Neuropsychological studies of mild traumatic brain injury: a meta-analytic review of research since 1995

Neuropsychological differential diagnosis of mild traumatic brain injury

The diagnosis and evaluation of mild traumatic brain injury (mTBI) is reviewed from the perspective of meta-analyses of neuropsychological outcome, showing full recovery from a single, uncomplicated mTBI by 90 days post-trauma. Persons with history of complicated mTBI characterized by day-of-injury computed tomography or magnetic resonance imaging abnormalities, and those who have suffered prior mTBIs may or may not show evidence of complete recovery similar to that experienced by persons suffering a single, uncomplicated mTBI. Persistent post-concussion syndrome (PCS) is considered as a somatoform presentation, influenced by the non-specificity of PCS symptoms which commonly occur in non-TBI samples and co-vary as a function of general life stress, and psychological factors including symptom expectation, depression and anxiety. A model is presented for forensic evaluation of the individual mTBI case, which involves open-ended interview, followed by structured interview, record review, and detailed neuropsychological testing. Differential diagnosis includes consideration of other neurologic and psychiatric disorders, symptom expectation, diagnosis threat, developmental disorders, and malingering.

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.

Practice effects reveal visuomotor vulnerability in school and university rugby players

This article reports on three pre- versus post-season prospective studies in which male university and high school contact sport players predominantly of Rugby Union (hereafter rugby) were compared with age, education, and IQ equivalent non-contact sport controls on the ImPACT (Immediate Postconcussion Assessment and Cognitive Testing) test. All analyses revealed a relative absence of practice effects on the Visual Motor Speed (VMS) composite for contact sport groups compared with controls. The VMS data for rugby players from each study were pooled and subjected to additional analysis (Rugby, n = 145; Controls, n = 106). Controls revealed significant improvement over the season (p < .001), whereas no learning effect was in evidence for rugby players whose performance remained the same (interaction effect, p = .028). It is apparent that practice effects have diagnostic potential in this context, implicating vulnerability on speeded visuomotor processing in association with participation in rugby. Pointers for further research and concussion management in the individual case are explored.

Community versus orthopaedic controls in traumatic brain injury research: how comparable are they?

BACKGROUND

Community (CC) or orthopaedic/injury (OC) control groups are typically used to evaluate the consequences of traumatic brain injuries (TBIs). Whereas CCs match for demographic variables and are readily available, OCs may additionally control for other pre- and post-injury variables but are more costly to recruit. Together, they enable an evaluation of brain- vs general-injury effects. However, the comparability of these two groups and the increase in control over confounding variables when OCs are used has rarely been examined.

METHOD

The current study compared samples of CCs (n = 71) and OCs (n = 69), aged between 18-80, on a range of demographic (age, gender, education, socio-economic status), background (medical history, handedness), psychosocial (alcohol use, fatigue, pain, depression, social support, community integration, 'post-concussion' symptoms) and cognitive (motor and processing speed, memory, intellectual ability) variables.

RESULTS

The two groups were comparable on all variables, except alcohol use, with the OC group having higher levels of alcohol consumption. However, alcohol use did not correlate with any other variable, including commonly used measures of outcome following TBI.

CONCLUSION

The current findings suggest that an orthopaedic injury control group does not have any clear advantages over a carefully recruited community control group.

Neuropsychological effects of self-reported deployment-related mild TBI and current PTSD in OIF/OEF veterans

Current combat veterans are exposed to many incidents that may result in mild traumatic brain injury (mTBI) and/or posttraumatic stress disorder (PTSD). While there is literature on the neuropsychological consequences of PTSD only (PTSD-o) and mTBI alone (mTBI-o), less has been done to explore their combined (mTBI+PTSD) effect. The goal of this study was to determine whether Operation Iraqi Freedom (OIF) and Operation Enduring Freedom (OEF) veterans with mTBI+PTSD have poorer cognitive and psychological outcomes than veterans with PTSD-o, mTBI-o, or combat exposure-only. The final sample included 20 OIF/OEF veterans with histories of self-reported deployment mTBI (mTBI-o), 19 with current PTSD (PTSD-o), 21 with PTSD and self-reported mTBI (mTBI+PTSD), and 21 combat controls (CC) (no PTSD and no reported mTBI). Groups were formed using structured interviews for mTBI and PTSD. All participants underwent comprehensive neuropsychological testing, including neurocognitive and psychiatric feigning tests. Results of cognitive tests revealed significant differences in performance in the mTBI+PTSD and PTSD-o groups relative to mTBI-o and CC. Consistent with previous PTSD literature, significant differences were found on executive (switching) tasks, verbal fluency, and verbal memory. Effect sizes tended to be large in both groups with PTSD. Thus, PTSD seems to be an important variable affecting neuropsychological profiles in the post-deployment time period. Consistent with literature on civilian mTBI, the current study did not find evidence that combat-related mTBI in and of itself contributes to objective cognitive impairment in the late stage of injury.

Neuropsychological functioning of combat veterans with posttraumatic stress disorder and mild traumatic brain injury

This study examined the neuropsychological performance of 125 outpatient Operation Enduring Freedom/Operation Iraqi Freedom combat veterans with posttraumatic stress disorder (PTSD) and nonacute mild traumatic brain injury (TBI) (n = 66) and PTSD (n = 59) across multiple cognitive domains to determine whether mild TBI results in greater impairment among those with PTSD. Profile analyses revealed that veterans with PTSD and mild TBI did not differ significantly from those with just PTSD across domains, suggesting that comorbid mild TBI does not result in an additive effect. A norms-based comparison also revealed that neither group demonstrated impaired performance on any of the objective neuropsychological measures examined. However, both groups endorsed moderately elevated symptoms of depression and anxiety, indicating that comorbid psychopathology may contribute to subjective cognitive complaints.

Integrating Interventions after Traumatic Brain Injury: A Synergistic Approach to Neurorehabilitation

Deficits in attention, processing speed and executive functioning are among the most commonly reported and functionally limiting cognitive impairments among individuals with TBI. Changes in mood can exacerbate cognitive deficits and reduce life quality. Contemporary hierarchical models of cognitive functioning suggest that attention/arousal processes underlie and support higher-order functions. Building on decades of clinical research, a synergistic, integrative approach to neurorehabilitation is described, which combines bottom-up and top-town cognitive interventions in addition to psychotherapeutic interventions for mood. This approach is intended to address directly impairments in both foundational (i.e., attention) and higher-order (i.e., executive functions) processes. Executive dysfunction is addressed in a top-down fashion through the application of a series of problem-solving and emotional regulation modules that teach and integrate strategies that can be generalised across situations with practice. Attention, arousal and information processing are necessary prerequisites of successful higher-order thinking, attention skills, and are addressed in a bottom-up fashion through intensive individualised attention and processing training tasks. Combining top-down and bottom-up approaches within a comprehensive day-treatment programme can effect a synergistic improvement of overall functioning.

Meta-analytic methods and the importance of non-TBI factors related to outcome in mild traumatic brain injury: response to Bigler et al. (2013)

Bigler et al. (2013, The Clinical Neuropsychologist) contend that weak methodology and poor quality of the studies comprising our recent meta-analysis led us to miss detecting a subgroup of mild traumatic brain injury (mTBI) characterized by persisting symptomatic complaint and positive biomarkers for neurological damage. Our computation of non-significant Q, tau(2), and I(2) statistics contradicts the existence of a subgroup of mTBI with poor outcome, or variation in effect size as a function of quality of research design. Consistent with this conclusion, the largest single contributor to our meta-analysis, Dikmen, Machamer, Winn, and Temkin (1995, Neuropsychology, 9, 80) yielded an effect size, -0.02, that was smaller than our overall effect size of -0.07 despite using the most liberal definition of mTBI: loss of consciousness less than 1 hour, with no exclusion of subjects who had positive CT scans. The evidence is weak for biomarkers of mTBI, such as diffusion tensor imaging and for demonstrable neuropathology in uncomplicated mTBI. Postconcussive symptoms, and reduced neuropsychological test scores are not specific to mTBI but can result from pre-existing psychosocial and psychiatric problems, expectancy effects and diagnosis threat. Moreover, neuropsychological impairment is seen in a variety of primary psychiatric disorders, which themselves are predictive of persistent complaints following mTBI. We urge use of prospective studies with orthopedic trauma controls in future investigations of mTBI to control for these confounding factors.

Reduced contribution of executive functions in impaired working memory performance in mild traumatic brain injury patients

AIM

Mild traumatic brain injury (MTBI) is associated with often selective impairment of both working memory (WM) and the executive functions (EFs). Research indicates that one of the commonest deficits present in MTBI patients falls in the domain of WM. We aimed to investigate the role of EFs in WM impairment following MTBI.

METHODS

Performance on the tests of EFs and the verbal and visuo-spatial WM of 30 consecutive MTBI patients were compared with age/education/IQ matched 30 normal healthy control participants. Correlation between EFs and WM was studied separately for the MTBI and the control group.

RESULTS

The MTBI and control group were tested on a range of EF tests and WM. The MTBI group was demonstrated impairment on verbal and visuo-spatial WM and category fluency tests only. Furthermore, the MTBI group had fewer significant correlations between the WM and EFs (5 out of 54 possible correlations) than in the control group (13 out of 54 possible correlations).

CONCLUSIONS

We suggest that MTBI may lead to WM deficits as the contribution of executive processes to support the WM is diminished following MTBI. Such an understanding of the poor WM performance in MTBI patients will be helpful when planning appropriate strategies for cognitive rehabilitation.

Decreased fractional anisotropy evaluated using tract-based spatial statistics and correlated with cognitive dysfunction in patients with mild traumatic brain injury in the chronic stage

BACKGROUND AND PURPOSE

The relationship between white matter disruption and cognitive dysfunction of patients with mTBI in the chronic stage remains unclear. The aim of this study was to identify white matter integrity by using DTI in patients with mTBI without morphologic traumatic abnormalities seen with conventional imaging and to evaluate the association of such regions with cognitive function.

MATERIALS AND METHODS

Diffusion tensor images from 51 consecutive patients with mTBI without morphologic traumatic abnormalities on conventional MRI were processed, and FA maps were generated as a measure of white matter integrity. All subjects underwent cognitive examinations (MMSE and WAIS-R FIQ). Correlations between the skeletonized FA values in the white matter and the cognitive function were analyzed by using regression analysis.

RESULTS

In patients with mTBI, significantly decreased FA value clusters in the white matter compared with the healthy controls were found in the superior longitudinal fasciculus, superior frontal gyrus, insula, and fornix. Cognitive examination scores positively correlated with FA values in a number of regions in deep brain structures, which were anatomically close or physiologically intimate to the regions with significant FA value reduction, in patients with mTBI.

CONCLUSIONS

The present study shows that patients with mTBI in the chronic stage have certain regions with abnormally reduced white matter integrity in the brain. Although the clinical and pathologic-anatomic correlation of these findings remains to be elucidated, these brain regions are strongly suggested to be related to chronic persistent cognitive impairments in these patients.

Multiple resting state network functional connectivity abnormalities in mild traumatic brain injury

Several reports show that traumatic brain injury (TBI) results in abnormalities in the coordinated activation among brain regions. Because most previous studies examined moderate/severe TBI, the extensiveness of functional connectivity abnormalities and their relationship to postconcussive complaints or white matter microstructural damage are unclear in mild TBI. This study characterized widespread injury effects on multiple integrated neural networks typically observed during a task-unconstrained "resting state" in mild TBI patients. Whole brain functional connectivity for twelve separate networks was identified using independent component analysis (ICA) of fMRI data collected from thirty mild TBI patients mostly free of macroscopic intracerebral injury and thirty demographically-matched healthy control participants. Voxelwise group comparisons found abnormal mild TBI functional connectivity in every brain network identified by ICA, including visual processing, motor, limbic, and numerous circuits believed to underlie executive cognition. Abnormalities not only included functional connectivity deficits, but also enhancements possibly reflecting compensatory neural processes. Postconcussive symptom severity was linked to abnormal regional connectivity within nearly every brain network identified, particularly anterior cingulate. A recently developed multivariate technique that identifies links between whole brain profiles of functional and anatomical connectivity identified several novel mild TBI abnormalities, and represents a potentially important new tool in the study of the complex neurobiological sequelae of TBI.

Validity of the Virtual Reality Stroop Task (VRST) in active duty military

Virtual environments provide the ability to systematically deliver test stimuli in simulated contexts relevant to real world behavior. The current study evaluated the validity of the Virtual Reality Stroop Task (VRST), which presents test stimuli during a virtual reality military convoy with simulated combat threats. Active duty Army personnel (N = 49) took the VRST, a customized version of the Automated Neuropsychological Assessment Metrics (ANAM)-Fourth Edition TBI Battery (2007) that included the addition of the ANAM Stroop and Tower tests, and traditional neuropsychological measures, including the Delis-Kaplan Executive Function System version of the Color-Word Interference Test. Preliminary convergent and discriminant validity was established, and performance on the VRST was significantly associated with computerized and traditional tests of attention and executive functioning. Valid virtual reality cognitive assessments open new lines of inquiry into the impact of environmental stimuli on performance and offer promise for the future of neuropsychological assessments used with military personnel.

Longitudinal volumetric changes following traumatic brain injury: a tensor-based morphometry study

After traumatic injury, the brain undergoes a prolonged period of degenerative change that is paradoxically accompanied by cognitive recovery. The spatiotemporal pattern of atrophy and the specific relationships of atrophy to cognitive changes are ill understood. The present study used tensor-based morphometry and neuropsychological testing to examine brain volume loss in 17 traumatic brain injury (TBI) patients and 13 controls over a 4-year period. Patients were scanned at 2 months, 1 year, and 4 years post-injury. High-dimensional warping procedures were used to create change maps of each subject's brain for each of the two intervals. TBI patients experienced volume loss in both cortical areas and white matter regions during the first interval. We also observed continuing volume loss in extensive regions of white matter during the second interval. Neuropsychological correlations indicated that cognitive tasks were associated with subsequent volume loss in task-relevant regions. The extensive volume loss in brain white matter observed well beyond the first year post-injury suggests that the injured brain remains malleable for an extended period, and the neuropsychological relationships suggest that this volume loss may be associated with subtle cognitive improvements.

Abnormal neurological exam findings in individuals with mild traumatic brain injury (mTBI) versus psychiatric and healthy controls

In those with a history of mild traumatic brain injury (mTBI), cognitive and emotional disturbances are often misattributed to that preexisting injury. However, causal determinations of current symptoms cannot be conclusively determined because symptoms are often nonspecific to etiology and offer virtually no differential diagnostic value in postacute or chronic phases. This population-based study examined whether the presence of abnormalities during neurological examination would distinguish between mTBI (in the chronic phase), healthy controls, and selected psychiatric conditions. Retrospective analysis of data from 4462 community-dwelling Army veterans was conducted. Diagnostically unique groups were compared on examination of cranial nerve function and other neurological signs. Results demonstrated that individuals with mTBI were no more likely than those with a major depressive disorder, generalized anxiety disorder, posttraumatic stress disorder, or somatoform disorder to show any abnormality. Thus, like self-reported cognitive and emotional symptoms, the presence of cranial nerve or other neurological abnormalities offers no differential diagnostic value. Clinical implications and study limitations are presented.

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).

Long-term cognitive complaint and post-concussive symptoms following mild traumatic brain injury: the role of cognitive and affective factors

PRIMARY OBJECTIVE

To determine whether neuropsychological test performance or affective factors predict long-term post-concussive symptoms and cognitive complaint following mild traumatic brain injury.

METHODS AND PROCEDURES

Participants included 21 individuals with mild traumatic brain injury, 19 individuals with spinal injury but no injury to the brain and 20 neurologically-normal controls. All participants completed measures of post-concussive symptoms, cognitive complaint, depression, anxiety, and personality and were administered a variety of neuropsychological tests.

MAIN OUTCOMES AND RESULTS

The hypothesis that depression, anxiety and neuroticism would be better predictors of post-concussive symptoms than neuropsychological test performance for all three groups was supported. Contrary to expectations, however, neuropsychological test performance was a unique predictor of cognitive complaint for the mild traumatic brain injury group.

CONCLUSIONS

It was concluded that long-term post-concussive symptoms are largely representative of psychological symptoms and not brain damage, but that genuine, albeit subtle, cognitive deficits also may be present for long-term periods following mild traumatic brain injury.

Traumatic brain injury and its neuropsychiatric sequelae in war veterans

The post-September 11, 2001 wars in and around Afghanistan and Iraq have increased awareness of traumatic brain injury (TBI), particularly blast-induced mild TBI. This article provides an overview of TBI and its neuropsychiatric sequelae in U.S. war veterans who participated in the current operations in and around Afghanistan and Iraq, with particular emphasis on blast-related mild TBI. Psychiatric disorders, particularly posttraumatic stress disorder, pain, and sensory impairments are prevalent in war veterans with TBI. Research is needed to more definitively characterize the epidemiology of TBI-related functional difficulties, the effects of blasts compared with other mechanisms of injury, recovery trajectories, and treatment outcomes in this population.

Mild traumatic brain injury in the occupational setting

The evaluation and management of mild traumatic brain injury (mTBI) in the occupational setting may pose significant challenges for even the most-seasoned practitioner. Providers must simultaneously address the clinical management of mTBI and be familiar with the systematic and administrative requirements related to the management of injured workers with mTBI who are covered by workers' compensation insurance, including causation, return to work, and the potential of permanent impairment. Given the primarily subjective nature of many mTBI symptoms, an injured worker with a delayed recovery may raise the question, if not suspicion, of symptom magnification and secondary gain. This review discusses the evaluation and treatment of the injured worker with mTBI, and focuses on the medicolegal issues that are present in the workers' compensation system, especially the role of neuropsychological evaluations. Although significant differences exist regarding classification schema, for the purposes of this discussion, mTBI is used to encompass the terms concussion, postconcussive syndrome, and persistent postconcussive syndrome.

Neuropsychological sequelae of PTSD and TBI following war deployment among OEF/OIF veterans

Posttraumatic stress disorder (PTSD) and mild traumatic brain injury (mTBI) are highly prevalent among Veterans of the conflicts in Iraq and Afghanistan. These conditions are associated with common and unique neuropsychological and neuroanatomical changes. This review synthesizes neuropsychological and neuroimaging studies for both of these disorders and studies examining their co-occurrence. Recommendations for future research, including use of combined neuropsychological and advanced neuroimaging techniques to study these disorders alone and in concert, are presented. It is clear from the dearth of literature that addiitonal studies are required to examine and understand the impact of specific factors on neurocognitive outcome. Of particular relevance are temporal relationships between PTSD and mTBI, risk and resilience factors associated with both disorders and their co-occurrence, and mTBI-specific factors such as time since injury and severity of injury, utilizing comprehensive, yet targeted cognitive tasks.

Performance monitoring and cognitive control in individuals with mild traumatic brain injury

Literature suggests that individuals with mild traumatic brain injury (mTBI) show subtle abnormalities in the cognitive control process of performance monitoring. The neural bases of performance monitoring can be measured using the error-related negaitivity (ERN) and post-error positivity (Pe) components of the scalp-recorded event-related potential (ERP). Thirty-six individuals with mTBI and 46 demographically similar controls completed a modified color-naming Stroop task while ERPs were recorded. Separate repeated-measures analyses of variance were used to examine the behavioral (response times [RT] and error rates) and ERP (ERN and Pe amplitudes) indices of performance monitoring. Both groups showed slower RTs and increased error rates on incongruent trials relative to congruent trials. Likewise, both groups showed more negative ERN and more positive Pe amplitude to error trials relative to correct trials. Notably, there were no significant main effects or interactions of group for behavioral and ERP measures. Subgroup and correlational analyses with post-concussive symptoms and indices of injury severity were also not significant. Findings suggest comparable performance to non-injured individuals in some aspects of cognitive control in this sample. Neuropsychological implications and comparison with other cognitive control component processes in individuals with TBI are provided.

Are self-reported symptoms of executive dysfunction associated with objective executive function performance following mild to moderate traumatic brain injury?

BACKGROUND AND OBJECTIVE

We examined the relationship between self-reported pre- and post-injury changes in executive dysfunction, apathy, disinhibition, and depression, and performance on neuropsychological tests of executive function, attention/processing speed, and memory in relation to mood levels and effort test performance in individuals in the early stages of recovery from mild to moderate traumatic brain injury (TBI).

METHOD

Participants were 71 noncombat military personnel who were in a semiacute stage of recovery (<3 months post injury) from mild to moderate TBI. Pre- and post-TBI behaviors were assessed with the Frontal Systems Behavior Scale (FrSBe; Grace & Malloy, 2001 ) and correlated with levels of depressive symptoms, effort test performance, and performance on objective measures of attention, executive function, and memory.

RESULTS

Self-reported symptoms of executive dysfunction generally failed to predict performance on objective measures of executive function and memory, although they predicted poorer performance on measures of attention/processing speed. Instead, higher levels of depressive symptomatology best predicted poorer performance on measures of executive function and memory. However, the relationship between memory performance and TBI symptoms was no longer significant when effort performance was controlled.

CONCLUSIONS

Our findings suggest that, among individuals in early recovery from mild to moderate TBI, self-reported depressive symptoms, rather than patients' cognitive complaints, are associated with objective executive function. However, self-reported cognitive complaints may be associated with objectively measured inattention and slow processing speed.

The "Miserable Minority" following mild traumatic brain injury: who are they and do meta-analyses hide them?

Ruff et al. (1994; Ruff, Camenzuli, & Mueller, 1996) hypothesized that some mild traumatic brain injury (MTBI) patients will suffer chronic symptomatic complaints and impairments, identifying this subgroup as the "miserable minority." However, several meta-analyses of the effects of MTBI have been published (e.g., Rohling et al., 2011) showing no significant cognitive impairments following recovery. Recently Pertab, James, and Bigler (2009) suggested that meta-analysis might be obscuring impairments in some MTBI patients, presenting a hypothetical score distribution to illustrate their claim. Our statistical analyses of their hypothetical figure and of several other potential distributions containing an impaired subgroup that varied as a function of effect size and base rate of occurrence did not support the existence of a miserable minority that is obscured in meta-analyses by the larger group of MTBI patients experiencing full recovery. Indeed, given our recent published MTBI effect size of -0.07 (Rohling et al., 2011), for an impaired subgroup to exist, the level of impairment would have to be just under a tenth of a standard deviation, equivalent to a WMS-IV Index score value of 1 point. At effect sizes this small, any cut score chosen on a test to diagnose patients would result in more false positives than true positives. This greatly increases the risk of misdiagnosis in persons who are susceptible to misattribution, expectancy effects, and "diagnosis threat," thereby increasing the risk of iatrogenic illness.

Neuropsychological and neuroimaging findings in traumatic brain injury and post-traumatic stress disorder

Advances in imaging technology, coupled with military personnel returning home from Iraq and Afghanistan with traumatic brain injury (TBI) and/or post-traumatic stress disorder (PTSD), have increased interest in the neuropsychology and neurobiology of these two conditions. There has been a particular focus on differential diagnosis. This paper provides an overview of findings regarding the neuropsychological and neurobiological underpinnings of TBI and for PTSD. A specific focus is on assessment using neuropsychological measures and imaging techniques. Challenges associated with the assessment of individuals with one or both conditions are also discussed. Although use of neuropsychological and neuroimaging test results may assist with diagnosis and treatment planning, further work is needed to identify objective biomarkers for each condition. Such advances would be expected to facilitate differential diagnosis and implementation of best treatment practices.

Slowing down after a mild traumatic brain injury: a strategy to improve cognitive task performance?

Long-term persistent attention and memory difficulties following a mild traumatic brain injury (TBI) often go undetected on standard neuropsychological tests, despite complaints by mild TBI individuals. We conducted a visual Repetition Detection working memory task to digits, in which we manipulated task difficulty by increasing cognitive load, to identify subtle deficits long after a mild TBI. Twenty-six undergraduate students with a self-report of one mild TBI, which occurred at least 6 months prior, and 31 non-head-injured controls took part in the study. Participants were not informed until study completion that the study's purpose was to examine cognitive changes following a mild TBI, to reduce the influence of "diagnosis threat" on performance. Neuropsychological tasks did not differentiate the groups, though mild TBI participants reported higher state anxiety levels. On our working memory task, the mild TBI group took significantly longer to accurately detect repeated targets on our task, suggesting that slowed information processing is a long-term consequence of mild TBI. Accuracy was comparable in the low-load condition and, unexpectedly, mild TBI performance surpassed that of controls in the high-load condition. Temporal analysis of target identification suggested a strategy difference between groups: mild TBI participants made a significantly greater number of accurate responses following the target's offset, and significantly fewer erroneous distracter responses prior to target onset, compared with controls. Results suggest that long after a mild TBI, high-functioning young adults invoke a strategy of delaying their identification of targets in order to maintain, and facilitate, accuracy on cognitively demanding tasks.

Thalamus and cognitive impairment in mild traumatic brain injury: a diffusional kurtosis imaging study

Conventional imaging is unable to detect damage that accounts for permanent cognitive impairment in patients with mild traumatic brain injury (mTBI). While diffusion tensor imaging (DTI) can help to detect diffuse axonal injury (DAI), it is a limited indicator of tissue complexity. It has also been suggested that the thalamus may play an important role in the development of clinical sequelae in mTBI. The purpose of this study was to determine if diffusional kurtosis imaging (DKI), a novel quantitative magnetic resonance imaging (MRI) technique, can provide early detection of damage in the thalamus and white matter (WM) of mTBI patients, and can help ascertain if thalamic injury is associated with cognitive impairment. Twenty-two mTBI patients and 14 controls underwent MRI and neuropsychological testing. Mean kurtosis (MK), fractional anisotropy (FA), and mean diffusivity (MD) were measured in the thalamus and several WM regions classically identified with DAI. Compared to controls, patients examined within 1 year after injury exhibited variously altered DTI- and DKI-derived measures in the thalamus and the internal capsule, while in addition to these regions, patients examined more than 1 year after injury also showed similar differences in the splenium of the corpus callosum and the centrum semiovale. Cognitive impairment was correlated with MK in the thalamus and the internal capsule. These findings suggest that combined use of DTI and DKI provides a more sensitive tool for identifying brain injury. In addition, MK in the thalamus might be useful for early prediction of permanent brain damage and cognitive outcome.

Long-term cognitive and emotional consequences of mild traumatic brain injury

BACKGROUND

The objective of this study was to investigate long-term cognitive and emotional sequelae of mild traumatic brain injury (mTBI), as previous research has remained inconclusive with respect to their prevalence and extent.

METHOD

Thirty-three individuals who had sustained mTBI on average 6 years prior to the study and 33 healthy control subjects were matched according to age, gender and education. Structural brain damage at time of testing was excluded by magnetic resonance imaging (MRI). A comprehensive neuropsychological test battery was conducted to assess learning, recall, working memory, attention and executive function. Psychiatric symptoms were assessed by the Structured Clinical Interview for DSM-IV Axis I Disorders (SCID-I) and the Beck Depression Inventory (BDI). Possible negative response bias was ruled out by implementing the Word Memory Test (WMT).

RESULTS

The mTBI individuals had significant impairments in all cognitive domains compared to the healthy control subjects. Effect sizes of cognitive deficits were medium to large, and could not be accounted for by self-perceived deficits, depression, compensation claims or negative response bias. BDI scores were significantly higher in the patient group, and three patients fulfilled DSM-IV criteria for a mild episode of major depression.

CONCLUSIONS

Primarily, well-recovered individuals who had sustained a minor trauma more than half a decade ago continue to have long-term cognitive and emotional sequelae relevant for everyday social and professional life. mTBI may lead to a lasting disruption of neurofunctional circuits not detectable by standard structural MRI and needs to be taken seriously in clinical and forensic evaluations.

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

BACKGROUND/OBJECTIVE

Soldiers of Operations Enduring Freedom (OEF) and Iraqi Freedom (OIF) sustain blast-related mild traumatic brain injury (concussion) with alarming regularity. This study discusses factors in addition to concussion, such as co-morbid psychological difficulty (e.g. post-traumatic stress) and symptom validity concerns that may complicate neuropsychological evaluation in the late stage of concussive injury.

CASE REPORT

The study presents the complexities that accompany neuropsychological evaluation of blast concussion through discussion of three case reports of OEF/OIF personnel.

DISCUSSION

The authors emphasize uniform assessment of blast concussion, the importance of determining concussion severity according to acute-injury characteristics and elaborate upon non-concussion-related factors that may impact course of cognitive limitation. The authors conclude with a discussion of the need for future research examining the impact of blast concussion (particularly recurrent concussion) and neuropsychological performance.

Parcellating the neuroanatomical basis of impaired decision-making in traumatic brain injury

Cognitive dysfunction is a devastating consequence of traumatic brain injury that affects the majority of those who survive with moderate-to-severe injury, and many patients with mild head injury. Disruption of key monoaminergic neurotransmitter systems, such as the dopaminergic system, may play a key role in the widespread cognitive dysfunction seen after traumatic axonal injury. Manifestations of injury to this system may include impaired decision-making and impulsivity. We used the Cambridge Gambling Task to characterize decision-making and risk-taking behaviour, outside of a learning context, in a cohort of 44 patients at least six months post-traumatic brain injury. These patients were found to have broadly intact processing of risk adjustment and probability judgement, and to bet similar amounts to controls. However, a patient preference for consistently early bets indicated a higher level of impulsiveness. These behavioural measures were compared with imaging findings on diffusion tensor magnetic resonance imaging. Performance in specific domains of the Cambridge Gambling Task correlated inversely and specifically with the severity of diffusion tensor imaging abnormalities in regions that have been implicated in these cognitive processes. Thus, impulsivity was associated with increased apparent diffusion coefficient bilaterally in the orbitofrontal gyrus, insula and caudate; abnormal risk adjustment with increased apparent diffusion coefficient in the right thalamus and dorsal striatum and left caudate; and impaired performance on rational choice with increased apparent diffusion coefficient in the bilateral dorsolateral prefrontal cortices, and the superior frontal gyri, right ventrolateral prefrontal cortex, the dorsal and ventral striatum, and left hippocampus. Importantly, performance in specific cognitive domains of the task did not correlate with diffusion tensor imaging abnormalities in areas not implicated in their performance. The ability to dissociate the location and extent of damage with performance on the various task components using diffusion tensor imaging allows important insights into the neuroanatomical basis of impulsivity following traumatic brain injury. The ability to detect such damage in vivo may have important implications for patient management, patient selection for trials, and to help understand complex neurocognitive pathways.

Postconcussive symptoms after blast and nonblast-related mild traumatic brain injuries in Afghanistan and Iraq war veterans

Blast injury is common in current warfare, but little is known about the effects of blast-related mild traumatic brain injury (mTBI). Profile analyses were conducted investigating differences in self-reported postconcussive (PC) symptoms in 339 veteran outpatients with mTBI histories reporting current symptoms based on mechanism of injury (blast only, nonblast only, or both blast and nonblast), number of blast injuries, and distance from the blast. Veterans with any blast-related mTBI history were younger and reported higher posttraumatic stress symptoms than veterans with nonblast-related mTBI histories, with a marginally significant difference in posttraumatic stress symptom report between veterans reporting blast-related mTBI only and those reporting nonblast-related mTBI. The groups did not differ in terms of PC symptom severity or PC symptom cluster profiles. Among veterans with blast-related mTBI histories, PC symptom report did not vary by number of blast-related mTBIs or proximity to blast. Overall, posttraumatic stress symptoms accounted for a substantial portion of variance in PC symptom report. In veteran outpatients with remote mTBI histories who have enduring symptom complaints related to the mTBI, mechanism of injury did not clearly contribute to differential PC symptom severity or PC symptom cluster profile. Proximal rather than distal factors may be important intervention targets in returning symptomatic veterans with mTBI histories.

Attention processing abnormalities in children with traumatic brain injury and attention-deficit/hyperactivity disorder: differential impairment of component processes

Individuals with acquired and neurodevelopmental brain disorders often exhibit deficits in attention. Recent models of attention have conceptualized it as a multicomponent system. One influential model proposed by Mirsky et al. (1991) consists of factors that include focus, sustain, shift, and encode components. This model has been used to examine the structure of attention in a variety of clinical populations although few studies have contrasted performance of various clinical groups in order to determine whether these components are differentially affected. To address this issue, the current study investigated the differential sensitivity of these attention components in 90 children: 30 who had sustained traumatic brain injury (TBI), 30 who were diagnosed with attention-deficit/hyperactivity disorder (ADHD), and 30 normal controls. Results demonstrated that the TBI group had significantly lower focus factor scores, the ADHD group had significantly lower sustain scores, and that both clinical groups had lower encode factor scores than controls. Stepwise discriminant function analysis (DFA) retained the focus and encode factors in predicting clinical groups from controls with 75.6% accuracy. A second DFA retained the focus factor in differentiating the two clinical groups with 70.0% accuracy. These findings provide evidence of differential attention deficits resulting from TBI and ADHD.

Concussion causes transient dysfunction in cortical inhibitory networks but not the corpus callosum

The corpus callosum (CC) is thought to be especially vulnerable in traumatic brain injury. Bimanual cost (a slowing of reaction time with bimanual compared to unimanual responses) is a sensitive indicator of CC function. To determine whether CC dysfunction is a significant feature of mild traumatic brain injury, unimanual and bimanual reaction times were studied in 10 recently concussed patients and 10 healthy participants. Reaction times were studied within 1 week of concussion and again after 1 month. Concussion symptoms were assessed with the Rivermead Postconcussion Symptoms Questionnaire. The bimanual cost was present at both testing sessions in patients and healthy controls. Although overall reaction times were slower in concussed patients during session 1, these had improved by session 2, as did the symptom scores. These findings suggest that the pathogenesis of mild traumatic brain injury involves intrahemispheric cortical networks rather than impaired interhemispheric communication via the CC.