenting to the Department of Emergency Medicine of the Royal Brisbane and Women's hospital was the basis of this project. The first empirical chapter (chapter 2), examined the psychometric properties of two measures of verbal learning and memory and investigated their potential for discriminating between mTBI and orthopaedic controls. The performance of 93 patients with mTBI and 68 participants with orthopaedic injuries was analysed to identify the number of individuals who performed at ceiling on the Hopkins Verbal Learning test (HVLT-R) versus a 5-word test of immediate and delayed recall. While both of these verbal recall measures were effective in separating the mTBI and orthopaedic groups, overall, the HVLT-R was shown to be a more suitable measure for screening for deficits in verbal learning and memory after mTBI. Given the superiority of the HVLT-R as a measure of verbal learning and memory, chapter 3 aimed to examine whether inclusion of this test could improve the sensitivity of the RSC in mTBI compared to orthopaedic and uninjured control samples. Results were generally within the direction predicted. Significant differences were found between groups on the majority of cognitive indices assessed. Both the orthopaedic and mTBI group performed more poorly than the uninjured group on all measures except the Hopkins delayed recognition. Additional performance decrements shown by the mTBI group compared to the orthopaedic group illustrate that factors beyond the general effects of trauma influence performance and may be related to cognitive impairment specific to sustaining mTBI. Overall it was concluded that the revised RSC is a sensitive instrument deserving investigation in assessing the more long term cognitive effects following mTBI. Chapter 4 applied this sensitive battery for investigation of group and individual recovery of neuropsychological test performance and post-concussive symptom reporting up to 3-months after mTBI. A sample of 30 mTBI participants and 30 uninjured controls were serially assessed on cognitive measures and symptom report scales immediately after injury and after 1-week, 1-month and 3-months. Symptom reporting on the Rivermead post-concussive inventory separated the mTBI and control groups after 1-week but diagnostic accuracy was no greater than chance at 1 and 3-months. In contrast the mTBI group performed more poorly than controls on measures on neuropsychological measures acutely, at 1-week and 1-month, with group differences still evident after 3-months. Nonethless, a trend of progressive recovery over time was seen in the mTBI group. In chapter 5, criteria utilising the concepts of reliable and statistically significant change were applied to the data. Overall, 73% of mTBI patients were impaired on one or more tests acutely. Significant recovery was demonstrated by 20% of mTBI participants by 3-months; however recovery remained incomplete for half of the mTBI participants by 3-months. These results highlighted the importance of an individual approach to the assessment of mTBI and support the notion that a proportion of mTBI cases may have protracted difficulties. Chapter 6 extended these findings by showing that the RSC has prognostic ability. It was found that acute neuropsychological performance on the RSC was a significant predictor of performance on an extended battery at 3-months. The final chapter provides a general discussion and synthesis of the findings. In summary, the present dissertation demonstrated that inclusion of a sensitive measure of verbal recall led to improved diagnostic validity of the RSC. Neuropsychological measures rather than symptom reporting were sensitive in detecting cognitive impairment at 3-months. Analysis of individuals showed that up to 50% of the group had failed to – demonstrate reliable recovery – that is, make improvements over and above practice effects after 3-months. Finally, acute neuropsychological performance was predictive of long term performance. Overall, the present thesis has identified a short battery of tests that is suitable for assessment of mTBI within 24 hours and may assist in identifying individuals at risk of poor cognitive outcomes after mTBI.

Mild Traumatic Brain injury (mTBI) is one of the most common forms of acquired neurological damage. However, the term 'mild' TBI is misleading because the physical, cognitive and emotional impairments that can follow from mTBI can be significant. In order to provide objective, prognostic measures for diagnosing the severity of mTBI and identifying individuals who may be at risk for poor outcomes a battery of neuropsychological measures for detecting cognitive impairment was evaluated. The Rapid Screen of Concussion (RSC) is a collection of tests assessing verbal recall, orientation, processing speed and speed of language comprehension. Previous studies have demonstrated that the RSC has acceptable reliability, validity and sensitivity to cognitive impairment that arises during the acute stages of injury. However, no studies have investigated the predictive validity of this instrument. Moreover it is unclear what additional patient or post injury variables could assist in identifying those individuals who may be at risk of poor neuropsychological outcomes following mTBI. These were among the main issues that were addressed across the five empirical studies in this thesis. A pragmatic, prospective, longitudinal and cross-sectional study of the sequelae of mTBI in patients presenting to the Department of Emergency Medicine of the Royal Brisbane and Women's hospital was the basis of this project. The first empirical chapter (chapter 2), examined the psychometric properties of two measures of verbal learning and memory and investigated their potential for discriminating between mTBI and orthopaedic controls. The performance of 93 patients with mTBI and 68 participants with orthopaedic injuries was analysed to identify the number of individuals who performed at ceiling on the Hopkins Verbal Learning test (HVLT-R) versus a 5-word test of immediate and delayed recall. While both of these verbal recall measures were effective in separating the mTBI and orthopaedic groups, overall, the HVLT-R was shown to be a more suitable measure for screening for deficits in verbal learning and memory after mTBI. Given the superiority of the HVLT-R as a measure of verbal learning and memory, chapter 3 aimed to examine whether inclusion of this test could improve the sensitivity of the RSC in mTBI compared to orthopaedic and uninjured control samples. Results were generally within the direction predicted. Significant differences were found between groups on the majority of cognitive indices assessed. Both the orthopaedic and mTBI group performed more poorly than the uninjured group on all measures except the Hopkins delayed recognition. Additional performance decrements shown by the mTBI group compared to the orthopaedic group illustrate that factors beyond the general effects of trauma influence performance and may be related to cognitive impairment specific to sustaining mTBI. Overall it was concluded that the revised RSC is a sensitive instrument deserving investigation in assessing the more long term cognitive effects following mTBI. Chapter 4 applied this sensitive battery for investigation of group and individual recovery of neuropsychological test performance and post-concussive symptom reporting up to 3-months after mTBI. A sample of 30 mTBI participants and 30 uninjured controls were serially assessed on cognitive measures and symptom report scales immediately after injury and after 1-week, 1-month and 3-months. Symptom reporting on the Rivermead post-concussive inventory separated the mTBI and control groups after 1-week but diagnostic accuracy was no greater than chance at 1 and 3-months. In contrast the mTBI group performed more poorly than controls on measures on neuropsychological measures acutely, at 1-week and 1-month, with group differences still evident after 3-months. Nonethless, a trend of progressive recovery over time was seen in the mTBI group. In chapter 5, criteria utilising the concepts of reliable and statistically significant change were applied to the data. Overall, 73% of mTBI patients were impaired on one or more tests acutely. Significant recovery was demonstrated by 20% of mTBI participants by 3-months; however recovery remained incomplete for half of the mTBI participants by 3-months. These results highlighted the importance of an individual approach to the assessment of mTBI and support the notion that a proportion of mTBI cases may have protracted difficulties. Chapter 6 extended these findings by showing that the RSC has prognostic ability. It was found that acute neuropsychological performance on the RSC was a significant predictor of performance on an extended battery at 3-months. The final chapter provides a general discussion and synthesis of the findings. In summary, the present dissertation demonstrated that inclusion of a sensitive measure of verbal recall led to improved diagnostic validity of the RSC. Neuropsychological measures rather than symptom reporting were sensitive in detecting cognitive impairment at 3-months. Analysis of individuals showed that up to 50% of the group had failed to – demonstrate reliable recovery – that is, make improvements over and above practice effects after 3-months. Finally, acute neuropsychological performance was predictive of long term performance. Overall, the present thesis has identified a short battery of tests that is suitable for assessment of mTBI within 24 hours and may assist in identifying individuals at risk of poor cognitive outcomes after mTBI.

Mild Traumatic Brain injury (mTBI) is one of the most common forms of acquired neurological damage. However, the term 'mild' TBI is misleading because the physical, cognitive and emotional impairments that can follow from mTBI can be significant. In order to provide objective, prognostic measures for diagnosing the severity of mTBI and identifying individuals who may be at risk for poor outcomes a battery of neuropsychological measures for detecting cognitive impairment was evaluated. The Rapid Screen of Concussion (RSC) is a collection of tests assessing verbal recall, orientation, processing speed and speed of language comprehension. Previous studies have demonstrated that the RSC has acceptable reliability, validity and sensitivity to cognitive impairment that arises during the acute stages of injury. However, no studies have investigated the predictive validity of this instrument. Moreover it is unclear what additional patient or post injury variables could assist in identifying those individuals who may be at risk of poor neuropsychological outcomes following mTBI. These were among the main issues that were addressed across the five empirical studies in this thesis. A pragmatic, prospective, longitudinal and cross-sectional study of the sequelae of mTBI in patients presenting to the Department of Emergency Medicine of the Royal Brisbane and Women's hospital was the basis of this project. The first empirical chapter (chapter 2), examined the psychometric properties of two measures of verbal learning and memory and investigated their potential for discriminating between mTBI and orthopaedic controls. The performance of 93 patients with mTBI and 68 participants with orthopaedic injuries was analysed to identify the number of individuals who performed at ceiling on the Hopkins Verbal Learning test (HVLT-R) versus a 5-word test of immediate and delayed recall. While both of these verbal recall measures were effective in separating the mTBI and orthopaedic groups, overall, the HVLT-R was shown to be a more suitable measure for screening for deficits in verbal learning and memory after mTBI. Given the superiority of the HVLT-R as a measure of verbal learning and memory, chapter 3 aimed to examine whether inclusion of this test could improve the sensitivity of the RSC in mTBI compared to orthopaedic and uninjured control samples. Results were generally within the direction predicted. Significant differences were found between groups on the majority of cognitive indices assessed. Both the orthopaedic and mTBI group performed more poorly than the uninjured group on all measures except the Hopkins delayed recognition. Additional performance decrements shown by the mTBI group compared to the orthopaedic group illustrate that factors beyond the general effects of trauma influence performance and may be related to cognitive impairment specific to sustaining mTBI. Overall it was concluded that the revised RSC is a sensitive instrument deserving investigation in assessing the more long term cognitive effects following mTBI. Chapter 4 applied this sensitive battery for investigation of group and individual recovery of neuropsychological test performance and post-concussive symptom reporting up to 3-months after mTBI. A sample of 30 mTBI participants and 30 uninjured controls were serially assessed on cognitive measures and symptom report scales immediately after injury and after 1-week, 1-month and 3-months. Symptom reporting on the Rivermead post-concussive inventory separated the mTBI and control groups after 1-week but diagnostic accuracy was no greater than chance at 1 and 3-months. In contrast the mTBI group performed more poorly than controls on measures on neuropsychological measures acutely, at 1-week and 1-month, with group differences still evident after 3-months. Nonethless, a trend of progressive recovery over time was seen in the mTBI group. In chapter 5, criteria utilising the concepts of reliable and statistically significant change were applied to the data. Overall, 73% of mTBI patients were impaired on one or more tests acutely. Significant recovery was demonstrated by 20% of mTBI participants by 3-months; however recovery remained incomplete for half of the mTBI participants by 3-months. These results highlighted the importance of an individual approach to the assessment of mTBI and support the notion that a proportion of mTBI cases may have protracted difficulties. Chapter 6 extended these findings by showing that the RSC has prognostic ability. It was found that acute neuropsychological performance on the RSC was a significant predictor of performance on an extended battery at 3-months. The final chapter provides a general discussion and synthesis of the findings. In summary, the present dissertation demonstrated that inclusion of a sensitive measure of verbal recall led to improved diagnostic validity of the RSC. Neuropsychological measures rather than symptom reporting were sensitive in detecting cognitive impairment at 3-months. Analysis of individuals showed that up to 50% of the group had failed to – demonstrate reliable recovery – that is, make improvements over and above practice effects after 3-months. Finally, acute neuropsychological performance was predictive of long term performance. Overall, the present thesis has identified a short battery of tests that is suitable for assessment of mTBI within 24 hours and may assist in identifying individuals at risk of poor cognitive outcomes after mTBI.

abstract: Traumatic brain injury (TBI) most frequently occurs in pediatric patients and remains a leading cause of childhood death and disability. Mild TBI (mTBI) accounts for 70-90% of all TBI cases, yet its neuropathophysiology is still poorly understood. While a single mTBI injury can lead to persistent deficits, repeat injuries increase the severity and duration of both acute symptoms and long term deficits. In this study, to model pediatric repetitive mTBI (rmTBI) we subjected unrestrained juvenile animals (post-natal day 20) to repeat weight drop impact. Animals were anesthetized and subjected to sham or rmTBI once per day for 5 days. At 14 days post injury (PID), magnetic resonance imaging (MRI) revealed that rmTBI animals displayed marked cortical atrophy and ventriculomegaly. Specifically, the thickness of the cortex was reduced up to 46% beneath and the ventricles increased up to 970% beneath the impact zone. Immunostaining with the neuron specific marker NeuN revealed an overall loss of neurons within the motor cortex but no change in neuronal density. Examination of intrinsic and synaptic properties of layer II/III pyramidal neurons revealed no significant difference between sham and rmTBI animals at rest or under convulsant challenge with the potassium channel blocker, 4-Aminophyridine. Overall, our findings indicate that the neuropathological changes reported after pediatric rmTBI can be effectively modeled by repeat weight drop in juvenile animals. Developing a better understanding of how rmTBI alters the pediatric brain may help improve patient care and direct "return to game" decision making in adolescents. / Dissertation/Thesis / Masters Thesis Biology 2014

abstract: Military veterans have a significantly higher incidence of mild traumatic brain injury (mTBI), depression, and Post-traumatic stress disorder (PTSD) compared to civilians. Military veterans also represent a rapidly growing subgroup of college students, due in part to the robust and financially incentivizing educational benefits under the Post-9/11 GI Bill. The overlapping cognitively impacting symptoms of service-related conditions combined with the underreporting of mTBI and psychiatric-related conditions, make accurate assessment of cognitive performance in military veterans challenging. Recent research findings provide conflicting information on cognitive performance patterns in military veterans. The purpose of this study was to determine whether service-related conditions and self-assessments predict performance on complex working memory and executive function tasks for military veteran college students. Sixty-one military veteran college students attending classes at Arizona State University campuses completed clinical neuropsychological tasks and experimental working memory and executive function tasks. The results revealed that a history of mTBI significantly predicted poorer performance in the areas of verbal working memory and decision-making. Depression significantly predicted poorer performance in executive function related to serial updating. In contrast, the commonly used clinical neuropsychological tasks were not sensitive service-related conditions including mTBI, PTSD, and depression. The differing performance patterns observed between the clinical tasks and the more complex experimental tasks support that researchers and clinicians should use tests that sufficiently tax verbal working memory and executive function when evaluating the subtle, higher-order cognitive deficits associated with mTBI and depression. / Dissertation/Thesis / Doctoral Dissertation Speech and Hearing Science 2017

The long-term consequences of repetitive mild traumatic brain injuries (mTBIs), or concussions, as well as the immediate acute dangers of head collisions in sport have become of growing concern in the field of medicine, research and athletics. An estimated 3.8 million sports-related concussions occur in the United States annually, with the highest incidence having been documented in football, hockey, soccer, basketball and rugby (Harmon et al., 2013). The incidence of concussion in the National Rugby League (NRL) corresponds to approximately 8.0-17.5 injuries per 1000 playing hours, with tackling having been identified as the most common cause (Gardner et al., 2014; King et al., 2014). The highest incidence of rugby concussive impacts is a result of shoulder-to-head collisions (35%) during tackles and game play (Gardner et al., 2014). Shoulder-to-head concussive events occur primarily on the ball carrier and secondarily on the tacklers (Hendricks et al., 2014; Quarrie & Hopkins, 2008). While some studies report that the ball carrier is at a greater risk of sustaining a concussion (Gardner et al., 2015; King et al., 2010, 2014), others have demonstrated a greater incidence of tacklers being removed from play for sideline concussion evaluation (Gardner et al., 2014). Given this discrepancy, the purpose of this study was to compare dynamic response and brain tissue deformation metrics for ball carriers and defensive tacklers in professional rugby during shoulder-to-head concussive impacts using in-laboratory reconstructions. Ten cases with an injured defensive tackler and ten cases with an injured ball carrier were reconstructed using a pneumatic linear impactor striking a 50th percentile Hybrid III headform to calculate dynamic response and maximum principal strain values. There was no significant difference between the two impact conditions for peak resultant linear and rotational accelerations, as well as brain tissue deformation. Differences between metrics in this research and past research where the impacting system was not reported were discussed. These differences reflect the importance of accounting for impact compliance when describing the risk associated with collisions in professional rugby.