Neuropsychological and Information Processing Performance and Its Relationship to White Matter Changes Following Moderate and Severe Traumatic Brain Injury: A Preliminary Study

MRI factors associated with cognitive functioning after acute onset brain injury: Systematic review and meta-analysis

Impairments of memory, attention, and executive functioning are frequently reported after acute onset brain injury. MRI markers hold potential to contribute to identification of patients at risk for cognitive impairments and clarification of mechanisms. The aim of this systematic review was to summarize and value the evidence on MRI markers of memory, attention, and executive functioning after acute onset brain injury. We included ninety-eight studies, on six classes of MRI factors (location and severity of damage (n = 15), volume/atrophy (n = 36), signs of small vessel disease (n = 15), diffusion-weighted imaging measures (n = 36), resting-state functional MRI measures (n = 13), and arterial spin labeling measures (n = 1)). Three measures showed consistent results regarding their association with cognition. Smaller hippocampal volume was associated with worse memory in fourteen studies (pooled correlation 0.58 [95% CI: 0.46-0.68] for whole, 0.11 [95% CI: 0.04-0.19] for left, and 0.34 [95% CI: 0.17-0.49] for right hippocampus). Lower fractional anisotropy in cingulum and fornix was associated with worse memory in six and five studies (pooled correlation 0.20 [95% CI: 0.08-0.32] and 0.29 [95% CI: 0.20-0.37], respectively). Lower functional connectivity within the default-mode network was associated with worse cognition in four studies. In conclusion, hippocampal volume, fractional anisotropy in cingulum and fornix, and functional connectivity within the default-mode network showed consistent associations with cognitive performance in all types of acute onset brain injury. External validation and cut off values for predicting cognitive impairments are needed for clinical implementation.

Processing efficiency in pediatric cancer survivors: A review and operationalization for outcomes research and clinical utility

OBJECTIVE

Childhood cancer and cancer-related treatments disrupt brain development and maturation, placing survivors at risk for cognitive late effects. Given that assessment tools vary widely across researchers and clinicians, it has been daunting to identify distinct patterns in outcomes across diverse cancer types and to implement systematic neurocognitive screening tools. This review aims to operationalize processing efficiency skill impairment-or inefficient neural processing as measured by working memory and processing speed abilities-as a worthwhile avenue for continued study within the context of childhood cancer.

METHODS

A comprehensive literature review was conducted to examine the existing research on cognitive late effects and biopsychosocial risk factors in order to conceptualize processing efficiency skill trends in childhood cancer survivors.

RESULTS

While a frequently reported pattern of neurobiological (white matter) and cognitive (working memory and processing speed) disruption is consistent with processing efficiency skill impairment, these weaknesses have not yet been fully operationalized in this population. We offer a theoretical model that highlights the impacts of a host of biological and environmental factors on the underlying neurobiological substrates of cancer survivors that precede and may even predict long-term cognitive outcomes and functional abilities following treatment.

CONCLUSION

The unified construct of processing efficiency may be useful in assessing and communicating neurocognitive skills in both outcomes research and clinical practice. Deficits in processing efficiency may serve as a possible indicator of cognitive late effects and functional outcomes due to the unique relationship between processing efficiency skills and neurobiological disruption following cancer treatment. Continued research along these lines is crucial for advancing childhood cancer outcomes research and improving quality of life for survivors.

Estimating premorbid intelligence in persons with traumatic brain injury: an examination of the Test of Premorbid Functioning

Knowledge of intelligence is essential for interpreting cognitive performance following traumatic brain injury (TBI). The Test of Premorbid Functioning (ToPF), a word reading test co-normed with the Wechsler Adult Intelligence Scale 4th Edition (WAIS-IV), was examined as a tool for estimating premorbid intelligence in persons with a history of TBI. Fifty-two participants with mild, moderate, or severe TBI were administered the ToPF and WAIS-IV between two weeks and 19 months post-injury. The independent ability of the ToPF/demographic score and the Verbal Comprehension Index (VCI) to predict WAIS-IV Full Scale IQ (FSIQ) was examined, as were discrepancies between ToPF and WAIS-IV scores within and between participants. The ToPF/demographic predicted FSIQ accounted for a significant proportion of variability in actual FSIQ, above and beyond that accounted for by education or time since injury. ToPF and WAIS-IV scores did not differ by injury severity. In our sample, the ToPF/demographic predicted FSIQ underestimated intelligence in a substantial portion of our participants (31%), particularly in those with high average to superior intelligence. Finally, VCI scores were more predictive of actual FSIQ than the ToPF/demographic predicted FSIQ. The ToPF frequently underestimated post-injury intelligence and is therefore not accurately measuring premorbid intelligence in our sample, particularly in those with above average to superior intelligence. Clinicians are encouraged to administer the entire WAIS-IV, or at minimum the VCI subtests, for a more accurate measure of intelligence in those with above average intelligence and history of TBI.

Attention and Communication Following TBI: Making the Connection through a Meta-Narrative Systematic Review

BACKGROUND AND AIM

Communication difficulties are one of the hallmark characteristics of adults following traumatic brain injury (TBI), a difficulty that incorporates multiple aspects of cognition and language. One aspect of cognition that impacts communication is attention. This review explores both attention and communication following moderate to severe TBI and aims to connect them through a narrative analysis of the discourse surrounding the terms and how they have evolved over time. This includes exploring and reviewing theories and specific constructs of these two aspects of cognition.

METHOD

A meta-narrative systematic literature review was completed according to RAMESES methodology.

RESULTS

A total of 37 articles were included in the review. The disciplines that populated the articles included, but were not limited to, speech language pathology (SLP) 36.5%, psychology 23.8%, and a collaboration of neuropsychology and SLP 7.9%. Of the papers that were included, 10% explored and supported theories of attention related to executive function affecting communication. Specific levels of attention were mapped onto specific communication skills with the corresponding year and authors to create a timeline and narrative of these concepts.

CONCLUSIONS

The main communication behaviours that are related to attention in the context of post-TBI cognition include discourse, tangential communication, social communication, auditory comprehension, verbal reasoning, topic maintenance, interpretation of social cues and emotions, verbal expression, reading comprehension, verbal response speed, and subvocal rehearsal.

A fixel-based analysis of micro- and macro-structural changes to white matter following adult traumatic brain injury

Diffusion tensor imaging is often used to assess white matter (WM) changes following traumatic brain injury (TBI), but is limited in voxels that contain multiple fibre tracts. Fixel-based analysis (FBA) addresses this limitation by using a novel method of analysing high angular resolution diffusion-weighted imaging (HARDI) data. FBA examines three aspects of each fibre tract within a voxel: tissue micro-structure (fibre density [FD]), tissue macro-structure (fibre-bundle cross section [FC]) and a combined measure of both (FD and fibre-bundle cross section [FDC]). This study used FBA to identify the location and extent of micro- and macro-structural changes in WM following TBI. A large TBI sample (Nmild = 133, Nmoderate-severe = 29) and control group (healthy and orthopaedic; N = 107) underwent magnetic resonance imaging with HARDI and completed reaction time tasks approximately 7 months after their injury (range: 98-338 days). The TBI group showed micro-structural differences (lower FD) in the corpus callosum and forceps minor, compared to controls. Subgroup analyses revealed that the mild TBI group did not differ from controls on any fixel metric, but the moderate to severe TBI group had significantly lower FD, FC and FDC in multiple WM tracts, including the corpus callosum, cerebral peduncle, internal and external capsule. The moderate to severe TBI group also had significantly slower reaction times than controls, but the mild TBI group did not. Reaction time was not related to fixel findings. Thus, the WM damage caused by moderate to severe TBI manifested as fewer axons and a reduction in the cross-sectional area of key WM tracts.

Electrophysiological Markers of Visuospatial Attention Recovery after Mild Traumatic Brain Injury

Objective: Attentional problems are amongst the most commonly reported complaints following mild traumatic brain injury (mTBI), including difficulties orienting and disengaging attention, sustaining it over time, and dividing attentional resources across multiple simultaneous demands. The objective of this study was to track, using a single novel electrophysiological task, various components associated with the deployment of visuospatial selective attention. Methods: A paradigm was designed to evoke earlier visual evoked potentials (VEPs), as well as attention-related and visuocognitive ERPs. Data from 36 individuals with mTBI (19 subacute, 17 chronic) and 22 uninjured controls are presented. Postconcussion symptoms (PCS), anxiety (BAI), depression (BDI-II) and visual attention (TEA Map Search, DKEFS Trail Making Test) were also assessed. Results: Earlier VEPs (P1, N1), as well as processes related to visuospatial orientation (N2pc) and encoding in visual short-term memory (SPCN), appear comparable in mTBI and control participants. However, there appears to be a disruption in the spatiotemporal dynamics of attention (N2pc-Ptc, P2) in subacute mTBI, which recovers within six months. This is also reflected in altered neuropsychological performance (information processing speed, attentional shifting). Furthermore, orientation of attention (P3a) and working memory processes (P3b) are also affected and remain as such in the chronic post-mTBI period, in co-occurrence with persisting postconcussion symptomatology. Conclusions: This study adds original findings indicating that such a sensitive and rigorous ERP task implemented at diagnostic and follow-up levels could allow for the identification of subtle but complex brain activation and connectivity deficits that can occur following mTBI.

Language Comprehension After Mild Traumatic Brain Injury: The Role of Speed

Purpose The aim of this study was to characterize language comprehension in mild traumatic brain injury (mTBI) by testing a speed-based hypothesis. We hypothesized that adults with mTBI would perform worse than a group of adults with orthopedic injuries (OIs) on an experimental language comprehension task. Method The study employed a prospective experimental design. Participants were 19 adults with mTBI and 19 adults with OI ages 18-55 years. Participants completed the Whatdunit task, a sentence agent selection task in speeded and unspeeded conditions. Results In the unspeeded condition, the mTBI group performed with a marginally significant higher accuracy than the OI group. In the speeded condition, the mTBI group performed with lower accuracy than the OI group; however, this difference did not reach statistical significance. There was a marginally significant interaction of Sentence Type × Group for reaction time in the speeded condition. Conclusions While our task might have been sensitive to cognitive processing abilities in both groups (as evidenced by the main effects of condition and sentence type), the task was not specific enough to capture mTBI-related deficits. The similarities in performance between both groups have clinical implications for the treatment of not just brain-related trauma but also trauma in general.

The Neuropsychological Syndrome of Agenesis of the Corpus Callosum

BACKGROUND

Agenesis of the corpus callosum (AgCC) involves congenital absence of all or part of the corpus callosum. Because the disorder can only be firmly diagnosed via neuroradiology, it has a short research history, and only recently has the cognitive syndrome become clear.

PURPOSE

Our purpose is to review the primary deficits in AgCC that constitute the core syndrome.

CONCLUSIONS

The cores syndrome includes: (1) reduced interhemispheric transfer of sensory-motor information; (2) reduced cognitive processing speed; and (3) deficits in complex reasoning and novel problem-solving. These domains do not appear to reflect different neuroanatomical abnormalities, but rather different domains of expression of reduced interhemispheric communication from callosal absence.

IMPLICATIONS

These core deficits are expressed across various domains of cognitive, behavioral, and social functioning. The impact of these deficits varies across development and may be moderated by individual factors such as co-occurrence of other neurodevelopmental conditions, general intellectual capacity, and environmental support. (JINS, 2019, 25, 324-330).

Diverging white matter trajectories in children after traumatic brain injury: The RAPBI study

OBJECTIVE

To examine longitudinal trajectories of white matter organization in pediatric moderate/severe traumatic brain injury (msTBI) over a 12-month period.

METHODS

We studied 21 children (16 M/5 F) with msTBI, assessed 2-5 months postinjury and again 13-19 months postinjury, as well as 20 well-matched healthy control children. We assessed corpus callosum function through interhemispheric transfer time (IHTT), measured using event-related potentials, and related this to diffusion-weighted MRI measures of white matter (WM) microstructure. At the first time point, half of the patients with TBI had significantly slower IHTT (TBI-slow-IHTT, n = 11) and half were in the normal range (TBI-normal-IHTT, n = 10).

RESULTS

The TBI-normal-IHTT group did not differ significantly from healthy controls, either in WM organization in the chronic phase or in the longitudinal trajectory of WM organization between the 2 evaluations. In contrast, the WM organization of the TBI-slow-IHTT group was significantly lower than in healthy controls across a large portion of the WM. Longitudinal analyses showed that the TBI-slow-IHTT group experienced a progressive decline between the 2 evaluations in WM organization throughout the brain.

CONCLUSIONS

We present preliminary evidence suggesting a potential biomarker that identifies a subset of patients with impaired callosal organization in the first months postinjury who subsequently experience widespread continuing and progressive degeneration in the first year postinjury.

Measurement of Peripheral Vision Reaction Time Identifies White Matter Disruption in Patients with Mild Traumatic Brain Injury

This study examined whether peripheral vision reaction time (PVRT) in patients with mild traumatic brain injury (mTBI) correlated with white matter abnormalities in centroaxial structures and impairments in neuropsychological testing. Within 24 h after mTBI, crossed reaction times (CRT), uncrossed reaction times (URT), and crossed-uncrossed difference (CUD) were measured in 23 patients using a laptop computer that displayed visual stimuli predominantly to either the left or the right visual field of the retina. The CUD is a surrogate marker of the interhemispheric transfer time (ITT). Within 7 days after the injury, patients received a diffusion tensor-MRI (DTI) scan and a battery of neuropsychological tests. Nine uninjured control subjects received similar testing. Patients 18-50 years of age were included if they had a post-resuscitation Glasgow Coma Scale >13 and an injury mechanism compatible with mTBI. Healthy controls were either age- and gender-matched family members of the TBI patients or healthy volunteers. CUD deficits >2 standard deviations (SD) were seen in 40.9% of patients. The CUD of injured patients correlated with mean diffusivity (MD) (p < 0.001, ρ = -0.811) in the posterior corpus callosum. Patients could be stratified on the basis of CUD on the Stroop 1, Controlled Oral Word Association Test (COWAT), and the obsessive-compulsive component of the Basic Symptom Inventory tests. These studies suggest that the PVRT indirectly measures white matter integrity in the posterior corpus callosum, a brain region frequently damaged by mTBI.

The UCLA Study of Children with Moderate-to-Severe Traumatic Brain Injury: Event-Related Potential Measure of Interhemispheric Transfer Time

Traumatic brain injury (TBI) frequently results in diffuse axonal injury and other white matter damage. The corpus callosum (CC) is particularly vulnerable to injury following TBI. Damage to this white matter tract has been associated with impaired neurocognitive functioning in children with TBI. Event-related potentials can identify stimulus-locked neural activity with high temporal resolution. They were used in this study to measure interhemispheric transfer time (IHTT) as an indicator of CC integrity in 44 children with moderate/severe TBI at 3-5 months post-injury, compared with 39 healthy control children. Neurocognitive performance also was examined in these groups. Nearly half of the children with TBI had IHTTs that were outside the range of the healthy control group children. This subgroup of TBI children with slow IHTT also had significantly poorer neurocognitive functioning than healthy controls-even after correction for premorbid intellectual functioning. We discuss alternative models for the relationship between IHTT and neurocognitive functioning following TBI. Slow IHTT may be a biomarker that identifies children at risk for poor cognitive functioning following moderate/severe TBI.

Callosal Function in Pediatric Traumatic Brain Injury Linked to Disrupted White Matter Integrity

Traumatic brain injury (TBI) often results in traumatic axonal injury and white matter (WM) damage, particularly to the corpus callosum (CC). Damage to the CC can lead to impaired performance on neurocognitive tasks, but there is a high degree of heterogeneity in impairment following TBI. Here we examined the relation between CC microstructure and function in pediatric TBI. We used high angular resolution diffusion-weighted imaging (DWI) to evaluate the structural integrity of the CC in humans following brain injury in a sample of 32 children (23 males and 9 females) with moderate-to-severe TBI (msTBI) at 1-5 months postinjury, compared with well matched healthy control children. We assessed CC function through interhemispheric transfer time (IHTT) as measured using event-related potentials (ERPs), and related this to DWI measures of WM integrity. Finally, the relation between DWI and IHTT results was supported by additional results of neurocognitive performance assessed using a single composite performance scale. Half of the msTBI participants (16 participants) had significantly slower IHTTs than the control group. This slow IHTT group demonstrated lower CC integrity (lower fractional anisotropy and higher mean diffusivity) and poorer neurocognitive functioning than both the control group and the msTBI group with normal IHTTs. Lower fractional anisotropy-a common sign of impaired WM-and slower IHTTs also predicted poor neurocognitive function. This study reveals that there is a subset of pediatric msTBI patients during the post-acute phase of injury who have markedly impaired CC functioning and structural integrity that is associated with poor neurocognitive functioning.

SIGNIFICANCE STATEMENT

Traumatic brain injury (TBI) is the primary cause of death and disability in children and adolescents. There is considerable heterogeneity in postinjury outcome, which is only partially explained by injury severity. Imaging biomarkers may help explain some of this variance, as diffusion weighted imaging is sensitive to the white matter disruption that is common after injury. The corpus callosum (CC) is one of the most commonly reported areas of disruption. In this multimodal study, we discovered a divergence within our pediatric moderate-to-severe TBI sample 1-5 months postinjury. A subset of the TBI sample showed significant impairment in CC function, which is supported by additional results showing deficits in CC structural integrity. This subset also had poorer neurocognitive functioning. Our research sheds light on postinjury heterogeneity.

Psychosocial and Adaptive Deficits Associated With Learning Disability Subtypes

Children with specific learning disabilities (SLD) have deficits in the basic psychological processes that interfere with learning and academic achievement, and for some SLD subtypes, these deficits can also lead to emotional and/or behavior problems. This study examined psychosocial functioning in 123 students, aged 6 to 11, who underwent comprehensive evaluations for learning and/or behavior problems in two Pacific Northwest school districts. Using concordance-discordance model (C-DM) processing strengths and weaknesses SLD identification criteria, results revealed working memory SLD (n = 20), processing speed SLD (n = 30), executive SLD (n = 32), and no disability groups (n = 41). Of the SLD subtypes, repeated measures MANOVA results revealed the processing speed SLD subtype exhibited the greatest psychosocial and adaptive impairment according to teacher behavior ratings. Findings suggest processing speed deficits may be behind the cognitive and psychosocial disturbances found in what has been termed "nonverbal" SLD. Limitations, implications, and future research needs are addressed.

Considerations for return to work following traumatic brain injury

Population-based studies have demonstrated that a history positive for traumatic brain injury (TBI) can result in cognitive impairment, behavioral alterations, and pain. These outcomes can and do influence occupational function, can affect others in the workplace, and raise concerns about workplace safety upon re-entry to the workplace. Risk for long-term impairment and disability can in some cases be mitigated by assessment of capabilities relative to job duties, conservative return-to-work schedules, and, in some cases, interventions to support that return. For those in occupations at high risk for brain injury, including first responders, soldiers, and construction workers, the long-term risk of brain injury as a risk factor for neurodegenerative disease must and should inform increased concern for those with repeated injuries to the brain over the course of their lifetime and career. This chapter reviews the risks of TBI, considers factors that optimize functional recovery, and discusses potential interventions and factors that aid in return to the workplace.

Traumatic brain injury and cognition

Traumatic brain injury (TBI) is a major cause of death and disability, and therefore an important health and socioeconomic problem for our society. Individuals surviving from a moderate to severe TBI frequently suffer from long-lasting cognitive deficits. Such deficits include different aspects of cognition such as memory, attention, executive functions, and awareness of their deficits. This chapter presents a review of the main neuropsychological and neuroimaging studies of patients with TBI. These studies found that patients evolve differently according to the severity of the injury, the mechanism causing the injury, and the lesion location. Further research is necessary to develop rehabilitation methods that enhance brain plasticity and recovery after TBI. In this chapter, we summarize current knowledge and controversies, focusing on cognitive sequelae after TBI. Recommendations from the Common Data Elements are provided, with an emphasis on diagnosis, outcome measures, and studies organization to make data more comparable across studies. Final considerations on neuroimaging advances, rehabilitation approaches, and genetics are described in the final section of the chapter.

Speed of perceptual grouping in acquired brain injury

Evidence exists that damage to white matter connections may contribute to reduced speed of information processing in traumatic brain injury and stroke. Damage to such axonal projections suggests a particular vulnerability to functions requiring integration across cortical sites. To test this prediction, measurements were made of perceptual grouping, which requires integration of stimulus components. A group of traumatic brain injury and cerebral vascular accident patients and a group of age-matched healthy control subjects viewed arrays of dots and indicated the pattern into which stimuli were perceptually grouped. Psychophysical measurements were made of perceptual grouping as well as processing speed. The patient group showed elevated grouping thresholds as well as extended processing time. In addition, most patients showed progressive slowing of processing speed across levels of difficulty, suggesting reduced resources to accommodate increased demands on grouping. These results support the prediction that brain injury results in a particular vulnerability to functions requiring integration of information across the cortex, which may result from dysfunction of long-range axonal connection.

Diffuse traumatic brain injury and the sensory brain

In this review we discuss the consequences to the brain's cortex, specifically to the sensory cortex, of traumatic brain injury. The thesis underlying this approach is that long-term deficits in cognition seen after brain damage in humans are likely underpinned by an impaired cortical processing of the sensory information needed to drive cognition or to be used by cognitive processes to produce a response. We take it here that the impairment to sensory processing does not arise from damage to peripheral sensory systems, but from disordered brain processing of sensory input.

Component analysis of verbal fluency performance in younger participants with moderate-to-severe traumatic brain injury

PRIMARY OBJECTIVE

To investigate phonemic and semantic verbal fluency performance in a group of young adult participants with and without traumatic brain injury.

RESEARCH DESIGN

Group comparison.

METHODS AND PROCEDURES

Twenty-five participants with moderate-to-severe TBI and 25 participants with no brain damage (NBD) were given phonemic and semantic verbal fluency tasks. Responses were analysed quantitatively and qualitatively.

MAIN OUTCOMES AND RESULTS

Young participants with moderate-to-severe TBI generated significantly fewer total correct words and sub-categories for both fluency conditions when compared to controls. The total number of correct words generated on the phonemic condition and for the semantic category of animals was positively correlated with the number of category switches produced during the task.

CONCLUSIONS

While young participants with moderate-to-severe TBI produced fewer total correct words on both verbal fluency conditions in comparison to controls, these differences were greater on the phonemic condition. Participants with moderate-to-severe TBI switched less frequently on both fluency tasks and produced smaller cluster sizes only on the phonemic task in comparison to controls. These results are in contrast with previous investigations that have observed greater age-related declines on semantic tasks when compared to phonemic tasks.

Electroencephalogram coherence in children with and without autism spectrum disorders: decreased interhemispheric connectivity in autism

Electroencephalogram coherence was measured in children with autism spectrum disorders (ASD) and control children at baseline and while watching videos of a familiar and unfamiliar person reading a story. Coherence was measured between the left and right hemispheres of the frontal, parietal, and temporal-parietal lobes (interhemispheric) and between the frontal and parietal lobes in each hemisphere (intrahemispheric). A data-reduction technique was employed to identify the frequency (alpha) that yielded significant differences in video conditions. Children with ASD displayed reduced coherence at the alpha frequency between the left and right temporal-parietal lobes in all conditions and reduced coherence at the alpha frequency between left and right frontal lobes during baseline. No group differences in intrahemispheric coherence at the alpha frequency emerged at the chosen statistical threshold. Results suggest decreased interhemispheric connectivity in frontal and temporal-parietal regions in children with ASD compared to controls.

Corpus callosum integrity and neuropsychological performance after traumatic brain injury: a diffusion tensor imaging study

OBJECTIVES

(1) Detailed analysis of diffusion tensor imaging (DTI) parameters (fractional anisotropy and radial diffusivity) to evaluate white matter integrity in the corpus callosum (CC), and (2) examine correlations between DTI data and performance on multiple measures of cognitive functioning.

PARTICIPANTS

Twelve individuals with a history of complicated mild, moderate, or severe traumatic brain injury (TBI) who were an average of 1.7 years postinjury and 12 control participants.

MAIN MEASURES

Standardized and experimental neuropsychological tests; detailed analysis of DTI parameters.

RESULTS

The TBI group demonstrated DTI values suggesting decreased white matter integrity and correlations with severity of injury. Both groups showed correlations between DTI parameters and cognitive measures, with more significant correlations observed for the TBI group. White matter changes in the CC were evident chronically and were related to severity of injury.

CONCLUSIONS

Diffusion tensor imaging parameters suggesting disruptions in white matter in the CC may be implicated in impaired performance, both in terms of cognitive tasks and reaction time, after TBI.

Improvement of verbal fluency in patients with diffuse brain injury over time

BACKGROUND

Diffuse axonal injury (DAI), a common cause of neurological sequelae in patients with traumatic brain injury (TBI), is considered one of the most prevalent forms of primary neuronal injury in patients with severe TBI. Cognitive deficits induced by DAI can persist over time, especially following moderate or severe injuries. The aim of the present study was to compare verbal fluency (VF) performance at 6 and 12 months after the trauma in a same group of patients with DAI.

METHODS

Eighteen patients with moderate to severe DAI and 17 healthy volunteers were enrolled. All DAI participants had sustained a TBI at least 6 months prior to the start of the study, were between 18 and 50 years of age, and had at least 4 years of education. The VF test was administered within an extensive neuropsychological test battery. We evaluated the same patients at 6 months (DAI1 group) and 12 months (DAI2 group) and compared the results of neuropsychological tests with a control group of healthy volunteers who were matched to patients for sex, age, and educational level.

RESULTS

In comparison to controls, the DAI1 group produced significantly fewer words. The DAI2 group produced significantly more semantic words than DAI1 (P<0.05) and demonstrated a trend towards the production of more clusters for letter A (P=0.09) and total words generated in a phonemic test (P=0.09). No significant differences were observed between DAI2 and the control group in the total number of words generated in phonetic FAS or semantic fluency scores.

CONCLUSION

The present findings may be useful in the construction of a management plan for long-term TBI rehabilitation that considers the trauma of each patient. Further, our results suggest the VF test is a suitable instrument for the assessment of cognitive difficulties following TBI.

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.

Component analysis of verbal fluency scores in severe traumatic brain injury

PRIMARY OBJECTIVE

This study set out to examine the sensitivity of verbal fluency component scores in severe traumatic brain injury (TBI).

RESEARCH DESIGN

A retrospective cross-sectional design was used, with control participants chosen at random from the community and TBI patients from litigation cases.

METHODS AND PROCEDURES

Fifty-four healthy controls and 28 patients who had incurred a severe TBI were included in the study. The Controlled Oral Word Association test was rescored to include clustering and switching scores for phonemic and semantic fluency separately. The scores were compared between controls and TBI patients using independent samples t-tests.

MAIN OUTCOMES AND RESULTS

The findings demonstrate that component scores for semantic fluency yielded the largest effect sizes overall (d = 1.32 and d = 1.53), but not phonemic fluency. Total words generated in phonemic fluency yielded the largest effect size, although still modest (d = 0.62).

CONCLUSIONS

While verbal fluency may be a useful test tool to elicit evidence of neuropsychological impairment after TBI, these findings are consistent with previous research demonstrating that component scores are more sensitive indices. There is potential clinical utility in using component scores for examining the specific severity of verbal fluency impairment in TBI and guiding rehabilitation efforts.

Whole brain approaches for identification of microstructural abnormalities in individual patients: comparison of techniques applied to mild traumatic brain injury

PURPOSE

Group-wise analyses of DTI in mTBI have demonstrated evidence of traumatic axonal injury (TAI), associated with adverse clinical outcomes. Although mTBI is likely to have a unique spatial pattern in each patient, group analyses implicitly assume that location of injury will be the same across patients. The purpose of this study was to optimize and validate a procedure for analysis of DTI images acquired in individual patients, which could detect inter-individual differences and be applied in the clinical setting, where patients must be assessed as individuals.

MATERIALS AND METHODS

After informed consent and in compliance with HIPAA, 34 mTBI patients and 42 normal subjects underwent 3.0 Tesla DTI. Four voxelwise assessment methods (standard Z-score, "one vs. many" t-test, Family-Wise Error Rate control using pseudo t-distribution, EZ-MAP) for use in individual patients, were applied to each patient's fractional anisotropy (FA) maps and tested for its ability to discriminate patients from controls. Receiver Operating Characteristic (ROC) analyses were used to define optimal thresholds (voxel-level significance and spatial extent) for reliable and robust detection of mTBI pathology.

RESULTS

ROC analyses showed EZ-MAP (specificity 71%, sensitivity 71%), "one vs. many" t-test and standard Z-score (sensitivity 65%, specificity 76% for both methods) resulted in a significant area under the curve (AUC) score for discriminating mTBI patients from controls in terms of the total number of abnormal white matter voxels detected while the FWER test was not significant. EZ-MAP is demonstrated to be robust to assumptions of Gaussian behavior and may serve as an alternative to methods that require strict Gaussian assumptions.

CONCLUSION

EZ-MAP provides a robust approach for delineation of regional abnormal anisotropy in individual mTBI patients.

Diffusion tensor imaging studies of mild traumatic brain injury: a meta-analysis

OBJECTIVES

To assess the possibility that diffusion tensor imaging (DTI) can detect white matter damage in mild traumatic brain injury (mTBI) patients via systematic review and meta-analysis.

METHODS

DTI studies that compared mTBI patients and controls were searched using MEDLINE, Web of Science, and EMBASE, (1980 through April 2012).

RESULTS

A comprehensive literature search identified 28 DTI studies, of which 13 independent DTI studies of mTBI patients were eligible for the meta-analysis. Random effect model demonstrated significant fractional anisotropy (FA) reduction in the corpus callosum (CC) (p=0.023, 95% CIs -0.466 to -0.035, 280 mTBIs and 244 controls) with no publication bias and minimum heterogeneity, and a significant increase in mean diffusivity (MD) (p=0.015, 95% CIs 0.062 to 0.581, 154 mTBIs and 100 controls). Meta-analyses of the subregions of the CC demonstrated in the splenium FA was significantly reduced (p=0.025, 95% CIs -0.689 to -0.046) and MD was significantly increased (p=0.013, 95% CIs 0.113 to 0.950). FA was marginally reduced in the midbody (p=0.099, 95% CIs -0.404 to 0.034), and no significant change in FA (p=0.421, 95% CIs -0.537 to 0.224) and MD (p=0.264, 95% CIs -0.120 to 0.438) in the genu of the CC.

CONCLUSIONS

Our meta-analysis revealed the posterior part of the CC was more vulnerable to mTBI compared with the anterior part, and suggested the potential utility of DTI to detect white matter damage in the CC of mTBI patients.

Hemispheric and executive influences on low-level language processing after traumatic brain injury

OBJECTIVE

The purpose of this study was to examine whether minor high-level language deficits found after traumatic brain injury (TBI) might be due to low-level language processing issues or executive control influences. A possible mechanism was also investigated.

METHOD

Nineteen age- and education-matched healthy controls (16 M, 3 F) and 19 persons who had experienced a complicated mild, moderate or severe TBI between 1-3 years prior (16 M, 3 F; mean GCS = 9.44) participated in two computerized behavioural experiments utilizing two paradigms standard in the psycholinguistic literature (priming with lexical decision and verb generation), which included trials of greater and lesser executive demand.

RESULTS

Response time and accuracy differences were found in both experiments, indicating deficits in single-word processing for the patient group. Disproportionate difficulty was found for trials which included an executive component. Right visual field (left hemisphere) preferences were found to be stronger in the TBI group than in controls.

CONCLUSIONS

Results suggest that persons with TBI may have difficulties in processing single words alone, especially under conditions of increased executive demand, and that atypical patterns of hemispheric recruitment may be associated with these difficulties.

Component analysis of verbal fluency in patients with mild traumatic brain injury

We set out to examine the sensitivity of switching and clustering component scores of verbal fluency in patients with mild traumatic brain injury (mTBI). Clustering and switching scores were compared between patients with mTBI and healthy normal controls as well as those with moderate TBI and severe TBI. Fifty-four healthy controls along with 20 mild TBI, 8 moderate TBI, and 12 severe TBI patients were included in the study. Our findings demonstrate that component score effect sizes were larger than those of total words generated for both phonemic and semantic fluency. This pattern of finding held true regardless of comparison group. In addition, semantic fluency component scores were found to correspond to larger component score effect sizes than did phonemic fluency component scores. Our findings demonstrate that component scores derived from the Controlled Oral Word Association Test may be sufficient to reliably capture the effects of unremitting injury (i.e., more than 3 months post status) to the frontal and temporal brain as evinced in cases of unremitting mTBI. This differential pattern of performance provides preliminary evidence for the potential usefulness of switching and clustering in the assessment of mTBI. Given the small sample sizes employed in our study, however, future studies are needed to determine whether component measures of verbal fluency have discriminative ability.

Is performance on the Wechsler test of adult reading affected by traumatic brain injury?

OBJECTIVES

The validity of the National Adult Reading Test (NART) as a predictor of premorbid IQ when used with patients who have sustained a traumatic brain injury (TBI) has been questioned in recent years. This study examined whether performance on the Wechsler Test of Adult Reading (WTAR) is similarly affected by TBI in the first year after an injury.

DESIGN AND METHOD

The WTAR scores of participants who had sustained a mild TBI (N=82), moderate TBI (N=73), severe TBI (N=61) or an orthopaedic injury (N=95) were compared (cross-sectional study). A subset of 21 mild TBI, 31 moderate TBI, 26 severe TBI and 21 control group participants were additionally reassessed 6 months later to assess the impact of recovery on WTAR scores (longitudinal study).

RESULTS

The severe TBI group had significantly lower scores on the WTAR than the mild TBI, moderate TBI and control groups in the cross-sectional study, despite being matched demographically. The findings from the longitudinal study revealed a significant group difference and a small improvement in performance over time but the interaction between group and time was not significant, suggesting that the improvements in WTAR performance over time were not restricted to more severely injured individuals whose performance was temporarily suppressed.

CONCLUSIONS

These findings suggest that reading performance may be affected by severe TBI and that the WTAR may underestimate premorbid IQ when used in this context, which may cause clinicians to underestimate the cognitive deficits experienced by these patients.

Blast-induced mild traumatic brain injury

Traumatic brain injury (TBI) has been a major cause of mortality and morbidity in the wars in Iraq and Afghanistan. Blast exposure has been the most common cause of TBI, occurring through multiple mechanisms. What is less clear is whether the primary blast wave causes brain damage through mechanisms that are distinct from those common in civilian TBI and whether multiple exposures to low-level blast can lead to long-term sequelae. Complicating TBI in soldiers is the high prevalence of posttraumatic stress disorder. At present, the relationship is unclear. Resolution of these issues will affect both treatment strategies and strategies for the protection of troops in the field.

Brain-behavior relationships in young traumatic brain injury patients: DTI metrics are highly correlated with postural control

Traumatic brain injury (TBI) is a major cause of impairment and functional disability in children and adolescents, including deterioration in fine as well as gross motor skills. The aim of this study was to assess deficits in sensory organization and postural ability in a young group of TBI patients versus controls by using quantitative force-platform recordings, and to test whether balance deficits are related to variation in structural properties of the motor and sensory white matter pathways. Twelve patients with TBI and 14 controls (aged 8-20 years) performed the Sensory Organisation Test (SOT) protocol of the EquiTest (Neurocom). All participants were scanned using Diffusion Tensor Imaging (DTI) along with standard anatomical scans. Quantitative comparisons of DTI parameters (fractional anisotropy, axial and radial diffusivity) between TBI patients and controls were performed. Correlations between DTI parameters and SOT balance scores were determined. Findings revealed that the TBI group scored generally lower than the control group on the SOT, indicative of deficits in postural control. In the TBI group, reductions in fractional anisotropy were noted in the cerebellum, posterior thalamic radiation, and corticospinal tract. Degree of white matter deterioration was highly correlated with balance deficits. This study supports the view that DTI is a valuable tool for assessing the integrity of white matter structures and for selectively predicting functional motor deficits in TBI patients.

Sick leave after traumatic brain injury. The person or the diagnosis--which has greater impact?

PURPOSE

The aim of this study was to describe if and when a sample of traumatic brain injury (TBI) patients could finish their time of sick leave during a 4-year follow up and to explore which factors that influenced the time for sick leave.

MATERIALS AND METHODS

All persons, 1999-2002, between 18 and 64 years of age (250 in total), admitted to the emergency room and diagnosed according to ICD 10 as S062 and S063, were included. Demographic data were gathered from medical charts and data concerning sick leave 1 year before trauma and 4 years after trauma, were collected from the Swedish social insurance system. To explore predictors of sick leave, two logistic regressions were performed.

RESULTS

The sample (mean age 39.68) consisted of 78% men. More than half of the accidents were due to fall. In the sample, 28 % was on sick leave on the day of trauma and 96 % of these were still on sick leave 4 years after trauma, compared with 39 % in the group not on sick leave on the day of TBI. Sick leave at the day for trauma was found to be a predictor for sick leave 4 years after trauma for the whole group (p = 0.000) together with Glasgow Coma Scale (GCS) (p = 0.002) and length of stay (p = 0.049). In the logistic regression with only the group not on sick leave, the only significant variable was GCS (p = 0.003).

CONCLUSION

The findings support the necessity to consider premorbid and social factors in the TBI rehabilitation.

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.

Validation of the Behavioral Dyscontrol Scale-Electronic Version: Sensitivity to subtle sequelae of mild traumatic brain injury

PRIMARY OBJECTIVE

To determine whether a new computer-administered battery (Behavioral Dyscontrol Scale-Electronic Version; BDS-EV) can detect subtle executive weaknesses among individuals with a self-reported history of mild head trauma (MHT), and to compare the utility of this battery to the original, non-electronic BDS and other traditional executive measures. Both BDS-EV and BDS are comprised of three factors (motor programming, environmental independence, and fluid intelligence).

METHOD

Participants with (n = 19) and without (n = 24) MHT were compared on their performance on the BDS-EV, the non-electronic BDS, and three traditional measures of executive abilities.

RESULTS

Participants with MHT differed from those without MHT on the BDS-EV motor programming and environmental independence, but not on any other measures.

CONCLUSION

The results show that electronic administration improved the sensitivity of the battery, and support prior findings that traditional executive measures are generally insensitive to subtle executive deficits associated with chronic MHT.

Long-term cognitive outcome in moderate to severe traumatic brain injury: a meta-analysis examining timed and untimed tests at 1 and 4.5 or more years after injury

OBJECTIVES

To examine long-term outcome of moderate to severe traumatic brain injury (TBI) on timed and untimed cognitive tests using meta-analysis.

DESIGN

Meta-analysis examining outcome at 2 epochs, 6 to 18 months postinjury (epoch 1) and 4.5 to 11 years postinjury (epoch 2).

SETTING

Data source was published articles (1966-2007) identified through electronic and manual search.

PARTICIPANTS

A total of 1380 subjects with moderate to severe TBI participated in the 16 studies meeting inclusion criteria.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Timed and untimed neuropsychologic tests with quantitative results (means, SDs, t, and df tests) from studies containing a healthy comparison group and a mean time since injury falling within 1 of the 2 epochs.

RESULTS

Patient versus control weighted effect sizes were medium to large at epoch 1 for both untimed tasks (r=-.46; confidence interval [CI], -.32 to -.65) and timed tasks (r=-.46; CI, -.35 to -.59). At epoch 2, effect sizes were slightly smaller for untimed tasks (r=-.38; CI, -.25 to -.60) and timed tasks (r=-.40; CI, -.32 to -.62).

CONCLUSIONS

Patients showed robust, persisting impairments on both timed and untimed tests at recovery plateau (ie, 6-18mo postinjury) and many years later. These findings converge with previous studies, though using an alternative approach that obviates some of the methodologic problems of longitudinal studies, such as selective attrition.

White matter and neurocognitive changes in adults with chronic traumatic brain injury

Diffusion tensor imaging was used to investigate white matter (WM) integrity in adults with traumatic brain injury (TBI) and healthy adults as controls. Adults with TBI had sustained severe vehicular injuries on the average of 7 years earlier. A multivariate analysis of covariance with verbal IQ as the covariate revealed that adults with TBI had lower fractional anisotropy and higher mean diffusivity than controls, specifically in the three regions of interest (ROIs), the centrum semiovale (CS), the superior frontal (SPF), and the inferior frontal (INF). Adults with TBI averaged in the normal range in motor speed and two of three executive functions and were below average in delayed verbal recall and inhibition, whereas controls were above average. Time since injury, but not age, was associated with WM changes in the SPF ROI, whereas age, but not time since injury, was associated with WM changes in the INF ROI, suggesting that the effects of WM on time since injury may interact with age. To understand the utility of WM changes in chronic recovery, larger sample sizes are needed to investigate associations between cognition and WM integrity of severely injured individuals who have substantial cognitive impairment compared to severely injured individuals with little cognitive impairment. (JINS, 2009, 15, 130-136.).

Relationship between intelligence and the size and composition of the corpus callosum

We investigated the relationship between the morphology of the corpus callosum (CC) and IQ in a healthy sample of individuals in their late teens and early twenties. The relationship between the area of the CC, measured at the midline, and IQ showed regional differences. We observed that a higher estimated performance IQ was associated with smaller area in the posterior regions of the CC, a finding that differs from a positive association previously observed in a somewhat older adult sample. In contrast, higher estimated verbal IQ was associated with decreased fractional anisotropy of the genu, an anterior portion of the CC. Age effects were also observed such that older age was associated with larger CC area. Our results suggest that CC morphology is related to cognitive performance, which may have implications for clinical populations in whom CC morphology is atypical.

Processing speed deficits associated with traumatic brain injury: processing inefficiency or cautiousness?

This study used speed-accuracy trade-off (SAT) methodology to test competing explanations for processing speed deficits due to traumatic brain injury (TBI): fixed limited capacity and volition. Twenty TBI participants and 20 comparison participants performed a visual scanning task with processing times controlled by the experimenter using a response deadline procedure. Results of the study demonstrated marked differences in SAT functions between the two groups. Participants who had TBIs were significantly slower on information accrual across processing deadlines (supporting a fixed limit explanation), but when early responding was allowed they chose to hold off responding despite being no more accurate in their responses with the additional time (a finding supporting a volitional explanation). Results of the study are discussed in terms of a resource allocation model that incorporates the influences of both processing capacity and volitional processes for individuals who suffer from brain injuries.

Neuropsychology and clinical neuroscience of persistent post-concussive syndrome

On the mild end of the acquired brain injury spectrum, the terms concussion and mild traumatic brain injury (mTBI) have been used interchangeably, where persistent post-concussive syndrome (PPCS) has been a label given when symptoms persist for more than three months post-concussion. Whereas a brief history of concussion research is overviewed, the focus of this review is on the current status of PPCS as a clinical entity from the perspective of recent advances in the biomechanical modeling of concussion in human and animal studies, particularly directed at a better understanding of the neuropathology associated with concussion. These studies implicate common regions of injury, including the upper brainstem, base of the frontal lobe, hypothalamic-pituitary axis, medial temporal lobe, fornix, and corpus callosum. Limitations of current neuropsychological techniques for the clinical assessment of memory and executive function are explored and recommendations for improved research designs offered, that may enhance the study of long-term neuropsychological sequelae of concussion.

Executive function outcomes following traumatic brain injury in young children: a five year follow-up

Little is known about the long-term effects of traumatic brain injury (TBI) in very young children. This study used a prospective, cross-sectional design to investigate the impact of TBI on executive function (EF) outcomes in children who sustained a TBI before the age of seven. The study aimed to identify specific or global EF deficits five years post-TBI, and to explore factors that predicted outcomes. Fifty-four children with a TBI and 17 uninjured comparison children participated. Their performance on several cognitive and behavioral EF measures was examined. Results suggested that executive difficulties were present following severe TBI, however children with mild and moderate injuries were relatively unaffected. Skills that develop early appeared to be relatively robust. Injury severity was found to be most predictive of long-term EF, however other injury, child and family-related variables also contributed to outcomes.

The Effects of Increasing Stimulus Complexity in Event-Related Potentials and Reaction Time Testing: Clinical Applications in Evaluating Patients with Traumatic Brain Injury

This study compared the effectiveness of P300 event related potentials (ERPs) and reaction time (RT) in discriminating patients with traumatic brain injury (TBI) from healthy control subjects. In particular, we examined how the use of more complex, ecologically relevant stimuli may affect the clinical utility of these tasks. We also evaluated how length of posttraumatic amnesia (PTA) and loss of consciousness (LOC) related to P300 and RT measures in our patient sample. There were 22 subjects (11 patients with TBI and 11 age-matched healthy control subjects). Four stimulus detection procedures were used: two using simple, conventional stimuli (auditory tone discrimination, AT; visual color discrimination, VC), and two using complex, ecologically relevant stimuli in the auditory and visual modalities (auditory word category discrimination, AWC; visual facial affect discrimination, VFA). Our results showed that RT measures were more effective in identifying TBI patients when complex stimuli were used (AWC and VFA). On the other hand, ERP measures were more effective in identifying TBI patients when simple stimuli were used (AT and VC). We also found a remarkably high correlation between duration of PTA and P300 amplitude.

Protein S-100 and neuropsychological functioning following severe traumatic brain injury

PRIMARY OBJECTIVE

To examine the relationship between serum concentrations of protein S-100beta and neuropsychological functioning following severe traumatic brain injury.

DESIGN

Matched control group.

METHODS

Blood samples were taken within 12 hours of injury and then daily up to 7 days post-injury (n=23). Within 2 weeks of emerging from post-traumatic amnesia (PTA), participants completed a battery of neuropsychological measures. These results were compared with a matched sample of healthy controls.

RESULTS

Early measurement of S-100 not only reflected overall brain injury severity, but also related to neuropsychological deficits, with higher serum concentrations associated with poorer performance across most cognitive domains. PTA duration, measured by the Westmead PTA Scale, was found to be the strongest predictor of S-100 concentration (R2=0.59, p<0.001).

CONCLUSIONS

These findings show that measurement of serum protein S-100 may further aid in the identification of individuals with severe TBI who are likely to experience cognitive difficulties.