Blast-Exposed Veterans With Mild Traumatic Brain Injury Show Greater Frontal Cortical Thinning and Poorer Executive Functioning

Neurocognitive Intraindividual Variability in Veterans with Mild Traumatic Brain Injury History and Posttraumatic Stress Disorder

OBJECTIVE

Veterans with a history of blast-related mild traumatic brain injury (mTBI) and posttraumatic stress disorder (PTSD) may be at risk for greater cognitive concerns and worse functional outcomes compared to those with either condition in isolation. However, traditional neuropsychological assessment approaches have yielded equivocal results in these populations. The present study examined an alternative method for detecting subtle cognitive inefficiencies: neurocognitive intraindividual variability (IIV), a measure of within-person performance consistency.

METHOD

Participants were 79 male Veterans with a history of blast-related mTBI and current PTSD (mTBI/PTSD group; n = 54) or neither diagnosis (controls; n = 25). Mean T-scores and IIV scores were calculated from neuropsychological measures of attention and speed of information processing (A/SoP) as well as executive functioning (EF).

RESULTS

Global IIV was significantly higher in the mTBI/PTSD group compared to controls (p = .047, Cohen's d = 0.49). At the domain level, larger effect sizes were observed for EF IIV (Cohen's d = 0.46) compared to A/SoP IIV (d = 0.32), although neither were statistically significant. Within the mTBI/PTSD group, higher Global IIV was associated with worse self-reported executive dysfunction, psychological quality of life, and cognitive post-concussive symptoms; at the domain level, these clinical outcomes were generally associated with greater A/SoP IIV (but not EF IIV).

CONCLUSION

Findings extend previous investigations of neurocognitive IIV in individuals with a history of mTBI across PTSD status. Among Veterans with a history of mTBI and comorbid PTSD, neurocognitive variability may be a better indicator of self-reported cognitive inefficiencies and Veteran experience of daily cognitive functioning than mean neuropsychological performances.

Short-term neural and glial response to mild traumatic brain injury in the hippocampus

Traumatic brain injury (TBI) is an established risk factor for developing neurodegenerative disease. However, how TBI leads from acute injury to chronic neurodegeneration is limited to postmortem models. There is a lack of connections between in vitro and in vivo TBI models that can relate injury forces to both macroscale tissue damage and brain function at the cellular level. Needle-induced cavitation (NIC) is a technique that can produce small cavitation bubbles in soft tissues, which allows us to relate small strains and strain rates in living tissue to ensuing acute cell death, tissue damage, and tissue remodeling. Here, we applied NIC to mouse brain slices to create a new model of TBI with high spatial and temporal resolution. We specifically targeted the hippocampus, which is a brain region critical for learning and memory and an area in which injury causes cognitive pathologies in humans and rodent models. By combining NIC with patch-clamp electrophysiology, we demonstrate that NIC in the cornu ammonis 3 region of the hippocampus dynamically alters synaptic release onto cornu ammonis 1 pyramidal neurons in a cannabinoid 1 receptor-dependent manner. Further, we show that NIC induces an increase in extracellular matrix protein GFAP associated with neural repair that is mitigated by cannabinoid 1 receptor antagonism. Together, these data lay the groundwork for advanced approaches in understanding how TBI impacts neural function at the cellular level and the development of treatments that promote neural repair in response to brain injury.

Neuroinflammatory Biomarkers and Their Associations With Cognitive, Affective, and Functional Outcomes 3 to 12 Months After a Traumatic Brain Injury: A Pilot Study

BACKGROUND

Neuroinflammation is an important feature of traumatic brain injury (TBI) that remains poorly understood in the 3- to 12-month period post-TBI.

OBJECTIVE

The purpose of our pilot study was to examine the relationships between biomarkers of neuroinflammation and functional outcomes in TBI patients 3 to 12 months postinjury.

METHODS

TBI patients (n = 36) 3 to 12 months post-TBI were recruited from a South Florida TBI clinic from May 2022 to June 2023. The Disability Rating Scale, Satisfaction with Life Scale, NIH Toolbox Sorting Working Memory, Neuro-Quality of Life Cognitive Function, Anxiety, Depression, and Sleep assessments were performed. Multiple plasma biomarkers were assayed. Analysis of variance was used to compare between-group results. Linear regression was performed to analyze relationships between biomarkers and outcomes.

RESULTS

Brain-derived neurotrophic factor concentrations were higher as postinjury time interval increased and were associated with cognitive battery outcomes. S-100β and glial fibrillary acidic protein were associated with anxiety score and hospital length of stay; S-100β was also associated with depression. Interleukin 6 was associated with cognitive function score and time since injury.

CONCLUSIONS

We found S-100β, glial fibrillary acidic protein, Interleukin 6, and brain-derived neurotrophic factor to play a larger role in the TBI recovery period than other biomarkers examined. Clinicians should continue to monitor for symptoms post-TBI, as the neuroinflammatory process continues to persist even into the later rehabilitation stage.

Mild Traumatic Brain Injury in the Maturing Brain: An Investigation of Symptoms and Cognitive Performance in Soldiers Returning From Afghanistan and Iraq

OBJECTIVE

The majority of traumatic brain injuries (TBIs) are classified as mild and occur in young individuals. The course of recovery varies but can result in chronic or troubling outcomes. The impact of age on TBI outcomes in young adults before complete brain maturation is not well studied.

METHODS

In this study, we compared the effects of mild TBI on cognitive performance and self-reported TBI symptoms and posttraumatic stress disorder (PTSD) in 903 soldiers in 3 different age groups: 24 years or younger, 25 to 27 years, and 28 to 40 years. The soldiers had returned from war zones in Iraq and were screened for TBI within a few days of return. Cognitive performance was measured with the Automated Neuropsychological Assessment Metrics of Military TBI Version 4 (ANAM4). Symptoms associated with mild TBI were self-reported on the Neurobehavioral Symptom Inventory, and the PTSD Checklist-Civilian Version (PCL-C).

RESULTS

Soldiers with TBI in every age group had significantly higher prevalence of most symptoms than those with no TBI. Soldiers with TBI also reported more chronic pain sites, regardless of age. Soldiers aged 28 to 40 years with TBI had the lowest cognitive performance scores (ANAM) across several subtests, both unadjusted and adjusted. The Global Deficit Score was significantly higher for soldiers aged 28 to 40 years and 25 to 27 years with TBI than for soldiers younger than 24 years with no TBI. After adjusting for PTSD symptoms, education, and number of lifetime TBIs, the overall test battery mean for soldiers aged 28 to 40 years with TBI was significantly lower than for soldiers younger than 24 years with no TBI.

CONCLUSION

Soldiers with mild TBI in the younger age group show more symptoms associated to frontal lobe function while soldiers in the older group suffer more cognitive impairment. This may warrant further study as it may indicate a propensity to later cognitive decline among soldiers who were older at the time of injury.

Perivascular Space Burden and Cerebrospinal Fluid Biomarkers in US Veterans With Blast-Related Mild Traumatic Brain Injury

Blast-related mild traumatic brain injury (mTBI) is recognized as the "signature injury" of the Iraq and Afghanistan wars. Sleep disruption, mTBI, and neuroinflammation have been individually linked to cerebral perivascular space (PVS) dilatation. Dilated PVSs are putative markers of impaired cerebrospinal fluid (CSF) and interstitial fluid exchange, which plays an important role in removing cerebral waste. The aim of this cross-sectional, retrospective study was to define associations between biomarkers of inflammation and MRI-visible PVS (MV-PVS) burden in Veterans after blast-related mTBI (blast-mTBI) and controls. The CSF and plasma inflammatory biomarker concentrations were compared between blast-mTBI and control groups and correlated with MV-PVS volume and number per white matter cm3. Multiple regression analyses were performed with inflammatory biomarkers as predictors and MV-PVS burden as the outcome. Correction for multiple comparisons was performed using the Banjamini-Hochberg method with a false discovery rate of 0.05. There were no group-wise differences in MV-PVS burden between Veterans with blast-mTBI and controls. Greater MV-PVS burden was significantly associated with higher concentrations of several proinflammatory biomarkers from CSF (i.e., eotaxin, MCP-1, IL-6, IL-8) and plasma (i.e., MCP-4, IL-13) in the blast-mTBI group only. After controlling for sleep time and symptoms of post-traumatic stress disorder, temporal MV-PVS burden remained significantly associated with higher CSF markers of inflammation in the blast-mTBI group only. These data support an association between central, rather than peripheral, neuroinflammation and MV-PVS burden in Veterans with blast-mTBI independent of sleep. Future studies should continue to explore the role of blast-mTBI related central inflammation in MV-PVS development, as well as investigate the impact of subclinical exposures on MV-PVS burden.

Twenty Years of Blast-Induced Neurotrauma: Current State of Knowledge

Blast-induced neurotrauma (BINT) is an important injury paradigm of neurotrauma research. This short communication summarizes the current knowledge of BINT. We divide the BINT research into several broad categories-blast wave generation in laboratory, biomechanics, pathology, behavioral outcomes, repetitive blast in animal models, and clinical and neuroimaging investigations in humans. Publications from 2000 to 2023 in each subdomain were considered. The analysis of the literature has brought out salient aspects. Primary blast waves can be simulated reasonably in a laboratory using carefully designed shock tubes. Various biomechanics-based theories of BINT have been proposed; each of these theories may contribute to BINT by generating a unique biomechanical signature. The injury thresholds for BINT are in the nascent stages. Thresholds for rodents are reasonably established, but such thresholds (guided by primary blast data) are unavailable in humans. Single blast exposure animal studies suggest dose-dependent neuronal pathologies predominantly initiated by blood-brain barrier permeability and oxidative stress. The pathologies were typically reversible, with dose-dependent recovery times. Behavioral changes in animals include anxiety, auditory and recognition memory deficits, and fear conditioning. The repetitive blast exposure manifests similar pathologies in animals, however, at lower blast overpressures. White matter irregularities and cortical volume and thickness alterations have been observed in neuroimaging investigations of military personnel exposed to blast. Behavioral changes in human cohorts include sleep disorders, poor motor skills, cognitive dysfunction, depression, and anxiety. Overall, this article provides a concise synopsis of current understanding, consensus, controversies, and potential future directions.

Subjective memory complaints are associated with decreased cortical thickness in Veterans with histories of mild traumatic brain injury

Objective: Memory problems are frequently endorsed in Veterans following mild traumatic brain injury (mTBI), but subjective complaints are poorly associated with objective memory performance. Few studies have examined associations between subjective memory complaints and brain morphometry. We investigated whether self-reported memory problems were associated with objective memory performance and cortical thickness in Veterans with a history of mTBI. Methods: 40 Veterans with a history of remote mTBI and 29 Veterans with no history of TBI completed the Prospective-Retrospective Memory Questionnaire (PRMQ), PTSD Checklist (PCL), California Verbal Learning Test-2nd edition (CVLT-II), and 3 T T1 structural magnetic resonance imaging. Cortical thickness was estimated in 14 a priori frontal and temporal regions. Multiple regressions adjusting for age and PCL scores examined associations between PRMQ, CVLT-II scores, and cortical thickness within each Veteran group. Results: Greater subjective memory complaints on the PRMQ were associated with lower cortical thickness in the right middle temporal gyrus (β = 0.64, q = .004), right inferior temporal gyrus (β = 0.56, q = .014), right rostral middle frontal gyrus (β = 0.45, q = .046), and right rostral anterior cingulate gyrus (β = 0.58, q = .014) in the mTBI group but not the control group (q's > .05). These associations remained significant after adjusting for CVLT-II learning. CVLT-II performance was not associated with PRMQ score or cortical thickness in either group. Conclusions: Subjective memory complaints were associated with lower cortical thickness in right frontal and temporal regions, but not with objective memory performance, in Veterans with histories of mTBI. Subjective complaints post-mTBI may indicate underlying brain morphometry independently of objective cognitive testing.

Repetitive, but Not Single, Mild Blast TBI Causes Persistent Neurological Impairments and Selective Cortical Neuronal Loss in Rats

Exposure to repeated mild blast traumatic brain injury (mbTBI) is common in combat soldiers and the training of Special Forces. Evidence suggests that repeated exposure to a mild or subthreshold blast can cause serious and long-lasting impairments, but the mechanisms causing these symptoms are unclear. In this study, we characterise the effects of single and tightly coupled repeated mbTBI in Sprague-Dawley rats exposed to shockwaves generated using a shock tube. The primary outcomes are functional neurologic function (unconsciousness, neuroscore, weight loss, and RotaRod performance) and neuronal density in brain regions associated with sensorimotor function. Exposure to a single shockwave does not result in functional impairments or histologic injury, which is consistent with a mild or subthreshold injury. In contrast, exposure to three tightly coupled shockwaves results in unconsciousness, along with persistent neurologic impairments. Significant neuronal loss following repeated blast was observed in the motor cortex, somatosensory cortex, auditory cortex, and amygdala. Neuronal loss was not accompanied by changes in astrocyte reactivity. Our study identifies specific brain regions particularly sensitive to repeated mbTBI. The reasons for this sensitivity may include exposure to less attenuated shockwaves or proximity to tissue density transitions, and this merits further investigation. Our novel model will be useful in elucidating the mechanisms of sensitisation to injury, the temporal window of sensitivity and the evaluation of new treatments.

Chronic frontal neurobehavioural symptoms in combat-deployed military personnel with and without a history of blast-related mild traumatic brain injury

OBJECTIVE

This study evaluated frontal behavioural symptoms, via the FrSBe self-report, in military personnel with and without a history of blast-related mild traumatic brain injury (mild TBI).

METHODS

Prospective observational cohort study of combat-deployed service members leveraging 1-year and 5-year demographic and follow up clinical outcome data.

RESULTS

The blast mild TBI group (n = 164) showed greater frontal behavioural symptoms, including clinically elevated apathy, disinhibition, and executive dysfunction, during a 5-year follow-up, compared to a group of combat-deployed controls (n = 107) without mild TBI history or history of blast exposure. We also explored changes inbehaviourall symptoms over a 4-year span, which showed clinically significant increases in disinhibition in the blast mild TBI group, whereas the control group did not show significant increases in symptoms over time.

CONCLUSION

Our findings add to the growing evidence that a proportion of individuals who sustain mild TBI experience persistent behavioural symptoms. We also offer a demonstration of a novel use of the FrSBe as a tool for longitudinal symptom monitoring in a military mild TBI population.

Exploring brain glutathione and peripheral blood markers in posttraumatic stress disorder: a combined [1H]MRS and peripheral blood study

Introduction

Oxidative stress has been implicated in psychiatric disorders, including posttraumatic stress disorder (PTSD). Currently, the status of glutathione (GSH), the brain's most abundant antioxidant, in PTSD remains uncertain. Therefore, the current study investigated brain concentrations of GSH and peripheral concentrations of blood markers in individuals with PTSD vs. Healthy Controls (HC).

Methods

GSH spectra was acquired in the anterior cingulate cortex (ACC) and dorsolateral prefrontal cortex (DLPFC) using MEGA-PRESS, a J-difference-editing acquisition method. Peripheral blood samples were analyzed for concentrations of metalloproteinase (MMP)-9, tissue inhibitors of MMP (TIMP)-1,2, and myeloperoxidase (MPO).

Results

There was no difference in GSH between PTSD and HC in the ACC (n = 30 PTSD, n = 20 HC) or DLPFC (n = 14 PTSD, n = 18 HC). There were no group differences between peripheral blood markers (P > 0.3) except for (non-significantly) lower TIMP-2 in PTSD. Additionally, TIMP-2 and GSH in the ACC were positively related in those with PTSD. Finally, MPO and MMP-9 were negatively associated with duration of PTSD.

Conclusions

We do not report altered GSH concentrations in the ACC or DLPFC in PTSD, however, systemic MMPs and MPO might be implicated in central processes and progression of PTSD. Future research should investigate these relationships in larger sample sizes.

Blast-Induced Neurotrauma Results in Spatially Distinct Gray Matter Alteration Alongside Hormonal Alteration: A Preliminary Investigation

Blast-induced neurotrauma (BINT) frequently occurs during military training and deployment and has been linked to long-term neuropsychological and neurocognitive changes, and changes in brain structure. As military personnel experience frequent exposures to stress, BINT may negatively influence stress coping abilities. This study aimed to determine the effects of BINT on gray matter volume and hormonal alteration. Participants were Canadian Armed Forces personnel and veterans with a history of BINT (n = 12), and first responder controls (n = 8), recruited due to their characteristic occupational stress professions. Whole saliva was collected via passive drool on the morning of testing and analyzed for testosterone (pg/mL), cortisol (μg/dL), and testosterone/cortisol (T/C) ratio. Voxel-based morphometry was performed to compare gray matter (GM) volume, alongside measurement of cortical thickness and subcortical volumes. Saliva analyses revealed distinct alterations following BINT, with significantly elevated testosterone and T/C ratio. Widespread and largely symmetric loci of reduced GM were found specific to BINT, particularly in the temporal gyrus, precuneus, and thalamus. These findings suggest that BINT affects hypothalamic-pituitary-adrenal and -gonadal axis function, and causes anatomically-specific GM loss, which were not observed in a comparator group with similar occupational stressors. These findings support BINT as a unique injury with distinct structural and endocrine consequences.

Poorer prospective memory performance is associated with reduced time monitoring among OEF/OIF/OND Veterans with a history of blast-related mild traumatic brain injury

Objective:Prospective memory (PM) or "remembering to remember" has been shown to be reduced in Veterans with histories of mild traumatic brain injury (mTBI), particularly on tasks with high strategic demands such as recalling time-based information in the absence of external cues. This study examined whether time monitoring during a PM task was reduced in Veterans with a history of mTBI and was associated with time-based PM performance. Method:Veterans with a history of mTBI (n = 49) and Veterans without a history of TBI (n = 16) completed the Memory for Intentions Screening Test (MIST) as a measure of PM during which their time monitoring (i.e. number of clock checks) was recorded. Results:Adjusting for age, education, depression, and PTSD symptoms, negative binomial regression revealed that the mTBI group checked the clock less frequently compared to the control group (Cohen's d = 0.84, p = 0.005). Within the mTBI group, less frequent time monitoring across the entire MIST task was associated with poorer time-based MIST performance (r_s = .57, p < 0.001), but not with event-based MIST (r_s = .04, p = 0.768). Conclusions:Veterans with a history of mTBI evidenced significantly reduced time monitoring during a PM task compared to Veterans without a history mTBI, which was associated with strategically-demanding PM. Current findings provide that mTBI-associated difficulties with strategic aspects of PM may be due to reduced time monitoring. Future studies are needed to determine if reduced time monitoring also contributes to mTBI-associated PM difficulties in the real-world (e.g. medication non-adherence).

Volumetric MRI Findings in Mild Traumatic Brain Injury (mTBI) and Neuropsychological Outcome

Region of interest (ROI) volumetric assessment has become a standard technique in quantitative neuroimaging. ROI volume is thought to represent a coarse proxy for making inferences about the structural integrity of a brain region when compared to normative values representative of a healthy sample, adjusted for age and various demographic factors. This review focuses on structural volumetric analyses that have been performed in the study of neuropathological effects from mild traumatic brain injury (mTBI) in relation to neuropsychological outcome. From a ROI perspective, the probable candidate structures that are most likely affected in mTBI represent the target regions covered in this review. These include the corpus callosum, cingulate, thalamus, pituitary-hypothalamic area, basal ganglia, amygdala, and hippocampus and associated structures including the fornix and mammillary bodies, as well as whole brain and cerebral cortex along with the cerebellum. Ventricular volumetrics are also reviewed as an indirect assessment of parenchymal change in response to injury. This review demonstrates the potential role and limitations of examining structural changes in the ROIs mentioned above in relation to neuropsychological outcome. There is also discussion and review of the role that post-traumatic stress disorder (PTSD) may play in structural outcome in mTBI. As emphasized in the conclusions, structural volumetric findings in mTBI are likely just a single facet of what should be a multimodality approach to image analysis in mTBI, with an emphasis on how the injury damages or disrupts neural network integrity. The review provides an historical context to quantitative neuroimaging in neuropsychology along with commentary about future directions for volumetric neuroimaging research in mTBI.

Acute metabolic alterations in the hippocampus are associated with decreased acetylation after blast induced TBI

INTRODUCTION

Blast induced Traumatic brain injury (BI-TBI) is common among military personnels as well as war affected civilians. In the war zone, people can also encounter repeated exposure of blast wave, which may affect their cognition and metabolic alterations.

OBJECTIVE

In this study we assess the metabolic and histological changes in the hippocampus of rats at 24 h post injury.

METHOD

Rats were divided into four groups: (i) Sham; (ii) Mild TBI (mi); (iii) Moderate TBI (mo); and (iv) Repetitive mild TBI (rm TBI) and then subjected to different intensities of blast exposure. Hippocampal tissues were collected after 24 h of injury for proton nuclear magnetic resonance spectroscopy (1H NMR spectroscopy) and immunohistochemical (IHC) analysis.

RESULTS

The metabolic alterations were found in the hippocampal tissue samples and these alterations showed significant change in glutamate, N-Acetylaspartic acid (NAA), acetate, creatine, phosphoethanolamine (PE), ethanolamine and PC/choline concentrations in rmTBI rats only. IHC studies revealed that AH3 (Acetyl histone) positive cells were decreased in rm TBI tissue samples in comparison to other TBI groups and sham rats. This might reflect an epigenetic alteration due to repeated blast exposure at 24 h post injury. Additionally, astrogliosis was observed in miTBI and moTBI hippocampal tissue while no change was observed in rmTBI tissues.

CONCLUSION

The present study reports altered acetylation in the presence of altered metabolism in hippocampal tissue of blast induced rmTBI at 24 h post injury. Mechanistic understanding of these intertwined processes may help in the development of better therapeutic pathways and agents for blast induced TBI in near future.

Self-reported physical functioning, cardiometabolic health conditions, and health care utilization patterns in Million Veteran Program enrollees with Traumatic Brain Injury Screening and Evaluation Program data

BACKGROUND

Examining the health outcomes of veterans who have completed the United States Veterans Health Administration's (VHA's) Traumatic Brain Injury (TBI) Screening and Evaluation Program may aid in the refinement and improvement of clinical care initiatives within the VHA. This study compared self-reported physical functioning, cardiometabolic health conditions, and health care utilization patterns in Million Veteran Program enrollees with TBI Screening and Evaluation Program data (collected between 2007 and 2019), with the goal of enhancing understanding of potentially modifiable health conditions in this population.

METHODS

In this observational cohort study, veterans (n = 16,452) were grouped based on the diagnostic outcome of the TBI Screening and Evaluation Program: 1) negative TBI screen (Screen^-); 2) positive TBI screen but no confirmed TBI diagnosis [Screen⁺/ Comprehensive TBI Evaluation (CTBIE)^-]; or 3) positive TBI screen and confirmed TBI diagnosis (Screen⁺/CTBIE⁺). Chi-square tests and analysis of covariance were used to explore group differences in physical functioning, cardiometabolic health conditions, and health care utilization patterns, and logistic regressions were used to examine predictors of Screen^+/- and CTBIE^+/- group status.

RESULTS

The results showed that veterans in the Screen⁺/CTBIE^- and Screen⁺/CTBIE⁺ groups generally reported poorer levels of physical functioning (P's < 0.001, n_p² = 0.02 to 0.03), higher rates of cardiometabolic health conditions (P's < 0.001, φ = 0.14 to 0.52), and increased health care utilization (P's < 0.001, φ = 0.14 to > 0.5) compared with the Screen^- group; however, health outcomes were generally comparable between the Screen⁺/CTBIE^- and Screen⁺/CTBIE⁺ groups. Follow-up analyses confirmed that while physical functioning, hypertension, stroke, healthcare utilization, and prescription medication use reliably distinguished between the Screen^- and Screen⁺ groups (P's < 0.02, OR's 0.78 to 3.38), only physical functioning distinguished between the Screen⁺/CTBIE^- and Screen⁺/CTBIE⁺ groups (P < 0.001, OR 0.99).

CONCLUSIONS

The findings suggest that veterans who screen positive for TBI, regardless of whether they are ultimately diagnosed with TBI, are at greater risk for negative health outcomes, signifying that these veterans represent a vulnerable group that may benefit from increased clinical care and prevention efforts.

Characterizing Sex Differences in Clinical and Functional Outcomes Among Military Veterans with a Comprehensive Traumatic Brain Injury Evaluation (CTBIE): A Million Veteran Program (MVP) Study

Using a diverse sample of military Veterans enrolled in the VA's Million Veteran Program (N=14,378; n=1,361 females [9.5%]; all previously deployed), we examined sex differences on the Comprehensive Traumatic Brain Injury Evaluation (CTBIE), a structured traumatic brain injury (TBI) interview routinely administered within the VA. Confirmed TBI diagnoses were more frequent among males than females (65% vs. 58%). Additionally, when compared to females, a greater proportion of males with CTBIE-confirmed TBI histories experienced blast-related injuries and were employed. In contrast, a greater proportion of females reported experiencing falls, sustaining a TBI since deployment, and having more severe neurobehavioral symptoms (particularly affective-related symptoms). Results indicate that males and females experience differential clinical and functional outcomes in the aftermath of military TBI. Findings underscore the need to increase female representation in TBI research to increase understanding of sex-specific experiences with TBI and to improve the clinical care targeted to this vulnerable population.

Close proximity to blast: No long-term or lasting effect on cognitive performance in service members with and without TBI during blast exposure

OBJECTIVE

Blast related characteristics may contribute to the diversity of findings on whether mild traumatic brain injury sustained during war zone deployment has lasting cognitive effects. This study aims to evaluate whether a history of blast exposure at close proximity, defined as exposure within 30 feet, has long-term or lasting influences on cognitive outcomes among current and former military personnel.

METHOD

One hundred participants were assigned to one of three groups based on a self-report history of blast exposure during combat deployments: 47 close blast, 14 non-close blast, and 39 comparison participants without blast exposure. Working memory, processing speed, verbal learning/memory, and cognitive flexibility were evaluated using standard neuropsychological tests. In addition, assessment of combat exposure and current post-concussive, posttraumatic stress, and depressive symptoms, and headache was performed via self-report measures. Variables that differed between groups were controlled as covariates.

RESULTS

No group differences survived Bonferroni correction for family-wise error rate; the close blast group did not differ from non-close blast and comparison groups on measures of working memory, processing speed, verbal learning/memory, or cognitive flexibility. Controlling for covariates did not alter these results.

CONCLUSION

No evidence emerged to suggest that a history of close blast exposure was associated with decreased cognitive performance when comparisons were made with the other groups. Limited characterization of blast contexts experienced, self-report of blast distance, and heterogeneity of injury severity within the groups are the main limitations of this study.

Recent Developments in Mouse Trauma Research Models: A Mini-Review

The urgency to investigate trauma in a controlled and reproducible environment rises since multiple trauma still account for the most deaths for people under the age of 45. The most common multiple trauma include head as well as blunt thorax trauma along with fractures. However, these trauma remain difficult to treat, partially because the molecular mechanisms that trigger the immediate immune response are not fully elucidated. To illuminate these mechanisms, investigators have used animal models, primarily mice as research subjects. This mini review aims to 1) emphasize the importance of the development of clinically relevant murine trauma research, 2) highlight and discuss the existing conflict between simulating clinically relevant situations and elucidating molecular mechanisms, 3) describe the advantages and disadvantages of established mouse trauma models developed to simulate clinically relevant situations, 4) summarize and list established mouse models in the field of trauma research developed to simulate clinically relevant situations.

Sex differences in cortical thickness and diffusion properties in patients with traumatic brain injury: a pilot study

OBJECTIVE

Cortical thickness and diffusion properties are important measures of gray and white matter integrity in those with traumatic brain injury (TBI). Many studies show that healthy adult females have greater cortical thickness than males across numerous brain sites. In this study, we explored this sex difference in patients with TBI.

METHOD

Participants consisted of 32 patients with TBI and 21 neurologically healthy controls. All were scanned by magnetic resonance imaging (MRI). Differences in cortical thickness and diffusion properties were examined between groups (i.e., TBI/control, male/female).

RESULTS

Patients with TBI had more cortical thinning (both hemispheres) compared to controls. They also showed decreased fractional anisotropy (FA) for several major white matter tracts. Healthy females had significantly greater cortical thickness compared to healthy males. However, this difference was smaller among the patients with TBI. We found no sex differences in diffusion properties. There were moderate correlations between cortical thickness, diffusion properties, and cognitive performance, as measured by the Trail Making Test B.

CONCLUSION

These findings contribute to a growing discussion on sex differences in cortical thickness and diffusion properties. Sexual dimorphism could necessitate different clinical profiles, targets, and rehabilitation strategies in patients with TBI.

Perspectives on Primary Blast Injury of the Brain: Translational Insights Into Non-inertial Low-Intensity Blast Injury

Most traumatic brain injuries (TBIs) during military deployment or training are clinically "mild" and frequently caused by non-impact blast exposures. Experimental models were developed to reproduce the biological consequences of high-intensity blasts causing moderate to severe brain injuries. However, the pathophysiological mechanisms of low-intensity blast (LIB)-induced neurological deficits have been understudied. This review provides perspectives on primary blast-induced mild TBI models and discusses translational aspects of LIB exposures as defined by standardized physical parameters including overpressure, impulse, and shock wave velocity. Our mouse LIB-exposure model, which reproduces deployment-related scenarios of open-field blast (OFB), caused neurobehavioral changes, including reduced exploratory activities, elevated anxiety-like levels, impaired nesting behavior, and compromised spatial reference learning and memory. These functional impairments associate with subcellular and ultrastructural neuropathological changes, such as myelinated axonal damage, synaptic alterations, and mitochondrial abnormalities occurring in the absence of gross- or cellular damage. Biochemically, we observed dysfunctional mitochondrial pathways that led to elevated oxidative stress, impaired fission-fusion dynamics, diminished mitophagy, decreased oxidative phosphorylation, and compensated cell respiration-relevant enzyme activity. LIB also induced increased levels of total tau, phosphorylated tau, and amyloid β peptide, suggesting initiation of signaling cascades leading to neurodegeneration. We also compare translational aspects of OFB findings to alternative blast injury models. By scoping relevant recent research findings, we provide recommendations for future preclinical studies to better reflect military-operational and clinical realities. Overall, better alignment of preclinical models with clinical observations and experience related to military injuries will facilitate development of more precise diagnosis, clinical evaluation, treatment, and rehabilitation.

Morphometric changes in the cortex following acute mild traumatic brain injury

Morphometric changes in cortical thickness (CT), cortical surface area (CSA), and cortical volume (CV) can reflect pathological changes after acute mild traumatic brain injury (mTBI). Most previous studies focused on changes in CT, CSA, and CV in subacute or chronic mTBI, and few studies have examined changes in CT, CSA, and CV in acute mTBI. Furthermore, acute mTBI patients typically show transient cognitive impairment, and few studies have reported on the relationship between cerebral morphological changes and cognitive function in patients with mTBI. This prospective cohort study included 30 patients with acute mTBI (15 males, 15 females, mean age 33.7 years) and 27 matched healthy controls (12 males, 15 females, mean age 37.7 years) who were recruited from the Second Xiangya Hospital of Central South University between September and December 2019. High-resolution T1-weighted images were acquired within 7 days after the onset of mTBI. The results of analyses using FreeSurfer software revealed significantly increased CSA and CV in the right lateral occipital gyrus of acute-stage mTBI patients compared with healthy controls, but no significant changes in CT. The acute-stage mTBI patients also showed reduced executive function and processing speed indicated by a lower score in the Digital Symbol Substitution Test, and reduced cognitive ability indicated by a longer time to complete the Trail Making Test-B. Both increased CSA and CV in the right lateral occipital gyrus were negatively correlated with performance in the Trail Making Test part A. These findings suggest that cognitive deficits and cortical alterations in CSA and CV can be detected in the acute stage of mTBI, and that increased CSA and CV in the right lateral occipital gyrus may be a compensatory mechanism for cognitive dysfunction in acute-stage mTBI patients. This study was approved by the Ethics Committee of the Second Xiangya Hospital of Central South University, China (approval No. 086) on February 9, 2019.

Characterization of Million Veteran Program (MVP) enrollees with Comprehensive Traumatic Brain Injury Evaluation (CTBIE) data: An analysis of neurobehavioral symptoms

The purpose of this study was to examine neurobehavioral symptom reporting in a large sample of military veterans (N = 12,144) who completed the Comprehensive Traumatic Brain Injury Evaluation (CTBIE) and enrolled in the VA's Million Veteran Program (MVP). The CTBIE is a clinician-administered interview that assesses for historical, deployment-related traumatic brain injury (TBI) and evaluates symptoms using the Neurobehavioral Symptom Inventory (NSI). Clinicians completing the CTBIE made clinical determinations about participants' (1) TBI diagnostic status (i.e., CTBIE+ or CTBIE-) and (2) current symptom etiology (i.e., Symptom Resolution, TBI, Behavioral Health, Comorbid TBI + Behavioral Health [Comorbid], or Other). We evaluated the association of TBI diagnostic status and symptom etiology group with neurobehavioral symptoms. Results showed a significant association between TBI diagnostic status and all NSI variables, with CTBIE+ veterans endorsing greater symptoms than CTBIE- veterans. There was also a significant association between symptom etiology group and all NSI variables; specifically, the Comorbid and Behavioral Health groups generally endorsed significantly greater symptoms compared to the other groups. Follow-up analyses showed that relative to the Symptom Resolution group, the Comorbid and Behavioral Health groups had increased odds of severe/very severe cognitive and affective symptoms, whereas the TBI and Other groups did not. Finally, presence of psychiatric symptoms, pain, post-traumatic amnesia, loss of consciousness, and blast exposure significantly predicted Comorbid symptom etiology group membership. Findings from this large epidemiologic MVP study have relevant clinical implications and further highlight the importance of prioritizing integrated behavioral health interventions for this vulnerable population.

Brain Volume in Veterans: Relationship to Posttraumatic Stress Disorder and Mild Traumatic Brain Injury

OBJECTIVE

Clarify associations between diagnosis of posttraumatic stress disorder (PTSD) and deployment traumatic brain injury (TBI) on salient regional brain volumes in returning combat veterans.

PARTICIPANTS

Iraq and Afghanistan era combat veterans, N = 163, 86.5% male.

MAIN MEASURES

Clinician-administered PTSD Scale (CAPS-5), Mid-Atlantic MIRECC Assessment of TBI (MMA-TBI), magnetic resonance imaging.

METHODS

Hierarchical regression analyses evaluated associations and interactions between current and lifetime PTSD diagnosis, deployment TBI, and bilateral volume of hippocampus, anterior cingulate cortex, amygdala, orbitofrontal cortex, precuneus, and insula.

RESULTS

Deployment TBI was associated with lower bilateral hippocampal volume (P = .007-.032) and right medial orbitofrontal cortex volume (P = .006). Neither current nor lifetime PTSD diagnosis was associated with volumetric outcomes beyond covariates and deployment TBI.

CONCLUSION

History of deployment TBI is independently associated with lower volumes in hippocampus and medial orbitofrontal cortex. These results support TBI as a potential contributing factor to consider in reduced cortical volume in PTSD.

Apolipoprotein E (APOE) ε4 Status Moderates the Relationship Between Close-Range Blast Exposure and Cognitive Functioning

OBJECTIVES

Recent studies suggest that close-range blast exposure (CBE), regardless of acute concussive symptoms, may have negative long-term effects on brain health and cognition; however, these effects are highly variable across individuals. One potential genetic risk factor that may impact recovery and explain the heterogeneity of blast injury's long-term cognitive outcomes is the inheritance of an apolipoprotein (APOE) ε4 allele, a well-known genetic risk factor for Alzheimer's disease. We hypothesized that APOE ε4 carrier status would moderate the impact of CBE on long-term cognitive outcomes.

METHODS

To test this hypothesis, we examined 488 post-9/11 veterans who completed assessments of neuropsychological functioning, psychiatric diagnoses, history of blast exposure, military and non-military mild traumatic brain injuries (mTBIs), and available APOE genotypes. We separately examined the effects of CBE on attention, memory, and executive functioning in individuals with and without the APOE ε4 allele.

RESULTS

As predicted, we observed a differential impact of CBE status on cognition as a function of APOE ε4 status, in which CBE ε4 carriers displayed significantly worse neuropsychological performance, specifically in the domain of memory. These results persisted after adjusting for clinical, demographic, and genetic factors and were not observed when examining other neurotrauma variables (i.e., lifetime or military mTBI, distant blast exposure), though these variables displayed similar trends.

CONCLUSIONS

These results suggest APOE ε4 carriers are more vulnerable to the impact of CBE on cognition and highlight the importance of considering genetic risk when studying cognitive effects of neurotrauma.

Functional and Structural Neuroimaging Correlates of Repetitive Low-Level Blast Exposure in Career Breachers

Combat military and civilian law enforcement personnel may be exposed to repetitive low-intensity blast events during training and operations. Persons who use explosives to gain entry (i.e., breach) into buildings are known as “breachers” or dynamic entry personnel. Breachers operate under the guidance of established safety protocols, but despite these precautions, breachers who are exposed to low-level blast throughout their careers frequently report performance deficits and symptoms to healthcare providers. Although little is known about the etiology linking blast exposure to clinical symptoms in humans, animal studies demonstrate network-level changes in brain function, alterations in brain morphology, vascular and inflammatory changes, hearing loss, and even alterations in gene expression after repeated blast exposure. To explore whether similar effects occur in humans, we collected a comprehensive data battery from 20 experienced breachers exposed to blast throughout their careers and 14 military and law enforcement controls. This battery included neuropsychological assessments, blood biomarkers, and magnetic resonance imaging measures, including cortical thickness, diffusion tensor imaging of white matter, functional connectivity, and perfusion. To better understand the relationship between repetitive low-level blast exposure and behavioral and imaging differences in humans, we analyzed the data using similarity-driven multi-view linear reconstruction (SiMLR). SiMLR is specifically designed for multiple modality statistical integration using dimensionality-reduction techniques for studies with high-dimensional, yet sparse, data (i.e., low number of subjects and many data per subject). We identify significant group effects in these data spanning brain structure, function, and blood biomarkers.

Chemokine signaling mediated monocyte infiltration affects anxiety-like behavior following blast injury

The activation of resident microglia and infiltrated monocytes are known potent mediators of chronic neuroinflammation following traumatic brain injury (TBI). In this study, we use a mouse model of blast-induced TBI (bTBI) to investigate whether microglia and monocytes contribute to the neuroinflammatory and behavioral consequences of bTBI. Eight-ten week old mice were subject to moderate TBI (180 kPa) in a shock tube. Using double transgenic CCR2^RFP/+: CX3CR1^GFP/+ mice, we were able to note that in addition to resident Cx3CR1+ microglia, infiltrating CCR2+ monocytes also contributed to the expanding macrophage population that was observed after bTBI. The microglia activation and monocyte infiltration occurred as early as 4 h and lasted up to 30d after blast exposure, suggesting chronic inflammation. The infiltration of monocytes may be partly mediated by chemokine CCL2-CCR2 signaling axis and compromised blood brain barrier permeability. Hence, bTBI-induced infiltration of monocytes and production of IL-1β were prevented in mice lacking CCR2 (CCR2 KO). Finally, this study showed that interference of monocyte infiltration using CCR2 KO, ameliorated the chronic effects of bTBI such as anxiety-like behavior and short-term memory decline. Taken together, these data suggest that bTBI leads to activation of both resident microglia and infiltrated monocytes. The infiltration of monocytes was partly mediated by CCL2-CCR2 signaling, which in turn contributes to increased production of IL-1β leading to behavioral deficits after bTBI. Furthermore, bTBI induced behavioral outcomes were reduced by targeting CCL2-CCR2 signaling, highlighting the significance of this signaling axis in bTBI pathology.

Blast exposure predisposes the brain to increased neurological deficits in a model of blast plus blunt traumatic brain injury

Soldiers are often exposed to more than one traumatic brain injury (TBI) over the course of their service. In recent years, more attention has been drawn to the increased risk of neurological deficits caused by the 'blast plus' polytrauma, which typically is a blast trauma combined with other forms of TBI. In this study, we investigated the behavioral and neuronal deficits resulting from a blast plus injury involving a mild-moderate blast followed by a mild blunt trauma using the fluid percussion injury model. We identified that the blast injury predisposed the brain to increased cognitive deficits, chronic ventricular enlargement, increased neurodegeneration at acute time points and chronic neuronal loss. Interestingly, a single blast and single blunt injury differed in their onset and manifestation of cognitive and regional neuronal loss. We also identified the presence of cleaved RIP1 from caspase 8 mediated apoptosis in the blunt injury while the blast injury did not activate immediate apoptosis but led to decreased hilar neuronal survival over time.