Midlife measurements of white matter microstructure predict subsequent regional white matter atrophy in healthy adults

Cluster-Based White Matter Signatures and the Risk of Dementia, Stroke, and Mortality in Community-Dwelling Adults

BACKGROUND AND OBJECTIVES

Markers of white matter (WM) injury on brain MRI are important indicators of brain health. Different patterns of WM atrophy, WM hyperintensities (WMHs), and microstructural integrity could reflect distinct pathologies and disease risks, but large-scale imaging studies investigating WM signatures are lacking. This study aims to identify distinct WM signatures using brain MRI in community-dwelling adults, determine underlying risk factor profiles, and assess risks of dementia, stroke, and mortality associated with each signature.

METHODS

Between 2005 and 2016, we measured WMH volume, WM volume, fractional anisotropy (FA), and mean diffusivity (MD) using automated pipelines on structural and diffusion MRI in community-dwelling adults aged older than 45 years of the Rotterdam study. Continuous surveillance was conducted for dementia, stroke, and mortality. We applied hierarchical clustering to identify separate WM injury clusters and Cox proportional hazard models to determine their risk of dementia, stroke, and mortality.

RESULTS

We included 5,279 participants (mean age 65.0 years, 56.0% women) and identified 4 distinct data-driven WM signatures: (1) above-average microstructural integrity and little WM atrophy and WMH; (2) above-average microstructural integrity and little WMH, but substantial WM atrophy; (3) poor microstructural integrity and substantial WMH, but little WM atrophy; and (4) poor microstructural integrity with substantial WMH and WM atrophy. Prevalence of cardiovascular risk factors, lacunes, and cerebral microbleeds was higher in clusters 3 and 4 than in clusters 1 and 2. During a median 10.7 years of follow-up, 291 participants developed dementia, 220 had a stroke, and 910 died. Compared with cluster 1, dementia risk was increased for all clusters, notably cluster 3 (hazard ratio [HR] 3.06, 95% CI 2.12-4.42), followed by cluster 4 (HR 2.31, 95% CI 1.58-3.37) and cluster 2 (HR 1.67, 95% CI 1.17-2.38). Compared with cluster 1, risk of stroke was higher only for clusters 3 (HR 1.55, 95% CI 1.02-2.37) and 4 (HR 1.94, 95% CI 1.30-2.89), whereas mortality risk was increased in all clusters (cluster 2: HR 1.27, 95% CI 1.06-1.53, cluster 3: HR 1.65, 95% CI 1.35-2.03, cluster 4: HR 1.76, 95% CI 1.44-2.15), compared with cluster 1. Models including clusters instead of an individual imaging marker showed a superior goodness of fit for dementia and mortality, but not for stroke.

DISCUSSION

Clustering can derive WM signatures that are differentially associated with dementia, stroke, and mortality risk. Future research should incorporate spatial information of imaging markers.

Distinct patterns of neurodegeneration after TBI and in Alzheimer's disease

INTRODUCTION

Traumatic brain injury (TBI) is a dementia risk factor, with Alzheimer's disease (AD) more common following injury. Patterns of neurodegeneration produced by TBI can be compared to AD and aging using volumetric MRI.

METHODS

A total of 55 patients after moderate to severe TBI (median age 40), 45 with AD (median age 69), and 61 healthy volunteers underwent magnetic resonance imaging over 2 years. Atrophy patterns were compared.

RESULTS

AD patients had markedly lower baseline volumes. TBI was associated with increased white matter (WM) atrophy, particularly involving corticospinal tracts and callosum, whereas AD rates were increased across white and gray matter (GM). Subcortical WM loss was shared in AD/TBI, but deep WM atrophy was TBI-specific and cortical atrophy AD-specific. Post-TBI atrophy patterns were distinct from aging, which resembled AD.

DISCUSSION

Post-traumatic neurodegeneration 1.9-4.0 years (median) following moderate-severe TBI is distinct from aging/AD, predominantly involving central WM. This likely reflects distributions of axonal injury, a neurodegeneration trigger.

HIGHLIGHTS

We compared patterns of brain atrophy longitudinally after moderate to severe TBI in late-onset AD and healthy aging. Patients after TBI had abnormal brain atrophy involving the corpus callosum and other WM tracts, including corticospinal tracts, in a pattern that was specific and distinct from AD and aging. This pattern is reminiscent of axonal injury following TBI, and atrophy rates were predicted by the extent of axonal injury on diffusion tensor imaging, supporting a relationship between early axonal damage and chronic neurodegeneration.

Association of Kidney Function Measures With Signs of Neurodegeneration and Small Vessel Disease on Brain Magnetic Resonance Imaging: The Atherosclerosis Risk in Communities (ARIC) Study

RATIONALE & OBJECTIVE

Chronic kidney disease (CKD) is a risk factor for cognitive decline, but evidence is limited on its etiology and morphological manifestation in the brain. We evaluated the association of estimated glomerular filtration rate (eGFR) and urinary albumin-creatinine ratio (UACR) with structural brain abnormalities visible on magnetic resonance imaging (MRI). We also assessed whether this association was altered when different filtration markers were used to estimate GFR.

STUDY DESIGN

Cross-sectional study nested in a cohort study.

SETTING & PARTICIPANTS

1,527 participants in the Atherosclerosis Risk in Communities (ARIC) Study.

PREDICTORS

Log(UACR) and eGFR based on cystatin C, creatinine, cystatin C and creatinine in combination, or β2-microglobulin (B2M).

OUTCOMES

Brain volume reduction, infarcts, microhemorrhages, white matter lesions.

ANALYTICAL APPROACH

Multivariable linear and logistic regression models fit separately for each predictor based on a 1-IQR difference in the predictor value.

RESULTS

Each 1-IQR lower eGFR was associated with reduced cortex volume (regression coefficient: -0.07 [95% CI, -0.12 to-0.02]), greater white matter hyperintensity volume (logarithmically transformed; regression coefficient: 0.07 [95% CI, 0.01-0.15]), and lower white matter fractional anisotropy (regression coefficient: -0.08 [95% CI, -0.17 to-0.01]). The results were similar when eGFR was estimated with different equations based on cystatin C, creatinine, a combination of cystatin C and creatinine, or B2M. Higher log(UACR) was similarly associated with these outcomes as well as brain infarcts and microhemorrhages (odds ratios per 1-IQR-fold greater UACR of 1.31 [95% CI, 1.13-1.52] and 1.30 [95% CI, 1.12-1.51], respectively). The degree to which brain volume was lower in regions usually susceptible to Alzheimer disease and LATE (limbic-predominant age-related TDP-43 [Tar DNA binding protein 43] encephalopathy) was similar to that seen in the rest of the cortex.

LIMITATIONS

No inference about longitudinal effects due to cross-sectional design.

CONCLUSIONS

We found eGFR and UACR are associated with structural brain damage across different domains of etiology, and eGFR- and UACR-related brain atrophy is not selective for regions typically affected by Alzheimer disease and LATE. Hence, Alzheimer disease or LATE may not be leading contributors to neurodegeneration associated with CKD.

Differences in Diffusion Tensor Imaging White Matter Integrity Related to Verbal Fluency Between Young and Old Adults

Throughout adulthood, the brain undergoes an array of structural and functional changes during the typical aging process. These changes involve decreased brain volume, reduced synaptic density, and alterations in white matter (WM). Although there have been some previous neuroimaging studies that have measured the ability of adult language production and its correlations to brain function, structural gray matter volume, and functional differences between young and old adults, the structural role of WM in adult language production in individuals across the life span remains to be thoroughly elucidated. This study selected 38 young adults and 35 old adults for diffusion tensor imaging (DTI) and performed the Controlled Oral Word Association Test to assess verbal fluency (VF). Tract-Based Spatial Statistics were employed to evaluate the voxel-based group differences of diffusion metrics for the values of fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD), radial diffusivity (RD), and local diffusion homogeneity (LDH) in 12 WM regions of interest associated with language production. To investigate group differences on each DTI metric, an analysis of covariance (ANCOVA) controlling for sex and education level was performed, and the statistical threshold was considered at p < 0.00083 (0.05/60 labels) after Bonferroni correction for multiple comparisons. Significant differences in DTI metrics identified in the ANCOVA were used to perform correlation analyses with VF scores. Compared to the old adults, the young adults had significantly (1) increased FA values on the bilateral anterior corona radiata (ACR); (2) decreased MD values on the right ACR, but increased MD on the left uncinate fasciculus (UF); and (3) decreased RD on the bilateral ACR. There were no significant differences between the groups for AD or LDH. Moreover, the old adults had only a significant correlation between the VF score and the MD on the left UF. There were no significant correlations between VF score and DTI metrics in the young adults. This study adds to the growing body of research that WM areas involved in language production are sensitive to aging.

Exercise Training-Related Changes in Cortical Gray Matter Diffusivity and Cognitive Function in Mild Cognitive Impairment and Healthy Older Adults

Individuals with Mild Cognitive Impairment (MCI) are at an elevated risk of dementia and exhibit deficits in cognition and cortical gray matter (GM) volume, thickness, and microstructure. Meanwhile, exercise training appears to preserve brain function and macrostructure may help delay or prevent the onset of dementia in individuals with MCI. Yet, our understanding of the neurophysiological effects of exercise training in individuals with MCI remains limited. Recent work suggests that the measures of gray matter microstructure using diffusion imaging may be sensitive to early cognitive and neurophysiological changes in the aging brain. Therefore, this study is aimed to determine the effects of exercise training in cognition and cortical gray matter microstructure in individuals with MCI vs. cognitively healthy older adults. Fifteen MCI participants and 17 cognitively intact controls (HC) volunteered for a 12-week supervised walking intervention. Following the intervention, MCI and HC saw improvements in cardiorespiratory fitness, performance on Trial 1 of the Rey Auditory Verbal Learning Test (RAVLT), a measure of verbal memory, and the Controlled Oral Word Association Test (COWAT), a measure of verbal fluency. After controlling for age, a voxel-wise analysis of cortical gray matter diffusivity showed individuals with MCI exhibited greater increases in mean diffusivity (MD) in the left insular cortex than HC. This increase in MD was positively associated with improvements in COWAT performance. Additionally, after controlling for age, the voxel-wise analysis indicated a main effect of Time with both groups experiencing an increase in left insular and left and right cerebellar MD. Increases in left insular diffusivity were similarly found to be positively associated with improvements in COWAT performance in both groups, while increases in cerebellar MD were related to gains in episodic memory performance. These findings suggest that exercise training may be related to improvements in neural circuits that govern verbal fluency performance in older adults through the microstructural remodeling of cortical gray matter. Furthermore, changes in left insular cortex microstructure may be particularly relevant to improvements in verbal fluency among individuals diagnosed with MCI.

Tract Specificity of Age Effects on Diffusion Tensor Imaging Measures of White Matter Health

Well-established literature indicates that older adults have poorer cerebral white matter integrity, as measured through diffusion tensor imaging (DTI). Age differences in DTI have been observed widely across white matter, although some tracts appear more sensitive to the effects of aging than others. Factors like APOE ε4 status and sex may contribute to individual differences in white matter integrity that also selectively impact certain tracts, and could influence DTI changes in aging. The present study explored the degree to which age, APOE ε4, and sex exerted global vs. tract specific effects on DTI metrics in cognitively healthy late middle-aged to older adults. Data from 49 older adults (ages 54–92) at two time-points separated by approximately 2.7 years were collected. DTI metrics, including fractional anisotropy (FA) and mean diffusivity (MD), were extracted from nine white matter tracts and global white matter. Results showed that across timepoints, FA and MD increased globally, with no tract-specific changes observed. Baseline age had a global influence on both measures, with increasing age associated with lower FA and higher MD. After controlling for global white matter FA, age additionally predicted FA for the genu, callosum body, inferior fronto-occipital fasciculus (IFOF), and both anterior and posterior cingulum. Females exhibited lower global FA on average compared to males. In contrast, MD was selectively elevated in the anterior cingulum and superior longitudinal fasciculus (SLF), for females compared to males. APOE ε4 status was not predictive of either measure. In summary, these results indicate that age and sex are associated with both global and tract-specific alterations to DTI metrics among a healthy older adult cohort. Older women have poorer white matter integrity compared to older men, perhaps related to menopause-induced metabolic changes. While age-related alterations to white matter integrity are global, there is substantial variation in the degree to which tracts are impacted, possibly as a consequence of tract anatomical variability. The present study highlights the importance of accounting for global sources of variation in DTI metrics when attempting to investigate individual differences (due to age, sex, or other factors) in specific white matter tracts.

Diffuse axonal injury predicts neurodegeneration after moderate-severe traumatic brain injury

Traumatic brain injury is associated with elevated rates of neurodegenerative diseases such as Alzheimer's disease and chronic traumatic encephalopathy. In experimental models, diffuse axonal injury triggers post-traumatic neurodegeneration, with axonal damage leading to Wallerian degeneration and toxic proteinopathies of amyloid and hyperphosphorylated tau. However, in humans the link between diffuse axonal injury and subsequent neurodegeneration has yet to be established. Here we test the hypothesis that the severity and location of diffuse axonal injury predicts the degree of progressive post-traumatic neurodegeneration. We investigated longitudinal changes in 55 patients in the chronic phase after moderate-severe traumatic brain injury and 19 healthy control subjects. Fractional anisotropy was calculated from diffusion tensor imaging as a measure of diffuse axonal injury. Jacobian determinant atrophy rates were calculated from serial volumetric T1 scans as a measure of measure post-traumatic neurodegeneration. We explored a range of potential predictors of longitudinal post-traumatic neurodegeneration and compared the variance in brain atrophy that they explained. Patients showed widespread evidence of diffuse axonal injury, with reductions of fractional anisotropy at baseline and follow-up in large parts of the white matter. No significant changes in fractional anisotropy over time were observed. In contrast, abnormally high rates of brain atrophy were seen in both the grey and white matter. The location and extent of diffuse axonal injury predicted the degree of brain atrophy: fractional anisotropy predicted progressive atrophy in both whole-brain and voxelwise analyses. The strongest relationships were seen in central white matter tracts, including the body of the corpus callosum, which are most commonly affected by diffuse axonal injury. Diffuse axonal injury predicted substantially more variability in white matter atrophy than other putative clinical or imaging measures, including baseline brain volume, age, clinical measures of injury severity and microbleeds (>50% for fractional anisotropy versus <5% for other measures). Grey matter atrophy was not predicted by diffuse axonal injury at baseline. In summary, diffusion MRI measures of diffuse axonal injury are a strong predictor of post-traumatic neurodegeneration. This supports a causal link between axonal injury and the progressive neurodegeneration that is commonly seen after moderate/severe traumatic brain injury but has been of uncertain aetiology. The assessment of diffuse axonal injury with diffusion MRI is likely to improve prognostic accuracy and help identify those at greatest neurodegenerative risk for inclusion in clinical treatment trials.

Association of Head Impact Exposure with White Matter Macrostructure and Microstructure Metrics

Prior studies have reported white matter abnormalities associated with a history of cumulative concussion and/or repetitive head impacts (RHI) in contact sport athletes. Growing evidence suggests these abnormalities may begin as more subtle changes earlier in life in active younger athletes. We investigated the relationship between prior concussion and contact sport exposure with multi-modal white matter microstructure and macrostructure using magnetic resonance imaging. High school and collegiate athletes (n = 121) completed up to four evaluations involving neuroimaging. Linear mixed-effects models examined associations of years of contact sport exposure (i.e., RHI proxy) and prior concussion across multiple metrics of white matter, including total white matter volume, diffusion tensor imaging (DTI) metrics, diffusion kurtosis imaging (DKI) metrics, and quantitative susceptibility mapping (QSM). A significant inverse association between cumulative years of contact sport exposure and QSM was observed, F(1, 237.77) = 4.67, p = 0.032. Cumulative contact sport exposure was also associated with decreased radial diffusivity, F(1, 114.56) = 5.81, p = 0.018, as well as elevated fractional anisotropy, F(1, 115.32) = 5.40, p = 0.022, and radial kurtosis, F(1, 113.45) = 4.03, p = 0.047. In contrast, macroscopic white matter volume was not significantly associated with cumulative contact sport exposure (p > 0.05). Concussion history was not significantly associated with QSM, DTI, DKI, or white matter volume (all, p > 0.05). Cumulative contact sport exposure is associated with subtle differences in white matter microstructure, but not gross white matter macrostructure, in young active athletes. Longitudinal follow-up is required to assess the progression of these findings to determine their contribution to potential adverse effects later in life.

Diagnosis of Alzheimer's Disease Using Brain Network

Recent studies suggest the brain functional connectivity impairment is the early event occurred in case of Alzheimer’s disease (AD) as well as mild cognitive impairment (MCI). We model the brain as a graph based network to study these impairment. In this paper, we present a new diagnosis approach using graph theory based features from functional magnetic resonance (fMR) images to discriminate AD, MCI, and healthy control (HC) subjects using different classification techniques. These techniques include linear support vector machine (LSVM), and regularized extreme learning machine (RELM). We used pairwise Pearson’s correlation-based functional connectivity to construct the brain network. We compare the classification performance of brain network using Alzheimer’s disease neuroimaging initiative (ADNI) datasets. Node2vec graph embedding approach is employed to convert graph features to feature vectors. Experimental results show that the SVM with LASSO feature selection method generates better classification accuracy compared to other classification technique.

The association of dietary patterns with cognition through the lens of neuroimaging-a Systematic review

Despite the reported benefits of diet on cognition in older adults, randomized controlled trials (RCT) testing the impact of dietary interventions on cognitive scores have yielded less promising results when cognition was assessed via neuropsychological tests. More recently, neuroimaging has been used to identify more subtle brain-related changes associated to cognition. Hence, employing a combination of neuroimaging techniques with neuropsychological tests could clarify this controversy. To determine the effect of diet on cognitive performance, we conducted a systematic review of PubMed and Scopus databases for all studies, on middle-aged and older adults, combining neuroimaging, neuropsychological tests, and data on dietary patterns. The inclusion criteria were met by 14 observational studies and no RCTs. The range of brain measures assessed varied from volumes to white matter integrity, functional connectivity, brain glucose metabolism and beta-amyloid deposition. Given the variability of methods used in assessing cognitive performance, diet and brain correlates, conducting a meta-analysis was not possible. Here the evidence suggests that, in observational studies, dietary patterns may be associated with brain correlates that have been shown to precede cognitive decline. As such, neuroimaging should be included in future RCTs to identify any benefits of diet on brain measures linked with cognitive health.

Accelerated Cognitive Ageing in epilepsy: exploring the effective connectivity between resting-state networks and its relation to cognitive decline

OBJECTIVE

This study aims at understanding the dynamic functional brain organization in Accelerated Cognitive Ageing (ACA) in epilepsy. We also assess to which extend the (abnormal) effective connectivity between brain networks correlates with the (estimated) decline in IQ scores observed in the ACA patients.

MATERIAL AND METHODS

Two multi-echo resting-state fMRI scans of 10 ACA patients and 14 age- and education-matched healthy controls were acquired. A task-based fMRI was acquired in-between those two scans, for possible cognitive fatigue effects on reserve capacity. Granger causality (GC), a measure of effective connectivity between brain regions, was applied on 7 major cognitive networks, and group-wise compared, using permutation testing statistics. This was performed on each of the resting-state sessions independently. We assessed the correlation between the cognitive deterioration scores (representing cognitive decline), and the paired-networks granger causality values.

RESULTS

The cingulate cortex appeared to be more engaged in ACA patients. Its dynamics towards the right fronto-parietal cortex, salience network, and the dorsal attention networks (DAN) was stronger than in controls, only in the first resting-state scan session. The Granger causality from the DAN to the default mode network (DMN) and from the ventral attention network (VAN) to the left fronto-parietal network (FPL) was also stronger in ACA patients and again only in the first scans. In the second resting-state scans, only the DMN was more strongly connected with the cingulate cortex in ACA patients. A weaker GC from DMN to FPL, and stronger GC from the salience network to cingulate cortex were associated with more decline in the Full-scale IQ and more GC from DMN to VAN would lead to more decline in the Perceptual Reasoning Index in ACA.

CONCLUSION

The results are in line with the hypothesis of over-recruitment at low cognitive load, and exhaustion at higher cognitive load, as shown by the compensation-related utilization of neural circuits hypothesis (CRUNCH) model for ageing. Moreover, the DMN to VAN directed connectivity strongly correlates with the (estimated) decline in the Perceptual Reasoning Index, which is also in line with a recent study on ageing with mild cognitive impairment in elderly, and the posterior-anterior shift in aging (PASA) model. This study therefore supports the idea that the cognitive decline in our patients resembles the decline observed in healthy ageing, but in an accelerated mode. This study also sheds light on the directions of the impaired connectivity between the main networks involved in the deterioration process, which can be helpful for future development of treatment solutions.

White Matter Network Alterations in Alzheimer’s Disease Patients

Previous studies have revealed the occurrence of alterations of white matter (WM) and grey matter (GM) microstructures in Alzheimer’s disease (AD) and their prodromal state amnestic mild cognitive impairment (MCI). In general, these alterations can be studied comprehensively by modeling the brain as a complex network, which describes many important topological properties, such as the small-world property, modularity, and efficiency. In this study, we systematically investigated white matter abnormalities using unbiased whole brain network analysis. We compared regional and network related WM features between groups of 19 AD and 25 MCI patients and 22 healthy controls (HC) using tract-based spatial statistics (TBSS), network based statistics (NBS) and graph theoretical analysis. We did not find significant differences in fractional anisotropy (FA) between two groups on TBSS analysis. However, observable alterations were noticed at a network level. Brain network measures such as global efficiency and small world properties were low in AD patients compared to HCs.

Association of white matter microstructural integrity with cognition and dementia

Late-life measures of white matter (WM) microstructural integrity may predict cognitive status, cognitive decline, and incident mild cognitive impairment (MCI) or dementia. We considered participants of the Atherosclerosis Risk in Communities study who underwent cognitive assessment and neuroimaging in 2011-2013 and were followed through 2016-2017 (n = 1775 for analyses of prevalent MCI and dementia, baseline cognitive performance, and longitudinal cognitive change and n = 889 for analyses of incident MCI, dementia, or death). Cross-sectionally, both overall WM fractional anisotropy and overall WM mean diffusivity were strongly associated with baseline cognitive performance and risk of prevalent MCI or dementia. Longitudinally, greater overall WM mean diffusivity was associated with accelerated cognitive decline, as well as incident MCI, incident dementia, and mortality, but WM fractional anisotropy was not robustly associated with cognitive change or incident cognitive impairment. Both cross-sectional and longitudinal associations were attenuated after additionally adjusting for likely downstream pathologic changes. Increased WM mean diffusivity may provide an early indication of dementia pathogenesis.

Attentional control abnormalities in posttraumatic stress disorder: Functional, behavioral, and structural correlates

BACKGROUND

Attentional disruptions are common in PTSD, but findings across neuropsychological and neuroimaging studies have been variable. Few PTSD studies have investigated abnormalities in attention networks using a multi-modal imaging approach and attentional tasks that include emotionally-salient images. This study combined a behavioral task that included these images (emotional Stroop) with functional and structural neuroimaging (fMRI and diffusion tensor imaging; DTI) methods to comprehensively investigate attentional control abnormalities in a highly-traumatized civilian sample.

METHODS

48 traumatized women with and without PTSD received clinical assessments, fMRI and DTI. During fMRI, the Affective Stroop (AS), an attentional control task that includes emotionally-salient distractor images (trauma-relevant, positive, neutral) and variable task demands, was administered.

RESULTS

In response to more difficult AS trials, participants with PTSD demonstrated lower activation in the dorsal and rostral anterior cingulate cortex and greater activation in the insula. This group also showed comparatively poorer performance on positive AS distractor trials, even after adjusting for trauma exposure. Performance on these trials inversely correlated with structural integrity of the cingulum bundle and uncinate fasciculus.

CONCLUSIONS

Even after adjusting for trauma exposure, participants with PTSD showed worse performance on an attentional control task in the context of emotional stimuli. They also showed relatively lower cognitive control network activation and greater salience network activation. Fronto-parietal and fronto-limbic white matter connectivity corresponded with AS performance. Our findings indicate that attentional control impairments in PTSD are most evident in the context of emotional cues, and are related to decrements in function and structure of cognitive control and salience networks.

Mean diffusivity in cortical gray matter in Alzheimer's disease: The importance of partial volume correction

Mean diffusivity (MD) measured by diffusion tensor imaging can reflect microstructural alterations of the brain's gray matter (GM). Therefore, GM MD may be a sensitive marker of neurodegeneration related to Alzheimer's Disease (AD). However, due to partial volume effects (PVE), differences in MD may be overestimated because of a higher degree of brain atrophy in AD patients and in cases with mild cognitive impairment (MCI). Here, we evaluated GM MD changes in AD and MCI compared with healthy controls, and the effect of partial volume correction (PVC) on diagnostic utility of MD. We determined region of interest (ROI) and voxel-wise group differences and diagnostic accuracy of MD and volume measures between matched samples of 39 AD, 39 MCI and 39 healthy subjects before and after PVC. Additionally, we assessed whether effects of GM MD values on diagnosis were mediated by volume. ROI and voxel-wise group differences were reduced after PVC. When using these ROIs for predicting group separation in logistic models, both PVE corrected and uncorrected GM MD values yielded a poorer diagnostic accuracy in single predictor models than regional volume. For the discrimination of AD patients and healthy controls, the effect of GM MD on diagnosis was significantly mediated by volume of hippocampus and posterior cingulate ROIs. Our results suggest that GM MD measurements are strongly confounded by PVE in the presence of brain atrophy, underlining the necessity of PVC when using these measurements as specific metrics of microstructural tissue degeneration. Independently of PVC, regional MD was not superior to regional volume in separating prodromal and clinical stages of AD from healthy controls.

Microstructural Changes of the Human Brain from Early to Mid-Adulthood

Despite numerous studies on the microstructural changes of the human brain throughout life, we have indeed little direct knowledge about the changes from early to mid-adulthood. The aim of this study was to investigate the microstructural changes of the human brain from early to mid-adulthood. We performed two sets of analyses based on the diffusion tensor imaging (DTI) data of 111 adults aged 18–55 years. Specifically, we first correlated age with skeletonized fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD) and radial diffusivity (RD) at global and regional level, and then estimated individuals’ ages based on each DTI metric using elastic net, a kind of multivariate pattern analysis (MVPA) method that aims at selecting the model that achieves the best trade-off between goodness of fit and model complexity. We observed statistically significant negative age-vs-FA correlations and relatively less changes of MD. The negative age-vs-FA correlations were associated with negative age-vs-AD and positive age-vs-RD correlations. Regional negative age-vs-FA correlations were observed in the bilateral genu of the corpus callosum (CCg), the corticospinal tract (CST), the fornix and several other tracts, and these negative correlations may indicate the earlier changes of the fibers with aging. In brain age estimation, the chronological-vs-estimated-age correlations based on FA, MD, AD and RD were R = 0.62, 0.44, 0.63 and 0.69 (P = 0.002, 0.008, 0.002 and 0.002 based on 500 permutations), respectively, and these results indicate that even the microstructural changes from early to mid-adulthood alone are sufficiently specific to decode individuals’ ages. Overall, the current results not only demonstrated statistically significant FA decreases from early to mid-adulthood and clarified the driving factors of the FA decreases (RD increases and AD decreases, in contrast to increases of both measures in late-adulthood), but highlighted the necessity of considering age effects in related studies.

A Life-Long Approach to Physical Activity for Brain Health

It is well established that engaging in lifelong Physical activity (PA) can help delay the onset of many chronic lifestyle related and non-communicable diseases such as cardiovascular disease, type two diabetes, cancer and chronic respiratory diseases. Additionally, growing evidence also documents the importance of PA for brain health, with numerous studies indicating regular engagement in physical activities may be protective against cognitive decline and dementia in late life. Indeed, the link between PA and brain health may be different at each stage of life from childhood, mid-life and late life. Building on this emerging body of multidisciplinary research, this review aims to summarize the current body of evidence linking regular PA and brain health across the lifespan. Specifically, we will focus on the relationship between PA and brain health at three distinct stages of life: childhood and adolescence, mid-life, late life in cognitively healthy adults and later life in adults living with age-related neurodegenerative disorders such as Parkinson's disease (PD) and Alzheimer's disease (AD).

Midlife and Late-Life Vascular Risk Factors and White Matter Microstructural Integrity: The Atherosclerosis Risk in Communities Neurocognitive Study

Background

Diffusion tensor imaging measures of white matter (WM) microstructural integrity appear to provide earlier indication of WM injury than WM hyperintensities; however, risk factors for poor WM microstructural integrity have not been established. Our study quantifies the association between vascular risk factors in midlife and late life with measures of late‐life WM microstructural integrity.

Methods and Results

We used data from 1851 participants in ARIC (Atherosclerosis Risk in Communities Study) who completed 3‐T magnetic resonance imaging, including diffusion tensor imaging, as part of the ARIC Neurocognitive Study (ARIC‐NCS). We quantified the association among lipids, glucose, and blood pressure from the baseline ARIC visit (1987–1989, ages 44–65, midlife) and visit 5 of ARIC (2011–2013, ages 67–90, late life, concurrent with ARIC‐NCS) with regional and overall WM mean diffusivity and fractional anisotropy obtained at ARIC visit 5 for ARIC participants. We also considered whether these associations were independent of or modified by WM hyperintensity volumes. We found that elevated blood pressure in midlife and late life and elevated glucose in midlife, but not late life, were associated with worse late‐life WM microstructural integrity. These associations were independent of the degree of WM hyperintensity, and the association between glucose and WM microstructural integrity appeared stronger for those with the least WM hyperintensity. There was little support for an adverse association between lipids and WM microstructural integrity.

Conclusions

Hypertension in both midlife and late life and elevated glucose in midlife are related to worse WM microstructural integrity in late life.

Microstructural white matter alterations in preclinical Alzheimer's disease detected using free water elimination diffusion tensor imaging

Brain changes associated with Alzheimer's disease (AD) begin decades before disease diagnosis. While β-amyloid plaques and neurofibrillary tangles are defining features of AD, neuronal loss and synaptic pathology are closely related to the cognitive dysfunction. Brain imaging methods that are tuned to assess degeneration of myelinated nerve fibers in the brain (collectively called white matter) include diffusion tensor imaging (DTI) and related techniques, and are expected to shed light on disease-related loss of structural connectivity. Participants (N = 70, ages 47-76 years) from the Wisconsin Registry for Alzheimer's Prevention study underwent DTI and hybrid diffusion imaging to determine a free-water elimination (FWE-DTI) model. The study assessed the extent to which preclinical AD pathology affects brain white matter. Preclinical AD pathology was determined using cerebrospinal fluid (CSF) biomarkers. The sample was enriched for AD risk (APOE ε4 and parental history of AD). AD pathology assessed by CSF analyses was significantly associated with altered microstructure on both DTI and FWE-DTI. Affected regions included frontal, parietal, and especially temporal white matter. The f-value derived from the FWE-DTI model appeared to be the most sensitive to the relationship between the CSF AD biomarkers and microstructural alterations in white matter. These findings suggest that white matter degeneration is an early pathological feature of AD that may have utility both for early disease detection and as outcome measures for clinical trials. More complex models of microstructural diffusion properties including FWE-DTI may provide increased sensitivity to early brain changes associated with AD over standard DTI.

Influence of Small Vessel Disease and Microstructural Integrity on Neurocognitive Functioning in Older Individuals: The DANTE Study Leiden

BACKGROUND AND PURPOSE

Small vessel disease is a major cause of neurocognitive dysfunction in the elderly. Small vessel disease may manifest as white matter hyperintensities, lacunar infarcts, cerebral microbleeds, and atrophy, all of which are visible on conventional MR imaging or as microstructural changes determined by diffusion tensor imaging. This study investigated whether microstructural integrity is associated with neurocognitive dysfunction in older individuals, irrespective of the conventional features of small vessel disease.

MATERIALS AND METHODS

The study included 195 participants (75 years of age or older) who underwent conventional 3T MR imaging with DTI to assess fractional anisotropy, mean diffusivity, axial diffusivity, and radial diffusivity. Cognitive tests were administered to assess cognitive domains, and the Geriatric Depression Scale-15 and Apathy Scale of Starkstein were used to assess symptoms of depression and apathy, respectively. The association between DTI measures and neurocognitive function was analyzed by using linear regression models.

RESULTS

In gray matter, a lower fractional anisotropy and higher mean diffusivity, axial diffusivity, and radial diffusivity were associated with worse executive function, psychomotor speed, and overall cognition and, in white matter, also with memory. Findings were independent of white matter hyperintensities, lacunar infarcts, and cerebral microbleeds. However, after additional adjustment for normalized brain volume, only lower fractional anisotropy in white and gray matter and higher gray matter radial diffusivity remained associated with executive functioning. DTI measures were not associated with scores on the Geriatric Depression Scale-15 or the Apathy Scale of Starkstein.

CONCLUSIONS

Microstructural integrity was associated with cognitive but not psychological dysfunction. Associations were independent of the conventional features of small vessel disease but attenuated after adjusting for brain volume.

STRUCTURAL AND FUNCTIONAL CONNECTIVITY IN POSTTRAUMATIC STRESS DISORDER: ASSOCIATIONS WITH FKBP5

BACKGROUND

The integrity of connections between the hippocampus and the anterior cingulate cortex (ACC) is critical for adaptive cognitive and emotional processing; these connections may be compromised in posttraumatic stress disorder (PTSD). However, there is a lack of PTSD research that combines structural and functional connectivity data, and no studies have examined whether abnormal ACC-hippocampal connectivity is associated with genetic variability, particularly for polymorphisms of a gene that has been previously associated with PTSD, FKBP5. This was the goal of the present study.

METHODS

Fifty-four women with and without PTSD underwent diffusion tensor imaging and resting-state MRI. Probabilistic tractography was used to examine ACC-hippocampal structural connectivity; mean fractional anisotropy (FA) values were extracted from connectivity streamlines, which represent the cingulum bundle. Genotype data were collected for a single nucleotide polymorphism (SNP) of FKBP5, rs1360780.

RESULTS

Participants with PTSD demonstrated poorer structural connectivity (lower cingulum FA) compared to traumatized controls (F1, 50 = 6.77, P < .05). An interaction of FKBP5 genotype and diagnostic group was also observed (F1, 37 = 4.52, P = .04), indicating lower cingulum FA in carriers of two risk alleles for this SNP, compared to other diagnostic and genotype groups. Carriers of two FKBP5 risk alleles also demonstrated poorer hippocampus-ACC connectivity at rest (P < .05). When cingulum FA was used a regressor in a brain-wide, seed-based regression analysis, significant associations were found between the hippocampus and dorsal regions of the ACC (P < .05).

CONCLUSIONS

Individuals with PTSD demonstrated compromised structural connectivity of the hippocampus-ACC pathway. Altered hippocampus-ACC connectivity may represent a highly salient intermediate neural phenotype for PTSD.

Macrophage inhibitory cytokine-1/growth differentiation factor 15 as a marker of cognitive ageing and dementia

PURPOSE OF REVIEW

As a divergent member of the transforming growth factor-β superfamily, macrophage inhibitory cytokine-1 (MIC-1/GDF15) is an autocrine regulatory molecule that plays important roles in diseases, such as cancer and cardiovascular disorders. More recently, this cytokine has been investigated for its contribution to ageing and age-related cognitive decline. This review aims at summarizing existing findings on the relationships of MIC-1/GDF15 with cognition, brain, and dementia in ageing populations and animal models.

RECENT FINDINGS

In community-dwelling samples, higher circulating MIC-1/GDF15 levels were associated with worsening cognitive function and decline from cognitively normal status to mild cognitive impairment or dementia. Higher MIC-1/GDF15 serum levels were also linked to decreased grey matter volumes and white matter integrity. Brain structural changes were shown to mediate the inverse relationships of MIC-1/GDF15 serum levels with cognition. Animal studies indicated that the expression of MIC-1/GDF15 in response to stress was neuroprotective and even promoted neurogenesis.

SUMMARY

From the available findings, MIC-1/GDF15 can be considered as a marker of age-related cognitive decline and brain structural changes. Combining MIC-1/GDF15 with other biomarkers may provide clinical diagnostic and prognostic utility. Threshold effects should be considered in future studies.

Monotonic non-linear transformations as a tool to investigate age-related effects on brain white matter integrity: A Box-Cox investigation

Non-linear effects of age on white matter integrity are ubiquitous in the brain and indicate that these effects are more pronounced in certain brain regions at specific ages. Box-Cox analysis is a technique to increase the log-likelihood of linear relationships between variables by means of monotonic non-linear transformations. Here we employ Box-Cox transformations to flexibly and parsimoniously determine the degree of non-linearity of age-related effects on white matter integrity by means of model comparisons using a voxel-wise approach. Analysis of white matter integrity in a sample of adults between 20 and 89years of age (n=88) revealed that considerable portions of the white matter in the corpus callosum, cerebellum, pallidum, brainstem, superior occipito-frontal fascicle and optic radiation show non-linear effects of age. Global analyses revealed an increase in the average non-linearity from fractional anisotropy to radial diffusivity, axial diffusivity, and mean diffusivity. These results suggest that Box-Cox transformations are a useful and flexible tool to investigate more complex non-linear effects of age on white matter integrity and extend the functionality of the Box-Cox analysis in neuroimaging.

Volumetric and fiber-tracing MRI methods for gray and white matter

Magnetic resonance imaging (MRI) is capable of generating high-resolution brain images with fine anatomic detail and unique tissue contrasts that reveal structures that are not visible to the eye. Sharply defined gray- and white-matter interfaces allow for quantitative anatomic analysis that can be accurately performed with largely automated segmentation methods. In an analogous fashion, diffusion MRI in the brain provides structural information based on contrasts derived from the diffusivity of water in brain tissue, which can highlight the orientation of neuronal axons. Also using largely automated methods, diffusion MRI can be used to generate models of white-matter tracts throughout the brain, a method known as tractography, as well as characterize the microstructural integrity of neuronal axons. Tractographic analysis has helped to define connectivity in the brain that powerfully informs understanding of brain function, and, together with other diffusion metrics, is useful in evaluation of the normal and diseased brain. The quantitative methods of brain segmentation, tractography, and diffusion MRI extend MRI into a realm beyond visual inspection and provide otherwise unachievable sensitivity and specificity in the analysis of brain structure and function.

An inverse relationship between serum macrophage inhibitory cytokine-1 levels and brain white matter integrity in community-dwelling older individuals

Macrophage inhibitory cytokine-1 (MIC-1/GDF15) is a marker of inflammation that has been associated with atherosclerosis. We have previously demonstrated its relationships with cognitive decline and cerebral gray matter volumes, suggesting its role as a biomarker of cognitive impairment. Considering that it is widely distributed in the brain, and both inflammation and vascular pathology impact on white matter (WM) integrity, we examined the relationship between MIC-1/GDF15 and measures of WM integrity, including WM volumes, mean fractional anisotropy (FA) values and WM hyperintensity (WMH) volumes in a community-dwelling non-demented sample of older individuals (n=327, 70-90 years old). We found that the mean FA values were negatively associated with MIC-1/GDF15 serum levels, after Bonferroni correction. The voxel-wise analysis showed negative relationships between MIC-1/GDF15 serum levels and FA values in corticospinal tract, corpus callosum (including genu, body and splenium parts), superior longitudinal fasciculus, cingulum, as well as anterior and posterior thalamic radiation. Whole brain WMH volumes, especially deep WMH volumes, showed a non-significant trend for a positive association with MIC-1/GDF15 serum levels. The associations between MIC-1/GDF15 serum levels and WM integrity showed a non-significant trend of being stronger for the individuals classified as mild cognitive impairment, compared to the normal ageing participants. The findings suggest that high serum MIC-1/GDF15 levels indicate reduced WM integrity and possibly greater WM pathology.

Fear-potentiated startle during extinction is associated with white matter microstructure and functional connectivity

BACKGROUND

Extinction of conditioned fear is an associative learning process that involves communication among the hippocampus, medial prefrontal cortex, and amygdala. Strength of connectivity between the hippocampus and the anterior cingulate cortex (ACC), and between the amygdala and ventromedial prefrontal cortex (vmPFC), may influence fear-potentiated startle (FPS) responses during extinction. Specific white matter tracts, the cingulum and uncinate fasciculus (UF), serve as primary routes of communication for these areas. Our objective was to investigate associations between FPS during extinction and cingulum and UF connectivity.

METHOD

Diffusion tensor imaging (DTI) and probabilistic tractography analyses were used to examine cingulum and UF structural connectivity in 40 female African-Americans with psychological trauma exposure. FPS responses during fear conditioning and extinction were assessed via electromyography (EMG) of the right orbicularis oculi muscle. Secondarily, functional connectivity analyses were performed with the seed regions of interest (ROIs) used for tractography.

RESULTS

A significant negative association between cingulum microstructure and FPS during early extinction (r = -.42, p = .01) and late extinction (r = -.36, p = .03) was observed after accounting for the effects of age, trauma exposure, and psychopathology (post-traumatic stress disorder symptoms); this pattern was similar for early extinction and functional connectivity between these regions (p < .05(corrected)). No significant correlations were observed between FPS and UF microstructure.

CONCLUSIONS

These data indicate that structural integrity of the cingulum is directly associated with extinction learning and appears to influence functional connectivity between these regions. Decrements in cingulum microstructure may interfere with extinction learning, thereby increasing risk for the development of pathological anxiety.

Regional cerebellar volume and cognitive function from adolescence to late middle age

Cerebellar morphology and function have been implicated in a variety of developmental disorders, and in healthy aging. Although recent work has sought to characterize the relationships between volume and age in this structure during adolescence, young, and older adulthood, there have been no investigations of regional cerebellar volume from adolescence through late middle age. Middle age in particular has been largely understudied, and investigating this period of the lifespan may be especially important for our understanding of senescence. Understanding regional patterns of cerebellar volume with respect to age during this portion of the lifespan may provide important insight into healthy aging and cognitive function as well as pathology from adolescence into later life. We investigated regional cerebellar volume using a highly novel lobular segmentation approach in conjunction with a battery of cognitive tasks in a cross-sectional sample of 123 individuals from 12 to 65 years old. Our results indicated that regional cerebellar volumes show different patterns with respect to age. In particular, the more posterior aspect of the neocerebellum follows a quadratic "inverse-U" pattern while the vermis and anterior cerebellum follow logarithmic patterns. In addition, we quantified the relationships between age and a variety of cognitive assessments and found relationships between regional cerebellar volumes and performance. Finally, exploratory analyses of sex differences in the relationships between regional cerebellar volume, age, and cognition were investigated. Taken together, these results provide key insights into the development and aging of the human cerebellum, and its role in cognitive function across the lifespan.

Frontal corpus callosum alterations in progressive supranuclear palsy but not in Parkinson's disease

BACKGROUND

Frontal lobe involvement is considered a clinical and magnetic resonance imaging (MRI) feature in later stages of progressive supranuclear palsy (PSP).

OBJECTIVE

Diffusion tensor imaging (DTI) was used to investigate the integrity of frontal pathways in PSP and Parkinson's disease (PD) patients.

METHODS

DTI and 3-D MRI were performed in 15 PSP patients (parkinsonism subtype: n = 8; Richardson subtype: n = 7), 15 PD patients, and 18 matched controls. DTI analysis was performed in order to identify differences along frontal white matter structures including the corpus callosum (CC) and was complemented by atlas-based volumetry and planimetry.

RESULTS

Significantly reduced regional fractional anisotropy was observed for PSP patients versus controls and PSP versus PD patients, respectively, in frontal areas including the area II of the CC and bilaterally in the callosal radiation. The DTI findings correlated with frontal lobe volumes. These differences were not observed between PD patients and controls.

CONCLUSION

DTI identified a PSP-associated microstructural alteration pattern in the frontal lobes and in the CC area II including the corresponding bilateral callosal radiation tracts that could not be identified in both control samples, supporting the prominent PSP-associated frontal involvement as a potential neuroimaging marker.

Early Brain Loss in Circuits Affected by Alzheimer's Disease is Predicted by Fornix Microstructure but may be Independent of Gray Matter

In a cohort of community-recruited elderly subjects with normal cognition at initial evaluation, we found that baseline fornix white matter (WM) microstructure was significantly correlated with early volumetric longitudinal tissue change across a region of interest (called fornix significant ROI, fSROI), which overlaps circuits known to be selectively vulnerable to Alzheimer’s dementia pathology. Other WM and gray matter regions had much weaker or non-existent associations with longitudinal tissue change. Tissue loss in fSROI was in turn a significant factor in a survival model of cognitive decline, as was baseline fornix microstructure. These findings suggest that WM deterioration in the fornix and tissue loss in fSROI may be the early beginnings of posterior limbic circuit and default mode network degeneration. We also found that gray matter baseline volumes in the entorhinal cortex and hippocampus predicted cognitive decline in survival models. But since GM regions did not also significantly predict brain-tissue loss, our results may imply a view in which early, prodromal deterioration appears as two quasi independent processes in white and gray matter regions of the limbic circuit crucial to memory.

FKBP5 genotype and structural integrity of the posterior cingulum

Alterations in the microarchitecture of the posterior cingulum (PC), a white matter tract proximal to the hippocampus that facilitates communication between the entorhinal and cingulate cortices, have been observed in individuals with psychiatric disorders, such as depression and post-traumatic stress disorder (PTSD). PC decrements may be a heritable source of vulnerability for the development of affective disorders; however, genetic substrates for these white matter abnormalities have not been identified. The FKBP5 gene product modulates glucocorticoid receptor function and has been previously associated with differential hippocampal structure, function, and affect disorder risk. Thus, FKBP5 is an attractive genetic target for investigations of PC integrity. We examined associations between PC integrity, measured through diffusion tensor imaging (DTI) and fractional anisotropy (FA; an index of white matter integrity), and polymorphisms in the FKBP5 SNP rs1360780 in a sample of 82 traumatized female civilians. Findings indicated that, compared with individuals without this allele, individuals who carried two 'risk' alleles for this FKBP5 SNP (T allele; previously associated with mood and anxiety disorder risk) demonstrated significantly lower FA in the left PC, even after statistically controlling for variance associated with age, trauma exposure, and PTSD symptoms. These data suggest that specific allelic variants for an FKBP5 polymorphism are associated with decrements in the left PC microarchitecture. These white matter abnormalities may be a heritable biological marker that indicates increased vulnerability for the development of psychiatric disorders, such as PTSD.

Imaging small vessel-associated white matter changes in aging

Alterations in cerebrovascular structure and function may underlie the most common age-associated cognitive, psychiatric, and neurological conditions presented by older adults. Although much remains to understand, existing research suggests several age-associated detrimental conditions may be mediated through sometimes subtle small vessel-induced damage to the cerebral white matter. Here we review a selected portion of the vast work that demonstrates links between changes in vascular and neural health as a function of advancing age, and how even changes in low-to-moderate risk individuals, potentially beginning early in the adult age-span, may have an important impact on functional status in late life.