Mechanisms of working memory dysfunction after mild and moderate TBI: evidence from functional MRI and neurogenetics

New method to induce mild traumatic brain injury in rodents produces differential outcomes in female and male Sprague Dawley rats

BACKGROUND

Mild traumatic brain injuries (mTBI) are an increasing health concern due to persistent behavioral and neurological effects. To better understand these effects, researchers frequently rely on animal injury models. Existing models, however, may not adequately reproduce the mechanism of injury as it occurs in humans.

NEW METHOD

Our new model for inducing mTBI in rodents entails acceleration of the animal toward a stationary impact zone to produce rapid rotational movement of the head. The aim of the present experiment was to characterize the effects of this injury in female and male rats on behavior, cognition, and neural plasticity.

RESULTS

mTBI produced the most widespread effects in females: they were more active during recovery within minutes of mTBI and more active in the center of the open field 4days after mTBI. Spatial learning deficits in the water maze were mild but persistent and accompanied by reduced numbers of immature neurons in the hippocampus along with reductions in sera levels of the neurotrophin, BDNF. By contrast, male mTBI rats mainly exhibited mild spatial learning deficits, with no other observed effects.

COMPARISON WITH EXISTING METHODS

Our model induced effects on behavior and biology in rats that aligned with existing models. However, new patterns were observed, particularly when comparing females and males.

CONCLUSIONS

Taken together, these findings confirm the validity of this model and point to key differences between females and males in symptom severity and type. Additionally, our model adds a novel injury mechanism that complements existing rodent models.

Reorganization of the Connectivity between Elementary Functions - A Model Relating Conscious States to Neural Connections

In the present paper it is argued that the "neural correlate of consciousness" (NCC) does not appear to be a separate "module" - but an aspect of information processing within the neural substrate of various cognitive processes. Consequently, NCC can only be addressed adequately within frameworks that model the general relationship between neural processes and mental states - and take into account the dynamic connectivity of the brain. We presently offer the REFGEN (general reorganization of elementary functions) model as such a framework. This model builds upon and expands the REF (reorganization of elementary functions) and REFCON (of elementary functions and consciousness) models. All three models integrate the relationship between the neural and mental layers of description via the construction of an intermediate level dealing with computational states. The importance of experience based organization of neural and cognitive processes is stressed. The models assume that the mechanisms of consciousness are in principle the same as the basic mechanisms of all aspects of cognition - when information is processed to a sufficiently "high level" it becomes available to conscious experience. The NCC is within the REFGEN model seen as aspects of the dynamic and experience driven reorganizations of the synaptic connectivity between the neurocognitive "building blocks" of the model - the elementary functions.

Loss of PAFR prevents neuroinflammation and brain dysfunction after traumatic brain injury

Traumatic brain injury (TBI) is a principal cause of death and disability worldwide, which is a major public health problem. Death caused by TBI accounts for a third of all damage related illnesses, which 75% TBI occurred in low and middle income countries. With the increasing use of motor vehicles, the incidence of TBI has been at a high level. The abnormal brain functions of TBI patients often show the acute and long-term neurological dysfunction, which mainly associated with the pathological process of malignant brain edema and neuroinflammation in the brain. Owing to the neuroinflammation lasts for months or even years after TBI, which is a pivotal causative factor that give rise to neurodegenerative disease at late stage of TBI. Studies have shown that platelet activating factor (PAF) inducing inflammatory reaction after TBI could not be ignored. The morphological and behavioral abnormalities after TBI in wild type mice are rescued by general knockout of PAFR gene that neuroinflammation responses and cognitive ability are improved. Our results thus define a key inflammatory molecule PAF that participates in the neuroinflammation and helps bring about cerebral dysfunction during the TBI acute phase.

Neuropsychological Profile of Lifetime Traumatic Brain Injury in Older Veterans

OBJECTIVES

The aim of this study was to characterize the neuropsychological profile of lifetime traumatic brain injury (TBI) in older Veterans.

METHODS

Participants were 169 older Veterans [mean age=79.1 years (range, 51-97 years), 89% male, 92% Caucasian], 88 with lifetime TBI and 81 without TBI, living in Veterans' retirement homes in independent residence. TBI history was ascertained with the Ohio State TBI Identification Method structured interview. Cognition was assessed with neuropsychological tests: Raw scores were converted to Z-scores compared to age-corrected normative data and combined into five domain composite Z-scores (attention/working memory, learning/memory, language, processing speed, executive functioning). We investigated the association between TBI and performance in each cognitive domain in linear mixed effects models, with and without adjustment for demographics, medical comorbidities, and psychiatric variables.

RESULTS

Compared to those without TBI, older Veterans with TBI had greater deficits in processing speed (estimate=-.52; p=.01; f 2=.08 in fully adjusted model) and executive functioning (estimate=-.41; p=.02; f 2=.06 in fully adjusted model) but performed similarly in the attention/working memory, learning/memory, and language domains (all p>.05). TBI-associated deficits were most prominent among individuals with multiple mild TBIs and those with any moderate-to-severe TBI, but were not clearly present among those with single mild TBI.

CONCLUSIONS

The neuropsychological profile of lifetime TBI in older Veterans is characterized by slowed processing speed and executive dysfunction, especially among those with greater injury burden. This pattern may reflect long-standing deficits or a TBI-associated cognitive decline process distinct from Alzheimer's disease. (JINS, 2017, 23, 56-64).

Biomarkers of Traumatic Brain Injury: Temporal Changes in Body Fluids

Traumatic brain injuries (TBIs) are caused by a hit to the head or a sudden acceleration/deceleration movement of the head. Mild TBIs (mTBIs) and concussions are difficult to diagnose. Imaging techniques often fail to find alterations in the brain, and computed tomography exposes the patient to radiation. Brain-specific biomolecules that are released upon cellular damage serve as another means of diagnosing TBI and assessing the severity of injury. These biomarkers can be detected from samples of body fluids using laboratory tests. Dozens of TBI biomarkers have been studied, and research related to them is increasing. We reviewed the recent literature and selected 12 biomarkers relevant to rapid and accurate diagnostics of TBI for further evaluation. The objective was especially to get a view of the temporal profiles of the biomarkers’ rise and decline after a TBI event. Most biomarkers are rapidly elevated after injury, and they serve as diagnostics tools for some days. Some biomarkers are elevated for months after injury, although the literature on long-term biomarkers is scarce. Clinical utilization of TBI biomarkers is still at a very early phase despite years of active research.

MR Imaging Applications in Mild Traumatic Brain Injury: An Imaging Update

Mild traumatic brain injury (mTBI), also commonly referred to as concussion, affects millions of Americans annually. Although computed tomography is the first-line imaging technique for all traumatic brain injury, it is incapable of providing long-term prognostic information in mTBI. In the past decade, the amount of research related to magnetic resonance (MR) imaging of mTBI has grown exponentially, partly due to development of novel analytical methods, which are applied to a variety of MR techniques. Here, evidence of subtle brain changes in mTBI as revealed by these techniques, which are not demonstrable by conventional imaging, will be reviewed. These changes can be considered in three main categories of brain structure, function, and metabolism. Macrostructural and microstructural changes have been revealed with three-dimensional MR imaging, susceptibility-weighted imaging, diffusion-weighted imaging, and higher order diffusion imaging. Functional abnormalities have been described with both task-mediated and resting-state blood oxygen level-dependent functional MR imaging. Metabolic changes suggesting neuronal injury have been demonstrated with MR spectroscopy. These findings improve understanding of the true impact of mTBI and its pathogenesis. Further investigation may eventually lead to improved diagnosis, prognosis, and management of this common and costly condition. (©) RSNA, 2016.

Mild Traumatic Brain Injury

Mild traumatic brain injury (MTBI) is a significant public health problem worldwide. Injured individuals have an increased relative risk of developing a variety of neuropsychiatric conditions associated with the profile of brain regions typically affected in TBI. Within a neurobiopsychosocial framework, this article reviews what is known about the neuropsychiatric sequelae of MTBI, with an emphasis on recent advances.

Chronic Cognitive Dysfunction after Traumatic Brain Injury Is Improved with a Phosphodiesterase 4B Inhibitor

Learning and memory impairments are common in traumatic brain injury (TBI) survivors. However, there are no effective treatments to improve TBI-induced learning and memory impairments. TBI results in decreased cAMP signaling and reduced cAMP-response-element binding protein (CREB) activation, a critical pathway involved in learning and memory. TBI also acutely upregulates phosphodiesterase 4B2 (PDE4B2), which terminates cAMP signaling by hydrolyzing cAMP. We hypothesized that a subtype-selective PDE4B inhibitor could reverse the learning deficits induced by TBI. To test this hypothesis, adult male Sprague-Dawley rats received sham surgery or moderate parasagittal fluid-percussion brain injury. At 3 months postsurgery, animals were administered a selective PDE4B inhibitor or vehicle before cue and contextual fear conditioning, water maze training and a spatial working memory task. Treatment with the PDE4B inhibitor significantly reversed the TBI-induced deficits in cue and contextual fear conditioning and water maze retention. To further understand the underlying mechanisms of these memory impairments, we examined hippocampal long-term potentiation (LTP). TBI resulted in a significant reduction in basal synaptic transmission and impaired expression of LTP. Treatment with the PDE4B inhibitor significantly reduced the deficits in basal synaptic transmission and rescued LTP expression. The PDE4B inhibitor reduced tumor necrosis factor-α levels and increased phosphorylated CREB levels after TBI, suggesting that this drug inhibited molecular pathways in the brain known to be regulated by PDE4B. These results suggest that a subtype-selective PDE4B inhibitor is a potential therapeutic to reverse chronic learning and memory dysfunction and deficits in hippocampal synaptic plasticity following TBI.

SIGNIFICANCE STATEMENT

Currently, there are an estimated 3.2-5.3 million individuals living with disabilities from traumatic brain injury (TBI) in the United States, and 8 of 10 of these individuals report cognitive disabilities (Thurman et al., 1999; Lew et al., 2006; Zaloshnja et al., 2008). One of the molecular mechanisms associated with chronic cognitive disabilities is impaired cAMP signaling in the hippocampus. In this study, we report that a selective phosphodiesterase 4B (PDE4B) inhibitor reduces chronic cognitive deficits after TBI and rescues deficits in hippocampal long-term potentiation. These results suggest that PDE4B inhibition has the potential to improve learning and memory ability and overall functioning for people living with TBI.

Treatment of persistent post-concussion syndrome due to mild traumatic brain injury: current status and future directions

Persistent post-concussion syndrome caused by mild traumatic brain injury has become a major cause of morbidity and poor quality of life. Unlike the acute care of concussion, there is no consensus for treatment of chronic symptoms. Moreover, most of the pharmacologic and non-pharmacologic treatments have failed to demonstrate significant efficacy on both the clinical symptoms as well as the pathophysiologic cascade responsible for the permanent brain injury. This article reviews the pathophysiology of PCS, the diagnostic tools and criteria, the current available treatments including pharmacotherapy and different cognitive rehabilitation programs, and promising new treatment directions. A most promising new direction is the use of hyperbaric oxygen therapy, which targets the basic pathological processes responsible for post-concussion symptoms; it is discussed here in depth.

COMT and ANKK1 Genetics Interact With Depression to Influence Behavior Following Severe TBI: An Initial Assessment

OBJECTIVE

Genetic variations in the dopamine (DA) system are associated with cortical-striatal behavior in multiple populations. This study assessed associations of functional polymorphisms in the ankyrin repeat and kinase domain (ANKK1; Taq1a) and catechol-O-methyltransferase (COMT; Val158Met) genes with behavioral dysfunction following traumatic brain injury (TBI).

PARTICIPANTS

This was a prospective study of 90 survivors of severe TBI recruited from a level 1 trauma center.

MAIN MEASURES

The Frontal Systems Behavior Scale, a self- or family report questionnaire evaluating behavior associated with frontal lobe dysfunction, was completed 6 and 12 months postinjury. Depression was measured concurrently with the Patient Health Questionnaire-9. Study participants were genotyped for Val158Met and Taq1a polymorphisms.

RESULTS

No statistically significant behavioral differences were observed by Taq1a or Val158Met genotype alone. At 12 months, among those with depression, Met homozygotes (Val158Met) self-reported worse behavior than Val carriers (P = .015), and A2 homozygotes (Taq1a) self-reported worse behavior than A1 carriers (P = .028) in bivariable analysis. Multivariable models suggest an interaction between depression and genetic variation with behavior at 12 months post-TBI, and descriptive analysis suggests that carriage of both risk alleles may contribute to worse behavioral performance than carriage of either risk allele alone.

CONCLUSION

In the context of depression, Val158Met and Taq1a polymorphisms are individually associated with behavioral dysfunction 12 months following severe TBI, with preliminary evidence suggesting cumulative, or perhaps epistatic, effects of COMT and ANKK1 on behavioral dysfunction.

The Relationship between Learning Style Preferences and Memory Strategy use in Adults

Deficits in working memory are pervasive, resistant to remediation and significantly impact a persons ability to perform activities of daily living. Internal strategies are effective for improving working memory. Learning style preferences may influence the use of various internal working memory strategies. This study compares the use of internal working memory strategies among four different learning style preferences; converger, diverger, assimilator and accommodator. A non-experimental group design was used to compare the use of internal working memory strategies and learning style preferences among 110 adults. There were some significant differences in the types of strategies used according to learning style preferences. Knowing the learning style preference of clients may help occupational therapists better tailor cognitive rehabilitation treatments to meet the client's needs.

Traumatic Brain Injury Causes Aberrant Migration of Adult-Born Neurons in the Hippocampus

Traumatic brain injury (TBI) promotes neural stem/progenitor cell (NSC) proliferation in an attempt to initiate innate repair mechanisms. However, all immature neurons in the CNS are required to migrate from their birthplace to their final destination to develop into functional neurons. Here we assessed the destination of adult-born neurons following TBI. We found that a large percentage of immature neurons migrated past their normal stopping site at the inner granular cell layer (GCL), and became misplaced in the outer GCL of the hippocampal dentate gyrus. The aberrant migration of adult-born neurons in the hippocampus occurred 48 hours after TBI, and lasted for 8 weeks, resulting in a great number of newly generated neurons misplaced in the outer GCL in the hippocampus. Those misplaced neurons were able to become mature and differentiate into granular neurons, but located ectopically in the outer GCL with reduced dendritic complexity after TBI. The adult-born neurons at the misplaced position may make wrong connections with inappropriate nearby targets in the pre-existing neural network. These results suggest that although stimulation of endogenous NSCs following TBI might offer new avenues for cell-based therapy, additional intervention is required to further enhance successful neurogenesis for repairing the damaged brain.

Associations between interhemispheric functional connectivity and the Automated Neuropsychological Assessment Metrics (ANAM) in civilian mild TBI

This study investigates cognitive deficits and alterations in resting state functional connectivity in civilian mild traumatic brain injury (mTBI) participants with high and low symptoms. Forty-one mTBI participants completed a resting state fMRI scan and the Automated Neuropsychological Assessment Metrics (ANAM) during initial testing (<10 days of injury) and a 1 month follow up. Data were compared to 30 healthy control subjects. Results from the ANAM demonstrate that mTBI participants performed significantly worse than controls on the code substitution delayed subtest (p = 0.032). [corrected]. Among the mTBI patients, high symptom mTBI participants performed worse than those with low symptoms on the code substitution delayed (p = 0.017), code substitution (p = 0.012), repeated simple reaction time (p = 0.031), and weighted throughput score (p = 0.019). [corrected]. Imaging results reveal that during the initial visit, low symptom mTBI participants had reduced interhemispheric functional connectivity (IH-FC) within the lateral parietal lobe (p = 0.020); however, during follow up, high symptom mTBI participants showed reduced IH-FC compared to the control group within the dorsolateral prefrontal cortex (DLPFC) (p = 0.013). Reduced IH-FC within the DLPFC during the follow-up was associated with reduced cognitive performance. Together, these findings suggest that reduced rs-FC may contribute to the subtle cognitive deficits noted in high symptom mTBI participants compared to control subjects and low symptom mTBI participants.

Increased working memory related fMRI signal in children following Tick Borne Encephalitis

OBJECTIVE

Tick Borne Encephalitis (TBE) is a viral infection in the central nervous system endemic in Europe and Asia. While pediatric infection may carry a lower risk for serious neurological sequelae compared to adults, a large proportion of children experience long term cognitive problems, most markedly decreased working memory capacity. We explored whether task related functional magnetic resonance imaging (MRI) and diffusion tensor imaging (DTI) could reveal a biological correlate of status-post TBE in children.

METHODS

We examined 11 serologically verified pediatric TBE patients with central nervous system involvement with 55 healthy controls with working memory tests and MRI.

RESULTS

The TBE patients showed a prominent deficit in working memory capacity and an increased task related functional MRI signal in working memory related cortical areas during a spatial working memory task performed without sedation. No diffusion differences could be found with DTI, in line with the reported paucity of anatomical abnormalities.

CONCLUSION

This study is the first to demonstrate functional MRI abnormalities in TBE patients that bears similarity to other patient groups with diffuse neuronal damage.

Compensation through Functional Hyperconnectivity: A Longitudinal Connectome Assessment of Mild Traumatic Brain Injury

Mild traumatic brain injury (mTBI) is a major public health concern. Functional MRI has reported alterations in several brain networks following mTBI. However, the connectome-scale brain network changes are still unknown. In this study, sixteen mTBI patients were prospectively recruited from an emergency department and followed up at 4-6 weeks after injury. Twenty-four healthy controls were also scanned twice with the same time interval. Three hundred fifty-eight brain landmarks that preserve structural and functional correspondence of brain networks across individuals were used to investigate longitudinal brain connectivity. Network-based statistic (NBS) analysis did not find significant difference in the group-by-time interaction and time effects. However, 258 functional pairs show group differences in which mTBI patients have higher functional connectivity. Meta-analysis showed that "Action" and "Cognition" are the most affected functional domains. Categorization of connectomic signatures using multiview group-wise cluster analysis identified two patterns of functional hyperconnectivity among mTBI patients: (I) between the posterior cingulate cortex and the association areas of the brain and (II) between the occipital and the frontal lobes of the brain. Our results demonstrate that brain concussion renders connectome-scale brain network connectivity changes, and the brain tends to be hyperactivated to compensate the pathophysiological disturbances.

Imaging assessment of traumatic brain injury

Traumatic brain injury (TBI) constitutes injury that occurs to the brain as a result of trauma. It should be appreciated as a heterogeneous, dynamic pathophysiological process that starts from the moment of impact and continues over time with sequelae potentially seen many years after the initial event. Primary traumatic brain lesions that may occur at the moment of impact include contusions, haematomas, parenchymal fractures and diffuse axonal injury. The presence of extra-axial intracranial lesions such as epidural and subdural haematomas and subarachnoid haemorrhage must be anticipated as they may contribute greatly to secondary brain insult by provoking brain herniation syndromes, cranial nerve deficits, oedema and ischaemia and infarction. Imaging is fundamental to the management of patients with TBI. CT remains the imaging modality of choice for initial assessment due to its ease of access, rapid acquisition and for its sensitivity for detection of acute haemorrhagic lesions for surgical intervention. MRI is typically reserved for the detection of lesions that may explain clinical symptoms that remain unresolved despite initial CT. This is especially apparent in the setting of diffuse axonal injury, which is poorly discerned on CT. Use of particular MRI sequences may increase the sensitivity of detecting such lesions: diffusion-weighted imaging defining acute infarction, susceptibility-weighted imaging affording exquisite data on microhaemorrhage. Additional advanced MRI techniques such as diffusion tensor imaging and functional MRI may provide important information regarding coexistent structural and functional brain damage. Gaining robust prognostic information for patients following TBI remains a challenge. Advanced MRI sequences are showing potential for biomarkers of disease, but this largely remains at the research level. Various global collaborative research groups have been established in an effort to combine imaging data with clinical and epidemiological information to provide much needed evidence for improvement in the characterisation and classification of TBI and in the identity of the most effective clinical care for this patient cohort. However, analysis of collaborative imaging data is challenging: the diverse spectrum of image acquisition and postprocessing limits reproducibility, and there is a requirement for a robust quality assurance initiative. Future clinical use of advanced neuroimaging should ensure standardised approaches to image acquisition and analysis, which can be used at the individual level, with the expectation that future neuroimaging advances, personalised to the patient, may improve prognostic accuracy and facilitate the development of new therapies.

Executive Functioning of Combat Mild Traumatic Brain Injury

This study investigates neuropsychological deficits in recently deployed veterans with mild traumatic brain injury (mTBI). Veterans discharged from 2007 to 2012 were recruited from Veterans Affairs clinics. Independent groups of participants with mTBI (n = 57) and those without TBI (n = 57) were administered the Beck Depression Inventory-II, Combat Exposure Scale, Word Memory Test, and the Self-Awareness of Deficits Interview. Neuropsychological instruments included the Rey-Osterrieth Complex Figure Test, Letter and Category Fluency, Trail-Making Test-Parts A and B, Christiansen H-abbreviated, Soper Neuropsychology Screen, Wechsler Memory Scale subtests Logical Memory I and II, and the Street Completion Test. The mTBI group performed significantly worse on all of the executive and nonexecutive measurements with the exception of Category Fluency, after controlling for age, depression effort, and combat exposure. Depression and combat exposure were greater for the mTBI group. The mTBI group scored poorer on effort, but only the Multiple Choice subtest was significant. The mTBI group had good awareness of their deficits.

Imaging of Traumatic Brain Injury

Imaging plays an important role in the management of patients with traumatic brain injury (TBI). Computed tomography (CT) is the first-line imaging technique allowing rapid detection of primary structural brain lesions that require surgical intervention. CT also detects various deleterious secondary insults allowing early medical and surgical management. Serial imaging is critical to identifying secondary injuries. MR imaging is indicated in patients with acute TBI when CT fails to explain neurologic findings. However, MR imaging is superior in patients with subacute and chronic TBI and also predicts neurocognitive outcome.

Brain activation during neurocognitive testing using functional near-infrared spectroscopy in patients following concussion compared to healthy controls

There is no accepted clinical imaging modality for concussion, and current imaging modalities including fMRI, DTI, and PET are expensive and inaccessible to most clinics/patients. Functional near-infrared spectroscopy (fNIRS) is a non-invasive, portable, and low-cost imaging modality that can measure brain activity. The purpose of this study was to compare brain activity as measured by fNIRS in concussed and age-matched controls during the performance of cognitive tasks from a computerized neurocognitive test battery. Participants included nine currently symptomatic patients aged 18-45 years with a recent (15-45 days) sport-related concussion and five age-matched healthy controls. The participants completed a computerized neurocognitive test battery while wearing the fNIRS unit. Our results demonstrated reduced brain activation in the concussed subject group during word memory, (spatial) design memory, digit-symbol substitution (symbol match), and working memory (X's and O's) tasks. Behavioral performance (percent-correct and reaction time respectively) was lower for concussed participants on the word memory, design memory, and symbol match tasks than controls. The results of this preliminary study suggest that fNIRS could be a useful, portable assessment tool to assess reduced brain activation and augment current approaches to assessment and management of patients following concussion.

Cognitive Improvement after Mild Traumatic Brain Injury Measured with Functional Neuroimaging during the Acute Period

Functional neuroimaging studies in mild traumatic brain injury (mTBI) have been largely limited to patients with persistent post-concussive symptoms, utilizing images obtained months to years after the actual head trauma. We sought to distinguish acute and delayed effects of mild traumatic brain injury on working memory functional brain activation patterns < 72 hours after mild traumatic brain injury (mTBI) and again one-week later. We hypothesized that clinical and fMRI measures of working memory would be abnormal in symptomatic mTBI patients assessed < 72 hours after injury, with most patients showing clinical recovery (i.e., improvement in these measures) within 1 week after the initial assessment. We also hypothesized that increased memory workload at 1 week following injury would expose different cortical activation patterns in mTBI patients with persistent post-concussive symptoms, compared to those with full clinical recovery. We performed a prospective, cohort study of working memory in emergency department patients with isolated head injury and clinical diagnosis of concussion, compared to control subjects (both uninjured volunteers and emergency department patients with extremity injuries and no head trauma). The primary outcome of cognitive recovery was defined as resolution of reported cognitive impairment and quantified by scoring the subject’s reported cognitive post-concussive symptoms at 1 week. Secondary outcomes included additional post-concussive symptoms and neurocognitive testing results. We enrolled 46 subjects: 27 with mild TBI and 19 controls. The time of initial neuroimaging was 48 (+22 S.D.) hours after injury (time 1). At follow up (8.7, + 1.2 S.D., days after injury, time 2), 18 of mTBI subjects (64%) reported moderate to complete cognitive recovery, 8 of whom fully recovered between initial and follow-up imaging. fMRI changes from time 1 to time 2 showed an increase in posterior cingulate activation in the mTBI subjects compared to controls. Increases in activation were greater in those mTBI subjects without cognitive recovery. As workload increased in mTBI subjects, activation increased in cortical regions in the right hemisphere. In summary, we found neuroimaging evidence for working memory deficits during the first week following mild traumatic brain injury. Subjects with persistent cognitive symptoms after mTBI had increased requirement for posterior cingulate activation to complete memory tasks at 1 week following a brain injury. These results provide insight into functional activation patterns during initial recovery from mTBI and expose the regional activation networks that may be involved in working memory deficits.

Sex Differences in Working Memory after Mild Traumatic Brain Injury: A Functional MR Imaging Study

PURPOSE

To evaluate sex differences in mild traumatic brain injury (MTBI) with working memory functional magnetic resonance (MR) imaging.

MATERIALS AND METHODS

Research ethics committee approval and patient written informed consent were obtained. Working memory brain activation patterns were assessed with functional MR imaging in 30 patients (15 consecutive men and 15 consecutive women) with MTBI and 30 control subjects (15 consecutive men and 15 consecutive women). Two imaging studies were performed in patients: the initial study, which was performed within 1 month after the injury, and a follow-up study, which was performed 6 weeks after the first study. For each participant, digit span and continuous performance testing were performed before functional MR imaging. Clinical data were analyzed by using Kruskal-Wallis, Mann-Whitney U, Wilcoxon signed rank, and Fisher exact tests. Within- and between-group differences of functional MR imaging data were analyzed with one- and two-sample t tests, respectively.

RESULTS

Among female participants, the total digit span score was lower in the MTBI group than in the control group (P = .044). In initial working memory functional MR imaging studies, hyperactivation was found in the male MTBI group and hypoactivation was found in the female MTBI group compared with control male and female groups, respectively. At the 6-week follow-up study, the female MTBI group showed persistent hypoactivation, whereas the male MTBI group showed a regression of hyperactivation at visual comparison of activation maps. The male MTBI group was also found to have a higher initial ß value than the male control group (P = .040), and there was no significant difference between the male MTBI group and the male control group (P = .221) at follow-up evaluation, which was comparable to findings on activation maps. In the female MTBI group, average ß values at both initial and follow-up studies were lower compared with those in the female control group but were not statistically significant (P = .663 and P = .191, respectively).

CONCLUSION

Female patients with MTBI had lower digit span scores than did female control subjects, and functional MR imaging depicted sex differences in working memory functional activation; hypoactivation with nonrecovery of activation change at follow-up studies may suggest a worse working memory outcome in female patients with MTBI.

A comparison of self-generated versus taught internal strategies for working memory

BACKGROUND

Internal strategies are effective for improving working memory. These internal working memory strategies can be taught or self-generated.

OBJECTIVE

This study compares working memory performance using taught versus self-generated internal working memory strategies and explores the quantity, type and carry-over of the use of these strategies.

METHODS

An experimental cohort design with randomly assigned groups compared the performances among 120 participants on 5 memory tests given prior, immediately following and at 1 month post intervention.

RESULTS

There were no significant differences in the number or type of internal memory strategies used by the groups with chunking, repetition and association used most commonly. The group that self-generated strategies performed significantly better on a contextual memory test and the group that was taught strategies performed better on a face/name recall test for which a specific strategy was taught. The group that was taught strategies performed significantly worse on contextual memory tests from pre-test to follow-up.

CONCLUSIONS

Participants who generated their own strategies or used a specific strategy for a specific task did as well as participants who were taught myriad internal WM strategies. Teaching too many strategies may overwhelm participants or may distract them from using the context that is available in such tasks.

Resting State Functional Connectivity in Mild Traumatic Brain Injury at the Acute Stage: Independent Component and Seed-Based Analyses

Mild traumatic brain injury (mTBI) accounts for more than 1 million emergency visits each year. Most of the injured stay in the emergency department for a few hours and are discharged home without a specific follow-up plan because of their negative clinical structural imaging. Advanced magnetic resonance imaging (MRI), particularly functional MRI (fMRI), has been reported as being sensitive to functional disturbances after brain injury. In this study, a cohort of 12 patients with mTBI were prospectively recruited from the emergency department of our local Level-1 trauma center for an advanced MRI scan at the acute stage. Sixteen age- and sex-matched controls were also recruited for comparison. Both group-based and individual-based independent component analysis of resting-state fMRI (rsfMRI) demonstrated reduced functional connectivity in both posterior cingulate cortex (PCC) and precuneus regions in comparison with controls, which is part of the default mode network (DMN). Further seed-based analysis confirmed reduced functional connectivity in these two regions and also demonstrated increased connectivity between these regions and other regions of the brain in mTBI. Seed-based analysis using the thalamus, hippocampus, and amygdala regions further demonstrated increased functional connectivity between these regions and other regions of the brain, particularly in the frontal lobe, in mTBI. Our data demonstrate alterations of multiple brain networks at the resting state, particularly increased functional connectivity in the frontal lobe, in response to brain concussion at the acute stage. Resting-state functional connectivity of the DMN could serve as a potential biomarker for improved detection of mTBI in the acute setting.

Aging, neurodegenerative disease, and traumatic brain injury: the role of neuroimaging

Traumatic brain injury (TBI) is a highly prevalent condition with significant effects on cognition and behavior. While the acute and sub-acute effects of TBI recover over time, relatively little is known about the long-term effects of TBI in relation to neurodegenerative disease. This issue has recently garnered a great deal of attention due to publicity surrounding chronic traumatic encephalopathy (CTE) in professional athletes, although CTE is but one of several neurodegenerative disorders associated with a history of TBI. Here, we review the literative on neurodegenerative disorders linked to remote TBI. We also review the evidence for neuroimaging changes associated with unhealthy brain aging in the context of remote TBI. We conclude that neuroimaging biomarkers have significant potential to increase understanding of the mechanisms of unhealthy brain aging and neurodegeneration following TBI, with potential for identifying those at risk for unhealthy brain aging prior to the clinical manifestation of neurodegenerative disease.

Mood disorders

Mood disturbances, especially depressive disorders, are the most frequent neuropsychiatric complication of traumatic brain injury (TBI). These disorders have a complex clinical presentation and are highly comorbid with anxiety, substance misuse, and other behavioral alterations such as impulsivity and aggression. Furthermore, once developed, mood disorders tend to have a chronic and refractory course. Thus, the functional repercussion of these disorders is huge, affecting the rehabilitation process and the long-term outcome of TBI patients. The pathophysiology of mood disorders involves the interplay of factors that precede trauma (e.g., genetic vulnerability and previous psychiatric history), factors that pertain to the traumatic injury itself (e.g., type, extent, and location of brain damage) and factors that influence the recovery process (e.g., family and social support). It is hardly surprising that mood disorders are associated with structural and functional changes of neural circuits linking brain areas specialized in emotional processing such as the prefrontal cortex, basal ganglia, and amygdala. In turn, the onset of mood disorders may contribute to further prefrontal dysfunction among TBI patients. Finally, in spite of the prevalence and impact of these disorders, there have been relatively few rigorous studies of therapeutic options. Development of treatment strategies constitutes a priority in this field of research.

Mild traumatic brain injury

Mild traumatic brain injury (TBI) is common but accurate diagnosis and defining criteria for mild TBI and its clinical consequences have been problematic. Mild TBI causes transient neurophysiologic brain dysfunction, sometimes with structural axonal and neuronal damage. Biomarkers, such as newer imaging technologies and protein markers, are promising indicators of brain injury but are not ready for clinical use. Diagnosis relies on clinical criteria regarding depth and duration of impaired consciousness and amnesia. These criteria are particularly difficult to confirm at the least severe end of the mild TBI continuum, especially when relying on subjective, retrospective accounts. The postconcussive syndrome is a controversial concept because of varying criteria, inconsistent symptom clusters and the evidence that similar symptom profiles occur with other disorders, and even in a proportion of healthy individuals. The clinical consequences of mild TBI can be conceptualized as two multidimensional disorders: (1) a constellation of acute symptoms that might be termed early phase post-traumatic disorder (e.g., headache, dizziness, imbalance, fatigue, sleep disruption, impaired cognition), that typically resolve in days to weeks and are largely related to brain trauma and concomitant injuries; (2) a later set of symptoms, a late phase post-traumatic disorder, evolving out of the early phase in a minority of patients, with a more prolonged (months to years), sometimes worsening set of somatic, emotional, and cognitive symptoms. The later phase disorder is highly influenced by a variety of psychosocial factors and has little specificity for brain injury, although a history of multiple concussions seems to increase the risk of more severe and longer duration symptoms. Effective early phase management may prevent or limit the later phase disorder and should include education about symptoms and expectations for recovery, as well as recommendations for activity modifications. Later phase treatment should be informed by thoughtful differential diagnosis and the multiplicity of premorbid and comorbid conditions that may influence symptoms. Treatment should incorporate a hierarchical, sequential approach to symptom management, prioritizing problems with significant functional impact and effective, available interventions (e.g., headache, depression, anxiety, insomnia, vertigo).

Increased brain activation during working memory processing after pediatric mild traumatic brain injury (mTBI)

PURPOSE

The neural substrate of post-concussive symptoms following the initial injury period after mild traumatic brain injury (mTBI) in pediatric populations remains poorly elucidated. This study examined neuropsychological, behavioral, and brain functioning in adolescents post-mTBI to assess whether persistent differences were detectable up to a year post-injury.

METHODS

Nineteen adolescents on average 7.5 months post-mTBI completed neuropsychological testing and an fMRI auditory-verbal N-back working memory task. Parents completed behavioral ratings. The comparison group included 19 healthy controls matched to the mTBI group for demographic variables and N-back task performance.

RESULTS

There were no between-group differences for cognition or behavior ratings. The expected decreased accuracy and increased reaction time as N-back task difficulty increased were apparent. The mTBI group showed significantly greater brain activation than controls during the most difficult working memory load condition.

CONCLUSION

Greater working memory task-related activation was found in adolescents up to one year post-mTBI relative to controls, potentially indicating compensatory activation to support normal task performance. Differences in brain activation in the mTBI group so long after injury may indicate residual alterations in brain function much later than would be expected based on the typical pattern of symptom recovery, which could have important clinical implications.

Altered regulation of protein kinase a activity in the medial prefrontal cortex of normal and brain-injured animals actively engaged in a working memory task

Cyclic adenosine monophosphate (cAMP)-dependent protein kinase A (PKA) signaling is required for short- and long-term memory. In contrast, enhanced PKA activity has been shown to impair working memory, a prefrontal cortex (PFC)-dependent, transient form of memory critical for cognition and goal-directed behaviors. Working memory can be impaired after traumatic brain injury (TBI) in the absence of overt damage to the PFC. The cellular and molecular mechanisms that contribute to this deficit are largely unknown. In the present study, we examined whether altered PKA signaling in the PFC as a result of TBI is a contributing mechanism. We measured PKA activity in medial PFC (mPFC) tissue homogenates prepared from sham and 14-day postinjury rats. PKA activity was measured both when animals were inactive and when actively engaged in a spatial working memory task. Our results demonstrate, for the first time, that PKA activity in the mPFC is actively suppressed in uninjured animals performing a working memory task. By comparison, both basal and working memory-related PKA activity was elevated in TBI animals. Inhibition of PKA activity by intra-mPFC administration of Rp-cAMPS into TBI animals had no influence on working memory performance 30 min postinfusion, but significantly improved working memory when tested 24 h later. This improvement was associated with reduced glutamic acid decarboxylase 67 messenger RNA levels. Taken together, these results suggest that TBI-associated working memory dysfunction may result, in part, from enhanced PKA activity, possibly leading to altered expression of plasticity-related genes in the mPFC.

Emergence of cognitive deficits after mild traumatic brain injury due to hyperthermia

Mild elevations in core temperature can occur in individuals involved in strenuous activities that are risky for potentially sustaining a mild traumatic brain injury (mTBI) or concussion. Recently, we have discovered that mild elevations in brain temperature can significantly aggravate the histopathological consequences of mTBI. However, whether this exacerbation of brain pathology translates into behavioral deficits is unknown. Therefore, we investigated the behavioral consequences of elevating brain temperature to mildly hyperthermic levels prior to mTBI. Adult male Sprague Dawley rats underwent mild fluid-percussion brain injury or sham surgery while normothermic (37 °C) or hyperthermic (39 °C) and were allowed to recover for 7 days. Animals were then assessed for cognition using the water maze and cue and contextual fear conditioning. We found that mTBI alone at normothermia had no effect on long-term cognitive measures whereas mTBI animals that were hyperthermic for 15 min prior to and for 4h after brain injury were significantly impaired on long-term retention for both the water maze and fear conditioning. In contrast, hyperthermic mTBI animals cooled within 15 min to normothermia demonstrated no significant long-term cognitive deficits. Mild TBI irrespective of temperature manipulations resulted in significant short-term working memory deficits. Cortical atrophy and contusions were detected in all mTBI treatment groups and contusion volume was significantly less in hyperthermic mTBI animals that were cooled as compared to hyperthermic mTBI animals that remained hyperthermic. These results indicate that brain temperature is an important variable for mTBI outcome and that mildly elevated temperatures at the time of injury result in persistent cognitive deficits. Importantly, cooling to normothermia after mTBI prevents the development of long-term cognitive deficits caused by hyperthermia. Reducing temperature to normothermic levels soon after mTBI represents a rational approach to potentially mitigate the long-term consequences of mTBI.

A longitudinal evaluation of diffusion kurtosis imaging in patients with mild traumatic brain injury

PRIMARY OBJECTIVE

To investigate longitudinal diffusion tensor imaging (DTI) and diffusion kurtosis imaging (DKI) changes in white and grey matter in patients with mild traumatic brain injury (mTBI).

RESEARCH DESIGN

A prospective case-control study.

METHODS AND PROCEDURES

DKI data was obtained from 24 patients with mTBI along with cognitive assessments within 10 days, 1 month and 6 months post-injury and compared with age-matched control (n¼ 24). Fractional anisotropy (FA), mean diffusivity (MD), radial diffusion (l(r)), mean kurtosis (MK) and radial kurtosis (Kr) were extracted from the thalamus, internal capsule and corpus callosum.

MAIN OUTCOMES AND RESULTS

Results demonstrate reduced Kr and MK in the anterior internal capsule in patients with mTBI across the three visits, and reduced MK in the posterior internal capsule during the 10 day time point. Correlations were observed between the change in MK or Kr between 1–6 months and the improvements in cognition between the 1 and 6 month visits in the thalamus, internal capsule and corpus callosum.

CONCLUSIONS

These data demonstrate that DKI may be sensitive in tracking pathophysiological changes associated with mTBI and may provide additional information to conventional DTI parameters in evaluating longitudinal changes following TBI.

Effort, symptom validity testing, performance validity testing and traumatic brain injury

BACKGROUND

To understand the neurocognitive effects of brain injury, valid neuropsychological test findings are paramount.

REVIEW

This review examines the research on what has been referred to a symptom validity testing (SVT). Above a designated cut-score signifies a 'passing' SVT performance which is likely the best indicator of valid neuropsychological test findings. Likewise, substantially below cut-point performance that nears chance or is at chance signifies invalid test performance. Significantly below chance is the sine qua non neuropsychological indicator for malingering. However, the interpretative problems with SVT performance below the cut-point yet far above chance are substantial, as pointed out in this review. This intermediate, border-zone performance on SVT measures is where substantial interpretative challenges exist. Case studies are used to highlight the many areas where additional research is needed. Historical perspectives are reviewed along with the neurobiology of effort. Reasons why performance validity testing (PVT) may be better than the SVT term are reviewed.

CONCLUSIONS

Advances in neuroimaging techniques may be key in better understanding the meaning of border zone SVT failure. The review demonstrates the problems with rigidity in interpretation with established cut-scores. A better understanding of how certain types of neurological, neuropsychiatric and/or even test conditions may affect SVT performance is needed.

The rich get richer: brain injury elicits hyperconnectivity in core subnetworks

There remains much unknown about how large-scale neural networks accommodate neurological disruption, such as moderate and severe traumatic brain injury (TBI). A primary goal in this study was to examine the alterations in network topology occurring during the first year of recovery following TBI. To do so we examined 21 individuals with moderate and severe TBI at 3 and 6 months after resolution of posttraumatic amnesia and 15 age- and education-matched healthy adults using functional MRI and graph theoretical analyses. There were two central hypotheses in this study: 1) physical disruption results in increased functional connectivity, or hyperconnectivity, and 2) hyperconnectivity occurs in regions typically observed to be the most highly connected cortical hubs, or the "rich club". The current findings generally support the hyperconnectivity hypothesis showing that during the first year of recovery after TBI, neural networks show increased connectivity, and this change is disproportionately represented in brain regions belonging to the brain's core subnetworks. The selective increases in connectivity observed here are consistent with the preferential attachment model underlying scale-free network development. This study is the largest of its kind and provides the unique opportunity to examine how neural systems adapt to significant neurological disruption during the first year after injury.

Reduced GABAergic inhibition in the basolateral amygdala and the development of anxiety-like behaviors after mild traumatic brain injury

Traumatic brain injury (TBI) is a major public health concern affecting a large number of athletes and military personnel. Individuals suffering from a TBI risk developing anxiety disorders, yet the pathophysiological alterations that result in the development of anxiety disorders have not yet been identified. One region often damaged by a TBI is the basolateral amygdala (BLA); hyperactivity within the BLA is associated with increased expression of anxiety and fear, yet the functional alterations that lead to BLA hyperexcitability after TBI have not been identified. We assessed the functional alterations in inhibitory synaptic transmission in the BLA and one mechanism that modulates excitatory synaptic transmission, the α7 containing nicotinic acetylcholine receptor (α7-nAChR), after mTBI, to shed light on the mechanisms that contribute to increased anxiety-like behaviors. Seven and 30 days after a mild controlled cortical impact (CCI) injury, animals displayed significantly greater anxiety-like behavior. This was associated with a significant loss of GABAergic interneurons and significant reductions in the frequency and amplitude of spontaneous and miniature GABAA-receptor mediated inhibitory postsynaptic currents (IPSCs). Decreases in the mIPSC amplitude were associated with reduced surface expression of α1, β2, and γ2 GABAA receptor subunits. However, significant increases in the surface expression and current mediated by α7-nAChR, were observed, signifying increases in the excitability of principal neurons within the BLA. These results suggest that mTBI causes not only a significant reduction in inhibition in the BLA, but also an increase in neuronal excitability, which may contribute to hyperexcitability and the development of anxiety disorders.

Longitudinal white matter changes after traumatic axonal injury

Diffusion tensor imaging (DTI) has been useful in showing compromise after traumatic axonal injury (TAI) at the chronic stage; however, white matter (WM) compromise from acute stage of TAI to chronic stage is not yet well understood. This study aims to examine changes in WM integrity following TAI by obtaining DTI, on average, 1 d post injury and again approximately seven months post-injury. Sixteen patients with complicated mild to severe brain injuries consistent with TAI were recruited in the intensive care unit of a Level I trauma center. Thirteen of these patients were studied longitudinally over the course of the first seven months post-injury. The first scan occurred, on average, 1 d after injury and the second an average of seven months post-injury. Ten healthy individuals, similar to the cohort of patients, were recruited as controls. Whole brain WM and voxel-based analyses of DTI data were conducted. DTI metrics of interest included: fractional anisotropy (FA), mean diffusivity, axial diffusivity (AD), and radial diffusivity (RD). tract-based spatial statistics were used to examine DTI metrics spatially. Acutely, AD and RD increased and RD positively correlated with injury severity. Longitudinal analysis showed reduction in FA and AD (p<0.01), but no change in RD. Possible explanations for the microstructural changes observed over time are discussed.

MLC901, a Traditional Chinese Medicine induces neuroprotective and neuroregenerative benefits after traumatic brain injury in rats

Traumatic brain injury (TBI) is a frequent and clinically highly heterogeneous neurological disorder with large socioeconomic consequences. NeuroAid (MLC601 and MLC901), a Traditional Medicine used in China for patients after stroke has been previously reported to induce neuroprotection and neuroplasticity. This study was designed to evaluate the neuroprotective and neuroregenerative effects of MLC901 in a rat model of TBI. TBI was induced by a moderate lateral fluid percussion applied to the right parietal cortex. MLC901 was injected intraperitoneally at 2h post-TBI, and then administered in drinking water at a concentration of 10mg/ml until sacrifice of the animals. The cognitive deficits induced by TBI were followed by using the "what-where-when" task, which allows the measurement of episodic-like memory. MLC901 treatment decreased brain lesions induced by TBI. It prevented the serum increase of S-100 beta (S100B) and neuron-specific enolase (NSE), which may be markers to predict the neurologic outcome in human patients with TBI. MLC901 reduced the infarct volume when injected up to 2h post-TBI, prevented edema formation and assisted its resolution, probably via the regulation of aquaporin 4. These positive MLC901 effects were associated with an upregulation of vascular endothelial growth factor (VEGF) as well as an increase of endogenous hippocampal neurogenesis and gliogenesis around the lesion. Furthermore, MLC901 reduced cognitive deficits induced by TBI. Rats subjected to TBI displayed a suppression of temporal order memory, which was restored by MLC901. This work provides evidence that MLC901 has neuroprotective and neurorestorative actions, which lead to an improvement in the recovery of cognitive functions in a model of traumatic brain injury.

Traumatic brain injury and young onset dementia: a nationwide cohort study

OBJECTIVE

To investigate the association between traumatic brain injuries (TBIs) and the risk of young onset dementia (YOD), that is, dementia before 65 years of age.

METHODS

The study cohort comprised 811,622 Swedish men (mean age 5 18 years) conscripted for military service between 1969 and 1986. TBIs, dementia, and covariates were extracted from national registers. Time-dependent exposures using Cox proportional hazard regression models were evaluated.

RESULTS

During a median follow-up period of 33 years, there were 45,249 men with at least 1 TBI in the cohort. After adjustment for covariates, 1 mild TBI (hazard ratio [HR] 5 1.0, 95% confidence interval [CI] 5 0.5–2.0), at least 2 mild TBIs (HR 5 2.5, 95% CI 5 0.8–8.1), or 1 severe TBI (HR 5 0.7, 95% CI 5 0.1–5.2) were not associated with Alzheimer dementia (AD). Other types of dementia were strongly associated with the risk of 1 mild TBI (HR 5 3.8, 95% CI 5 2.8–5.2), at least 2 mild TBIs (HR 5 10.4, 95% CI 5 6.3–17.2), and 1 severe TBI (HR 5 11.4, 95% CI 5 7.4–17.5) in age-adjusted analysis. However, these associations were largely attenuated after adjustment for covariates (1 mild TBI: HR 5 1.7; at least 2 mild TBIs: HR 5 1.7; 1 severe TBI: HR 5 2.6; p < 0.05 for all).

INTERPRETATION

In the present study, we found strong associations between YOD of non-AD forms and TBIs of different severity. These associations were, however, markedly attenuated after multivariate adjustment.

Significant improvements in cognitive performance post-transcranial, red/near-infrared light-emitting diode treatments in chronic, mild traumatic brain injury: open-protocol study

This pilot, open-protocol study examined whether scalp application of red and near-infrared (NIR) light-emitting diodes (LED) could improve cognition in patients with chronic, mild traumatic brain injury (mTBI). Application of red/NIR light improves mitochondrial function (especially in hypoxic/compromised cells) promoting increased adenosine triphosphate (ATP) important for cellular metabolism. Nitric oxide is released locally, increasing regional cerebral blood flow. LED therapy is noninvasive, painless, and non-thermal (cleared by the United States Food and Drug Administration [FDA], an insignificant risk device). Eleven chronic, mTBI participants (26-62 years of age, 6 males) with nonpenetrating brain injury and persistent cognitive dysfunction were treated for 18 outpatient sessions (Monday, Wednesday, Friday, for 6 weeks), starting at 10 months to 8 years post- mTBI (motor vehicle accident [MVA] or sports-related; and one participant, improvised explosive device [IED] blast injury). Four had a history of multiple concussions. Each LED cluster head (5.35 cm diameter, 500 mW, 22.2 mW/cm(2)) was applied for 10 min to each of 11 scalp placements (13 J/cm(2)). LEDs were placed on the midline from front-to-back hairline; and bilaterally on frontal, parietal, and temporal areas. Neuropsychological testing was performed pre-LED, and at 1 week, and 1 and 2 months after the 18th treatment. A significant linear trend was observed for the effect of LED treatment over time for the Stroop test for Executive Function, Trial 3 inhibition (p=0.004); Stroop, Trial 4 inhibition switching (p=0.003); California Verbal Learning Test (CVLT)-II, Total Trials 1-5 (p=0.003); and CVLT-II, Long Delay Free Recall (p=0.006). Participants reported improved sleep, and fewer post-traumatic stress disorder (PTSD) symptoms, if present. Participants and family reported better ability to perform social, interpersonal, and occupational functions. These open-protocol data suggest that placebo-controlled studies are warranted.

Visual perception from the perspective of a representational, non-reductionistic, level-dependent account of perception and conscious awareness

This article proposes a new model to interpret seemingly conflicting evidence concerning the correlation of consciousness and neural processes. Based on an analysis of research of blindsight and subliminal perception, the reorganization of elementary functions and consciousness framework suggests that mental representations consist of functions at several different levels of analysis, including truly localized perceptual elementary functions and perceptual algorithmic modules, which are interconnections of the elementary functions. We suggest that conscious content relates to the 'top level' of analysis in a 'situational algorithmic strategy' that reflects the general state of an individual. We argue that conscious experience is intrinsically related to representations that are available to guide behaviour. From this perspective, we find that blindsight and subliminal perception can be explained partly by too coarse-grained methodology, and partly by top-down enhancing of representations that normally would not be relevant to action.

Interventions for attention problems after pediatric traumatic brain injury: what is the evidence?

OBJECTIVE

To gain an understanding of the current state of the evidence for management of attention problems after traumatic brain injury (TBI) in children, determine gaps in the literature, and make recommendations for future research. TYPE: Focused systematic review.

LITERATURE SURVEY

PubMed/Medline and PsychINFO databases were searched for relevant articles published in English during the last 20 years. Keywords included "attention" "attention deficit and disruptive behavior disorders," and "brain injuries." Studies were limited to children.

METHODOLOGY

Titles were examined first and eliminated based on lack of relevancy to attention problems after brain injury in children. This was followed by an abstract and full text review. Article quality was determined based on the US Preventative Services Task Force recommendations for evidence grading.

SYNTHESIS

Four pharmacologic and 10 cognitive therapy intervention studies were identified. These studies varied in level of evidence quality but were primarily nonrandomized or cohort studies.

CONCLUSIONS

There are studies that demonstrate benefits of varying pharmacologic and cognitive therapies for the management of attention problems after TBI. However, there is a paucity of evidence available to definitively guide management of attention problems after pediatric TBI. Larger randomized, controlled trials and multicenter studies are needed to elucidate optimal treatment strategies in this population.

Mediating effects of cognitive effort and depression on intelligence, memory, and executive functions in individuals with mild traumatic brain injury

OBJECTIVE

Mild traumatic brain injury (mTBI) is frequently associated with psychiatric symptoms and cognitive dysfunction, as well as with the receipt of workers' compensation, as many mTBIs occur due to work-related accidents. We hypothesized that depression and insufficient cognitive effort mediate the relationship between sociodemographic variables and cognitive dysfunction in mTBI.

METHODS

A retrospective chart review study was conducted using 115 records of patients with mTBI. Cognitive effort was measured based on scores on the Rey 15-Item Test. Multivariate linear regression analysis was performed to examine factors predictive of cognitive functions. Path analysis was subsequently performed to investigate the mediating effects of depression and cognitive effort in relation to receipt of workers' compensation and demographic variables.

RESULTS

Fifteen of the 115 participants (13.0%) received failing scores on the Rey 15-Item Test, which indicated insufficient cognitive effort. Path analysis indicated that cognitive effort mediated the effects of age and workers' compensation on cognitive functions.

CONCLUSION

Given the significant mediating effects of cognitive effort on cognitive performance, it is important to address patient motivation and encourage mTBI patients covered by workers' compensation to perform tests with authentic effort.