The predictive brain state: timing deficiency in traumatic brain injury?

The Predictive Role of the Posterior Cerebellum in the Processing of Dynamic Emotions

Recent studies have bolstered the important role of the cerebellum in high-level socio-affective functions. In particular, neuroscientific evidence shows that the posterior cerebellum is involved in social cognition and emotion processing, presumably through its involvement in temporal processing and in predicting the outcomes of social sequences. We used cerebellar transcranial random noise stimulation (ctRNS) targeting the posterior cerebellum to affect the performance of 32 healthy participants during an emotion discrimination task, including both static and dynamic facial expressions (i.e., transitioning from a static neutral image to a happy/sad emotion). ctRNS, compared to the sham condition, significantly reduced the participants' accuracy to discriminate static sad facial expressions, but it increased participants' accuracy to discriminate dynamic sad facial expressions. No effects emerged with happy faces. These findings may suggest the existence of two different circuits in the posterior cerebellum for the processing of negative emotional stimuli: a first-time-independent mechanism which can be selectively disrupted by ctRNS, and a second time-dependent mechanism of predictive "sequence detection" which can be selectively enhanced by ctRNS. This latter mechanism might be included among the cerebellar operational models constantly engaged in the rapid adjustment of social predictions based on dynamic behavioral information inherent to others' actions. We speculate that it might be one of the basic principles underlying the understanding of other individuals' social and emotional behaviors during interactions.

Emotional Resilience Predicts Preserved White Matter Microstructure Following Mild Traumatic Brain Injury

BACKGROUND

Adult patients with mild traumatic brain injury (mTBI) exhibit distinct phenotypes of emotional and cognitive functioning identified by latent profile analysis of clinical neuropsychological assessments. When discerned early after injury, these latent clinical profiles have been found to improve prediction of long-term outcomes from mTBI. The present study hypothesized that white matter (WM) microstructure is better preserved in an emotionally resilient mTBI phenotype compared with a neuropsychiatrically distressed mTBI phenotype.

METHODS

The present study used diffusion magnetic resonance imaging to investigate and compare WM microstructure in major association, projection, and commissural tracts between the two phenotypes and over time. Diffusion magnetic resonance images from 172 patients with mTBI were analyzed to compute individual diffusion tensor imaging maps at 2 weeks and 6 months after injury.

RESULTS

By comparing the diffusion tensor imaging parameters between the two phenotypes at global, regional, and voxel levels, emotionally resilient patients were shown to have higher axial diffusivity compared with neuropsychiatrically distressed patients early after mTBI. Longitudinal analysis revealed greater compromise of WM microstructure in neuropsychiatrically distressed patients, with greater decrease of global axial diffusivity and more widespread decrease of regional axial diffusivity during the first 6 months after injury compared with emotionally resilient patients.

CONCLUSIONS

These results provide neuroimaging evidence of WM microstructural differences underpinning mTBI phenotypes identified from neuropsychological assessments and show differing longitudinal trajectories of these biological effects. These findings suggest that diffusion magnetic resonance imaging can provide short- and long-term imaging biomarkers of resilience.

Case report: Neural timing deficits prevalent in developmental disorders, aging, and concussions remediated rapidly by movement discrimination exercises

Background

The substantial evidence that neural timing deficits are prevalent in developmental disorders, aging, and concussions resulting from a Traumatic Brain Injury (TBI) is presented.

Objective

When these timing deficits are remediated using low-level movement-discrimination training, then high-level cognitive skills, including reading, attention, processing speed, problem solving, and working memory improve rapidly and effectively.

Methods

In addition to the substantial evidence published previously, new evidence based on a neural correlate, MagnetoEncephalography physiological recordings, on an adult dyslexic, and neuropsychological tests on this dyslexic subject and an older adult were measured before and after 8-weeks of contrast sensitivity-based left-right movement-discrimination exercises were completed.

Results

The neuropsychological tests found large improvements in reading, selective and sustained attention, processing speed, working memory, and problem-solving skills, never before found after such a short period of training. Moreover, these improvements were found 4 years later for older adult. Substantial MEG signal increases in visual Motion, Attention, and Memory/Executive Control Networks were observed following training on contrast sensitivity-based left-right movement-discrimination. Improving the function of magnocells using figure/ground movement-discrimination at both low and high levels in dorsal stream: (1) improved both feedforward and feedback pathways to modulate attention by enhancing coupled theta/gamma and alpha/gamma oscillations, (2) is adaptive, and (3) incorporated cycles of feedback and reward at multiple levels.

Conclusion

What emerges from multiple studies is the essential role of timing deficits in the dorsal stream that are prevalent in developmental disorders like dyslexia, in aging, and following a TBI. Training visual dorsal stream function at low levels significantly improved high-level cognitive functions, including processing speed, selective and sustained attention, both auditory and visual working memory, problem solving, and reading fluency. A paradigm shift for treating cognitive impairments in developmental disorders, aging, and concussions is crucial. Remediating the neural timing deficits of low-level dorsal pathways, thereby improving both feedforward and feedback pathways, before cognitive exercises to improve specific cognitive skills provides the most rapid and effective methods to improve cognitive skills. Moreover, this adaptive training with substantial feedback shows cognitive transfer to tasks not trained on, significantly improving a person's quality of life rapidly and effectively.

Cognitive control subprocess deficits and compensatory modulation mechanisms in patients with frontal lobe injury revealed by EEG markers: a basic study to guide brain stimulation

Background

Frontal lobe injury (FLI) is related to cognitive control impairments, but the influences of FLI on the internal subprocesses of cognitive control remain unclear.

Aims

We sought to identify specific biomarkers for long-term dysfunction or compensatory modulation in different cognitive control subprocesses.

Methods

A retrospective case-control study was conducted. Event-related potentials (ERP), oscillations and functional connectivity were used to analyse electroencephalography (EEG) data from 12 patients with unilateral frontal lobe injury (UFLI), 12 patients with bilateral frontal lobe injury (BFLI) and 26 healthy controls (HCs) during a Go/NoGo task, which included several subprocesses: perceptual processing, anticipatory preparation, conflict monitoring and response decision.

Results

Compared with the HC group, N2 (the second negative peak in the averaged ERP waveform) latency, and frontal and parietal oscillations were decreased only in the BFLI group, whereas P3 (the third positive peak in the averaged ERP waveform) amplitudes and sensorimotor oscillations were decreased in both patient groups. The functional connectivity of the four subprocesses was as follows: alpha connections of posterior networks in the BFLI group were lower than in the HC and UFLI groups, and these alpha connections were negatively correlated with neuropsychological tests. Theta connections of the dorsal frontoparietal network in the bilateral hemispheres of the BFLI group were lower than in the HC and UFLI groups, and these connections in the uninjured hemisphere of the UFLI group were higher than in the HC group, which were negatively correlated with behavioural performances. Delta and theta connections of the midfrontal-related networks in the BFLI group were lower than in the HC group. Theta across-network connections in the HC group were higher than in the BFLI group but lower than in the UFLI group.

Conclusions

The enhancement of low-frequency connections reflects compensatory mechanisms. In contrast, alpha connections are the opposite, therefore revealing more abnormal neural activity and less compensatory connectivity as the severity of injury increases. The nodes of the above networks may serve as stimulating targets for early treatment to restore corresponding functions. EEG biomarkers can measure neuromodulation effects in heterogeneous patients.

Multisensory integration and white matter pathology: Contributions to cognitive dysfunction

The ability to simultaneously process and integrate multiple sensory stimuli is paramount to effective daily function and essential for normal cognition. Multisensory management depends critically on the interplay between bottom-up and top-down processing of sensory information, with white matter (WM) tracts acting as the conduit between cortical and subcortical gray matter (GM) regions. White matter tracts and GM structures operate in concert to manage both multisensory signals and cognition. Altered sensory processing leads to difficulties in reweighting and modulating multisensory input during various routine environmental challenges, and thus contributes to cognitive dysfunction. To examine the specific role of WM in altered sensory processing and cognitive dysfunction, this review focuses on two neurologic disorders with diffuse WM pathology, multiple sclerosis and mild traumatic brain injury, in which persistently altered sensory processing and cognitive impairment are common. In these disorders, cognitive dysfunction in association with altered sensory processing may develop initially from slowed signaling in WM tracts and, in some cases, GM pathology secondary to WM disruption, but also because of interference with cognitive function by the added burden of managing concurrent multimodal primary sensory signals. These insights promise to inform research in the neuroimaging, clinical assessment, and treatment of WM disorders, and the investigation of WM-behavior relationships.

Measuring subjective clustering of verbal information after moderate-severe traumatic brain injury: a preliminary study

BACKGROUND

There is no agreed upon measure of subjective clustering for clinical use in patients following moderate-severe traumatic brain injury (TBI).

OBJECTIVE

This study investigated whether measures of subjective clustering, subjective organization (SO) and adjusted ratio of clustering (ARC), were appropriate for use in patients following moderate-severe TBI.

METHODS

Twenty participants with moderate-severe TBI in the chronic stage of recovery and 20 control participants recalled a list of unrelated words over six trials. The authors assessed if the SO and ARC measures could discriminate the groups' ability to subjectively cluster the words. The authors also examined whether the SO and ARC measures correlated with recall and learning rate, and if combining the measures improved the predictive accuracy.

RESULTS

Participants with moderate-severe TBI performed significantly worse on the SO measure, but there were no group differences regarding the ARC measure. The SO measure positively correlated with recall, but not learning rate. The ARC measure did not positively correlate with recall or learning rate, and combining the measures did not enhance the predictive accuracy.

CONCLUSIONS

The SO measure is likely an appropriate candidate for clinical use. However, there are problems with the ARC measure that limit its use as a clinical tool.

Dysfunctional Timing in Traumatic Brain Injury Patients: Co-occurrence of Cognitive, Motor, and Perceptual Deficits

Timing is an essential part of human cognition and of everyday life activities, such as walking or holding a conversation. Previous studies showed that traumatic brain injury (TBI) often affects cognitive functions such as processing speed and time-sensitive abilities, causing long-term sequelae as well as daily impairments. However, the existing evidence on timing capacities in TBI is mostly limited to perception and the processing of isolated intervals. It is therefore open whether the observed deficits extend to motor timing and to continuous dynamic tasks that more closely match daily life activities. The current study set out to answer these questions by assessing audio motor timing abilities and their relationship with cognitive functioning in a group of TBI patients (n = 15) and healthy matched controls. We employed a comprehensive set of tasks aiming at testing timing abilities across perception and production and from single intervals to continuous auditory sequences. In line with previous research, we report functional impairments in TBI patients concerning cognitive processing speed and perceptual timing. Critically, these deficits extended to motor timing: The ability to adjust to tempo changes in an auditory pacing sequence was impaired in TBI patients, and this motor timing deficit covaried with measures of processing speed. These findings confirm previous evidence on perceptual and cognitive timing deficits resulting from TBI and provide first evidence for comparable deficits in motor behavior. This suggests basic co-occurring perceptual and motor timing impairments that may factor into a wide range of daily activities. Our results thus place TBI into the wider range of pathologies with well-documented timing deficits (such as Parkinson’s disease) and encourage the search for novel timing-based therapeutic interventions (e.g., employing dynamic and/or musical stimuli) with high transfer potential to everyday life activities.

Classification of Comprehensive Neuro-Ophthalmologic Measures of Postacute Concussion

IMPORTANCE

Symptom-based methods of concussion diagnosis in contact sports result in underdiagnosis and repeated head injury exposure, increasing the risk of long-term disability. Measures of neuro-ophthalmologic (NO) function have the potential to serve as objective aids, but their diagnostic utility is unknown.

OBJECTIVE

To identify NO measures that accurately differentiate athletes with and without concussion.

DESIGN, SETTING, AND PARTICIPANTS

This cohort study was conducted among athletes with and without concussion who were aged 17 to 22 years between 2016 and 2017. Eye movements and cognitive function were measured a median of 19 days after injury among patients who had an injury meeting the study definition of concussion while playing a sport (retrospectively selected from a concussion clinic), then compared with a control group of participants without concussion (enrolled from 104 noncontact collegiate athlete volunteers without prior head injury). Data analysis was conducted from November 2019 through May 2020.

EXPOSURE

Concussion.

MAIN OUTCOMES AND MEASURES

Classification accuracy of clinically important discriminator eye-tracking (ET) metrics. Participants' eye movements were evaluated with a 12-minute ET procedure, yielding 42 metrics related to smooth pursuit eye movement (SPEM), saccades, dynamic visual acuity, and reaction time. Clinically important discriminator metrics were defined as those with significantly different group differences and area under the receiver operator characteristic curves (AUROCs) of at least 0.70.

RESULTS

A total of 34 participants with concussions (mean [SD] age, 19.7 [2.4] years; 20 [63%] men) and 54 participants without concussions (mean [SD] age, 20.8 [2.2] years; 31 [57%] men) completed the study. Six ET metrics (ie, simple reaction time, discriminate reaction time, discriminate visual reaction speed, choice visual reaction speed, and reaction time on 2 measures of dynamic visual acuity 2) were found to be clinically important; all were measures of reaction time, and none were related to SPEM. Combined, these 6 metrics had an AUROC of 0.90 (95% CI, 0.80-0.99), a sensitivity of 77.8%, and a specificity of 92.6%. The 6 metrics remained significant on sensitivity testing.

CONCLUSIONS AND RELEVANCE

In this study, ET measures of slowed visual reaction time had high classification accuracy for concussion. Accurate, objective measures of NO function have the potential to improve concussion recognition and reduce the disability associated with underdiagnosis.

Practice modality of motor sequences impacts the neural signature of motor imagery

Motor imagery is conceptualized as an internal simulation that uses motor-related parts of the brain as its substrate. Many studies have investigated this sharing of common neural resources between the two modalities of motor imagery and motor execution. They have shown overlapping but not identical activation patterns that thereby result in a modality-specific neural signature. However, it is not clear how far this neural signature depends on whether the imagined action has previously been practiced physically or only imagined. The present study aims to disentangle whether the neural imprint of an imagined manual pointing sequence within cortical and subcortical motor areas is determined by the nature of this prior practice modality. Each participant practiced two sequences physically, practiced two other sequences mentally, and did a behavioural pre-test without any further practice on a third pair of sequences. After a two-week practice intervention, participants underwent fMRI scans while imagining all six sequences. Behavioural data demonstrated practice-related effects as well as very good compliance with instructions. Functional MRI data confirmed the previously known motor imagery network. Crucially, we found that mental and physical practice left a modality-specific footprint during mental motor imagery. In particular, activation within the right posterior cerebellum was stronger when the imagined sequence had previously been practiced physically. We conclude that cerebellar activity is shaped specifically by the nature of the prior practice modality.

Increased myoinositol in the anterior cingulate cortex of veterans with a history of traumatic brain injury: a proton magnetic resonance spectroscopy study

In this study of veterans, we used a state-of-the-art neuroimaging tool to probe the neurometabolic profile of the anterior cingulate cortex in veterans with traumatic brain injury (TBI). We report significantly elevated myoinositol levels in veterans with TBI compared with those without TBI.

Clinical validation of an optimized multimodal neurocognitive assessment of chronic mild TBI

OBJECTIVE

Previous laboratory-based studies have shown that neurocognitive eye-tracking metrics are sensitive to chronic effects of mild traumatic brain injury (mTBI), even in individuals with normal performance on traditional neuropsychological measures. In this study, we sought to replicate and extend these findings in a military medical environment. We expected that metrics from the multimodal Fusion n-Back test would successfully distinguish chronic mTBI participants from controls, particularly eye movement metrics from the more cognitively challenging "1-Back" subtest.

METHODS

We compared performance of participants with chronic mTBI (n = 46) and controls (n = 33) on the Fusion n-Back test and a battery of conventional neuropsychological tests. Additionally, we examined test reliability and the impact of potential confounds to neurocognitive assessment.

RESULTS

Our results supported hypotheses; Fusion 1-Back metrics were successful in multimodal (saccadic and manual) classification of chronic mTBI versus control. In contrast, conventional neuropsychological measures could not distinguish these groups. Additional findings demonstrated the reliability of Fusion n-Back test metrics and provided evidence that saccadic metrics are resistant to confounding influences of age, intelligence, and psychiatric symptoms.

INTERPRETATION

The Fusion n-Back test could provide advantages in differential diagnosis for complex brain injury populations. Additionally, the rapid administration of this test could be valuable for screening patients in clinical settings where longer test batteries are not feasible.

Disrupted White Matter Microstructure of the Cerebellar Peduncles in Scholastic Athletes After Concussion

Concussion, or mild traumatic brain injury (mTBI), is a major public health concern, linked with persistent post-concussive syndrome, and chronic traumatic encephalopathy. At present, standard clinical imaging fails to reliably detect traumatic axonal injury associated with concussion and post-concussive symptoms. Diffusion tensor imaging (DTI) is an MR imaging technique that is sensitive to changes in white matter microstructure. Prior studies using DTI did not jointly investigate white matter microstructure in athletes, a population at high risk for concussive and subconcussive head traumas, with those in typical emergency room (ER) patients. In this study, we determine DTI scalar metrics in both ER patients and scholastic athletes who suffered concussions and compared them to those in age-matched healthy controls. In the early subacute post-concussion period, athletes demonstrated an elevated rate of regional decreases in axial diffusivity (AD) compared to controls. These regional decreases of AD were especially pronounced in the cerebellar peduncles, and were more frequent in athletes compared to the ER patient sample. The group differences may indicate differences in the mechanisms of the concussive impacts as well as possible compound effects of cumulative subconcussive impacts in athletes. The prevalence of white matter abnormality in cerebellar tracts lends credence to the hypothesis that post-concussive symptoms are caused by shearing of axons within an attention network mediated by the cerebellum, and warrant further study of the correlation between cerebellar DTI findings and clinical, neurocognitive, oculomotor, and vestibular outcomes in mTBI patients.

Evaluation of extent and pattern of neurocognitive functions in mild and moderate traumatic brain injury patients by using Montreal Cognitive Assessment (MoCA) score as a screening tool: An observational study from India

INTRODUCTION

Cognitive impairment is one of the most important culprit influencing the long-term neurological outcome commonlyobserved in TBI survivors.

AIMS

To examine the performance of patients with Mild and Moderate traumatic brain injury (TBI) on the Montreal Cognitive Assessment (MoCA) using as a screening tool.

RESULTS

Total 228 (127 Mild TBI & 101 Moderate TBI) patients were recruited in this study. Results showed that patients with moderate TBI had lower score on the MoCA as compared to patients with mild TBI (p Value = 0.031). This difference was observed statistically significant among mild and moderate TBI for the cube copy (p = 0.039) and clock (p = 0.017) i.e. visuospatial/executive function, Digit span test (p value = 0.040) i.e. concentration and recall memory (p = 0.04). MoCA Score were higher for patients with higher GCS score at admission. Education status was also correlated with MoCA scores; those patients with higher level of education had significant association with higher MoCA scores (p value = 0.012). This study showed that age and gender were insignificant variables to determine cognitive function.

CONCLUSION

Assessment of cognitive impairment should be considered as a mandatory protocol while evaluating post TBI patients, even in cases of mild TBI. Visuospatial/Executive function, memory and attention are the most commonly impaired cognitive functions in patients of TBI, and these are the main domain of cognition which differentiates mild impairment from moderate impairment. This information enables us and provides insight to our experience to predict the burdens of problem and plan to develop post TBI dedicated rehabilitating programme.

Dynamic cognitive remediation for a Traumatic Brain Injury (TBI) significantly improves attention, working memory, processing speed, and reading fluency

BACKGROUND

In the U.S. 3.8 million people have a Traumatic Brain Injury (TBI) each year. Rapid brain training exercises to improve cognitive function after a mild TBI are needed.

OBJECTIVE

This study determines whether cognitive remediation by discriminating the direction a test pattern moves relative to a stationary background (movement figure-ground discrimination) improves the vision and cognitive deficits that result from a TBI, providing a paradigm shift in treatment methods.

METHODS

Movement-discrimination neurotraining was used to remediate low-level visual timing deficits in the dorsal stream to determine whether it improved high-level cognitive functions, such as processing speed, reading fluency, and the executive control functions of attention and working memory in four men with a TBI between the ages of 15-68. Standardized tests, as well as Magnetoencephalography (MEG) brain imaging, were administered at the beginning and end of 8-16 weeks of intervention training to evaluate improvements in cognitive skills.

RESULTS

Movement-discrimination cognitive neurotraining remediated both low-level visual timing deficits and high-level cognitive functioning, including selective and sustained attention, reading fluency, processing speed, and working memory for all TBI patients we studied. MEG brain imaging, using the Fast-VESTAL procedure, showed that this movement-discrimination training improved time-locked activity in the dorsal stream, attention, and executive control networks.

CONCLUSIONS

Remediating visual timing deficits in the dorsal stream revealed the causal role of visual movement discrimination training in improving high-level cognitive functions such as focusing and switching attention, working memory, processing speed, and reading. This study found that movement-discrimination training was very rapid and effective in remediating cognitive deficits, providing a new approach that is very beneficial for treating a mild TBI.

Spectral analysis of centre of pressure identifies altered balance control in individuals with moderate-severe traumatic brain injury

Purpose: To identify impairments and recovery of balance control after moderate-severe traumatic brain injury (TBI) through spectral analyses of static balance tasks and to characterise the contributions of each limb to balance control.Methods: A retrospective analysis of longitudinal balance data from force platforms at 2, 5, and 12 months post-injury in 31 individuals with moderate to severe TBI was performed. Single-visit data from age-matched controls (n = 22) were collected for descriptive comparison. Net and individual limb centre of pressure measures and inter-limb centre of pressure coherence were calculated in low (≤0.4 Hz) and high (≥0.4 Hz) frequencies in the anteroposterior and mediolateral directions during standing with the eyes open and closed.Results: Standing with the eyes closed increased net centre of pressure spectral power in low and high frequencies. Individuals with TBI demonstrated recovery in high frequencies in net centre of pressure in the mediolateral direction. Inter-limb coherence in the anteroposterior and mediolateral directions increased (recovered) over time in high frequencies. Weight-bearing asymmetry was visible in high frequencies in the anteroposterior and mediolateral directions.Conclusions: Increased amplitude of low and high-frequency power suggests that individuals with TBI included in this study have impaired anticipatory and reactive balance mechanisms, which may be driven by weight-bearing asymmetries and which recover over time.Implications for rehabilitationAnticipatory and reactive balance impairments after traumatic brain injury may place individuals at increased risk for falls.Analyses from postural sway in static balance tasks infer changes in anticipatory or reactive balance control after traumatic brain injury.Addressing weight-bearing asymmetries in rehabilitation interventions post-traumatic brain injury may improve between-limb coordination for anticipatory and reactive balance control.

Association of Visual Tracking Metrics With Post-concussion Symptomatology

Attention impairment may provide a cohesive neurobiological explanation for clusters of clinical symptoms that occur after a concussion; therefore, objective quantification of attention is needed. Visually tracking a moving target is an attention-dependent sensorimotor function, and eye movement can be recorded easily and objectively to quantify performance. Our previous work suggested the utility of gaze-target synchronization metrics of a predictive visual tracking task in concussion screening and recovery monitoring. Another objectively quantifiable performance measure frequently suggested for concussion screening is simple visuo-manual reaction time (simple reaction time, SRT). Here, we used visual tracking and SRT tasks to assess changes between pre- and within-2-week post-concussion performances and explore their relationships to post-concussion symptomatology. Athletes participating in organized competitive sports were recruited. Visual tracking and SRT records were collected from the recruited athlete pool as baseline measures over a 4-year period. When athletes experienced a concussion, they were re-assessed within 2 weeks of their injury. We present the data from a total of 29 concussed athletes. Post-concussion symptom burden was assessed with the Rivermead Post-Concussion Symptoms Questionnaire and subscales of the Brain Injury Screening Questionnaire. Post-concussion changes in visual tracking and SRT performance were examined using a paired t-test. Correlations of changes in visual tracking and SRT performance to symptom burden were examined using Pearson's coefficients. Post-concussion changes in visual tracking performance were not consistent among the athletes. However, changes in several visual tracking metrics had moderate to strong correlations to symptom scales (r up to 0.68). On the other hand, while post-concussion SRT performance was reduced (p < 0.01), the changes in the performance metrics were not meaningfully correlated to symptomatology (r ≤ 0.33). Results suggest that visual tracking performance metrics reflect clinical symptoms when assessed within 2 weeks of concussion. Evaluation of concussion requires assessments in multiple domains because the clinical profiles are heterogeneous. While most individuals show recovery within a week of injury, others experience prolonged recovery periods. Visual tracking performance metrics may serve as a biomarker of debilitating symptoms of concussion implicating attention as a root cause of such pathologies.

The Dynamics of Concussion: Mapping Pathophysiology, Persistence, and Recovery With Causal-Loop Diagramming

Despite increasing public awareness and a growing body of literature on the subject of concussion, or mild traumatic brain injury, an urgent need still exists for reliable diagnostic measures, clinical care guidelines, and effective treatments for the condition. Complexity and heterogeneity complicate research efforts and indicate the need for innovative approaches to synthesize current knowledge in order to improve clinical outcomes. Methods from the interdisciplinary field of systems science, including models of complex systems, have been increasingly applied to biomedical applications and show promise for generating insight for traumatic brain injury. The current study uses causal-loop diagramming to visualize relationships between factors influencing the pathophysiology and recovery trajectories of concussive injury, including persistence of symptoms and deficits. The primary output is a series of preliminary systems maps detailing feedback loops, intrinsic dynamics, exogenous drivers, and hubs across several scales, from micro-level cellular processes to social influences. Key system features, such as the role of specific restorative feedback processes and cross-scale connections, are examined and discussed in the context of recovery trajectories. This systems approach integrates research findings across disciplines and allows components to be considered in relation to larger system influences, which enables the identification of research gaps, supports classification efforts, and provides a framework for interdisciplinary collaboration and communication-all strides that would benefit diagnosis, prognosis, and treatment in the clinic.

Concussion Alters the Functional Brain Processes of Visual Attention and Working Memory

Millions of North Americans sustain a concussion or a mild traumatic brain injury annually, and are at risk of cognitive, emotional, and physical sequelae. Although functional MRI (fMRI) studies have provided an initial framework for examining functional deficits induced by concussion, particularly working memory and attention, the temporal dynamics underlying these deficits are not well understood. We used magnetoencephalography (MEG), a modality with millisecond temporal resolution, in conjunction with a 1-back visual working memory (VWM) paradigm using scenes from everyday life to characterize spatiotemporal functional differences at specific VWM stages, in adults had had or had not had a recent concussion. MEG source-level differences between groups were determined by whole-brain analyses during encoding and recognition phases. Despite comparable behavioral performance, abnormal hypo- and hyperactivation patterns were found in brain areas involving frontoparietal, ventral occipitotemporal, temporal, and subcortical areas in concussed patients. These patterns and their timing varied as a function of VWM stagewise processing, linked to early attentional control, visuoperceptual scene processing, and VWM maintenance and retrieval processes. Parietal hypoactivation, starting at 60 ms during encoding, was correlated with symptom severity, possibly linked to impaired top-down attentional processing. Hyperactivation in the scene-selective occipitotemporal areas, the medial temporal complex, specifically the right hippocampus and orbitofrontal areas during encoding and/or recognition, lead us to posit inefficient but compensatory visuoperceptual, relational, and retrieval processing. Although injuries sustained after the concussion were considered "mild," these data suggest that they can have prolonged effects on early attentional and VWM processes.

Feasibility of using normobaric hypoxic stress in mTBI research

Studies of mild traumatic brain injury (mTBI) recovery generally assess patients in unstressed conditions that permit compensation for impairments through increased effort expenditure. This possibility may explain why a subgroup of individuals report persistent mTBI symptoms yet perform normally on objective assessment. Accordingly, the development and utilization of stress paradigms may be effective for enhancing the sensitivity of mTBI assessment. Previous studies, discussed here, indirectly but plausibly support the use of normobaric hypoxia as a stressor in uncovering latent mTBI symptoms due to the overlapping symptomatology induced by both normobaric hypoxia and mTBI. Limited studies by our group and others further support this plausibility through proof-of-concept demonstrations that hypoxia reversibly induces disproportionately severe impairments of oculomotor, pupillometric, cognitive and autonomic function in mTBI individuals.

Concussion As a Multi-Scale Complex System: An Interdisciplinary Synthesis of Current Knowledge

Traumatic brain injury (TBI) has been called "the most complicated disease of the most complex organ of the body" and is an increasingly high-profile public health issue. Many patients report long-term impairments following even "mild" injuries, but reliable criteria for diagnosis and prognosis are lacking. Every clinical trial for TBI treatment to date has failed to demonstrate reliable and safe improvement in outcomes, and the existing body of literature is insufficient to support the creation of a new classification system. Concussion, or mild TBI, is a highly heterogeneous phenomenon, and numerous factors interact dynamically to influence an individual's recovery trajectory. Many of the obstacles faced in research and clinical practice related to TBI and concussion, including observed heterogeneity, arguably stem from the complexity of the condition itself. To improve understanding of this complexity, we review the current state of research through the lens provided by the interdisciplinary field of systems science, which has been increasingly applied to biomedical issues. The review was conducted iteratively, through multiple phases of literature review, expert interviews, and systems diagramming and represents the first phase in an effort to develop systems models of concussion. The primary focus of this work was to examine concepts and ways of thinking about concussion that currently impede research design and block advancements in care of TBI. Results are presented in the form of a multi-scale conceptual framework intended to synthesize knowledge across disciplines, improve research design, and provide a broader, multi-scale model for understanding concussion pathophysiology, classification, and treatment.

Rehabilitation of emergent awareness of errors post traumatic brain injury: A pilot intervention

Impaired awareness of errors is common following traumatic brain injury (TBI) and can be a barrier to successful rehabilitation. The objective of this study was to develop and evaluate a computer-based intervention programme aimed at improving error awareness in individuals with TBI. A further aim was to explore its effects on metacognitive awareness and variability of performance. Participants were 11 individuals with TBI and impaired error awareness who performed a sustained attention task twice-weekly for four weeks. The intervention consisted of audio-visual feedback-on-errors during the sustained attention task. Six participants received audio-visual feedback-on-error, five did not receive feedback. Emergent and metacognitive awareness were measured pre- and post-intervention. Between-groups comparisons of emergent awareness from pre- to post-intervention showed that audio-visual feedback-on-error improved emergent awareness compared to no feedback-on-error. Some changes in metacognitive awareness of executive behaviours as a result of feedback were observed. Audio-visual feedback-on-error improved emergent awareness in individuals with TBI following a four-week/eight-session intervention. This improvement was not observed in the no-feedback group. This pilot intervention is not a stand-alone treatment but it has potential to be usefully incorporated into cognitive or clinical rehabilitation programmes to improve emergent awareness.

Mild and Mild-to-Moderate Traumatic Brain Injury-Induced Significant Progressive and Enduring Multiple Comorbidities

Traumatic brain injury (TBI) can produce life-long disabilities, including anxiety, cognitive, balance, and motor deficits. The experimental model of closed head TBI (cTBI) induced by weight drop/impact acceleration is known to produce hallmark TBI injuries. However, comprehensive long-term characterization of comorbidities induced by graded mild-to- mild/moderate intensities using this experimental cTBI model has not been reported. The present study used two intensities of weight drop (1.0 m and 1.25 m/450 g) to produce cTBI in a rat model to investigate initial and long-term disability of four comorbidities: anxiety, cognitive, vestibulomotor, and spinal reflex that related to spasticity. TBI and sham injuries were produced under general anesthesia. Time for righting recoveries post-TBI recorded to estimate duration of unconsciousness, revealed that the TBI mild/moderate group required a mean of 1 min 27 sec longer than the values observed for noninjured sham animals. Screening magnetic resonance imaging images revealed no anatomical changes, mid-line shifts, or hemorrhagic volumes. However, compared to sham injuries, significant long-term anxiety, cognitive, balance, and physiological changes in motor reflex related to spasticity were observed post-TBI for both TBI intensities. The longitudinal trajectory of anxiety and balance disabilities tested at 2, 4, 8, and 18 weeks revealed progressively worsening disabilities. In general, disability magnitudes were proportional to injury intensity for three of the four measures. A natural hypothesis would pose that all disabilities would increase incrementally relative to injury severity. Surprisingly, anxiety disability progressed over time to be greater in the mildest injury. Collectively, translational implications of these observations suggest that patients with mild TBI should be evaluated longitudinally at multiple time points, and that anxiety disorder could potentially have a particularly low threshold for appearance and progressively worsen post-injury.

Increased risk for age-related impairment in visual attention associated with mild traumatic brain injury: Evidence from saccadic response times

It was hypothesized that risk for age-related impairment in attention would be greater among those with remote history of mild TBI than individuals without history of head injury. Twenty-seven adults with remote history of mild TBI and a well-matched comparison group of 54 uninjured controls completed a computerized test of visual attention while saccadic and manual response times were recorded. Within the mild TBI group only, older age was associated with slower saccadic responses and poorer saccadic inhibition. Saccadic slowing was mitigated in situations where the timing and location of attention targets was fully predictable. Mild TBI was not associated with age-related increases in risk for neuropsychological impairment or neurobehavioral symptoms. These results provide preliminary evidence that risk for age-related impairment in visual attention may be higher among those with a history of mild TBI. Saccadic measures may provide enhanced sensitivity to this subtle form of cognitive impairment.

Effects of a rapid-resisted elliptical training program on motor, cognitive and neurobehavioral functioning in adults with chronic traumatic brain injury

This small clinical trial utilized a novel rehabilitation strategy, rapid-resisted elliptical training, in an effort to increase motor, and thereby cognitive, processing speed in ambulatory individuals with traumatic brain injury (TBI). As an initial step, multimodal functional abilities were quantified and compared in 12 ambulatory adults with and 12 without TBI. After the baseline assessment, the group with TBI participated in an intensive 8-week daily exercise program using an elliptical trainer and was reassessed after completion and at an 8-week follow-up. The focus of training was on achieving a fast movement speed, and once the target was reached, resistance to motion was increased in small increments to increase intensity of muscle activation. Primary outcomes were: High-Level Mobility Assessment Tool (HiMAT), instrumented balance tests, dual-task (DT) performance and neurobehavioral questionnaires. The group with TBI had poorer movement excursion during balance tests and poorer dual-task (DT) performance. After training, balance reaction times improved and were correlated with gains in the HiMAT and DT. Sleep quality also improved and was correlated with improved depression and learning. This study illustrates how brain injury can affect multiple linked aspects of functioning and provides preliminary evidence that intensive rapid-resisted training has specific positive effects on dynamic balance and more generalized effects on sleep quality in TBI.

Chronic Post-Concussion Neurocognitive Deficits. I. Relationship with White Matter Integrity

We previously identified visual tracking deficits and associated degradation of integrity in specific white matter tracts as characteristics of concussion. We re-explored these characteristics in adult patients with persistent post-concussive symptoms using independent new data acquired during 2009–2012. Thirty-two patients and 126 normal controls underwent cognitive assessments and MR-DTI. After data collection, a subset of control subjects was selected to be individually paired with patients based on gender and age. We identified patients’ cognitive deficits through pairwise comparisons between patients and matched control subjects. Within the remaining 94 normal subjects, we identified white matter tracts whose integrity correlated with metrics that indicated performance degradation in patients. We then tested for reduced integrity in these white matter tracts in patients relative to matched controls. Most patients showed no abnormality in MR images unlike the previous study. Patients’ visual tracking was generally normal. Patients’ response times in an attention task were slowed, but could not be explained as reduced integrity of white matter tracts relating to normal response timing. In the present patient cohort, we did not observe behavioral or anatomical deficits that we previously identified as characteristic of concussion. The recent cohort likely represented those with milder injury compared to the earlier cohort. The discrepancy may be explained by a change in the patient recruitment pool circa 2007 associated with an increase in public awareness of concussion.

Individual differences in oscillatory brain activity in response to varying attentional demands during a word recall and oculomotor dual task

Every day, we face situations that involve multi-tasking. How our brain utilizes cortical resources during multi-tasking is one of many interesting research topics. In this study, we tested whether a dual-task can be differentiated in the neural and behavioral responses of healthy subjects with varying degree of working memory capacity (WMC). We combined word recall and oculomotor tasks because they incorporate common neural networks including the fronto-parietal (FP) network. Three different types of oculomotor tasks (eye fixation, Fix-EM; predictive and random smooth pursuit eye movement, P-SPEM and R-SPEM) were combined with two memory load levels (low-load: five words, high-load: 10 words) for a word recall task. Each of those dual-task combinations was supposed to create varying cognitive loads on the FP network. We hypothesize that each dual-task requires different cognitive strategies for allocating the brain's limited cortical resources and affects brain oscillation of the FP network. In addition, we hypothesized that groups with different WMC will show differential neural and behavioral responses. We measured oscillatory brain activity with simultaneous MEG and EEG recordings and behavioral performance by word recall. Prominent frontal midline (FM) theta (4-6 Hz) synchronization emerged in the EEG of the high-WMC group experiencing R-SPEM with high-load conditions during the early phase of the word maintenance period. Conversely, significant parietal upper alpha (10-12 Hz) desynchronization was observed in the EEG and MEG of the low-WMC group experiencing P-SPEM under high-load conditions during the same period. Different brain oscillatory patterns seem to depend on each individual's WMC and varying attentional demands from different dual-task combinations. These findings suggest that specific brain oscillations may reflect different strategies for allocating cortical resources during combined word recall and oculomotor dual-tasks.

Transiently lowering tumor necrosis factor-α synthesis ameliorates neuronal cell loss and cognitive impairments induced by minimal traumatic brain injury in mice

Background

The treatment of traumatic brain injury (TBI) represents an unmet medical need, as no effective pharmacological treatment currently exists. The development of such a treatment requires a fundamental understanding of the pathophysiological mechanisms that underpin the sequelae resulting from TBI, particularly the ensuing neuronal cell death and cognitive impairments. Tumor necrosis factor-alpha (TNF-α) is a cytokine that is a master regulator of systemic and neuroinflammatory processes. TNF-α levels are reported to become rapidly elevated post TBI and, potentially, can lead to secondary neuronal damage.

Methods

To elucidate the role of TNF-α in TBI, particularly as a drug target, the present study evaluated (i) time-dependent TNF-α levels and (ii) markers of apoptosis and gliosis within the brain and related these to behavioral measures of ‘well being’ and cognition in a mouse closed head 50 g weight drop mild TBI (mTBI) model in the presence and absence of post-treatment with an experimental TNF-α synthesis inhibitor, 3,6′-dithiothalidomide.

Results

mTBI elevated brain TNF-α levels, which peaked at 12 h post injury and returned to baseline by 18 h. This was accompanied by a neuronal loss and an increase in astrocyte number (evaluated by neuronal nuclei (NeuN) and glial fibrillary acidic protein (GFAP) immunostaining), as well as an elevation in the apoptotic death marker BH3-interacting domain death agonist (BID) at 72 h. Selective impairments in measures of cognition, evaluated by novel object recognition and passive avoidance paradigms - without changes in well being, were evident at 7 days after injury. A single systemic treatment with the TNF-α synthesis inhibitor 3,6′-dithiothalidomide 1 h post injury prevented the mTBI-induced TNF-α elevation and fully ameliorated the neuronal loss (NeuN), elevations in astrocyte number (GFAP) and BID, and cognitive impairments. Cognitive impairments evident at 7 days after injury were prevented by treatment as late as 12 h post mTBI but were not reversed when treatment was delayed until 18 h.

Conclusions

These results implicate that TNF-α in mTBI induced secondary brain damage and indicate that pharmacologically limiting the generation of TNF-α post mTBI may mitigate such damage, defining a time-dependent window of up to 12 h to achieve this reversal.

Neurocognitive Late Effects of Chemotherapy in Survivors of Acute Lymphoblastic Leukemia: Focus on Methotrexate

Childhood cancer survivors frequently experience long-lasting consequences of chemotherapy on health outcomes. Neurocognitive late effects of chemotherapy occur in 40 - 60% of acute lymphoblastic leukemia (ALL) survivors. These deficits affect mental health, school performance, job success, and are associated with poor quality of life, therefore presenting a clinical challenge for psychiatrists. However, not all cancer survivors are impacted by treatment in the same manner and emerging evidence suggests that genetic variation may modulate neurocognitive outcomes. Much like other complex psychopathologies, neurocognitive deficits in cancer survivors are the result of complex interactions between genetic and environmental variables. This review describes adverse neurocognitive outcomes observed in survivors of acute lymphoblastic leukemia (ALL) and discusses genetic variability in biochemical pathways targeted by chemotherapeutic agents as a possible mechanism contributing to psychopathology in ALL survivors.

Multimodal imaging of mild traumatic brain injury and persistent postconcussion syndrome

BACKGROUND

Persistent postconcussion syndrome (PCS) occurs in around 5-10% of individuals after mild traumatic brain injury (mTBI), but research into the underlying biology of these ongoing symptoms is limited and inconsistent. One reason for this could be the heterogeneity inherent to mTBI, with individualized injury mechanisms and psychological factors. A multimodal imaging study may be able to characterize the injury better.

AIM

To look at the relationship between functional (fMRI), structural (diffusion tensor imaging), and metabolic (magnetic resonance spectroscopy) data in the same participants in the long term (>1 year) after injury. It was hypothesized that only those mTBI participants with persistent PCS would show functional changes, and that these changes would be related to reduced structural integrity and altered metabolite concentrations.

METHODS

Functional changes associated with persistent PCS after mTBI (>1 year postinjury) were investigated in participants with and without PCS (both n = 8) and non-head injured participants (n = 9) during performance of working memory and attention/processing speed tasks. Correlation analyses were performed to look at the relationship between the functional data and structural and metabolic alterations in the same participants.

RESULTS

There were no behavioral differences between the groups, but participants with greater PCS symptoms exhibited greater activation in attention-related areas (anterior cingulate), along with reduced activation in temporal, default mode network, and working memory areas (left prefrontal) as cognitive load was increased from the easiest to the most difficult task. Functional changes in these areas correlated with reduced structural integrity in corpus callosum and anterior white matter, and reduced creatine concentration in right dorsolateral prefrontal cortex.

CONCLUSION

These data suggest that the top-down attentional regulation and deactivation of task-irrelevant areas may be compensating for the reduction in working memory capacity and variation in white matter transmission caused by the structural and metabolic changes after injury. This may in turn be contributing to secondary PCS symptoms such as fatigue and headache. Further research is required using multimodal data to investigate the mechanisms of injury after mTBI, but also to aid individualized diagnosis and prognosis.

Degradation of cognitive timing mechanisms in behavioural variant frontotemporal dementia

The current study examined motor timing in frontotemporal dementia (FTD), which manifests as progressive deterioration in social, behavioural and cognitive functions. Twenty-patients fulfilling consensus clinical criteria for behavioural variant FTD (bvFTD), 11 patients fulfilling consensus clinical criteria for semantic-variant primary progressive aphasia (svPPA), four patients fulfilling criteria for nonfluent/agrammatic primary progressive aphasia (naPPA), eight patients fulfilling criteria for Alzheimer׳s disease (AD), and 31 controls were assessed on both an externally- and self-paced finger-tapping task requiring maintenance of a regular, 1500 ms beat over 50 taps. Grey and white matter correlates of deficits in motor timing were examined using voxel-based morphometry (VBM) and diffusion tensor imaging (DTI). bvFTD patients exhibited significant deficits in aspects of both externally- and self-paced tapping. Increased mean inter-response interval (faster than target tap time) in the self-paced task was associated with reduced grey matter volume in the cerebellum bilaterally, right middle temporal gyrus, and with increased axial diffusivity in the right superior longitudinal fasciculus, regions and tracts which have been suggested to be involved in a subcortical–cortical network of structures underlying timing abilities. This suggests that such structures can be affected in bvFTD, and that impaired motor timing may underlie some characteristics of the bvFTD phenotype.

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We examine motor timing in behavioural variant FTD.

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Patients with behavioural variant FTD showed impaired motor timing.

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Patients tended to tap faster than target and speed up during the task.

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Faster tapping was associated with reduced grey matter in the cerebellum.

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Impaired timing might underlie some other behavioural features of FTD.

Visual and auditory synchronization deficits among dyslexic readers as compared to non-impaired readers: a cross-correlation algorithm analysis

Visual and auditory temporal processing and crossmodal integration are crucial factors in the word decoding process. The speed of processing (SOP) gap (Asynchrony) between these two modalities, which has been suggested as related to the dyslexia phenomenon, is the focus of the current study. Nineteen dyslexic and 17 non-impaired University adult readers were given stimuli in a reaction time (RT) procedure where participants were asked to identify whether the stimulus type was only visual, only auditory or crossmodally integrated. Accuracy, RT, and Event Related Potential (ERP) measures were obtained for each of the three conditions. An algorithm to measure the contribution of the temporal SOP of each modality to the crossmodal integration in each group of participants was developed. Results obtained using this model for the analysis of the current study data, indicated that in the crossmodal integration condition the presence of the auditory modality at the pre-response time frame (between 170 and 240 ms after stimulus presentation), increased processing speed in the visual modality among the non-impaired readers, but not in the dyslexic group. The differences between the temporal SOP of the modalities among the dyslexics and the non-impaired readers give additional support to the theory that an asynchrony between the visual and auditory modalities is a cause of dyslexia.

Frontal white matter damage impairs response inhibition in children following traumatic brain injury

Inhibition, the ability to suppress inappropriate cognitions or behaviors, can be measured using computer tasks and questionnaires. Inhibition depends on the frontal cortex, but the role of the underlying white matter (WM) is unclear. We assessed the specific impact of frontal WM damage on inhibition in 29 children with moderate-to-severe traumatic brain injury (15 with and 14 without frontal WM damage), 21 children with orthopedic injury, and 29 population controls. We used the Stop Signal Task to measure response inhibition, the Behavior Rating Inventory of Executive Function to assess everyday inhibition, and T2 fluid-attenuated inversion recovery magnetic resonance imaging to identify lesions. Children with frontal WM damage had impaired response inhibition compared with all other groups and poorer everyday inhibition than the orthopedic injury group. Frontal WM lesions most often affected the superior frontal gyrus. These results provide evidence for the critical role of frontal WM in inhibition.

Prediction of human actions: expertise and task-related effects on neural activation of the action observation network

The action observation network (AON) is supposed to play a crucial role when athletes anticipate the effect of others' actions in sports such as tennis. We used functional magnetic resonance imaging to explore whether motor expertise leads to a differential activation pattern within the AON during effect anticipation and whether spatial and motor anticipation tasks are associated with a differential activation pattern within the AON depending on participant expertise level. Expert (N=16) and novice (N=16) tennis players observed video clips depicting forehand strokes with the instruction to either indicate the predicted direction of ball flight (spatial anticipation) or to decide on an appropriate response to the observed action (motor anticipation). The experts performed better than novices on both tennis anticipation tasks, with the experts showing stronger neural activation in areas of the AON, namely, the superior parietal lobe, the intraparietal sulcus, the inferior frontal gyrus, and the cerebellum. When novices were contrasted with experts, motor anticipation resulted in stronger activation of the ventral premotor cortex, the supplementary motor area, and the superior parietal lobe than spatial anticipation task did. In experts, the comparison of motor and spatial anticipation revealed no increased activation. We suggest that the stronger activation of areas in the AON during the anticipation of action effects in experts reflects their use of the more fine-tuned motor representations they have acquired and improved during years of training. Furthermore, results suggest that the neural processing of different anticipation tasks depends on the expertise level.

Dynamic visuomotor synchronization: quantification of predictive timing

When a moving target is tracked visually, spatial and temporal predictions are used to circumvent the neural delay required for the visuomotor processing. In particular, the internally generated predictions must be synchronized with the external stimulus during continuous tracking. We examined the utility of a circular visual-tracking paradigm for assessment of predictive timing, using normal human subjects. Disruptions of gaze–target synchronization were associated with anticipatory saccades that caused the gaze to be temporarily ahead of the target along the circular trajectory. These anticipatory saccades indicated preserved spatial prediction but suggested impaired predictive timing. We quantified gaze–target synchronization with several indices, whose distributions across subjects were such that instances of extremely poor performance were identifiable outside the margin of error determined by test–retest measures. Because predictive timing is an important element of attention functioning, the visual-tracking paradigm and dynamic synchronization indices described here may be useful for attention assessment.

Traumatic brain injury impairs small-world topology

OBJECTIVE

We test the hypothesis that brain networks associated with cognitive function shift away from a "small-world" organization following traumatic brain injury (TBI).

METHODS

We investigated 20 TBI patients and 21 age-matched controls. Resting-state functional MRI was used to study functional connectivity. Graph theoretical analysis was then applied to partial correlation matrices derived from these data. The presence of white matter damage was quantified using diffusion tensor imaging.

RESULTS

Patients showed characteristic cognitive impairments as well as evidence of damage to white matter tracts. Compared to controls, the graph analysis showed reduced overall connectivity, longer average path lengths, and reduced network efficiency. A particular impact of TBI is seen on a major network hub, the posterior cingulate cortex. Taken together, these results confirm that a network critical to cognitive function shows a shift away from small-world characteristics.

CONCLUSIONS

We provide evidence that key brain networks involved in supporting cognitive function become less small-world in their organization after TBI. This is likely to be the result of diffuse white matter damage, and may be an important factor in producing cognitive impairment after TBI.

Morphological and genetic activation of microglia after diffuse traumatic brain injury in the rat

Traumatic brain injury (TBI) survivors experience long-term post-traumatic morbidities. In diffuse brain-injured rats, a chronic sensory sensitivity to whisker stimulation models the agitation of TBI survivors and provides anatomical landmarks across the whisker-barrel circuit to evaluate post-traumatic neuropathology. As a consequence of TBI, acute and chronic microglial activation can contribute to degenerative and reparative events underlying post-traumatic morbidity. Here we hypothesize that a temporal sequence of microglial activation states contributes to the circuit pathology responsible for post-traumatic morbidity, and test the hypothesis by examining microglial morphological activation and neuroinflammatory markers for activation states through gene expression and receptor-binding affinity. Adult male, Sprague-Dawley rats were subjected to a single moderate midline fluid percussion injury (FPI) or sham injury. Microglial activation was determined by immunohistochemistry, quantitative real-time PCR and receptor autoradiography in the primary somatosensory barrel field (S1BF) and ventral posterior medial nucleus (VPM) of the thalamus at 7 and 28 days following FPI. Morphological changes indicative of microglial activation, including swollen cell body with thicker, shrunken processes, were evident in S1BF and VPM at 7 and 28 days post-injury. Principally at 7 days post-injury in VPM, general inflammatory gene expression (major histocompatibility complex I, major histocompatibility complex II, translocator protein 18 kDa [TSPO]) is increased above sham level and TSPO gene expression confirmed by receptor autoradiography. Further, CD45, a marker of classical activation, and TGF-βI, an acquired deactivation marker, were elevated significantly above sham at 7 days post-injury. Daily administration of the anti-inflammatory ibuprofen (20mg/kg, i.p.) significantly reduced the expression of these genes. Evidence for alternative activation (arginase 1) was not observed. Thus, these data demonstrate concomitant classical activation and acquired deactivation phenotypes of microglia in diffuse TBI in the absence of overt contusion or cavitation. Anti-inflammatory treatment may further alleviate the neuropathological burden of post-traumatic inflammation.

Exploring the fundamental dynamics of error-based motor learning using a stationary predictive-saccade task

The maintenance of movement accuracy uses prior performance errors to correct future motor plans; this motor-learning process ensures that movements remain quick and accurate. The control of predictive saccades, in which anticipatory movements are made to future targets before visual stimulus information becomes available, serves as an ideal paradigm to analyze how the motor system utilizes prior errors to drive movements to a desired goal. Predictive saccades constitute a stationary process (the mean and to a rough approximation the variability of the data do not vary over time, unlike a typical motor adaptation paradigm). This enables us to study inter-trial correlations, both on a trial-by-trial basis and across long blocks of trials. Saccade errors are found to be corrected on a trial-by-trial basis in a direction-specific manner (the next saccade made in the same direction will reflect a correction for errors made on the current saccade). Additionally, there is evidence for a second, modulating process that exhibits long memory. That is, performance information, as measured via inter-trial correlations, is strongly retained across a large number of saccades (about 100 trials). Together, this evidence indicates that the dynamics of motor learning exhibit complexities that must be carefully considered, as they cannot be fully described with current state-space (ARMA) modeling efforts.

Pathophysiological distortions in time perception and timed performance

Distortions in time perception and timed performance are presented by a number of different neurological and psychiatric conditions (e.g. Parkinson's disease, schizophrenia, attention deficit hyperactivity disorder and autism). As a consequence, the primary focus of this review is on factors that define or produce systematic changes in the attention, clock, memory and decision stages of temporal processing as originally defined by Scalar Expectancy Theory. These findings are used to evaluate the Striatal Beat Frequency Theory, which is a neurobiological model of interval timing based upon the coincidence detection of oscillatory processes in corticostriatal circuits that can be mapped onto the stages of information processing proposed by Scalar Timing Theory.

Tumor necrosis factor-α synthesis inhibitor, 3,6'-dithiothalidomide, reverses behavioral impairments induced by minimal traumatic brain injury in mice

Mild traumatic brain injury (mTBI) patients do not show clear structural brain defects and, in general, do not require hospitalization, but frequently suffer from long-lasting cognitive, behavioral and emotional difficulties. Although there is no current effective treatment or cure for mTBI, tumor necrosis factor-alpha (TNF-α), a cytokine fundamental in the systemic inflammatory process, represents a potential drug target. TNF-α levels increase after mTBI and may induce or exacerbate secondary damage to brain tissue. The present study evaluated the efficacy of the experimental TNF-α synthesis inhibitor, 3,6'-dithiothalidomide, on recovery of mice from mTBI in a closed head weight-drop model that induces an acute elevation in brain TNF-α and an impairment in cognitive performance, as assessed by the Y-maze, by novel object recognition and by passive avoidance paradigms at 72 h and 7 days after injury. These impairments were fully ameliorated in mice that received a one time administration of 3,6'-dithiothalidomide at either a low (28 mg/kg) or high (56 mg/kg) dose provided either 1 h prior to injury, or at 1 or 12 h post-injury. Together, these results implicate TNF-α as a drug target for mTBI and suggests that 3,6'-dithiothalidomide may act as a neuroprotective drug to minimize impairment.

Verbal learning strategy following mild traumatic brain injury

That learning and memory deficits persist many years following mild traumatic brain injury (mTBI) is controversial due to inconsistent objective evidence supporting subjective complaints. Our prior work demonstrated significant reductions in performance on the initial trial of a verbal learning task and overall slower rate of learning in well-motivated mTBI participants relative to demographically matched controls. In our previous work, we speculated that differences in strategy use could explain the differences in rate of learning. The current study serves to test this hypothesis by examining strategy use on the California Verbal Learning Test-Second Edition. Our present findings support the primary hypothesis that mTBI participants under-utilize semantic clustering strategies during list-learning relative to control participants. Despite achieving comparable total learning scores, we posit that the persisting learning and memory difficulties reported by some mTBI patients may be related to reduced usage of efficient internally driven strategies that facilitate learning. Given that strategy training has demonstrated improvements in learning and memory in educational and occupational settings, we offer that these findings have translational value in offering an additional approach in remediation of learning and memory complaints reported by some following mTBI.

Mapping traumatic axonal injury using diffusion tensor imaging: correlations with functional outcome

BACKGROUND

Traumatic brain injury is a major cause of morbidity and mortality worldwide. Ameliorating the neurocognitive and physical deficits that accompany traumatic brain injury would be of substantial benefit, but the mechanisms that underlie them are poorly characterized. This study aimed to use diffusion tensor imaging to relate clinical outcome to the burden of white matter injury.

METHODOLOGY/PRINCIPAL FINDINGS

Sixty-eight patients, categorized by the Glasgow Outcome Score, underwent magnetic resonance imaging at a median of 11.8 months (range 6.6 months to 3.7 years) years post injury. Control data were obtained from 36 age-matched healthy volunteers. Mean fractional anisotropy, apparent diffusion coefficient (ADC), and eigenvalues were obtained for regions of interest commonly affected in traumatic brain injury. In a subset of patients where conventional magnetic resonance imaging was completely normal, diffusion tensor imaging was able to detect clear abnormalities. Significant trends of increasing ADC with worse outcome were noted in all regions of interest. In the white matter regions of interest worse clinical outcome corresponded with significant trends of decreasing fractional anisotropy.

CONCLUSIONS/SIGNIFICANCE

This study found that clinical outcome was related to the burden of white matter injury, quantified by diffusivity parameters late after traumatic brain injury. These differences were seen even in patients with the best outcomes and patients in whom conventional magnetic resonance imaging was normal, suggesting that diffusion tensor imaging can detect subtle injury missed by other techniques. An improved in vivo understanding of the pathology of traumatic brain injury, including its distribution and extent, may enhance outcome evaluation and help to provide a mechanistic basis for deficits that remain unexplained by other approaches.

Pivotal role of anterior cingulate cortex in working memory after traumatic brain injury in youth

In this fMRI study, the functions of the anterior cingulate cortex (ACC) were studied in a group of adolescents who had sustained a moderate to severe traumatic brain injury (TBI). A spatial working memory task with varying working memory loads, representing experimental conditions of increasing difficulty, was administered. In a cross-sectional comparison between the patients and a matched control group, patients performed worse than Controls, showing longer reaction times and lower response accuracy on the spatial working memory task. Brain imaging findings suggest a possible double-dissociation: activity of the ACC in the TBI group, but not in the Control group, was associated with task difficulty; conversely, activity of the left sensorimotor cortex (lSMC) in the Control group, but not in the TBI group, was correlated with task difficulty. In addition to the main cross-sectional study, a longitudinal study of a group of adolescent patients with moderate to severe TBI was done using fMRI and the same spatial working memory task. The patient group was studied at two time-points: one time-point during the post-acute phase and one time-point 12 months later, during the chronic phase. Results indicated that patients' behavioral performance improved over time, suggesting cognitive recovery. Brain imaging findings suggest that, over this 12-month period, patients recruited less of the ACC and more of the lSMC in response to increasing task difficulty. The role of ACC in executive functions following a moderate to severe brain injury in adolescence is discussed within the context of conflicting models of the ACC functions in the existing literature.