Neuropsychological evaluation of blast-related concussion: illustrating the challenges and complexities through OEF/OIF case studies

The relationship between blast-related mild traumatic brain injury and executive function is moderated by white matter integrity

Blast-related mild traumatic brain injury (BR mTBI) is a critical research area in recent combat veterans due to increased prevalence of survived blasts. Post-BR mTBI outcomes are highly heterogeneous and defining neurological differences may help in discrimination and prediction of cognitive outcomes. This study investigates whether white matter integrity, measured with diffusion tensor imaging (DTI), could influence how remote BR mTBI history is associated with executive control. The sample included 151 Veterans from the Minneapolis Veterans Affairs Medical Center who were administered a clinical/TBI assessment, neuropsychological battery, and DTI scan as part of a larger battery. From previous research, six white matter tracts were identified as having a putative relationship with blast severity: the cingulum, hippocampal cingulum, corticospinal tract, inferior fronto-occipital fasciculus, superior longitudinal fasciculus and uncinate. Fractional anisotropy (FA) of the a priori selected white matter tracts and report of BR mTBI were used as predictors of Trail-Making Test B (TMT-B) performance in a multiple linear regression model. Statistical analysis revealed that FA of the hippocampal cingulum moderated the association between report of at least one BR mTBI and poorer TMT-B performance (p < 0.008), such that lower FA value was associated with worse TMT-B outcomes in individuals with BR mTBI. No significant moderation existed for other selected tracts, and the effect was not observed with predictors aside from history of BR mTBI. Investigation at the individual-tract level may lead to a deeper understanding of neurological differences between blast-related and non-blast related injuries.

Posttraumatic reexperiencing and alcohol use: mediofrontal theta as a neural mechanism for negative reinforcement

Objective

Over half of US military veterans with posttraumatic stress disorder (PTSD) use alcohol heavily, potentially to cope with their symptoms. This study investigated the neural underpinnings of PTSD symptoms and heavy drinking in veterans. We focused on brain responses to salient outcomes within predictive coding theory. This framework suggests the brain generates prediction errors (PEs) when outcomes deviate from expectations. Alcohol use might provide negative reinforcement by reducing the salience of negatively-valenced PEs and dampening experiences like loss.

Methods

We analyzed electroencephalography (EEG) responses to unpredictable gain/loss feedback in veterans of Operations Enduring and Iraqi Freedom. We used time-frequency principal components analysis of event-related potentials to isolate neural responses indicative of PEs, identifying mediofrontal theta linked to losses (feedback-related negativity, FRN) and central delta associated with gains (reward positivity, RewP).

Results

Intrusive reexperiencing symptoms of PTSD were associated with intensified mediofrontal theta signaling during losses, suggesting heightened negative PE sensitivity. Conversely, increased hazardous alcohol use was associated with reduced theta responses, implying a dampening of these negative PEs. The separate delta-RewP component showed associations with alcohol use but not PTSD symptoms.

Conclusions

Findings suggest a common neural component of PTSD and hazardous alcohol use involving altered PE processing. We suggest that reexperiencing enhances the intensity of salient negative PEs, while chronic alcohol use may reduce their intensity, thereby providing negative reinforcement by muting emotional disruption from reexperienced trauma. Modifying the mediofrontal theta response could address the intertwined nature of PTSD symptoms and alcohol use, providing new avenues for treatment.

Relationship between clinician documented blast exposure and pulmonary function: a retrospective chart review from a national specialty clinic

Background

Service member exposure to explosive blast overpressure waves is common with considerable attention to traumatic brain injury (TBI) and neuropsychological sequalae. Less is known about the impacts on the respiratory system, particularly long-term effects, despite vulnerability to overpressure. Using a national registry, we previously observed an independent relationship between self-reported blast exposure and respiratory symptoms; however, the impact on objective measures of pulmonary function is poorly understood.

Methods

307 Veterans referred to our national specialty center for post-deployment health concerns underwent a comprehensive multi-day evaluation that included complete pulmonary function testing (PFT), occupational and environmental medicine history, neuropsychological or psychological evaluation. We developed an a priori chart abstraction process and template to classify Veterans into blast exposure groups: (1) none, (2) single-mild, or (3) multiple-mild. This template focused primarily on clinician documented notes of blast related TBI that were used as proxy for blast overpressure injury to thorax. PFT variables characterizing flow (FEV₁%; %∆FEV₁), volume (TLC%), diffusion (DL_CO%) and respiratory mechanics (forced oscillometry) were selected for analysis.

Results

Veterans (40.5 ± 9.7 years; 16.3% female) were referred 8.6 ± 3.6 years after their last deployment and presented with considerable comorbid conditions and health problems (e.g., 62% post-traumatic stress, 55% dyspnea). After chart abstraction, Veterans were assigned to none (n = 208), single mild (n = 52) and multiple mild (n = 47) blast exposure groups. Among the blast exposed, clinicians documented 73.7% were < 50 m from the blast and 40.4% were physically moved by blast. PFT outcome measures were similar across all groups (p value range: 0.10–0.99).

Conclusions

In this referred sample of deployed Veterans, PFT measures of flow, volume, diffusion, and respiratory mechanics were not associated with clinician documented blast exposure per the retrospective chart abstraction methodology applied. Yet, these clinical findings suggest future research should determine and assess distinction between Veteran recollections of perceived blast experiences versus overpressure wave exposure to the respiratory system.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12931-022-02071-0.

Inefficient Attentional Control Explains Verbal-Memory Deficits Among Military Veterans With Posttraumatic Reexperiencing Symptoms

Among individuals with posttraumatic stress disorder (PTSD), verbal learning and memory are areas of weakness compared with other cognitive domains (e.g., visuospatial memory). In this study, previously deployed military veterans completed clinical assessments of word memory and vocabulary (n = 243) and a laboratory task measuring encoding, free recall, repetition priming, and recognition of words (n = 147). Impaired verbal memory was selectively related to reexperiencing symptoms of PTSD but was not associated with other symptom groupings or blast-induced traumatic brain injury. Implicit priming of response times following word repetition was also unrelated to clinical symptoms. Instead, slowed response times during encoding explained associations between reexperiencing and memory performance. These findings are consistent with alterations in attentional control explaining PTSD-related verbal-memory deficits. Such findings have implications for understanding trauma-focused psychotherapy and recovery, which may depend on efficient attentional processing of words to alter posttraumatic reexperiencing symptoms.

Network Analysis of Research on Mild Traumatic Brain Injury in US Military Service Members and Veterans During the Past Decade (2010-2019)

OBJECTIVE

To evaluate trends in the extant literature on mild traumatic brain injury (mTBI) in military service members and veterans using network analysis based on a comprehensive search of original, peer-reviewed research articles involving human participants published between January 1, 2010, and December 31, 2019. Specifically, we employed network analysis to evaluate associations in the following areas: (1) peer-reviewed journals, (2) authors, (3) organizations/institutions, and (4) relevant key words.

PARTICIPANTS

Included studies were published in peer-reviewed journals available on Web of Science database, using US military service members or veterans.

DESIGN

Bibliometric network analytical review.

MAIN MEASURES

Outcomes for each analysis included number of articles, citations, total link strength, and clusters.

RESULTS

The top publishing journals were (1) Journal of Head Trauma and Rehabilitation, (2) Military Medicine, (3) Brain Injury, (4) Journal of Neurotrauma, and (5) Journal of Rehabilitation Research and Development. The top publishing authors were (1) French, (2) Lange, (3) Cooper, (4) Vanderploeg, and (5) Brickell. The top research institutions were (1) Defense and Veterans Brain Injury Center, (2) Uniformed Services University of the Health Sciences, (3) University of California San Diego, (4) Walter Reed National Military Medical Center, and (5) Boston University. The top co-occurring key words in this analysis were (1) posttraumatic stress disorder (PTSD), (2) persistent postconcussion symptoms (PPCS), (3) blast injury, (4) postconcussion syndrome (PCS), and (5) Alzheimer's disease.

CONCLUSIONS

The results of this network analysis indicate a clear focus on veteran health, as well as investigations on chronic effects of mTBI. Research in civilian mTBI indicates that delaying treatment for symptoms and impairments related to mTBI may not be the most precise treatment strategy. Increasing the number of early, active, and targeted treatment trials in military personnel could translate to meaningful improvements in clinical practices for managing mTBI in this population.

Coordinating Global Multi-Site Studies of Military-Relevant Traumatic Brain Injury: Opportunities, Challenges, and Harmonization Guidelines

Traumatic brain injury (TBI) is common among military personnel and the civilian population and is often followed by a heterogeneous array of clinical, cognitive, behavioral, mood, and neuroimaging changes. Unlike many neurological disorders that have a characteristic abnormal central neurologic area(s) of abnormality pathognomonic to the disorder, a sufficient head impact may cause focal, multifocal, diffuse or combination of injury to the brain. This inconsistent presentation makes it difficult to establish or validate biological and imaging markers that could help improve diagnostic and prognostic accuracy in this patient population. The purpose of this manuscript is to describe both the challenges and opportunities when conducting military-relevant TBI research and introduce the Enhancing NeuroImaging Genetics through Meta-Analysis (ENIGMA) Military Brain Injury working group. ENIGMA is a worldwide consortium focused on improving replicability and analytical power through data sharing and collaboration. In this paper, we discuss challenges affecting efforts to aggregate data in this patient group. In addition, we highlight how "big data" approaches might be used to understand better the role that each of these variables might play in the imaging and functional phenotypes of TBI in Service member and Veteran populations, and how data may be used to examine important military specific issues such as return to duty, the late effects of combat-related injury, and alteration of the natural aging processes.

Association of Optical Coherence Tomography With Longitudinal Neurodegeneration in Veterans With Chronic Mild Traumatic Brain Injury

IMPORTANCE

Mild traumatic brain injury (TBI) may predispose individuals to progressive neurodegeneration.

OBJECTIVE

To identify evidence of neurodegeneration through longitudinal evaluation of changes in retinal layer thickness using optical coherence tomography in veterans with a history of mild TBI.

DESIGN, SETTING, AND PARTICIPANTS

This longitudinal cohort study evaluated veterans who were receiving services at the Minneapolis Veterans Affairs Health Care System. Symptomatic or mild TBI was diagnosed according to the Mayo TBI Severity Classification System. Participants in the age-matched control group had no history of TBI. Participants with any history or evidence of retinal or optic nerve disease that could affect retinal thickness were excluded. Data analysis was performed from July 2019 to February 2020.

EXPOSURES

The presence and severity of mild TBI were determined through consensus review of self-report responses during the Minnesota Blast Exposure Screening Tool semistructured interview.

MAIN OUTCOMES AND MEASURES

Change over time of retinal nerve fiber layer (RNFL) thickness.

RESULTS

A total of 139 veterans (117 men [84%]; mean [SD] age, 49.9 [11.1] years) were included in the study, 69 in the TBI group and 70 in the control group. Veterans with mild TBI showed significantly greater RNFL thinning compared with controls (mean [SE] RNFL slope, -1.47 [0.24] μm/y vs -0.31 [0.32] μm/y; F1,122 = 8.42; P = .004; Cohen d = 0.52). Functionally, veterans with mild TBI showed greater declines in visual field mean deviation (mean [SE] slope, -0.09 [0.14] dB/y vs 0.46 [0.23] dB/y; F1,122 = 4.08; P = .046; Cohen d = 0.36) and pattern standard deviation (mean [SE] slope, 0.09 [0.06] dB/y vs -0.10 [0.07] dB/y; F1,122 = 4.78; P = .03; Cohen d = 0.39) and high spatial frequency (12 cycles/degree) contrast sensitivity compared with controls. Cognitively, there was a significantly greater decrease in the number of errors over time during the Groton Maze Learning Test (GMLT) in controls compared with veterans with mild TBI (mean [SE] slope, -9.30 [1.48] errors/y vs -5.23 [1.24] errors/y; F1,127 = 4.43; P = .04; Cohen d = 0.37). RNFL tissue loss was significantly correlated with both worsening performance on the GMLT over time (Spearman ρ = -0.20; P = .03) and mild TBI severity (Spearman ρ = -0.25; P = .006). The more severe the mild TBI (larger Minnesota Blast Exposure Screening Tool severity score), the faster the reduction in RNFL thickness (ie, the more negative the slope) across time.

CONCLUSIONS AND RELEVANCE

This cohort study found longitudinal evidence for significant, progressive neural degeneration over time in veterans with mild TBI, as indicated by greater RNFL tissue loss in patients with mild TBI vs controls, as well as measures of function. These results suggest that these longitudinal measures may be useful biomarkers of neurodegeneration. Changes in this biomarker may provide early detection of subsequent cognitive and functional deficits that may impact veterans' independence and need for care.

Posttraumatic stress symptomatology and abnormal neural responding during emotion regulation under cognitive demands: mediating effects of personality

Posttraumatic stress disorder (PTSD) is often complicated by the after-effects of mild traumatic brain injury (mTBI). The mixture of brain conditions results in abnormal affective and cognitive functioning, as well as maladaptive behavior. To better understand how brain activity explains cognitive and emotional processes in these conditions, we used an emotional N-back task and functional magnetic resonance imaging (fMRI) to study neural responses in US military veterans after deployments to Iraq and Afghanistan. Additionally, we sought to examine whether hierarchical dimensional models of maladaptive personality could account for the relationship between combat-related brain conditions and fMRI responses under cognitive and affective challenge. FMRI data, measures of PTSD symptomatology (PTSS), blast-induced mTBI (bmTBI) severity, and maladaptive personality (MMPI-2-RF) were gathered from 93 veterans. Brain regions central to emotion regulation were selected for analysis, and consisted of bilateral amygdala, bilateral dorsolateral prefrontal (dlPFC), and ventromedial prefrontal/subgenual anterior cingulate (vmPFC-sgACC). Cognitive load increased activity in dlPFC and reduced activity in emotional responding brain regions. However, individuals with greater PTSS showed blunted deactivations in bilateral amygdala and vmPFC-sgACC, and weaker responses in right dlPFC. Additionally, we found that elevated emotional/internalizing dysfunction (EID), specifically low positive emotionality (RC2), accounted for PTSS-related changes in bilateral amygdala under increased cognitive load. Findings suggest that PTSS might result in amygdala and vmPFC-sgACC activity resistant to moderation by cognitive demands, reflecting emotion dysregulation despite a need to marshal cognitive resources. Anhedonia may be an important target for interventions that improve the affective and cognitive functioning of individuals with PTSD.

Blast concussion and posttraumatic stress as predictors of postcombat neuropsychological functioning in OEF/OIF/OND veterans

OBJECTIVES

Many combat veterans exhibit cognitive limitations of uncertain origin. In this study, we examined factors that predict cognitive functioning by considering effects of blast-related concussion (BRC), non-blast-related concussion (NBRC), and posttraumatic stress disorder (PTSD) symptoms. Analyses specifically tested whether (a) BRC and NBRC were distinct in their prediction of cognitive performance; (b) a dose-response relationship existed between recurrent concussion (BRC and NBRC) and cognitive impairment; and (c) PTSD symptoms mediated the relationship between BRC and cognitive performance.

METHOD

Two hundred eighty veterans with combat zone deployment histories completed semistructured clinical interviews to define BRC and NBRC histories, current and past mental health disorders, and dimensional ratings of PTSD symptomatology. Participants were also administered a number of neuropsychological measures to appraise cognitive functioning.

RESULTS

A structural equation model (SEM) suggested that BRC and NBRC were not distinct in their prediction of cognitive performance, and there was no evidence that recurrent concussion (blast or nonblast) was directly associated with cognitive performance. BRC was significantly associated with PTSD symptoms (r = .24), PTSD symptoms were significantly associated with cognitive performance in the SEM (r = -.27), and PTSD symptoms significantly mediated the link between BRC and cognitive performance (p = .03).

CONCLUSIONS

These results suggest that concussion history fails to directly contribute to cognitive performance, regardless of mechanism (blast or nonblast) and recurrence. BRC is nonetheless unique in its contribution to PTSD and PTSD-related cognitive deficits. Results support interventions specific to PTSD management in the interest of promoting neuropsychological functioning among war veterans. (PsycINFO Database Record (c) 2020 APA, all rights reserved).

The impact of PTSD and mTBI on the relationship between subjective and objective cognitive deficits in combat-exposed veterans

OBJECTIVE

Cognitive complaints, such as attentional or memory concerns, are commonly reported by veterans diagnosed with posttraumatic stress disorder (PTSD) or a history of mild traumatic brain injury (mTBI). The degree to which those complaints actually map onto measurable cognitive deficits is unclear and is likely complicated by the severity of trauma-related sequelae. In the present study we sought to characterize the degree to which PTSD symptoms and mTBI accounted for the relationship of subjective cognitive complaints to objective cognitive performance, with the goal of facilitating the accurate assessment of trauma-exposed veterans complaining of cognitive decline.

METHOD

A sample of 203 U.S. military veterans previously deployed to Iraq and/or Afghanistan were assessed for PTSD severity, history of blast and impact mTBI, objective cognitive function, and subjective cognitive complaints. Separate mediation analyses were conducted to explore the degree that PTSD severity, blast mTBI severity, and impact mTBI severity influenced the association between subjective cognitive complaints and objective cognitive performance. Models reflecting significant mediation were followed by post hoc moderated mediation analyses.

RESULTS

Subjective cognitive complaints and objective cognitive performance were significantly associated (β = -6.49, SE = 2.85, p = .03), but this relationship was mediated by PTSD severity (β= -2.95, SE = 2.86, p = .30). PTSD mediation was not moderated by either blast or impact mTBI.

CONCLUSION

The present results delineate the prominent impact of PTSD symptoms, relative to blast and impact mTBI, on cognition following combat. These findings highlight the importance of assessing for trauma-related psychopathology in those seeking neuropsychological assessment or rehabilitative care for cognitive complaints. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Retrospective and Prospective Memory Among OEF/OIF/OND Veterans With a Self-Reported History of Blast-Related mTBI

OBJECTIVES

To evaluate prospective and retrospective memory abilities in Operation Enduring Freedom (OEF), Operation Iraqi Freedom (OIF), and Operation New Dawn (OND) Veterans with and without a self-reported history of blast-related mild traumatic brain injury (mTBI).

METHODS

Sixty-one OEF/OIF/OND Veterans, including Veterans with a self-reported history of blast-related mTBI (mTBI group; n=42) and Veterans without a self-reported history of TBI (control group; n=19) completed the Memory for Intentions Test, a measure of prospective memory (PM), and two measures of retrospective memory (RM), the California Verbal Learning Test-II and the Brief Visuospatial Memory Test-Revised.

RESULTS

Veterans in the mTBI group exhibited significantly lower PM performance than the control group, but the groups did not differ in their performance on RM measures. Further analysis revealed that Veterans in the mTBI group with current PTSD (mTBI/PTSD+) demonstrated significantly lower performance on the PM measure than Veterans in the control group. PM performance by Veterans in the mTBI group without current PTSD (mTBI/PTSD-) was intermediate between the mTBI/PTSD+ and control groups, and results for the mTBI/PTSD- group were not significantly different from either of the other two groups.

CONCLUSIONS

Results suggest that PM performance may be a sensitive marker of cognitive dysfunction among OEF/OIF/OND Veterans with a history of self-reported blast-related mTBI and comorbid PTSD. Reduced PM may account, in part, for complaints of cognitive difficulties in this Veteran cohort, even years post-injury. (JINS, 2018, 24, 324-334).

Symptoms of Posttraumatic Stress Rather Than Mild Traumatic Brain Injury Best Account for Altered Emotional Responses in Military Veterans

Emotional dysfunction is evident in posttraumatic stress disorder (PTSD), yet it is unclear what aspects of the disorder most directly relate to aberrant emotional responding. Also, the frequent co-occurrence of blast-related mild traumatic brain injuries (mTBIs) among recently deployed U.S. military personnel complicates efforts to understand the basis for emotional disruption. We studied a cross-sectional sample (enriched for PTSD and mTBI) of 123 U.S. veterans of wars in Iraq and Afghanistan. We measured subjective affective evaluations and peripheral psychophysiological responses to images with pleasant, neutral, unpleasant, and combat-related aversive content. When compared with other postdeployment participants, those who had combat-related PTSD rated pleasant image content as less positive (ηp2 = .04) and less arousing (ηp2 = .06), and exhibited heightened physiological responsivity to combat image content (ηp2 = .07). Symptoms of PTSD were associated with elevated skin conductance responses (β = .28), reduced heart rate deceleration (β = .44 to .47), and increased corrugator facial muscle electromyography (β = .47). No effects for blast-related mTBI were observed across any affective modulation measures. These findings point to a greater impact of PTSD symptomatology than blast-related mTBI on emotional functioning and highlight the utility of dimensional assessments of psychopathology for understanding the effects of combat-stress conditions on adjustment to civilian life.

PTSD confounds detection of compromised cerebral white matter integrity in military veterans reporting a history of mild traumatic brain injury

PRIMARY OBJECTIVE

Based on high comorbidity between mild traumatic brain injury (mTBI) and post-traumatic stress disorder (PTSD) among deployed military service members, this study tested the hypothesis that the presence of PTSD disrupts the association between mTBI and lower white matter integrity identified in non-military samples. Research design/Methods and procedures: In a sample of 124 recent veterans with a range of mTBI and PTSD history, diffusion tensor imaging (DTI) metrics of white matter integrity in 20 regions were compared using multiple mTBI and PTSD contrasts.

MAIN OUTCOMES AND RESULTS

Civilian mTBI was associated with lower global anisotropy, higher global diffusivity and higher diffusivity in 17 of 20 regions. No main effects of deployment mTBI were observed, but an interaction between deployment mTBI and lifetime PTSD on FA was observed globally and in 10 regions. Impact and blast mTBI demonstrated similar but weaker effects to those of civilian and deployment mTBI, respectively, demonstrating the context of mTBI is more relevant to white matter integrity than mechanism of injury.

CONCLUSIONS

Overall, a main effect of civilian mTBI indicates long-term disruptions to white matter are likely present, while the interaction between deployment mTBI and PTSD indicates that a history of PTSD alters this relationship.

Longitudinal evaluation of ventricular volume changes associated with mild traumatic brain injury in military service members

PRIMARY OBJECTIVE

To investigate differences in longitudinal trajectories of ventricle-brain ratio (VBR), a general measure of brain atrophy, between Veterans with and without history of mild traumatic brain injury (mTBI).

RESEARCH DESIGN

Structural magnetic resonance imaging (MRI) was used to calculate VBR in 70 Veterans with a history of mTBI and 34 Veterans without such history at two time points approximately 3 and 8 years after a combat deployment.

MAIN OUTCOMES AND RESULTS

Both groups demonstrated a quadratic relationship between VBR and age that is consistent with normal developmental trajectories. Veterans with history of mTBI had larger total brain volume, but no interaction between mTBI and age was observed for brain volume, ventricular volume, or VBR.

CONCLUSIONS

In our longitudinal sample of deployed Veterans, mTBI was not associated with gross brain atrophy as reflected by abnormally high VBR or abnormal increases in VBR over time.

Predictors of Postdeployment Functioning in Combat-Exposed U.S. Military Veterans

Posttraumatic stress disorder (PTSD) and sequelae of mild traumatic brain injury (mTBI) are presumed to contribute to reintegration difficulties in combat-exposed veterans. Yet their relative impacts on postdeployment functioning are not well understood. The current study used structural equation modeling (SEM) to clarify the extent to which symptoms of internalizing disorders (e.g., depression, anxiety), mTBI symptoms, and cognitive performance are associated with functional impairment in 295 combat-exposed veterans. SEM results showed that internalizing symptoms most significantly predicted functional impairment (r = 0.72). Blast mTBI and cognitive performance were associated with internalizing (r = 0.24 and -0.25, respectively), but functional impairment was only modestly related to cognition (r = -0.17) and unrelated to mTBI. These results indicate that internalizing symptoms are the strongest predictor of functioning in trauma-exposed veterans, exceeding the effects of mTBI and cognitive performance. This evidence supports prioritizing interventions that target internalizing psychopathology to improve functioning in cases of co-occurring PTSD and mTBI.

Reduced P3b brain response during sustained visual attention is associated with remote blast mTBI and current PTSD in U.S. military veterans

Approximately 275,000 American service members deployed to Iraq or Afghanistan have sustained a mild traumatic brain injury (mTBI), with 75% of these incidents involving an explosive blast. Combat-related mTBI is frequently associated with comorbid mental health disorders, especially posttraumatic stress disorder (PTSD). Attention problems, including sustained attention, are common cognitive complaints of veterans with TBI and PTSD. The present study sought to examine neural correlates of sustained attention in veterans with blast mTBI and/or current PTSD. In 124 veterans of Operations Enduring and Iraqi Freedom (OEF/OIF), we examined event-related potentials (ERPs) elicited by targets and non-targets during performance of a degraded-stimulus continuous performance task (DS-CPT). Four groups, consisting of veterans with blast-related mTBI only, current PTSD only, both blast mTBI and PTSD, and a control group, were studied. Compared to all other groups, blast mTBI only participants were more likely to respond regardless of stimulus type during the DS-CPT. During target detection, the three mTBI/PTSD groups showed reduced amplitude of the P3b (i.e., P300) ERP at Pz compared to the control group. P3b of the three affected groups did not differ from each other. These results suggest that parietal P3b amplitude reduction during target detection in the DS-CPT task may be an index of brain pathology after combat trauma, yet the diminished brain response fails to differentiate independent effects of blast-related mTBI or severity of PTSD symptomatology.

Deficits in Visual System Functional Connectivity after Blast-Related Mild TBI are Associated with Injury Severity and Executive Dysfunction

INTRODUCTION

Approximately, 275,000 American service members deployed to Iraq or Afghanistan have sustained a mild traumatic brain injury (mTBI), with 75% of these incidents involving an explosive blast. Visual processing problems and cognitive dysfunction are common complaints following blast-related mTBI.

METHODS

In 127 veterans, we examined resting fMRI functional connectivity (FC) of four key nodes within the visual system: lateral geniculate nucleus (LGN), primary visual cortex (V1), lateral occipital gyrus (LO), and fusiform gyrus (FG). Regression analyses were performed (i) to obtain correlations between time-series from each seed and all voxels in the brain, and (ii) to identify brain regions in which FC variability was related to blast mTBI severity. Blast-related mTBI severity was quantified as the sum of the severity scores assigned to each of the three most significant blast-related injuries self-reported by subjects. Correlations between FC and performance on executive functioning tasks were performed across participants with available behavioral data (n = 94).

RESULTS

Greater blast mTBI severity scores were associated with lower FC between: (A) LGN seed and (i) medial frontal gyrus, (ii) lingual gyrus, and (iii) right ventral anterior nucleus of thalamus; (B) V1 seed and precuneus; (C) LO seed and middle and superior frontal gyri; (D) FG seed and (i) superior and medial frontal gyrus, and (ii) left middle frontal gyrus. Finally, lower FC between visual network regions and frontal cortical regions predicted worse performance on the WAIS digit-symbol coding task.

CONCLUSION

These are the first published results that directly illustrate the relationship between blast-related mTBI severity, visual pathway neural networks, and executive dysfunction - results that highlight the detrimental relationship between blast-related brain injury and the integration of visual sensory input and executive processes.

Detecting Behavioral Deficits Post Traumatic Brain Injury in Rats

Traumatic brain injury (TBI), ranging from mild to severe, almost always elicits an array of behavioral deficits in injured subjects. Some of these TBI-induced behavioral deficits include cognitive and vestibulomotor deficits as well as anxiety and other consequences. Rodent models of TBI have been (and still are) fundamental in establishing many of the pathophysiological mechanisms of TBI. Animal models are also utilized in screening and testing pharmacological effects of potential therapeutic agents for brain injury treatment. This chapter details validated protocols for each of these behavioral deficits post traumatic brain injury in Sprague-Dawley male rats. The elevated plus maze (EPM) protocol is described for assessing anxiety-like behavior; the Morris water maze protocol for assessing cognitive deficits in learning memory and spatial working memory and the rotarod test for assessing vestibulomotor deficits.

Blast Overpressure Waves Induce Transient Anxiety and Regional Changes in Cerebral Glucose Metabolism and Delayed Hyperarousal in Rats

Physiological alterations, anxiety, and cognitive disorders are strongly associated with blast-induced traumatic brain injury (blast TBI), and are common symptoms in service personnel exposed to blasts. Since 2006, 25,000–30,000 new TBI cases are diagnosed annually in U.S. Service members; increasing evidence confirms that primary blast exposure causes diffuse axonal injury and is often accompanied by altered behavioral outcomes. Behavioral and acute metabolic effects resulting from blast to the head in the absence of thoracic contributions from the periphery were examined, following a single blast wave directed to the head of male Sprague-Dawley rats protected by a lead shield over the torso. An 80 psi head blast produced cognitive deficits that were detected in working memory. Blast TBI rats displayed increased anxiety as determined by elevated plus maze at day 9 post-blast compared to sham rats; blast TBI rats spent significantly more time than the sham controls in the closed arms (p < 0.05; n = 8–11). Interestingly, anxiety symptoms were absent at days 22 and 48 post-blast. Instead, blast TBI rats displayed increased rearing behavior at day 48 post-blast compared to sham rats. Blast TBI rats also exhibited suppressed acoustic startle responses, but similar pre-pulse inhibition at day 15 post-blast compared to sham rats. Acute physiological alterations in cerebral glucose metabolism were determined by positron emission tomography 1 and 9 days post-blast using ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG). Global glucose uptake in blast TBI rat brains increased at day 1 post-blast (p < 0.05; n = 4–6) and returned to sham levels by day 9. Our results indicate a transient increase in cerebral metabolism following a blast injury. Markers for reactive astrogliosis and neuronal damage were noted by immunoblotting motor cortex tissue from day 10 post-blast in blast TBI rats compared to sham controls (p < 0.05; n = 5–6).

White matter abnormalities associated with military PTSD in the context of blast TBI

Mild traumatic brain injury (mTBI) and post-traumatic stress disorder (PTSD) are common among recent military veterans and involve substantial symptom overlap, making clinical distinction and effective intervention difficult. Emerging evidence of cerebral white matter abnormalities associated with mTBI may provide a biological measure to inform diagnosis and treatment, but the potentially confounding effects between PTSD and mTBI have largely gone unexamined. We collected diffusion imaging data from 133 recently-deployed American service members who developed PTSD and/or sustained mTBI, or had neither condition. Effects of PTSD and mTBI on traditional tensor-based measures of cerebral white matter integrity (fractional anisotropy [FA] and mean diffusivity [MD]) were compared in anatomical regions of interest and individual voxels throughout the brain. Generalized FA (GFA), which allows for multiple fiber orientations per voxel, was also included to improve sensitivity in white matter areas containing crossing or diverging axon bundles. PTSD was consistently associated with high GFA in select brain regions, greater likelihood of regions and voxels with abnormally low MD, and a greater number of voxels with abnormally high FA, while mTBI was associated with fewer high MD regions. Overall, PTSD was associated with more restricted diffusion (low MD) and greater anisotropy (high GFA) in regions of crossing/diverging fibers poorly characterized by a single tensor (FA), suggesting that interstitial fibers may be involved. Contrary to earlier results in a sample without PTSD, mTBI was not associated with anisotropy abnormalities, perhaps indicating the cooccurrence of PTSD and mTBI requires special consideration with regard to structural brain connectivity.

Assessing neuro-systemic & behavioral components in the pathophysiology of blast-related brain injury

Among the U.S. military personnel, blast injury is among the leading causes of brain injury. During the past decade, it has become apparent that even blast injury as a form of mild traumatic brain injury (mTBI) may lead to multiple different adverse outcomes, such as neuropsychiatric symptoms and long-term cognitive disability. Blast injury is characterized by blast overpressure, blast duration, and blast impulse. While the blast injuries of a victim close to the explosion will be severe, majority of victims are usually at a distance leading to milder form described as mild blast TBI (mbTBI). A major feature of mbTBI is its complex manifestation occurring in concert at different organ levels involving systemic, cerebral, neuronal, and neuropsychiatric responses; some of which are shared with other forms of brain trauma such as acute brain injury and other neuropsychiatric disorders such as post-traumatic stress disorder. The pathophysiology of blast injury exposure involves complex cascades of chronic psychological stress, autonomic dysfunction, and neuro/systemic inflammation. These factors render blast injury as an arduous challenge in terms of diagnosis and treatment as well as identification of sensitive and specific biomarkers distinguishing mTBI from other non-TBI pathologies and from neuropsychiatric disorders with similar symptoms. This is due to the “distinct” but shared and partially identified biochemical pathways and neuro-histopathological changes that might be linked to behavioral deficits observed. Taken together, this article aims to provide an overview of the current status of the cellular and pathological mechanisms involved in blast overpressure injury and argues for the urgent need to identify potential biomarkers that can hint at the different mechanisms involved.

Effects and outcomes in civilian and military traumatic brain injury: similarities, differences, and forensic implications

Traumatic brain injury (TBI) is a prominent public health problem in both civilian and military settings. This article discusses similarities and differences in the assessment and treatment of TBI and the attendant forensic implications. Acute care and management of moderate/severe TBI tend to be similar across environments, as is the recognition of disability status in affected individuals. By contrast, an increased focus on mild TBI in recent years has resulted in a reliance on self-report and screening measures to validate the occurrence of events leading to injury. This has complicated assessment, treatment and subsequent medicolegal proceedings. The neuropsychological literature has provided significant guidance on these difficult issues, although the complexity of disability adjudication for active duty members of the military and veterans continues to pose challenges for clinicians in evaluative and treatment contexts.

The use of virtual reality in the military's assessment of service members with traumatic brain injury: recent developments and emerging opportunities

Traumatic brain injury (TBI) is a common event in the current extended conflicts by American service members, with estimates that as many as 300,000 have sustained combat-related concussions during Operation Iraqi Freedom and Operation Enduring Freedom. The limited ecological validity of traditional neuropsychological assessment measures presents a challenge to effective postconcussion evaluation of service members in relation to fitness-for-duty decisions or rehabilitation needs. Virtual reality (VR) technology offers a promising opportunity to advance the field of functional assessment for TBI. This article reviews the current professional literature on VR applications for TBI assessment, with special emphasis on those that are particularly relevant to U.S. service members. VR affords several advantages for clinical use. These include assessment of complex sets of cognitive and behavioral functions rather than the isolated components assessed by traditional measures; more precise control over the standardized presentation of task stimuli and the recording of response data; and enhanced ecological validity that can lead to more useful assessment data in the applied contexts faced by the U.S. military.

Chronic postconcussion symptoms and functional outcomes in OEF/OIF veterans with self-report of blast exposure

Postconcussion symptoms (PCS) and functional outcomes were evaluated in 91 OEF/OIF outpatient veterans with reported histories of blast-exposure, with the goal of evaluating (1) the association between these outcomes and a clinical diagnosis of mild traumatic brain injury (mTBI) with or without loss of consciousness (LOC); and (2) the influence of post-traumatic stress disorder (PTSD) and depression on PCS reporting and perceived functional limitations. Individuals who reported mTBI with LOC had greater PCS complaints than individuals who reported mTBI without LOC or individuals without mTBI. However, after adjusting for severity of PTSD and depression symptoms, this group difference disappeared. Functional limitations were particularly prominent in the psychosocial domain. Again, PTSD was significantly associated with functional outcomes, but the mTBI with LOC group had greater psychosocial limitations than the other two groups, even when PTSD and depression symptoms were taken into account. These findings highlight the role of mental health in both outcomes, but additionally point to the impact of mTBI with LOC on long-term psychosocial adjustment.

Neuropsychological outcomes of U.S. Veterans with report of remote blast-related concussion and current psychopathology

This study explored whether remote blast-related MTBI and/or current Axis I psychopathology contribute to neuropsychological outcomes among OEF/OIF veterans with varied combat histories. OEF/OIF veterans underwent structured interviews to evaluate history of blast-related MTBI and psychopathology and were assigned to MTBI (n = 18), Axis I (n = 24), Co-morbid MTBI/Axis I (n = 34), or post-deployment control (n = 28) groups. A main effect for Axis I diagnosis on overall neuropsychological performance was identified (F(3,100) = 4.81; p = .004), with large effect sizes noted for the Axis I only (d = .98) and Co-morbid MTBI/Axis I (d = .95) groups relative to the control group. The latter groups demonstrated primary limitations on measures of learning/memory and processing speed. The MTBI only group demonstrated performances that were not significantly different from the remaining three groups. These findings suggest that a remote history of blast-related MTBI does not contribute to objective cognitive impairment in the late stage of injury. Impairments, when present, are subtle and most likely attributable to PTSD and other psychological conditions. Implications for clinical neuropsychologists and future research are discussed. (JINS, 2012, 18, 1-11).

Diffuse and spatially variable white matter disruptions are associated with blast-related mild traumatic brain injury

Mild traumatic brain injury (mTBI) due to explosive blast is common among military service members and often associated with long term psychological and cognitive disruptions. Little is known about the neurological effects of blast-related mTBI and whether they differ from those of civilian, non-blast mTBI. Given that brain damage from blasts may be diffuse and heterogeneous, we tested the hypothesis that blast mTBI is associated with subtle white matter disruptions in the brain that are spatially inconsistent across individuals. We used diffusion tensor imaging to examine white matter integrity, as quantified by fractional anisotropy (FA), in a group of American military service members with (n=25) or without (n=33) blast-related mTBI who had been deployed as part of Operation Iraqi Freedom or Operation Enduring Freedom. History of civilian non-blast mTBI was equally common across groups, which enabled testing of both blast and non-blast mTBI effects on measures sensitive to (1) concentrated, spatially consistent (average FA within a region of interest [ROI]), (2) concentrated, spatially variable (number of ROIs with low average FA), and (3) diffuse (number of voxels with low FA) disruptions of white matter integrity. Blast mTBI was associated with a diffuse, global pattern of lower white matter integrity, and this pattern was not affected by previous civilian mTBI. Neither type of mTBI had an effect on the measures sensitive to more concentrated and spatially consistent white matter disruptions. Additionally, individuals with more than one blast mTBI tended to have a larger number of low FA voxels than individuals with a single blast injury. These results indicate that blast mTBI is associated with disrupted integrity of several white matter tracts, and that these disruptions are diluted by averaging across the large number of voxels within an ROI. The reported pattern of effects supports the conclusion that the neurological effects of blast mTBI are diffuse, widespread, and spatially variable.