Fatigue – but not mTBI history, PTSD, or sleep quality – directly contributes to reduced prospective memory performance in Iraq and Afghanistan era Veterans

Increased [18F]Fluorodeoxyglucose Uptake in the Left Pallidum in Military Veterans with Blast-Related Mild Traumatic Brain Injury: Potential as an Imaging Biomarker and Mediation with Executive Dysfunction and Cognitive Impairment

Blast-related mild traumatic brain injury (blast-mTBI) can result in a spectrum of persistent symptoms leading to substantial functional impairment and reduced quality of life. Clinical evaluation and discernment from other conditions common to military service can be challenging and subject to patient recall bias and the limitations of available assessment measures. The need for objective biomarkers to facilitate accurate diagnosis, not just for symptom management and rehabilitation but for prognostication and disability compensation purposes is clear. Toward this end, we compared regional brain [18F]fluorodeoxyglucose-positron emission tomography ([18F]FDG-PET) intensity-scaled uptake measurements and motor, neuropsychological, and behavioral assessments in 79 combat Veterans with retrospectively recalled blast-mTBI with 41 control participants having no lifetime history of TBI. Using an agnostic and unbiased approach, we found significantly increased left pallidum [18F]FDG-uptake in Veterans with blast-mTBI versus control participants, p < 0.0001; q = 3.29 × 10-9 [Cohen's d, 1.38, 95% confidence interval (0.96, 1.79)]. The degree of left pallidum [18F]FDG-uptake correlated with the number of self-reported blast-mTBIs, r2 = 0.22; p < 0.0001. Greater [18F]FDG-uptake in the left pallidum provided excellent discrimination between Veterans with blast-mTBI and controls, with a receiver operator characteristic area under the curve of 0.859 (p < 0.0001) and likelihood ratio of 21.19 (threshold:SUVR ≥ 0.895). Deficits in executive function assessed using the Behavior Rating Inventory of Executive Function-Adult Global Executive Composite T-score were identified in Veterans with blast-mTBI compared with controls, p < 0.0001. Regression-based mediation analyses determined that in Veterans with blast-mTBI, increased [18F]FDG-uptake in the left pallidum-mediated executive function impairments, adjusted causal mediation estimate p = 0.021; total effect estimate, p = 0.039. Measures of working and prospective memory (Auditory Consonant Trigrams test and Memory for Intentions Test, respectively) were negatively correlated with left pallidum [18F]FDG-uptake, p < 0.0001, with mTBI as a covariate. Increased left pallidum [18F]FDG-uptake in Veterans with blast-mTBI compared with controls did not covary with dominant handedness or with motor activity assessed using the Unified Parkinson's Disease Rating Scale. Localized increased [18F]FDG-uptake in the left pallidum may reflect a compensatory response to functional deficits following blast-mTBI. Limited imaging resolution does not allow us to distinguish subregions of the pallidum; however, the significant correlation of our data with behavioral but not motor outcomes suggests involvement of the ventral pallidum, which is known to regulate motivation, behavior, and emotions through basal ganglia-thalamo-cortical circuits. Increased [18F]FDG-uptake in the left pallidum in blast-mTBI versus control participants was consistently identified using two different PET scanners, supporting the generalizability of this finding. Although confirmation of our results by single-subject-to-cohort analyses will be required before clinical deployment, this study provides proof of concept that [18F]FDG-PET bears promise as a readily available noninvasive biomarker for blast-mTBI. Further, our findings support a causative relationship between executive dysfunction and increased [18F]FDG-uptake in the left pallidum.

Fatigue in patients with acquired brain damage

Fatigue is a complex, multidimensional syndrome that is prevalent in patients with acquired brain damage and has a negative impact on the neurorehabilitation process. It presents from early stages after the injury, and may persist over time, regardless of whether sequelae have resolved. Fatigue is conditioned by upper neuronal circuits, and is defined as an abnormal perception of overexertion. Its prevalence ranges from 29% to 77% after stroke, from 18% to 75% after traumatic brain injury, and from 47% to 97% after brain tumours. Fatigue is associated with factors including female sex, advanced age, dysfunctional families, history of specific health conditions, functional status (eg, fatigue prior to injury), comorbidities, mood, secondary disability, and the use of certain drugs. Assessment of fatigue is fundamentally based on such scales as the Fatigue Severity Scale (FSS). Advances have recently been made in imaging techniques for its diagnosis, such as in functional MRI. Regarding treatment, no specific pharmacological treatment currently exists; however, positive results have been reported for some conventional neurorehabilitation therapies, such as bright light therapy, neurofeedback, electrical stimulation, and transcranial magnetic stimulation. This review aims to assist neurorehabilitation professionals to recognise modifiable factors associated with fatigue and to describe the treatments available to reduce its negative effect on patients.

Self-reported fatigue was associated with increased white-matter alterations in long-term traumatic brain injury and posttraumatic stress disorder patients

Fatigue is a long-lasting problem in traumatic brain injury (TBI) and post-traumatic stress disorder (PTSD), with limited research that investigated the fatigue-related white-matter changes within TBI and/or PTSD cohorts. This exploratory cross-sectional study used diffusion tensor imaging (DTI) and neuropsychological data collected from 153 male Vietnam War veterans, as part of the Alzheimer's Disease Neuroimaging Initiative - Department of Defense, and were divided clinically into control veterans, PTSD, TBI, and with both TBI and PTSD (TBI+PTSD). The existence of fatigue was defined by the question "Do you often feel tired, fatigued, or sleepy during the daytime?". DTI data were compared between fatigue and non-fatigue subgroups in each clinical group using tract-based spatial statistics voxel-based differences. Fatigue was reported in controls (29.55%), slightly higher in TBI (52.17%, P_Benf = 0.06), and significantly higher in both TBI+PTSD (66.67%, P_Benf = 0.001) and PTSD groups (79.25%, P_Benf < 0.001). Compared to non-fatigued subgroups, no white-matter differences were observed in the fatigued subgroups of control or TBI, while the fatigued PTSD subgroup only showed increased diffusivity measures (i.e., radial and axial), and the fatigued TBI+PTSD subgroup showed decreased fractional anisotropy and increased diffusivity measures (P_FWE ≤ 0.05). The results act as preliminary findings suggesting fatigue to be significantly reported in TBI+PTSD and PTSD decades post-trauma with a possible link to white-matter microstructural differences in both PTSD and TBI+PTSD. Future studies with larger cohorts and detailed fatigue assessments would be required to identify the white-matter changes associated with fatigue in these cohorts.

Repetitive Blast Exposure Increases Appetitive Motivation and Behavioral Inflexibility in Male Mice

Blast exposure (via detonation of high explosives) represents a major potential trauma source for Servicemembers and Veterans, often resulting in mild traumatic brain injury (mTBI). Executive dysfunction (e.g., alterations in memory, deficits in mental flexibility, difficulty with adaptability) is commonly reported by Veterans with a history of blast-related mTBI, leading to impaired daily functioning and decreased quality of life, but underlying mechanisms are not fully understood and have not been well studied in animal models of blast. To investigate potential underlying behavioral mechanisms contributing to deficits in executive functioning post-blast mTBI, here we examined how a history of repetitive blast exposure in male mice affects anxiety/compulsivity-like outcomes and appetitive goal-directed behavior using an established mouse model of blast mTBI. We hypothesized that repetitive blast exposure in male mice would result in anxiety/compulsivity-like outcomes and corresponding performance deficits in operant-based reward learning and behavioral flexibility paradigms. Instead, results demonstrate an increase in reward-seeking and goal-directed behavior and a congruent decrease in behavioral flexibility. We also report chronic adverse behavioral changes related to anxiety, compulsivity, and hyperarousal. In combination, these data suggest that potential deficits in executive function following blast mTBI are at least in part related to enhanced compulsivity/hyperreactivity and behavioral inflexibility and not simply due to a lack of motivation or inability to acquire task parameters, with important implications for subsequent diagnosis and treatment management.

Resting-State Correlations of Fatigue Following Military Deployment

OBJECTIVE

Persistent fatigue is common among military servicemembers returning from deployment, especially those with a history of mild traumatic brain injury (mTBI). The purpose of this study was to characterize fatigue following deployment using the Multidimensional Fatigue Inventory (MFI), a multidimensional self-report instrument. The study was developed to test the hypothesis that if fatigue involves disrupted effort/reward processing, this should manifest as altered basal ganglia functional connectivity as observed in other amotivational states.

METHODS

Twenty-eight current and former servicemembers were recruited and completed the MFI. All 28 participants had a history of at least one mTBI during deployment. Twenty-six participants underwent resting-state functional MRI. To test the hypothesis that fatigue was associated with basal ganglia functional connectivity, the investigators measured correlations between MFI subscale scores and the functional connectivity of the left and right caudate, the putamen, and the globus pallidus with the rest of the brain, adjusting for the presence of depression.

RESULTS

The investigators found a significant correlation between functional connectivity of the left putamen and bilateral superior frontal gyri and mental fatigue scores. No correlations with the other MFI subscales survived multiple comparisons correction.

CONCLUSIONS

This exploratory study suggests that mental fatigue in military servicemembers with a history of deployment with at least one mTBI may be related to increased striatal-prefrontal functional connectivity, independent of depression. A finding of effort/reward mismatch may guide future treatment approaches.

Fatigue in patients with acquired brain damage

Fatigue is a complex, multidimensional syndrome that is prevalent in patients with acquired brain damage and has a negative impact on the neurorehabilitation process. It presents from early stages after the injury, and may persist over time, regardless of whether sequelae have resolved. Fatigue is conditioned by upper neuronal circuits, and is defined as an abnormal perception of overexertion. Its prevalence ranges from 29% to 77% after stroke, from 18% to 75% after traumatic brain injury, and from 47% to 97% after brain tumours. Fatigue is associated with factors including female sex, advanced age, dysfunctional families, history of specific health conditions, functional status (eg, fatigue prior to injury), comorbidities, mood, secondary disability, and the use of certain drugs. Assessment of fatigue is fundamentally based on such scales as the Fatigue Severity Scale (FSS). Advances have recently been made in imaging techniques for its diagnosis, such as in functional MRI. Regarding treatment, no specific pharmacological treatment currently exists; however, positive results have been reported for some conventional neurorehabilitation therapies, such as bright light therapy, neurofeedback, electrical stimulation, and transcranial magnetic stimulation. This review aims to assist neurorehabilitation professionals to recognise modifiable factors associated with fatigue and to describe the treatments available to reduce its negative effect on patients.

Forgetting to Remember: The Impact of Post-traumatic Stress Disorder on Prospective and Retrospective Memory Performance

OBJECTIVE

We examined the impact of post-traumatic stress disorder (PTSD) on both prospective (PM) and retrospective (RM) memory performance among a cross-sectional veteran sample.

METHOD

Data from tests of PM/RM memory and PTSD, anxiety, depression and sleep disturbance symptoms were examined among a prospectively recruited sample of 26 veterans with confirmed PTSD (PTSD+) and 26 well-matched, combat-exposed controls who did not meet criteria for PTSD (PTSD-).

RESULTS

Small-to-moderate negative correlations emerged between PTSD symptom severity, visuospatial RM and some aspects of PM; general anxiety correlated more strongly with memory. The PTSD+ group demonstrated significantly worse, but still average visuospatial RM; differences in PM were nonsignificant between groups. Regression analyses implicated generalized anxiety, but not other psychiatric symptomology, as significant contributors to all memory performances.

CONCLUSIONS

Minimal memory differences were found between veterans with and without PTSD. PM/RM memory performance was better explained by generalized anxiety rather that PTSD-specific symptoms.

Self-perceived irritability among OEF/OIF/OND veterans with a history of deployment-related mTBI: Associations with prospective memory and quality of life

OBJECTIVE

Examine relationships between self-perceived irritability, prospective memory, and quality of life (QOL) following mild traumatic brain injury (mTBI). Methods: 75 OEF/OIF/OND-era Veterans (56 deployment-related mTBI; 19 no history of TBI), were administered a battery of neuropsychological tests and self-report measures of mood and QOL. Self-perceived irritability was measured using the Neurobehavioral Symptom Inventory. Prospective memory (PM) was measured using the Memory for Intentions Test (MIST). Results: Self-perceived irritability was significantly higher for Veterans with, versus without, a history of deployment-related mTBI. Among Veterans with a history of mTBI, self-perceived irritability was inversely associated with PM performance, even after adjusting for PTSD severity. Greater self-perceived irritability was also associated with higher depressive symptoms and reduced QOL for perceived physical health, psychological health, social support, and environmental factors; however, only social support remained significant after adjusting for PTSD severity. Depression symptom severity was not significantly associated with PM, suggesting that PM may be uniquely related to self-perceived irritability rather than mood dysregulation more generally. Conclusions: Findings provide preliminary evidence of a relationship between PM and self-perceived irritability in Veterans with a history of mTBI. PM and irritability may be related via their mutual reliance on high-level cognitive control. Results illustrate possible cognitive and affective factors contributing to psychological and interpersonal challenges for this population. Future investigations with larger and more diverse samples are needed to replicate findings and explore potential mechanisms linking irritability and PM following mTBI.

Comparing Composite Scores for the ANAM4 TBI-MIL for Research in Mild Traumatic Brain Injury

OBJECTIVE

The Automated Neuropsychological Assessment Metrics (Version 4) Traumatic Brain Injury Military (ANAM4 TBI-MIL) is commonly administered among U.S. service members both pre-deployment and following TBI. The current study used the ANAM4 TBI-MIL to develop a cognition summary score for TBI research and clinical trials, comparing eight composite scores based on their distributions and sensitivity/specificity when differentiating between service members with and without mild TBI (MTBI).

METHOD

Male service members with MTBI (n = 56; Mdn = 11 days-since-injury) or no self-reported TBI history (n = 733) completed eight ANAM4 TBI-MIL tests. Their throughput scores (correct responses/minute) were used to calculate eight composite scores: the overall test battery mean (OTBM); global deficit score (GDS); neuropsychological deficit score-weighted (NDS-W); low score composite (LSC); number of scores <50th, ≤16th percentile, or ≤5th percentile; and the ANAM Composite Score (ACS).

RESULTS

The OTBM and ACS were normally distributed. Other composites had skewed, zero-inflated distributions (62.9% had GDS = 0). All composites differed significantly between participants with and without MTBI (p < .001), with deficit scores showing the largest effect sizes (d = 1.32-1.47). The Area Under the Curve (AUC) was lowest for number of scores ≤5th percentile (AUC = 0.653) and highest for the LSC, OTBM, ACS, and NDS-W (AUC = 0.709-0.713).

CONCLUSIONS

The ANAM4 TBI-MIL has no well-validated composite score. The current study examined multiple candidate composite scores, finding that deficit scores showed larger group differences than the OTBM, but similar AUC values. The deficit scores were highly correlated. Future studies are needed to determine whether these scores show less redundancy among participants with more severe TBIs.

PTSD Susceptibility and Challenges: Pathophysiological Consequences of Behavioral Symptoms

Introduction

Posttraumatic stress disorder (PTSD) can develop during the aftermath of traumatic events. Although many are impacted by several stressors, nearly 3.6% suffer from PTSD in the United States with higher incidence reported in military service personnel. Any injury to the blood-brain barrier can ignite an array of biological signaling molecules in the immune-privileged brain parenchyma, which can disrupt the synaptic neural network, resulting in altered behavior.

Materials and Methods

In this preliminary study, we compared 20 PTSD veterans with age-matched healthy veterans to identify plasma levels of brain-specific protein markers using enzyme-linked immunosorbent assay/immunofluorometric sandwich assay for neurotrophic factors and neuropoietic cytokines, and catalytic activity of matrix metalloproteinase (MMP) by zymography.

Results

We observed an increased level of glial fibrillary acidic protein, tumor necrosis factor-alpha, interleukin 6, and MMP2 and MMP9 but decreased level of brain-derived neurotrophic factor, nerve growth factor-beta, and negligible difference in astroglial marker S100 calcium-binding protein B compared to controls.

Conclusion

Identification of neural biomarkers is essential to understand the subclinical symptoms for the diagnosis PTSD, which may not be visible by magnetic resonance imaging (MRI/fMRI) and may take years to clinically manifest.

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).

Prospective memory assessment in acute mild traumatic brain injury

Objective: Prospective memory (PM) is the ability to remember to perform an intention at the appropriate time in the future. It is of primary importance for daily living, and its disruption may impact functional autonomy. To date, few studies have examined PM during the acute phase of mild traumatic brain injury (mTBI), despite the high prevalence of this neurological condition and its potential impact on cognition. Method: Twenty mTBI patients (time since injury ranged from 45 to 73 days) and 15 healthy control participants performed the Ecological Test of Prospective Memory (TEMP), a simulated errand task in which participants were required to execute 10 event-based (EB) and five time-based (TB) tasks. The TEMP separately evaluates PM phases as well as prospective and retrospective components in event- and time-based conditions. Participants also completed a neuropsychological test battery. Correlations were performed between cognitive composite scores and the TEMP. Results: mTBI patients experienced difficulty in learning the content of intentions, retrieving these intentions in the time-based condition (prospective component) and recalling the associated actions in the event- and time-based conditions (retrospective component). Retrospective memory composite score was correlated with the learning and retention phases of the TEMP, whereas attention/working memory and executive composite scores were correlated with the time-based condition and performance on the ongoing task. Conclusion: These results suggest the presence of global PM impairment during the acute phase of mTBI, as well as impairment of retrospective memory, attention/working memory, and executive functions, which are key components for PM performance.