The Shrinking Brain: Cerebral Atrophy Following Traumatic Brain Injury

Exploring hyperelastic material model discovery for human brain cortex: Multivariate analysis vs. artificial neural network approaches

The human brain, characterized by its intricate architecture, exhibits complex mechanical properties that underpin its critical functional capabilities. Traditional computational methods, such as finite element analysis, have been instrumental in uncovering the fundamental mechanisms governing the brain's physical behaviors. However, accurate predictions of brain mechanics require effective constitutive models to represent the nuanced mechanical properties of brain tissue. In this study, we aimed to identify well-suited material models for human brain tissue by leveraging artificial neural network and multiple regression techniques. These methods were applied to a generalized framework of widely accepted classic models, and their respective outcomes were systematically compared. To evaluate model efficacy, all setups were maintained consistent across both approaches, except for strategies employed to mitigate potential overfitting. Our findings reveal that artificial neural networks are capable of automatically identifying accurate constitutive models from given admissible estimators. However, the five-term and two-term neural network models trained under single-mode and multi-mode loading scenarios, respectively, were found to be suboptimal. These models could be further simplified into two-term and single-term formulations using multiple regression, achieving even higher predictive accuracy. This refinement underscores the importance of rigorous cross-validations of regularization parameters in neural network-based methods to ensure globally optimal model selection. Additionally, our study demonstrates that traditional multivariable regression methods, when combined with appropriate information criterion, are also highly effective in discovering optimal constitutive models. These insights contribute to the ongoing development of advanced material constitutive models, particularly for complex biological tissues.

An iterative ROC procedure identifies white matter tracts diagnostic for traumatic brain injury: an exploratory analysis in U.S. Veterans

OBJECTIVE

Understanding the pathophysiology of traumatic brain injury (TBI) is crucial for effectively managing care. Diffusion tensor imaging (DTI) is an MRI technology that evaluates TBI pathology in brain white matter. However, DTI analysis generates numerous measures. Choosing between them remains an obstacle to clinical translation. In this study, we leveraged an iterative receiver operating characteristic (ROC) analysis to examine white matter tracts in a group of 380 Veterans, consisting of TBI (n = 243) and non-TBI patients (n = 137).

METHOD

For each participant, we obtained a whole brain tractography and extracted DTI measures from 50 tracts. The ROC analyzed these variables and produced decision trees of tracts diagnostic for TBI. We expanded our findings by applying jackknife resampling. This procedure removed potential outliers and yielded tracts not observed in the initial ROCs. Finally, we used logistic regression to confirm the tracts predicted TBI status.

RESULTS

Our results indicate ROC can identify tracts diagnostic for TBI. We also found that groups of tracts are more predictive than any single one.

CONCLUSIONS

These analyses show that ROC is a useful tool for exploring large, multivariate datasets and may inform the design of clinical algorithms.

Brain Atrophy Is Associated with Hematoma Expansion in Intracerebral Hemorrhage, Depending on Coagulation Status

Background/Objectives: This study aimed to research the potential association between brain atrophy and hematoma expansion (HE) in intracerebral hemorrhage (ICH). Methods: A retrospective analysis was conducted using data from patients with primary ICH in our stroke database. ICH volumes from initial and follow-up CT scans were manually segmented. Total brain and intracranial volumes were quantified using an automated head CT segmentation method. Normalized brain volume (NBV) was calculated by dividing the total brain volume by the total intracranial volume to account for individual head size differences. The relationship between the NBV and hematoma expansion was assessed using linear regression, adjusting for other variables influencing hematoma expansion. Results: Our final analysis included 420 patients. Brain atrophy (lower NBV) was associated with hematoma growth (>0 mL) in patients not on oral anticoagulants (β = -0.159, p = 0.032). A strong association was observed in patients using vitamin K antagonists (β = -0.667, p = 0.006) but not in those on direct oral anticoagulants (DOACs; (β = -0.159, p = 0.436)). Results remained significant in patients not on oral anticoagulants and in those on VKAs when hematoma expansion was defined as a volume increase >6 mL or >33%. Conclusions: This research provides initial evidence that brain atrophy is a risk factor for hematoma expansion, depending on the patient's coagulation status. These findings could enhance risk stratification for acute clinical management and deepen understanding of the biological mechanisms behind hematoma expansion.

Brain Volume Loss After Stereotactic Laser Interstitial Thermal Therapy in Patients With Temporal Lobe Epilepsy

BACKGROUND AND PURPOSE

Temporal lobe epilepsy is the most common form of focal epilepsy. MR-guided laser interstitial thermal therapy (LITT) of the amygdalohippocampal complex has become an established therapy option in case of drug resistance. Long-term anatomic network effects on the brain due to deafferentiation have not yet been evaluated.

METHODS

We analyzed brain volumes of 11 patients with temporal lobe epilepsy before and 1-year after hippocampal LITT with FastSurfer segmenting T1-weighted data. Additionally, we performed visual ratings and measurements.

RESULTS

A total of 11 patients with temporal lobe epilepsy (7 left-sided, 4 right-sided) were included (5 females); the mean age years (±standard deviation) at surgery was 41.5 (±18.4) years. The mean postoperative defect size was 1427 (±517) mm3. Volumetry as well as visual ratings found a progressive volume loss after left-sided surgery in the ipsilateral temporal lobe, the contralateral (right) part of the thalamus, and especially contralateral (right) fusiform cortex. These changes could not be detected for right-sided surgery.

CONCLUSION

A (partial) ablation of the left (dominant) hippocampus appears to exert long-term effects on the right thalamus and right-sided temporal cortices. However, we could not observe this effect in the reverse direction. Volumetric studies for larger cohorts should be conducted to investigate these findings.

Time restricted feeding alters the behavioural and physiological outcomes to repeated mild traumatic brain injury in male and female rats

Mild traumatic brain injury (mTBI) research has had limited success translating treatments from preclinical models to clinical application for concussion. One major factor that has been overlooked is the near 24-hour availability of food, both for experimental nocturnal rodents and patients suffering from mTBI. Here, we characterised the impact of food restriction limited to either the inactive (day) or the active phase (night), on repetitive mTBI (RmTBI) - induced outcomes in male and female rats. We found that active phase fed rats consumed more food, had increased body weight, and reduced brain weights. Behaviourally, active phase feeding increased motor coordination deficits and caused changes to thermal nociceptive processing following RmTBI. Hypothalamic transcriptomic analysis revealed minor changes in response to RmTBI, and genes associated with oxytocin-vasopressin regulation in response to inactive phase, but not active phase feeding. These transcript changes were absent in females, where the overall effect of RmTBI was minor. Prefrontal cortex lipidomics revealed an increase in sphingomyelin synthesis following injury and marked sex differences in response to feeding. Of the lipids that changed and overlapped between the prefrontal cortex and serum, dihydroceramides, sphingomyelins, and hexosylceramides, were higher in the serum but lower in the prefrontal cortex. Together, these results demonstrate that feeding time alters outcomes to RmTBI, independent of the hypothalamic transcriptome, and injury-specific lipids may serve as useful biomarkers in RmTBI diagnosis.

Dense convolution-based attention network for Alzheimer's disease classification

Recently, deep learning-based medical image classification models have made substantial advancements. However, many existing models prioritize performance at the cost of efficiency, limiting their practicality in clinical use. Traditional Convolutional Neural Network (CNN)-based methods, Transformer-based methods, and hybrid approaches combining these two struggle to balance performance and model complexity. To achieve efficient predictions with a low parameter count, we propose DenseAttentionNetwork (DANet), a lightweight model for Alzheimer's disease detection in 3D MRI images. DANet leverages dense connections and a linear attention mechanism to enhance feature extraction and capture long-range dependencies. Its architecture integrates convolutional layers for localized feature extraction with linear attention for global context, enabling efficient multi-scale feature reuse across the network. By replacing traditional self-attention with a parameter-efficient linear attention mechanism, DANet overcomes some limitations of standard self-attention. Extensive experiments across multi-institutional datasets demonstrate that DANet achieves the best performance in area under the receiver operating characteristic curve (AUC), which underscores the model's robustness and effectiveness in capturing relevant features for Alzheimer's disease detection while also attaining a strong accuracy structure with fewer parameters. Visualizations based on activation maps further verify the model's ability to highlight AD-relevant regions in 3D MRI images, providing clinically interpretable insights into disease progression.

Relationship Between Structural and Functional Network Connectivity Changes for Patients With Traumatic Brain Injury and Chronic Health Symptoms

Combination of structural and functional brain connectivity methods provides a more complete and effective avenue into the investigation of cortical network responses to traumatic brain injury (TBI) and subtle alterations in brain connectivity associated with TBI. Structural connectivity (SC) can be measured using diffusion tensor imaging to evaluate white matter integrity, whereas functional connectivity (FC) can be studied by examining functional correlations within or between functional networks. In this study, the alterations of SC and FC were assessed for TBI patients, with and without chronic symptoms (TBIcs/TBIncs), compared with a healthy control group (CG). The correlation between global SC and FC was significantly increased for both TBI groups compared with CG. SC was significantly lower in the TBIcs group compared with CG, and FC changes were seen in the TBIncs group compared with CG. When comparing TBI groups, FC differences were observed in the TBIcs group compared with the TBIncs group. These observations show that the presence of chronic symptoms is associated with a distinct pattern of SC and FC changes including the atrophy of the SC and a mixture of functional hypoconnectivity and hyperconnectivity, as well as loss of segregation of functional networks.

A universal material model subroutine for soft matter systems

Soft materials play an integral part in many aspects of modern life including autonomy, sustainability, and human health, and their accurate modeling is critical to understand their unique properties and functions. Today's finite element analysis packages come with a set of pre-programmed material models, which may exhibit restricted validity in capturing the intricate mechanical behavior of these materials. Regrettably, incorporating a modified or novel material model in a finite element analysis package requires non-trivial in-depth knowledge of tensor algebra, continuum mechanics, and computer programming, making it a complex task that is prone to human error. Here we design a universal material subroutine, which automates the integration of novel constitutive models of varying complexity in non-linear finite element packages, with no additional analytical derivations and algorithmic implementations. We demonstrate the versatility of our approach to seamlessly integrate innovative constitutive models from the material point to the structural level through a variety of soft matter case studies: a frontal impact to the brain; reconstructive surgery of the scalp; diastolic loading of arteries and the human heart; and the dynamic closing of the tricuspid valve. Our universal material subroutine empowers all users, not solely experts, to conduct reliable engineering analysis of soft matter systems. We envision that this framework will become an indispensable instrument for continued innovation and discovery within the soft matter community at large.

Cerebral Gray Matter May Not Explain Sleep Slow-Wave Characteristics after Severe Brain Injury

Sleep slow waves are the hallmark of deeper non-rapid eye movement sleep. It is generally assumed that gray matter properties predict slow-wave density, morphology, and spectral power in healthy adults. Here, we tested the association between gray matter volume (GMV) and slow-wave characteristics in 27 patients with moderate-to-severe traumatic brain injury (TBI, 32.0 ± 12.2 years old, eight women) and compared that with 32 healthy controls (29.2 ± 11.5 years old, nine women). Participants underwent overnight polysomnography and cerebral MRI with a 3 Tesla scanner. A whole-brain voxel-wise analysis was performed to compare GMV between groups. Slow-wave density, morphology, and spectral power (0.4-6 Hz) were computed, and GMV was extracted from the thalamus, cingulate, insula, precuneus, and orbitofrontal cortex to test the relationship between slow waves and gray matter in regions implicated in the generation and/or propagation of slow waves. Compared with controls, TBI patients had significantly lower frontal and temporal GMV and exhibited a subtle decrease in slow-wave frequency. Moreover, higher GMV in the orbitofrontal cortex, insula, cingulate cortex, and precuneus was associated with higher slow-wave frequency and slope, but only in healthy controls. Higher orbitofrontal GMV was also associated with higher slow-wave density in healthy participants. While we observed the expected associations between GMV and slow-wave characteristics in healthy controls, no such associations were observed in the TBI group despite lower GMV. This finding challenges the presumed role of GMV in slow-wave generation and morphology.

Mitigating Traumatic Brain Injury: A Narrative Review of Supplementation and Dietary Protocols

Traumatic brain injuries (TBIs) constitute a significant public health issue and a major source of disability and death in the United States and worldwide. TBIs are strongly associated with high morbidity and mortality rates, resulting in a host of negative health outcomes and long-term complications and placing a heavy financial burden on healthcare systems. One promising avenue for the prevention and treatment of brain injuries is the design of TBI-specific supplementation and dietary protocols centred around nutraceuticals and biochemical compounds whose mechanisms of action have been shown to interfere with, and potentially alleviate, some of the neurophysiological processes triggered by TBI. For example, evidence suggests that creatine monohydrate and omega-3 fatty acids (DHA and EPA) help decrease inflammation, reduce neural damage and maintain adequate energy supply to the brain following injury. Similarly, melatonin supplementation may improve some of the sleep disturbances often experienced post-TBI. The scope of this narrative review is to summarise the available literature on the neuroprotective effects of selected nutrients in the context of TBI-related outcomes and provide an evidence-based overview of supplementation and dietary protocols that may be considered in individuals affected by-or at high risk for-concussion and more severe head traumas. Prophylactic and/or therapeutic compounds under investigation include creatine monohydrate, omega-3 fatty acids, BCAAs, riboflavin, choline, magnesium, berry anthocyanins, Boswellia serrata, enzogenol, N-Acetylcysteine and melatonin. Results from this analysis are also placed in the context of assessing and addressing important health-related and physiological parameters in the peri-impact period such as premorbid nutrient and metabolic health status, blood glucose regulation and thermoregulation following injury, caffeine consumption and sleep behaviours. As clinical evidence in this research field is rapidly emerging, a comprehensive approach including appropriate nutritional interventions has the potential to mitigate some of the physical, neurological, and emotional damage inflicted by TBIs, promote timely and effective recovery, and inform policymakers in the development of prevention strategies.

Serum NfL and GFAP as biomarkers of progressive neurodegeneration in TBI

BACKGROUND

We examined spatial patterns of brain atrophy after mild, moderate, and severe traumatic brain injury (TBI), the relationship between progression of brain atrophy with initial traumatic axonal injury (TAI), cognitive outcome, and with serum biomarkers of brain injury.

METHODS

A total of 143 patients with TBI and 43 controls were studied cross-sectionally and longitudinally up to 5 years with multiple assessments, which included brain magnetic resonance imaging, cognitive testing, and serum biomarkers.

RESULTS

TBI patients showed progressive volume loss regardless of injury severity over several years, and TAI was independently associated with accelerated brain atrophy. Cognitive performance improved over time. Higher baseline serum neurofilament light (NfL) and glial fibrillary acidic protein (GFAP) were associated with greater rate of brain atrophy over 5 years.

DISCUSSSION

Spatial patterns of atrophy differ by injury severity and TAI is associated with the progression of brain atrophy. Serum NfL and GFAP show promise as non-invasive prognostic biomarkers of progressive neurodegeneration in TBI.

HIGHLIGHTS

In this longitudinal study of patient with mild, moderate, and severe traumatic brain injury (TBI) who were assessed with paired magnetic resonance imaging (MRI), blood biomarkers, and cognitive assessments, we found that brain atrophy after TBI is progressive and continues for many years even after a mild head trauma without signs of brain injury on conventional MRI. We found that spatial pattern of brain atrophy differs between mild, moderate, and severe TBI, where in patients with mild TBI , atrophy is mainly seen in the gray matter, while in those with moderate to severe brain injury atrophy is predominantly seen in the subcortical gray matter and whiter matter. Cognitive performance improves over time after a TBI. Serum measures of neurofilament light or glial fibrillary acidic protein are associated with progression of brain atrophy after TBI.

Loss of microRNA-15a/16-1 function promotes neuropathological and functional recovery in experimental traumatic brain injury

The diffuse axonal damage in white matter and neuronal loss, along with excessive neuroinflammation, hinder long-term functional recovery after traumatic brain injury (TBI). MicroRNAs (miRs) are small noncoding RNAs that negatively regulate protein-coding target genes in a posttranscriptional manner. Recent studies have shown that loss of function of the miR-15a/16-1 cluster reduced neurovascular damage and improved functional recovery in ischemic stroke and vascular dementia. However, the role of the miR-15a/16-1 cluster in neurotrauma is poorly explored. Here, we report that genetic deletion of the miR-15a/16-1 cluster facilitated the recovery of sensorimotor and cognitive functions, alleviated white matter/gray matter lesions, reduced cerebral glial cell activation, and inhibited infiltration of peripheral blood immune cells to brain parenchyma in a murine model of TBI when compared with WT controls. Moreover, intranasal delivery of the miR-15a/16-1 antagomir provided similar brain-protective effects conferred by genetic deletion of the miR-15a/16-1 cluster after experimental TBI, as evidenced by showing improved sensorimotor and cognitive outcomes, better white/gray matter integrity, and less inflammatory responses than the control antagomir-treated mice after brain trauma. miR-15a/16-1 genetic deficiency and miR-15a/16-1 antagomir also significantly suppressed inflammatory mediators in posttrauma brains. These results suggest miR-15a/16-1 as a potential therapeutic target for TBI.

What Is Brain Damage and Does Electroconvulsive Therapy Cause It?

ABSTRACT

Surveys show public misperceptions and confusion about brain damage and electroconvulsive therapy (ECT). Fictional movies have misrepresented ECT to suggest brain damage and to ridicule mental illness and psychiatric patients. "Brain damage" has become a colloquial expression without consistent meaning. In contrast, brain injury is the medical term for destruction of brain cells, such as from kinetic impact (concussion), hypoxia, or infection. Studies of both high-resolution magnetic resonance imaging (MRI) and enzyme assays find that causes of brain injury are accompanied by observable structural changes on MRI and elevated blood and cerebrospinal fluid levels of brain enzymes that leak from injured brain cells. Concussion is also followed by intracerebral bleeding, progressive brain atrophy, diffuse axonal injury, cranial nerve injury, and 2-4 fold increased risk for dementia. In contrast, there is no evidence that ECT produces any of these. Studies of ECT patients find no brain edema, structural change persisting 6 months, or elevated levels of leaked brain enzymes. Statistical comparisons between brain injury and ECT effects indicate no similarity ( P < 0.00000001). Moreover, the kinetic, thermal, and electrical effects of ECT are far below levels that could possibly cause harm. This robust evidence shows that there is no basis to claim that ECT causes brain injury.

The Effects of Early Life History of TBI on the Progression of Normal Brain Aging with Implications for Increased Dementia Risk

There is increasing interest in the risk conferred on neurological health by a traumatic brain injury (TBI) and how that influences the lifespan trajectory of brain aging. This chapter explores the importance of this issue, population, and methodological considerations, including injury documentation and outcome assessment. We then explore some of the findings in the neuroimaging and neuropsychological research literature examining the interaction between an earlier life history of TBI and the normal aging process. Finally, we consider the limitations of our current knowledge and where the field needs to go in the future.

Chronic Stress in Early Development and Effects on Traumatic Brain Injury Outcome

In recent years, significant advances have been made in the study of mild traumatic brain injury (mTBI). Complete recovery from mTBI normally requires days to weeks, yet a subset of the population suffers from symptoms for weeks to months after injury. The risk factors for these prolonged symptoms have not yet been fully understood. In this chapter, we address one proposed risk factor, early life stress (ELS) and its influence on mTBI recovery. To study the effects of ELS on mTBI recovery, accepted animal models of ELS, including maternal separation, limited bedding and nesting, and chronic unpredictable stress, have been implemented. Combining these ELS models with standardized mTBI models, such as fluid percussion injury or controlled cortical impact, has allowed for a deeper understanding of the neuronal, hormonal, and cognitive changes that occur after mTBI following ELS. These preclinical findings are being used to understand how adverse childhood experiences may predispose a subset of individuals to poorer recovery after mTBI.

Increased brain age and relationships with blood-based biomarkers following concussion in younger populations

OBJECTIVE

Brain age is increasingly being applied to the spectrum of brain injury to define neuropathological changes in conjunction with blood-based biomarkers. However, data from the acute/sub-acute stages of concussion are lacking, especially among younger cohorts.

METHODS

Predicted brain age differences were independently calculated in large, prospectively recruited cohorts of pediatric concussion and matched healthy controls (total N = 446), as well as collegiate athletes with sport-related concussion and matched non-contact sport controls (total N = 184). Effects of repetitive head injury (i.e., exposure) were examined in a separate cohort of contact sport athletes (N = 82), as well as by quantifying concussion history through semi-structured interviews and years of contact sport participation.

RESULTS

Findings of increased brain age during acute and sub-acute concussion were independently replicated across both cohorts, with stronger evidence of recovery for pediatric (4 months) relative to concussed athletes (6 months). Mixed evidence existed for effects of repetitive head injury, as brain age was increased in contact sport athletes, but was not associated with concussion history or years of contact sport exposure. There was no difference in brain age between concussed and contact sport athletes. Total tau decreased immediately (~ 1.5 days) post-concussion relative to the non-contact group, whereas pro-inflammatory markers were increased in both concussed and contact sport athletes. Anti-inflammatory markers were inversely related to brain age, whereas markers of axonal injury (neurofilament light) exhibited a trend positive association.

CONCLUSION

Current and previous findings collectively suggest that the chronicity of brain age differences may be mediated by age at injury (adults > children), with preliminary findings suggesting that exposure to contact sports may also increase brain age.

Spatiotemporal profile of atrophy in the first year following moderate-severe traumatic brain injury

Traumatic brain injury (TBI) triggers progressive neurodegeneration resulting in brain atrophy that continues months-to-years following injury. However, a comprehensive characterization of the spatial and temporal evolution of TBI-related brain atrophy remains incomplete. Utilizing a sensitive and unbiased morphometry analysis pipeline optimized for detecting longitudinal changes, we analyzed a sample consisting of 37 individuals with moderate-severe TBI who had primarily high-velocity and high-impact injury mechanisms. They were scanned up to three times during the first year after injury (3 months, 6 months, and 12 months post-injury) and compared with 33 demographically matched controls who were scanned once. Individuals with TBI already showed cortical thinning in frontal and temporal regions and reduced volume in the bilateral thalami at 3 months post-injury. Longitudinally, only a subset of cortical regions in the parietal and occipital lobes showed continued atrophy from 3 to 12 months post-injury. Additionally, cortical white matter volume and nearly all deep gray matter structures exhibited progressive atrophy over this period. Finally, we found that disproportionate atrophy of cortex along sulci relative to gyri, an emerging morphometric marker of chronic TBI, was present as early as 3 month post-injury. In parallel, neurocognitive functioning largely recovered during this period despite this pervasive atrophy. Our findings demonstrate msTBI results in characteristic progressive neurodegeneration patterns that are divergent across regions and scale with the severity of injury. Future clinical research using atrophy during the first year of TBI as a biomarker of neurodegeneration should consider the spatiotemporal profile of atrophy described in this study.

Multimodal magnetic resonance imaging after experimental moderate and severe traumatic brain injury: A longitudinal correlative assessment of structural and cerebral blood flow changes

Traumatic brain injury (TBI) is a worldwide problem that results in death or disability for millions of people every year. Progressive neurological complications and long-term impairment can significantly disrupt quality of life. We demonstrated the feasibility of multiple magnetic resonance imaging (MRI) modalities to investigate and predict aberrant changes and progressive atrophy of gray and white matter tissue at several acute and chronic time points after moderate and severe parasagittal fluid percussion TBI. T2-weighted imaging, diffusion tensor imaging (DTI), and perfusion weighted imaging (PWI) were performed. Adult Sprague-Dawley rats were imaged sequentially on days 3, 14, and 1, 4, 6, 8, and 12 months following surgery. TBI caused dynamic white and gray matter alterations with significant differences in DTI values and injury-induced alterations in cerebral blood flow (CBF) as measured by PWI. Regional abnormalities after TBI were observed in T2-weighted images that showed hyperintense cortical lesions and significant cerebral atrophy in these hyperintense areas 1 year after TBI. Temporal DTI values indicated significant injury-induced changes in anisotropy in major white matter tracts, the corpus callosum and external capsule, and in gray matter, the hippocampus and cortex, at both early and chronic time points. These alterations were primarily injury-severity dependent with severe TBI exhibiting a greater degree of change relative to uninjured controls. PWI evaluating CBF revealed sustained global reductions in the cortex and in the hippocampus at most time points in an injury-independent manner. We next sought to investigate prognostic correlations across MRI metrics, timepoints, and cerebral pathology, and found that diffusion abnormalities and reductions in CBF significantly correlated with specific vulnerable structures at multiple time points, as well as with the degree of cerebral atrophy observed 1 year after TBI. This study further supports using DTI and PWI as a means of prognostic imaging for progressive structural changes after TBI and emphasizes the progressive nature of TBI damage.

Integrating Neuroimaging Measures in Nursing Research

BACKGROUND

Medical and scientific advancement worldwide has led to a longer lifespan. With the population aging comes the risk of developing cognitive decline. The incorporation of neuroimaging measures in evaluating cognitive changes is limited in nursing research. The aim of this review is to introduce nurse scientists to neuroimaging measures employed to assess the association between brain and cognitive changes.

METHODS

Relevant literature was identified by searching CINAHL, Web of Science, and PubMed databases using the following keywords: "neuroimaging measures," "aging," "cognition," "qualitative scoring," "cognitive ability," "molecular," "structural," and "functional."

RESULTS

Neuroimaging measures can be categorized into structural, functional, and molecular imaging approaches. The structural imaging technique visualizes the anatomical regions of the brain. Visual examination and volumetric segmentation of select structural sequences extract information such as white matter hyperintensities and cerebral atrophy. Functional imaging techniques evaluate brain regions and underlying processes using blood-oxygen-dependent signals. Molecular imaging technique is the real-time visualization of biological processes at the cellular and molecular levels in a given region. Examples of biological measures associated with neurodegeneration include decreased glutamine level, elevated total choline, and elevated Myo-inositol.

DISCUSSION

Nursing is at the forefront of addressing upstream factors impacting health outcomes across a lifespan of a population at increased risk of progressive cognitive decline. Nurse researchers can become more facile in using these measures both in qualitative and quantitative methodology by leveraging previously gathered neuroimaging clinical data for research purposes to better characterize the associations between symptom progression, disease risk, and health outcomes.

Chronic motor performance following different traumatic brain injury severity-A systematic review

Introduction

Traumatic brain injury (TBI) is now known to be a chronic disease, causing ongoing neurodegeneration and linked to increased risk of neurodegenerative motor diseases, such as Parkinson's disease and amyotrophic lateral sclerosis. While the presentation of motor deficits acutely following traumatic brain injury is well-documented, however, less is known about how these evolve in the long-term post-injury, or how the initial severity of injury affects these outcomes. The purpose of this review, therefore, was to examine objective assessment of chronic motor impairment across the spectrum of TBI in both preclinical and clinical models.

Methods

PubMed, Embase, Scopus, and PsycINFO databases were searched with a search strategy containing key search terms for TBI and motor function. Original research articles reporting chronic motor outcomes with a clearly defined TBI severity (mild, repeated mild, moderate, moderate-severe, and severe) in an adult population were included.

Results

A total of 97 studies met the inclusion criteria, incorporating 62 preclinical and 35 clinical studies. Motor domains examined included neuroscore, gait, fine-motor, balance, and locomotion for preclinical studies and neuroscore, fine-motor, posture, and gait for clinical studies. There was little consensus among the articles presented, with extensive differences both in assessment methodology of the tests and parameters reported. In general, an effect of severity was seen, with more severe injury leading to persistent motor deficits, although subtle fine motor deficits were also seen clinically following repeated injury. Only six clinical studies investigated motor outcomes beyond 10 years post-injury and two preclinical studies to 18-24 months post-injury, and, as such, the interaction between a previous TBI and aging on motor performance is yet to be comprehensively examined.

Conclusion

Further research is required to establish standardized motor assessment procedures to fully characterize chronic motor impairment across the spectrum of TBI with comprehensive outcomes and consistent protocols. Longitudinal studies investigating the same cohort over time are also a key for understanding the interaction between TBI and aging. This is particularly critical, given the risk of neurodegenerative motor disease development following TBI.

Prevalence and risk factors of brain atrophy and associated confusion state among adults from three hospitals in northern Tanzania

Introduction

brain atrophy is the reduction of brain volume often accompanied with cognitive changes. Despite the availability of computerized-tomography (CT) scanners in Tanzania, little is known about the magnitude of brain atrophy, its associated confusion state and the risk factors in adults. This study aimed to fill those knowledge gaps.

Methods

a retrospective cross-sectional hospital-based survey was conducted in northern Tanzania using a sample size of 384 CT images of adults who underwent brain CT scans in three referral hospitals. CT images were evaluated using a diagonal brain fraction (DBF) method to determine the presence of brain atrophy. Data for other covariates were also collected.

Results

we report a prevalence of 60.67% for brain atrophy and 35% for the associated confusion state. Association between confusion state and brain atrophy was statistically significant (χ² = 21.954, p<0.001). Brain atrophy was prognosticated by: age (adjusted OR: 1.11; 95% CI [1.05, 1.20], p<0.001), smoking (adjusted OR: 6.97; 95% CI [2.12, 26.19], p<0.001), alcohol-consumption (adjusted OR: 11.87; 95% CI [3.44, 40.81], p<0.001), hypertension (adjusted OR: 61.21; 95 CI [15.20, 349.43], p<0.001), type-2 diabetes mellitus (adjusted OR: 15.67; 95% CI [5.32, 52.77], p<0.001) and white matter demyelination (adjusted OR: 13.45; 95% CI [4.66, 44.25], p<0.001).

Conclusion

there is high prevalence of brain atrophy and associated confusion state among hospitalized adults in northern Tanzania. Reported prognostic factors for brain atrophy such as age, smoking, alcohol consumption, hypertension, type-2 diabetes mellitus and white matter demyelination could help focus interventions in this area.

Volumetric MRI Findings in Mild Traumatic Brain Injury (mTBI) and Neuropsychological Outcome

Region of interest (ROI) volumetric assessment has become a standard technique in quantitative neuroimaging. ROI volume is thought to represent a coarse proxy for making inferences about the structural integrity of a brain region when compared to normative values representative of a healthy sample, adjusted for age and various demographic factors. This review focuses on structural volumetric analyses that have been performed in the study of neuropathological effects from mild traumatic brain injury (mTBI) in relation to neuropsychological outcome. From a ROI perspective, the probable candidate structures that are most likely affected in mTBI represent the target regions covered in this review. These include the corpus callosum, cingulate, thalamus, pituitary-hypothalamic area, basal ganglia, amygdala, and hippocampus and associated structures including the fornix and mammillary bodies, as well as whole brain and cerebral cortex along with the cerebellum. Ventricular volumetrics are also reviewed as an indirect assessment of parenchymal change in response to injury. This review demonstrates the potential role and limitations of examining structural changes in the ROIs mentioned above in relation to neuropsychological outcome. There is also discussion and review of the role that post-traumatic stress disorder (PTSD) may play in structural outcome in mTBI. As emphasized in the conclusions, structural volumetric findings in mTBI are likely just a single facet of what should be a multimodality approach to image analysis in mTBI, with an emphasis on how the injury damages or disrupts neural network integrity. The review provides an historical context to quantitative neuroimaging in neuropsychology along with commentary about future directions for volumetric neuroimaging research in mTBI.

Prospective Study of Gray Matter Atrophy Following Pediatric Mild Traumatic Brain Injury

BACKGROUND AND OBJECTIVES

The clinical and physiologic time course for recovery following pediatric mild traumatic brain injury (pmTBI) remains actively debated. The primary objective of the current study was to prospectively examine structural brain changes (cortical thickness and subcortical volumes) and age-at-injury effects. A priori study hypotheses predicted reduced cortical thickness and hippocampal volumes up to 4 months postinjury, which would be inversely associated with age at injury.

METHODS

Prospective cohort study design with consecutive recruitment. Study inclusion adapted from American Congress of Rehabilitation Medicine (upper threshold) and Zurich Concussion in Sport Group (minimal threshold) and diagnosed by Emergency Department and Urgent Care clinicians. Major neurologic, psychiatric, or developmental disorders were exclusionary. Clinical (Common Data Element) and structural (3 T MRI) evaluations within 11 days (subacute visit [SA]) and at 4 months (early chronic visit [EC]) postinjury. Age- and sex-matched healthy controls (HC) to control for repeat testing/neurodevelopment. Clinical outcomes based on self-report and cognitive testing. Structural images quantified with FreeSurfer (version 7.1.1).

RESULTS

A total of 208 patients with pmTBI (age = 14.4 ± 2.9; 40.4% female) and 176 HC (age = 14.2 ± 2.9; 42.0% female) were included in the final analyses (>80% retention). Reduced cortical thickness (right rostral middle frontal gyrus; d = -0.49) and hippocampal volumes (d = -0.24) observed for pmTBI, but not associated with age at injury. Hippocampal volume recovery was mediated by loss of consciousness/posttraumatic amnesia. Significantly greater postconcussive symptoms and cognitive deficits were observed at SA and EC visits, but were not associated with the structural abnormalities. Structural abnormalities slightly improved balanced classification accuracy above and beyond clinical gold standards (∆+3.9%), with a greater increase in specificity (∆+7.5%) relative to sensitivity (∆+0.3%).

DISCUSSION

Current findings indicate that structural brain abnormalities may persist up to 4 months post-pmTBI and are partially mediated by initial markers of injury severity. These results contribute to a growing body of evidence suggesting prolonged physiologic recovery post-pmTBI. In contrast, there was no evidence for age-at-injury effects or physiologic correlates of persistent symptoms in our sample.

Fixel-based analysis of the diffusion properties of the patients with brain injury and chronic health symptoms

The diffusion properties from diffusion tensor imaging (DTI) are sensitive to white matter (WM) abnormalities and could serve as indicators of diffuse axonal damages incurred during a traumatic brain injury (TBI). Analyses of diffusion metrics in the regions of interest (ROIs) were used to compare the differences in the 18 major fiber tracts in 46 participants, between TBI participants with (n = 17) or without (n = 16) chronic symptoms (CS) and a control group (CG, n = 13). In addition to the widely used diffusion metrics, such as fractional anisotropy (FA), mean (MD), axial (AD) and radial (RD) diffusivities, apparent fiber density (AFD), complexity (CX) and fixel number (FN) derived from Mrtrix3 software package were used to characterize WM tracts and compare between participant groups in the ROIs defined by the fixel numbers. Significant differences were found in FA, AFD, MD, RD and CX in ROIs with different FNs in the corpus callosum forceps minor, left and right inferior longitudinal fasciculus, and left and right uncinate fasciculus for both TBI groups compared to controls. Diffusion properties in ROIs with different FNs can serve as detailed biomarkers of WM abnormalities, especially for individuals with chronic TBI related symptoms.

Dialysis adequacy and hemoglobin levels predict cerebral atrophy in maintenance-hemodialysis patients

The pathogenesis of cerebral atrophy (CA) is not clear. Previous studies show a high incidence of preterm CA in hemodialysis patients. This study aims to investigate the factors influencing CA and to derive a CA prediction nomogram in maintenance-hemodialysis patients. First, brain volumes of hemodialysis patients (≤55 years) were compared against age- and sex-matched healthy controls, and differences were revealed in bilateral insular cisterns width, maximum cerebral sulci width, Evans index, ventricular-brain ratio, frontal atrophy index, and temporal lobe ratio. Then, the patients were divided equally into "no or mild" or "severe" CA groups. Potential factors influencing CA were screened. Kt/V (urea removal index) and hemoglobin levels negatively correlated with CA degree, and were used to establish a nomogram within randomly assigned training and validation patient groups. The areas under the receiver operating characteristic curves (AUROC) for training and validation groups were 0.703 and 0.744, respectively. When potassium and calcium were added to the nomogram, the AUROC for training/validation group increased to 0.748/0.806. The nomogram had optimal AUROC for training (0.759) and validation (0.804) groups when albumin was also included. Hemodialysis patients showed reduced anterior brain volumes and the nomogram established herein may have predictive value for developing CA.

Sclerostin, vascular risk factors, and brain atrophy in excessive drinkers

Objective

Heavy alcohol consumption causes several organic complications, including vessel wall calcification. Vascular damage may be involved in the development of brain atrophy and cognitive impairment. Recently, sclerostin (whose levels may be altered in alcoholics) has emerged as a major vascular risk factor. The objective of the present study is to analyze the prevalence of vascular calcifications in alcoholics, and the relationships of these lesions with brain atrophy, as well as the role of sclerostin on these alterations.

Patients and methods

A total of 299 heavy drinkers and 32 controls were included. Patients underwent cranial computed tomography, and several indices related to brain atrophy were calculated. In addition, patients and controls underwent plain radiography and were evaluated for the presence or absence of vascular calcium deposits, cardiovascular risk factors, liver function, alcohol intake, serum sclerostin, and routine laboratory variables.

Results

A total of 145 (48.47%) patients showed vascular calcium deposits, a proportion significantly higher than that observed in controls (χ² = 16.31; p < 0.001). Vascular calcium deposits were associated with age (t = 6.57; p < 0.001), hypertension (t = 5.49; p < 0.001), daily ethanol ingestion (Z = 2.18; p = 0.029), duration of alcohol consumption (Z = 3.03; p = 0.002), obesity (χ² = 4.65; p = 0.031), total cholesterol (Z = 2.04; p = 0.041), triglycerides (Z = 2.05; p = 0.04), and sclerostin levels (Z = 2.64; p = 0.008). Calcium deposits were significantly related to Bifrontal index (Z = 2.20; p = 0.028) and Evans index (Z = 2.25; p = 0.025). Serum sclerostin levels were related to subcortical brain atrophy, assessed by cella media index (Z = 2.43; p = 0.015) and Huckmann index (ρ = 0.204; p = 0.024). Logistic regression analyses disclosed that sclerostin was the only variable independently related to brain atrophy assessed by altered cella media index. Sclerostin was also related to the presence of vascular calcifications, although this relationship was displaced by age if this variable was also included.

Conclusion

Prevalence of vascular calcification in alcoholics is very high. Vascular calcium deposits are related to brain atrophy. Serum sclerostin is strongly related to brain shrinkage and also shows a significant relationship with vascular calcifications, only displaced by advanced age.

A single closed head injury in male adult mice induces chronic, progressive white matter atrophy and increased phospho-tau expressing oligodendrocytes

Traumatic brain injury (TBI) acutely damages the brain; this injury can evolve into chronic neurodegeneration. While much is known about the chronic effects arising from multiple mild TBIs, far less is known about the long-term effects of a single moderate to severe TBI. We found that a single moderate closed head injury to mice induces diffuse axonal injury within 1-day post-injury (DPI). At 14 DPI, injured animals have atrophy of ipsilesional cortex, thalamus, and corpus callosum, with bilateral atrophy of the dorsal fornix. Atrophy of the ipsilesional corpus callosum is accompanied by decreased fractional anisotropy and increased mean and radial diffusivity that remains unchanged between 14 and 180 DPI. Injured animals show an increased density of phospho-tau immunoreactive (pTau+) cells in the ipsilesional cortex and thalamus, and bilaterally in corpus callosum. Between 14 and 180 DPI, atrophy occurs in the ipsilesional ventral fornix, contralesional corpus callosum, and bilateral internal capsule. Diffusion tensor MRI parameters remain unchanged in white matter regions with delayed atrophy. Between 14 and 180 DPI, pTau+ cell density increases bilaterally in corpus callosum, but decreases in cortex and thalamus. The location of pTau+ cells within the ipsilesional corpus callosum changes between 14 and 180 DPI; density of all cells increases including pTau+ or pTau- cells. >90% of the pTau+ cells are in the oligodendrocyte lineage in both gray and white matter. Density of thioflavin-S+ cells in thalamus increases by 180 DPI. These data suggest a single closed head impact produces multiple forms of chronic neurodegeneration. Gray and white matter regions proximal to the impact site undergo early atrophy. More distal white matter regions undergo chronic, progressive white matter atrophy with an increasing density of oligodendrocytes containing pTau. These data suggest a complex chronic neurodegenerative process arising from a single moderate closed head injury.

Genetic deletion of Krüppel-like factor 11 aggravates traumatic brain injury

BACKGROUND

The long-term functional recovery of traumatic brain injury (TBI) is hampered by pathological events, such as parenchymal neuroinflammation, neuronal death, and white matter injury. Krüppel-like transcription factor 11 (KLF 11) belongs to the zinc finger family of transcription factors and actively participates in various pathophysiological processes in neurological disorders. Up to now, the role and molecular mechanisms of KLF11 in regulating the pathogenesis of brain trauma is poorly understood.

METHODS

KLF11 knockout (KO) and wild-type (WT) mice were subjected to experimental TBI, and sensorimotor and cognitive functions were evaluated by rotarod, adhesive tape removal, foot fault, water maze, and passive avoidance tests. Brain tissue loss/neuronal death was examined by MAP2 and NeuN immunostaining, and Cresyl violet staining. White matter injury was assessed by Luxol fast blue staining, and also MBP/SMI32 and Caspr/Nav1.6 immunostaining. Activation of cerebral glial cells and infiltration of blood-borne immune cells were detected by GFAP, Iba-1/CD16/32, Iba-1/CD206, Ly-6B, and F4/80 immunostaining. Brian parenchymal inflammatory cytokines were measured with inflammatory array kits.

RESULTS

Genetic deletion of KLF11 worsened brain trauma-induced sensorimotor and cognitive deficits, brain tissue loss and neuronal death, and white matter injury in mice. KLF11 genetic deficiency in mice also accelerated post-trauma astrocytic activation, promoted microglial polarization to a pro-inflammatory phenotype, and increased the infiltration of peripheral neutrophils and macrophages into the brain parenchyma. Mechanistically, loss-of-KLF11 function was found to directly increase the expression of pro-inflammatory cytokines in the brains of TBI mice.

CONCLUSION

KLF11 acts as a novel protective factor in TBI. KLF11 genetic deficiency in mice aggravated the neuroinflammatory responses, grey and white matter injury, and impaired long-term sensorimotor and cognitive recovery. Elucidating the functional importance of KLF11 in TBI may lead us to discover novel pharmacological targets for the development of effective therapies against brain trauma.

Purkinje cell vulnerability induced by diffuse traumatic brain injury is linked to disruption of long-range neuronal circuits

Cerebellar dysfunction is commonly observed following traumatic brain injury (TBI). While direct impact to the cerebellum by TBI is rare, cerebellar pathology may be caused by indirect injury via cortico-cerebellar pathways. To address the hypothesis that degeneration of Purkinje cells (PCs), which constitute the sole output from the cerebellum, is linked to long-range axonal injury and demyelination, we used the central fluid percussion injury (cFPI) model of widespread traumatic axonal injury in mice. Compared to controls, TBI resulted in early PC loss accompanied by alterations in the size of pinceau synapses and levels of non-phosphorylated neurofilament in PCs. A combination of vDISCO tissue clearing technique and immunohistochemistry for vesicular glutamate transporter type 2 show that diffuse TBI decreased mossy and climbing fiber synapses on PCs. At 2 days post-injury, numerous axonal varicosities were found in the cerebellum supported by fractional anisotropy measurements using 9.4 T MRI. The disruption and demyelination of the cortico-cerebellar circuits was associated with poor performance of brain-injured mice in the beam-walk test. Despite a lack of direct input from the injury site to the cerebellum, these findings argue for novel long-range mechanisms causing Purkinje cell injury that likely contribute to cerebellar dysfunction after TBI.

Systematic Review of Syndrome of the Trephined and Reconstructive Implications

Syndrome of the trephined (SoT) is a severe complication following decompressive craniectomy resulting in neurological decline which can progress to aphasia, catatonia, and even death. While cranioplasty can reverse neurological symptoms of SoT, awareness of SoT is poor outside of the neurosurgery community. The authors performed a systematic review of the literature on SoT with a focus on reconstructive implications. Search terms "syndrome of the trephined" and "sunken flap syndrome" were applied to PubMed to identify primary studies through October 2021. Full-text review yielded 11 articles discussing SoT and reconstructive techniques or implications with 56 patients undergoing cranial reconstruction. Average age of the patients was 41.8±9.5 years. Sixty-three percent of the patients were male. The most common indication for craniectomy was traumatic brain injury (43%), followed by tumor resection (23%), intracerebral hemorrhage (11%), and aneurysmal subarachnoid hemorrhage (2%). Patients most commonly suffered from motor deficits (52%), decreased wakefulness (30%), depression or anxiety (21%), speech deficits (16%), headache (16%), and cognitive difficulties (2%). Time until presentation of symptoms following decompression was 4.4±8.9 months. Patients typically underwent cranioplasty with polyetheretherketone (48%), titanium mesh (21%), split thickness calvarial bone (16%), full thickness calvarial bone (14%), or split thickness rib graft (4%). Eight percent of patients required free tissue transfer for soft tissue coverage. Traumatic Brain Injury (TBI) was a risk factor for development of SoT when adjusting for age and sex (odds ratio: 8.2, 95% confidence interval: 1.2-8.9). No difference significant difference was observed between length until initial improvement of neurological symptoms following autologous versus allograft reconstruction (P=0.47). SoT can be a neurologically devastating complication of decompressive craniectomy which can resolve following urgent cranioplasty. Familiarity with this syndrome and its reconstructive implications is critical for the plastic surgery provider, who may be called upon to assist with these urgent cases.

The focused quantitative EEG bio-marker in studying childhood atrophic encephalopathy

Although it is a normal involution process in advanced age, brain atrophy—also termed atrophic encephalopathy—can also occur prematurely in childhood as a consequential effect of brain tissues injury through trauma or central nervous system infection, though in both normal and premature occurrences this condition always presents with loss of volume relative to the skull. A common tool for the functional study of brain activities is an electroencephalogram, but analyses of this have reportedly identified mismatches between qualitative and quantitative forms, particularly in the use of Delta-alpha ratio (DAR) indices, meaning that the values may be case dependent. The current study thus examines the value of Focused Occipital Beta-Alpha Ratio (FOBAR) as a modified biomarker for evaluating brain functional changes resulting from brain atrophy. This cross-sectional design study involves 260 patients under 18 years of age. Specifically, 207 patients with brain atrophy are compared with 53 control subjects with CT scan-proven normal brain volume. All the children underwent digital electroencephalography with brain mapping. Results show that alpha posterior dominant rhythm was present in 88 atrophic children and 44 controls. Beta as posterior dominant rhythm was present in an overwhelming 91.5% of atrophic subjects, with 0.009 p-values. The focused occipital Beta-alpha ratio correlated significantly with brain volume loss presented in diagonal brain fraction. The FOBAR and DAR values of the QEEG showed no significant correlation. This work concludes that QEEG cerebral dysfunctional studies may be etiologically and case dependent from the nature of the brain injury. Also, the focused Beta-alpha ratio of the QEEG is a prospective and potential biomarker of consideration in studying childhood atrophic encephalopathy.

“Atypical” Mild Clinical Presentation in Elderly Patients With Ruptured Intracranial Aneurysm: Causes and Clinical Characteristics

Objective

Thunderclap-like severe headache or consciousness disturbance is the common “typical” clinical presentation after aneurysmal subarachnoid hemorrhage (aSAH); however, a slowly developing “atypical” clinical pattern, with mild headache, vomiting, or dizziness, is frequently noted in elderly patients. The aim of this study was to evaluate the clinical characteristics of this “atypical” subgroup, as well as related factors associated with the presence of these mild symptoms.

Methods

The data of 176 elderly patients (≥70 years old) with ruptured intracranial aneurysms (IAs) treated at our center from January 2016 to January 2020 were retrospectively collected and analyzed. The patients were divided into “typical” and “atypical” groups based on their initial and development of clinical symptoms after the diagnosis of aSAH. Intergroup differences were analyzed, and factors related to the presence of these two clinical patterns were explored through multiple logistic regression analyses.

Results

Despite significant admission delay (P &lt; 0.001) caused by mild initial symptoms with slow development, patients in the “atypical” group achieved better clinical prognosis, as indicated by a significantly higher favourable outcome ratio and lower death rate upon discharge and at different time points during the 1-year follow-up, than the “typical” group (P &lt; 0.05). Multiple logistic regression analysis revealed that modified Fisher grade III-IV (OR = 11.182, P = 0.003), brain atrophy (OR = 10.010, P = 0.001), a larger lesion diameter (OR = 1.287, P &lt; 0.001) and current smoking (OR = 5.728, P &lt; 0.001) were independently associated with the presence of “typical” symptoms. Aneurysms with wide necks (OR = 0.013, P &lt; 0.001) were independently associated with the presence of “atypical” symptoms.

Conclusions

“Atypical” presentations, with mild clinical symptoms and slow development, were commonly recorded in elderly patients after the onset of aSAH. Despite the prolonged admission delay, these “atypical” patients achieved better clinical outcomes than those with “typical” symptoms. Modified Fisher grade (III-IV), current smoking, brain atrophy and larger lesion diameter were factors predictive of “typical” symptoms, while aneurysms with wide necks were independently associated with “atypical” symptoms.

K18- and CAG-hACE2 Transgenic Mouse Models and SARS-CoV-2: Implications for Neurodegeneration Research

COVID-19, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is a global pandemic that might lead to very serious consequences. Notably, mental status change, brain confusion, and smell and taste disorders along with neurological complaints have been reported in patients infected with SARS-CoV-2. Furthermore, human brain tissue autopsies from COVID-19 patients show the presence of SARS-CoV-2 neuroinvasion, which correlates with the manifestation of meningitis, encephalitis, leukocyte infiltration, and neuronal damage. The olfactory mucosa has been suggested as a way of entry into the brain. SARS-CoV-2 infection is also known to provoke a hyper-inflammatory reaction with an exponential increase in the production of pro-inflammatory cytokines leading to systemic responses, even in the absence of direct infection of brain cells. Angiotensin-converting enzyme 2 (ACE2), the entry receptor of SARS-CoV-2, has been extensively demonstrated to be present in the periphery, neurons, and glial cells in different brain regions. To dissect the details of neurological complications and develop therapies helping COVID-19 survivors regain pre-infection quality of life, the development of robust clinical models is highly warranted. Several human angiotensin-converting enzyme 2 (hACE2) transgenic mouse models have been developed and used for antiviral drug screening and vaccine development, as well as for better understanding of the molecular pathogenetic mechanisms of SARS-CoV-2 infection. In this review, we summarize recent results from the studies involving two such mouse models, namely K18- and CAG-hACE2 transgenics, to evaluate the direct and indirect impact of SARS-CoV-2 infection on the central nervous system.

Brain age in chronic traumatic brain injury

Traumatic brain injury (TBI) is associated with greater 'brain age' that may be caused by atrophy in grey and white matter. Here, we investigated 'brain age' in a chronic TBI (≥10 years) sample. We examined whether 'brain age' increases with years post injury, and whether it is associated with injury severity, cognition and functional outcome. We recruited 102 participants with moderate to severe TBI aged between 40 and 85 years. TBI participants were assessed on average 22 years post-injury. Seventy-seven healthy controls were also recruited. Participants' 'brain age' was determined using T1-weighted MRI images. TBI participants were estimated to have greater 'brain age' compared to healthy controls. 'Brain age' gap was unrelated to time since injury or long-term functional outcome on the Glasgow Outcome Scale-Extended. Greater brain age was associated with greater injury severity measured by post traumatic amnesia duration and Glasgow Coma Scale. 'Brain age' was significantly and inversely associated with verbal memory, but unrelated to visual memory/ability and cognitive flexibility and processing speed. A longitudinal study is required to determine whether TBI leads to a 'one-off' change in 'brain age' or progressive ageing of the brain over time.

Multiple-region grey matter atrophy as a predictor for the development of dementia in a community: the Hisayama Study

OBJECTIVE

To assess the association of regional grey matter atrophy with dementia risk in a general older Japanese population.

METHODS

We followed 1158 dementia-free Japanese residents aged ≥65 years for 5.0 years. Regional grey matter volume (GMV) at baseline was estimated by applying voxel-based morphometry methods. The GMV-to-total brain volume ratio (GMV/TBV) was calculated, and its association with dementia risk was estimated using Cox proportional hazard models. We assessed whether the predictive ability of a model based on known dementia risk factors could be improved by adding the total number of regions with grey matter atrophy among dementia-related brain regions, where the cut-off value for grey matter atrophy in each region was determined by receiver operating characteristic curves.

RESULTS

During the follow-up, 113 participants developed all-cause dementia, including 83 with Alzheimer's disease (AD). Lower GMV/TBV of the medial temporal lobe, insula, hippocampus and amygdala were significantly/marginally associated with higher risk of all-cause dementia and AD (all p for trend ≤0.08). The risks of all-cause dementia and AD increased significantly with increasing total number of brain regions exhibiting grey matter atrophy (both p for trend <0.01). Adding the total number of regions with grey matter atrophy into a model consisting of known risk factors significantly improved the predictive ability for AD (Harrell's c-statistics: 0.765-0.802; p=0.02).

CONCLUSIONS

Our findings suggest that the total number of regions with grey matter atrophy among the medial temporal lobe, insula, hippocampus and amygdala is a significant predictor for developing dementia, especially AD, in the general older population.

Sex differences in cortical thickness and diffusion properties in patients with traumatic brain injury: a pilot study

OBJECTIVE

Cortical thickness and diffusion properties are important measures of gray and white matter integrity in those with traumatic brain injury (TBI). Many studies show that healthy adult females have greater cortical thickness than males across numerous brain sites. In this study, we explored this sex difference in patients with TBI.

METHOD

Participants consisted of 32 patients with TBI and 21 neurologically healthy controls. All were scanned by magnetic resonance imaging (MRI). Differences in cortical thickness and diffusion properties were examined between groups (i.e., TBI/control, male/female).

RESULTS

Patients with TBI had more cortical thinning (both hemispheres) compared to controls. They also showed decreased fractional anisotropy (FA) for several major white matter tracts. Healthy females had significantly greater cortical thickness compared to healthy males. However, this difference was smaller among the patients with TBI. We found no sex differences in diffusion properties. There were moderate correlations between cortical thickness, diffusion properties, and cognitive performance, as measured by the Trail Making Test B.

CONCLUSION

These findings contribute to a growing discussion on sex differences in cortical thickness and diffusion properties. Sexual dimorphism could necessitate different clinical profiles, targets, and rehabilitation strategies in patients with TBI.

Diffuse traumatic injury in the mouse disrupts axon-myelin integrity in the cerebellum

Cerebellar dysfunction following traumatic brain injury (TBI) is commonly suspected based on clinical symptoms, although cerebellar pathology has rarely been investigated. To address the hypothesis that the cerebellar axon-myelin unit is altered by diffuse TBI, we used the central fluid percussion injury (cFPI) model in adult mice to create wide-spread axonal injury by delivering the impact to the forebrain. We specifically focused on changes in myelin components (myelin basic protein (MBP), 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNPase), nodal/paranodal domains (neurofascin, ankyrin G), and phosphorylated neurofilaments (SMI-31, SMI-312) in the cerebellum, remote from the impact, at 2, 7 and 30-day post-injury. When compared to sham-injured controls, cerebellar MBP and CNPase protein levels were decreased at 2 days post-injury (dpi) that remained reduced up to 30 dpi. Diffuse TBI induced different effects on neuronal (Nfasc 186, Nfasc 140) and glial (Nfasc 155) neurofascin isoforms that play a key role in the assembly of the nodes of Ranvier. Expression of Nfasc 140 in the cerebellum increased at 7 dpi, in contrast to Nfasc 155 levels which were decreased. Although neurofascin binding partner ankyrin G protein levels decreased acutely after cFPI, its expression levels increased at 7 dpi and remained unchanged up to 30 dpi. TBI-induced reduction in neurofilament phosphorylation (SMI-31) observed in the cerebellum was closely associated with decreased levels of the myelin proteins MBP and CNPase. This is the first evidence of temporal and spatial structural changes in the axon-myelin unit in the cerebellum, remote from the location of the impact site in a diffuse TBI model in mice.

Myelin Content in Mild Traumatic Brain Injury Patients with Post-Concussion Syndrome: Quantitative Assessment with a Multidynamic Multiecho Sequence

Objective

This study aimed to explore the myelin volume change in patients with mild traumatic brain injury (mTBI) with post-concussion syndrome (PCS) using a multidynamic multiecho (MDME) sequence and automatic whole-brain segmentation.

Materials and Methods

Forty-one consecutive mTBI patients with PCS and 29 controls, who had undergone MRI including the MDME sequence between October 2016 and April 2018, were included. Myelin volume fraction (MVF) maps were derived from the MDME sequence. After three dimensional T1-based brain segmentation, the average MVF was analyzed at the bilateral cerebral white matter (WM), bilateral cerebral gray matter (GM), corpus callosum, and brainstem. The Mann–Whitney U-test was performed to compare MVF and myelin volume between patients with mTBI and controls. Myelin volume was correlated with neuropsychological test scores using the Spearman rank correlation test.

Results

The average MVF at the bilateral cerebral WM was lower in mTBI patients with PCS (median [interquartile range], 25.2% [22.6%–26.4%]) than that in controls (26.8% [25.6%–27.8%]) (p = 0.004). The region-of-interest myelin volume was lower in mTBI patients with PCS than that in controls at the corpus callosum (1.87 cm³ [1.70–2.05 cm³] vs. 2.21 cm³ [1.86–3.46 cm³]; p = 0.003) and brainstem (9.98 cm³ [9.45–11.00 cm³] vs. 11.05 cm³ [10.10–11.53 cm³]; p = 0.015). The total myelin volume was lower in mTBI patients with PCS than that in controls at the corpus callosum (0.45 cm³ [0.39–0.48 cm³] vs. 0.48 cm³ [0.45–0.54 cm³]; p = 0.004) and brainstem (1.45 cm³ [1.28–1.59 cm³] vs. 1.54 cm³ [1.42–1.67 cm³]; p = 0.042). No significant correlation was observed between myelin volume parameters and neuropsychological test scores, except for the total myelin volume at the bilateral cerebral WM and verbal learning test (delayed recall) (r = 0.425; p = 0.048).

Conclusion

MVF quantified from the MDME sequence was decreased at the bilateral cerebral WM in mTBI patients with PCS. The total myelin volumes at the corpus callosum and brainstem were decreased in mTBI patients with PCS due to atrophic changes.

Brain aging mechanisms with mechanical manifestations

Brain aging is a complex process that affects everything from the subcellular to the organ level, begins early in life, and accelerates with age. Morphologically, brain aging is primarily characterized by brain volume loss, cortical thinning, white matter degradation, loss of gyrification, and ventricular enlargement. Pathophysiologically, brain aging is associated with neuron cell shrinking, dendritic degeneration, demyelination, small vessel disease, metabolic slowing, microglial activation, and the formation of white matter lesions. In recent years, the mechanics community has demonstrated increasing interest in modeling the brain's (bio)mechanical behavior and uses constitutive modeling to predict shape changes of anatomically accurate finite element brain models in health and disease. Here, we pursue two objectives. First, we review existing imaging-based data on white and gray matter atrophy rates and organ-level aging patterns. This data is required to calibrate and validate constitutive brain models. Second, we review the most critical cell- and tissue-level aging mechanisms that drive white and gray matter changes. We focuse on aging mechanisms that ultimately manifest as organ-level shape changes based on the idea that the integration of imaging and mechanical modeling may help identify the tipping point when normal aging ends and pathological neurodegeneration begins.

Morphometric evaluation of traumatic axonal injury and the correlation with post-traumatic cerebral atrophy and functional outcome

INTRODUCTION

Imaging plays a crucial role in the diagnosis, prognosis and follow-up of traumatic brain injury. Whereas computed tomography plays a pivotal role in the acute setting, magnetic resonance imaging is best suited to detect the true extent of traumatic brain injury, and more specifically diffuse axonal injury. Post-traumatic brain atrophy is a well-known complication of traumatic brain injury.

PURPOSE

This study investigated the correlation between diffuse axonal injury detected with fluid-attenuated inversion recovery and susceptibility-weighted imaging magnetic resonance imaging, post-traumatic brain atrophy and functional outcome (Glasgow outcome scale - extended).

MATERIALS AND METHODS

Twenty patients with a closed head injury and diffuse axonal injury detected with fluid-attenuated inversion recovery and susceptibility-weighted imaging were included. The total volumes of the diffuse axonal injury fluid-attenuated inversion recovery lesions were determined for each subject's initial (<14 days) and follow-up magnetic resonance scan (average: day 303 ± 83 standard deviation). The different brain volumes were automatically quantified using a validated and both US Food and Drug Administration-cleared and CE-marked machine learning algorithm (icobrain). The number of susceptibility-weighted imaging lesions and functional outcome scores (Glasgow outcome scale - extended) were retrieved from the Collaborative European NeuroTrauma Effectiveness Research Traumatic Brain Injury dataset.

RESULTS

The volumetric fluid-attenuated inversion recovery diffuse axonal injury lesion load showed a significant inverse correlation with functional outcome (Glasgow outcome scale - extended) (r = -0.57; P = 0.0094) and white matter volume change (r = -0.50; P = 0.027). In addition, white matter volume change correlated significantly with the Glasgow outcome scale - extended score (P = 0.0072; r = 0.58). Moreover, there was a strong inverse correlation between longitudinal fluid-attenuated inversion recovery lesion volume change and whole brain volume change (r = -0.63; P = 0.0028). No significant correlation existed between the number of diffuse axonal injury susceptibility-weighted imaging lesions, brain atrophy and functional outcome.

CONCLUSIONS

Volumetric analysis of diffuse axonal injury on fluid-attenuated inversion recovery imaging and automated brain atrophy calculation are potentially useful tools in the clinical management and follow-up of traumatic brain injury patients with diffuse axonal injury.

Global hippocampal and selective thalamic nuclei atrophy differentiate chronic TBI from Non-TBI

Traumatic brain injury (TBI) may increase susceptibility to neurodegenerative diseases later in life. One neurobiological parallel between chronic TBI and neurodegeneration may be accelerated aging and the nature of atrophy across subcortical gray matter structures. The main aim of the present investigation is to evaluate and rank the degree that subcortical gray matter atrophy differentiates chronic moderate-severe TBI from non-TBI participants by evaluating morphometric differences between groups. Forty individuals with moderate-severe chronic TBI (9.23 yrs from injury) and 33 healthy controls (HC) underwent high resolution 3D T1-weighted structural magnetic resonance imaging. Whole brain volume was classified into white matter, cortical and subcortical gray matter structures with hippocampi and thalami further segmented into subfields and nuclei, respectively. Extensive atrophy was observed across nearly all brain regions for chronic TBI participants. A series of multivariate logistic regression models identified subcortical gray matter structures of the hippocampus and thalamus as the most sensitive to differentiating chronic TBI from non-TBI participants (McFadden R² = .36, p < .001). Further analyses revealed the pattern of hippocampal atrophy to be global, occurring across nearly all subfields. The pattern of thalamic atrophy appeared to be much more selective and non-uniform, with largest between-group differences evident for nuclei bordering the ventricles. Subcortical gray matter was negatively correlated with time since injury (r = -.31, p = .054), while white matter and cortical gray matter were not. Cognitive ability was lower in the chronic TBI group (Cohen's d = .97, p = .003) and correlated with subcortical structures including the pallidum (r² = .23, p = .038), thalamus (r² = .36, p = .007) and ventral diencephalon (r² = .23, p = .036). These data may support an accelerated aging hypothesis in chronic moderate-severe TBI that coincides with a similar neuropathological profile found in neurodegenerative diseases.

Roadmap for Advancing Pre-Clinical Science in Traumatic Brain Injury

Pre-clinical models of disease have long played important roles in the advancement of new treatments. However, in traumatic brain injury (TBI), despite the availability of numerous model systems, translation from bench to bedside remains elusive. Integrating clinical relevance into pre-clinical model development is a critical step toward advancing therapies for TBI patients across the spectrum of injury severity. Pre-clinical models include in vivo and ex vivo animal work-both small and large-and in vitro modeling. The wide range of pre-clinical models reflect substantial attempts to replicate multiple aspects of TBI sequelae in humans. Although these models reveal multiple putative mechanisms underlying TBI pathophysiology, failures to translate these findings into successful clinical trials call into question the clinical relevance and applicability of the models. Here, we address the promises and pitfalls of pre-clinical models with the goal of evolving frameworks that will advance translational TBI research across models, injury types, and the heterogenous etiology of pathology.

Synergistic effects of brain injury and aging: common mechanisms of proteostatic dysfunction

The aftermath of TBI is associated with an acute stress response and the accumulation of insoluble protein aggregates. Even after the symptoms of TBI are resolved, insidious molecular processes continue to develop, which often ultimately result in the development of age-associated neurodegenerative disorders. The precise molecular cascades that drive unhealthy brain aging are still largely unknown. In this review, we discuss proteostatic dysfunction as a converging mechanism contributing to accelerated brain aging after TBI. We examine evidence from human tissue and in vivo animal models, spanning both the aging and injury contexts. We conclude that TBI has a sustained debilitating effect on the proteostatic machinery, which may contribute to the accelerated pathological and cognitive hallmarks of aging that are observed following injury.

Brain Shape Changes Associated With Cerebral Atrophy in Healthy Aging and Alzheimer's Disease

Both healthy and pathological brain aging are characterized by various degrees of cognitive decline that strongly correlate with morphological changes referred to as cerebral atrophy. These hallmark morphological changes include cortical thinning, white and gray matter volume loss, ventricular enlargement, and loss of gyrification all caused by a myriad of subcellular and cellular aging processes. While the biology of brain aging has been investigated extensively, the mechanics of brain aging remains vastly understudied. Here, we propose a multiphysics model that couples tissue atrophy and Alzheimer's disease biomarker progression. We adopt the multiplicative split of the deformation gradient into a shrinking and an elastic part. We model atrophy as region-specific isotropic shrinking and differentiate between a constant, tissue-dependent atrophy rate in healthy aging, and an atrophy rate in Alzheimer's disease that is proportional to the local biomarker concentration. Our finite element modeling approach delivers a computational framework to systematically study the spatiotemporal progression of cerebral atrophy and its regional effect on brain shape. We verify our results via comparison with cross-sectional medical imaging studies that reveal persistent age-related atrophy patterns. Our long-term goal is to develop a diagnostic tool able to differentiate between healthy and accelerated aging, typically observed in Alzheimer's disease and related dementias, in order to allow for earlier and more effective interventions.

Quantitative multimodal imaging in traumatic brain injuries producing impaired cognition

PURPOSE OF REVIEW

Cognitive impairments are a devastating long-term consequence following traumatic brain injury (TBI). This review provides an update on the quantitative mutimodal neuroimaging studies that attempt to elucidate the mechanism(s) underlying cognitive impairments and their recovery following TBI.

RECENT FINDINGS

Recent studies have linked individual specific behavioural impairments and their changes over time to physiological activity and structural changes using EEG, PET and MRI. Multimodal studies that combine measures of physiological activity with knowledge of neuroanatomical and connectivity damage have also illuminated the multifactorial function-structure relationships that underlie impairment and recovery following TBI.

SUMMARY

The combined use of multiple neuroimaging modalities, with focus on individual longitudinal studies, has the potential to accurately classify impairments, enhance sensitivity of prognoses, inform targets for interventions and precisely track spontaneous and intervention-driven recovery.