scholarly journals Structural Connectivity Remote From Lesions Correlates With Somatosensory Outcome Poststroke

Stroke ◽  
2021 ◽  
Author(s):  
Chia-Lin Koh ◽  
Chun-Hung Yeh ◽  
Xiaoyun Liang ◽  
Rishma Vidyasagar ◽  
Rüdiger J. Seitz ◽  
...  
Keyword(s):  
White Matter ◽  
Cross Section ◽  
Fiber Bundle ◽  
Spatial Information ◽  
Structural Connectivity ◽  
Healthy Adults ◽  
Lesion Group ◽  
Fiber Density ◽  
White Matter Tracts ◽  
Stroke Lesion

Background and Purpose: Changes in connectivity of white matter fibers remote to a stroke lesion, suggestive of structural connectional diaschisis, may impact on clinical impairment and recovery after stroke. However, until recently, we have not had tract-specific techniques to map changes in white matter tracts in vivo in humans to enable investigation of potential mechanisms and clinical impact of such remote changes. Our aim was to identify and quantify white matter tracts that are affected remote from a stroke lesion and to investigate the associations between reductions in tract-specific connectivity and impaired touch discrimination function after stroke. Methods: We applied fixel-based analysis to diffusion magnetic resonance imaging data from 37 patients with stroke (right lesion =16; left lesion =21) and 26 age-matched healthy adults. Three quantitative metrics were compared between groups: fiber density; fiber-bundle cross-section; and a combined measure of both (fiber-bundle cross-section) that reflects axonal structural connectivity. Results: Compared with healthy adults, patients with stroke showed significant common fiber-bundle cross-section and fiber density reductions in 4 regions remote from focal lesions that play roles in somatosensory and spatial information processing. Structural connectivity along the somatosensory fibers of the lesioned hemisphere was correlated with contralesional hand touch function. Touch function of the ipsilesional hand was associated with connectivity of the superior longitudinal fasciculus, and, for the right-lesion group, the corpus callosum. Conclusions: Remote tract-specific reductions in axonal connectivity indicated by diffusion imaging measures are observed in the somatosensory network after stroke. These remote white matter connectivity reductions, indicative of structural connectional diaschisis, are associated with touch impairment in patients with stroke.

scholarly journals Pervasive White Matter Fiber Degeneration in Ischemic Stroke

Stroke ◽  
2020 ◽  
Vol 51 (5) ◽  
pp. 1507-1513 ◽  
Author(s):  
Natalia Egorova ◽  
Thijs Dhollander ◽  
Mohamed Salah Khlif ◽  
Wasim Khan ◽  
Emilio Werden ◽  
...  
Keyword(s):  
Ischemic Stroke ◽  
White Matter ◽  
Cross Section ◽  
Corticospinal Tract ◽  
Brain Volume ◽  
Morphological Changes ◽  
Axonal Loss ◽  
Fiber Density ◽  
Whole Brain ◽  
Brain Volume Loss

Background and Purpose— We examined if ischemic stroke is associated with white matter degeneration predominantly confined to the ipsi-lesional tracts or with widespread bilateral axonal loss independent of lesion laterality. Methods— We applied a novel fixel-based analysis, sensitive to fiber tract–specific differences within a voxel, to assess axonal loss in stroke (N=104, 32 women) compared to control participants (N=40, 15 women) across the whole brain. We studied microstructural differences in fiber density and macrostructural (morphological) changes in fiber cross-section. Results— In participants with stroke, we observed significantly lower fiber density and cross-section in areas adjacent, or connected, to the lesions (eg, ipsi-lesional corticospinal tract). In addition, the changes extended beyond directly connected tracts, independent of the lesion laterality (eg, corpus callosum, bilateral inferior fronto-occipital fasciculus, right superior longitudinal fasciculus). Conclusions— We conclude that ischemic stroke is associated with extensive neurodegeneration that significantly affects white matter integrity across the whole brain. These findings expand our understanding of the mechanisms of brain volume loss and delayed cognitive decline in stroke.

scholarly journals Fiber-specific white matter reductions in Parkinson hallucinations and visual dysfunction

Neurology ◽  
2020 ◽  
Vol 94 (14) ◽  
pp. e1525-e1538 ◽  
Author(s):  
Angeliki Zarkali ◽  
Peter McColgan ◽  
Louise-Ann Leyland ◽  
Andrew J. Lees ◽  
Geraint Rees ◽  
...  
Keyword(s):  
White Matter ◽  
Corpus Callosum ◽  
Parkinson Disease ◽  
Fiber Bundle ◽  
Visual Performance ◽  
Visual Hallucinations ◽  
Fiber Density ◽  
Left Posterior ◽  
Parkinson Dementia ◽  
Attentional Models

ObjectiveTo investigate the microstructural and macrostructural white matter changes that accompany visual hallucinations and low visual performance in Parkinson disease, a risk factor for Parkinson dementia.MethodsWe performed fixel-based analysis, a novel technique that provides metrics of specific fiber-bundle populations within a voxel (or fixel). Diffusion MRI data were acquired from patients with Parkinson disease (n = 105, of whom 34 were low visual performers and 19 were hallucinators) and age-matched controls (n = 35). We used whole-brain fixel-based analysis to compare microstructural differences in fiber density (FD), macrostructural differences in fiber bundle cross section (FC), and the combined FD and FC (FDC) metric across all white matter fixels. We then performed a tract-of-interest analysis comparing the most sensitive FDC metric across 11 tracts within the visual system.ResultsPatients with Parkinson disease hallucinations exhibited macrostructural changes (reduced FC) within the splenium of the corpus callosum and the left posterior thalamic radiation compared to patients without hallucinations. While there were no significant changes in FD, we found large reductions in the combined FDC metric in Parkinson hallucinators within the splenium (>50% reduction compared to nonhallucinators). Patients with Parkinson disease and low visual performance showed widespread microstructural and macrostructural changes within the genu and splenium of the corpus callosum, bilateral posterior thalamic radiations, and left inferior fronto-occipital fasciculus.ConclusionsWe demonstrate specific white matter tract degeneration affecting posterior thalamic tracts in patients with Parkinson disease with hallucinations and low visual performance, providing direct mechanistic support for attentional models of visual hallucinations.

scholarly journals Disrupted structural connectivity in ArcAβ mouse model of Aβ amyloidosis

2020 ◽  
Author(s):  
Md. Mamun Al-Amin ◽  
Joanes Grandjean ◽  
Jan Klohs ◽  
Jungsu Kim
Keyword(s):  
White Matter ◽  
Transgenic Mice ◽  
Structural Connectivity ◽  
Brain Regions ◽  
Mice Model ◽  
Network Efficiency ◽  
Fiber Density ◽  
Neurofilament Light ◽  
Diffusion Weighted Images ◽  
Network Properties

AbstractAlthough amyloid beta (Aβ) deposition is one of the major causes of white matter (WM) alterations in Alzheimer’s disease (AD), little is known about the underlying basis of WM damage and its association with global structural connectivity and network topology. We aimed to dissect the contributions of WM microstructure to structural connectivity and network properties in the ArcAβ mice model of Aβ amyloidosis.We acquired diffusion-weighted images (DWI) of wild type (WT) and ArcAβ transgenic (TG) mice using a 9.4 T MRI scanner. Fixel-based analysis (FBA) was performed to measure fiber tract-specific properties. We also performed three complementary experiments; to identify the global differences in structural connectivity, to compute network properties and to measure cellular basis of white matter alterations.Transgenic mice displayed disrupted structural connectivity centered to the entorhinal cortex (EC) and a lower fiber density and fiber bundle cross-section. In addition, there was a reduced network efficiency and degree centrality in weighted structural connectivity in the transgenic mice. To further examine the underlying neuronal basis of connectivity and network deficits, we performed histology experiments. We found no alteration in myelination and an increased level of neurofilament light (NFL) in the brain regions with disrupted connectivity in the TG mice. Furthermore, TG mice had a reduced number of perineuronal nets (PNN) in the EC.The observed FDC reductions may indicate a decrease in axonal diameter or axon count which would explain the basis of connectivity deficits and reduced network efficiency in TG mice. The increase in NFL suggests a breakdown of axonal integrity, which would reduce WM fiber health. Considering the pivotal role of the EC in AD, Aβ deposition may primarily increase NFL release, damaging PNN in the entorhinal pathway, resulting in disrupted structural connectivity.

scholarly journals Early childhood development of white matter fiber density and morphology

2019 ◽  
Author(s):  
Dennis Dimond ◽  
Christiane S. Rohr ◽  
Robert E. Smith ◽  
Thijs Dhollander ◽  
Ivy Cho ◽  
...  
Keyword(s):  
Early Childhood ◽  
White Matter ◽  
Fiber Bundle ◽  
Early Childhood Development ◽  
Diffusion Tensor ◽  
Childhood Development ◽  
Fiber Density ◽  
White Matter Maturation ◽  
One Year ◽  
Axonal Density

ABSTRACTEarly childhood is an important period for cognitive and brain development, though white matter changes specific to this period remain understudied. Here we utilize a novel analytic approach to quantify and track developmental changes in white matter micro- and macro-structure, calculated from individually oriented fiber-bundle populations, termed “fixels”. Fixel-based analysis and mixed-effects models were used to assess tract-wise changes in fiber density and bundle morphology in 73 girls scanned at baseline (ages 4.09-7.02, mean=5.47, SD=0.81), 6-month (N=7), and one-year follow-up (N=42). For comparison, we also assessed changes in commonly utilized diffusion tensor metrics: fractional anisotropy (FA), and mean, radial and axial diffusivity (MD, RD, AD). Maturational increases in fixel-metrics were seen in most major white matter tracts, with the most rapid increases in the corticospinal tract and slowest or non-significant increases in the genu of the corpus callosum and uncinate fasciculi. As expected, we observed developmental increases in FA and decreases in MD, RD and AD, though percentage changes were smaller relative to fixel-metrics. The majority of tracts showed more substantial morphological than microstructural changes. These findings highlight early childhood as a period of dynamic white matter maturation, characterized by large increases in macroscopic fiber bundle size, mild changes in axonal density, and parallel, albeit less substantial, changes in diffusion tensor metrics.

scholarly journals Fiber-specific white matter alterations in early-stage tremor-dominant Parkinson’s disease

2021 ◽  
Vol 7 (1) ◽  
Author(s):  
Christina Andica ◽  
Koji Kamagata ◽  
Yuya Saito ◽  
Wataru Uchida ◽  
Shohei Fujita ◽  
...  
Keyword(s):  
Parkinson’S Disease ◽  
Parkinson's Disease ◽  
White Matter ◽  
Cross Section ◽  
Corticospinal Tract ◽  
Early Stage ◽  
Brain Regions ◽  
Fiber Density ◽  
Compensation Mechanisms ◽  
Progression Markers

AbstractUsing a fixel-based analysis (FBA), we assessed the fiber-specific white matter (WM) alterations in nonmedicated patients with early-stage Parkinson’s disease (PD) with tremor-dominant (TD; n = 53; mean age, 61.7 ± 8.7 years) and postural instability and gait disorder (PIGD; n = 27; mean age, 57.8 ± 8.1 years) motor subtypes and age- and sex-matched healthy controls (HC; n = 43; mean age, 61.6 ± 9.2 years) from Parkinson’s Progression Markers Initiative dataset. FBA revealed significantly increased macrostructural fiber cross section and a combination of fiber density and cross section metrics within the corticospinal tract in patients with TD-PD compared with HC. Nonetheless, no significant changes in FBA-derived metrics were found in patients with PIGD-PD compared with HC or patients with TD-PD. Our results may provide evidence of WM neural compensation mechanisms in patients with TD-PD marked by increases in fiber bundle size and the ability to relay information between brain regions.

Rest–activity functioning is related to white matter microarchitecture and modifiable risk factors in older adults at-risk for dementia

SLEEP ◽  
2021 ◽  
Author(s):  
Jake R Palmer ◽  
Shantel L Duffy ◽  
Susanne Meares ◽  
Jonathon Pye ◽  
Fernando Calamante ◽  
...  
Keyword(s):  
Risk Factors ◽  
Older Adults ◽  
At Risk ◽  
Depressive Symptoms ◽  
White Matter ◽  
Cross Section ◽  
Vascular Risk Factors ◽  
Vascular Risk ◽  
Fiber Density ◽  
Rest Activity

Abstract Study Objectives Growing evidence demonstrates pronounced alterations in rest–activity functioning in older adults at-risk for dementia. White matter degeneration, poor cardiometabolic functioning, and depression have also been linked to a greater risk of decline; however, limited studies have examined the white matter in relation to rest–activity functioning in at-risk older adults. Methods We investigated associations between nonparametric actigraphy measures and white matter microarchitecture using whole-brain fixel-based analysis of diffusion-weighted imaging in older adults (aged 50 years or older) at-risk for cognitive decline and dementia. The fixel-based metrics assessed were fiber density, fiber cross-section, and combined fiber-density, and cross-section. Interactions between rest–activity functioning and known clinical risk factors, specifically body mass index (BMI), vascular risk factors, depressive symptoms and self-reported exercise, and their association with white matter properties were then investigated. Results Sixty-seven older adults were included (mean = 65.78 years, SD = 7.89). Lower relative amplitude, poorer 24-h synchronization and earlier onset of the least active 5-h period were associated with reductions in markers of white matter atrophy in widespread regions, including cortico-subcortical and cortical association pathways. Preliminary evidence was also found indicating more pronounced white matter alterations in those with lower amplitude and higher BMI (β = 0.25, 95% CI [0.05, 0.46]), poorer 24-h synchronization and more vascular risk factors (β = 0.17, 95% CI [–0.02, 0.36]) and earlier onset of inactivity and greater depressive symptoms (β = 0.17, 95% CI [0.03, 0.30]). Conclusions These findings highlight the complex interplay between rest–activity rhythms, white matter, and clinical risk factors in individuals at-risk for dementia that should be considered in future studies.

scholarly journals Dorsal-to-ventral imbalance in the superior longitudinal fasciculus mediates methylphenidate’s effect on beta oscillations in ADHD

2020 ◽  
Author(s):  
C. Mazzetti ◽  
C. G. Damatac ◽  
E. Sprooten ◽  
N. ter Huurne ◽  
J.K. Buitelaar ◽  
...  
Keyword(s):  
White Matter ◽  
Diffusion Tensor ◽  
Structural Connectivity ◽  
Superior Longitudinal Fasciculus ◽  
Beta Oscillations ◽  
Double Blind ◽  
Attention Task ◽  
White Matter Tracts ◽  
Fiber Tracts ◽  
Beta Power

AbstractBackgroundWhile pharmacological treatment with Methylphenidate (MPH) is a first line intervention for ADHD, its mechanisms of action have yet to be elucidated. In a previous MEG study, we demonstrated that MPH in ADHD normalizes beta depression in preparation to motor responses (1). We here seek to identify the white matter tracts that mediate MPH’s effect on beta oscillations.MethodsWe implemented a double-blind placebo-controlled crossover design, where boys diagnosed with ADHD underwent behavioral and MEG measurements during a spatial attention task while on and off MPH. Results were compared with an age/IQ-matched typically developing (TD) group performing the same task. Estimates of white matter tracts were obtained through diffusion tensor imaging (DTI). Based on aprioristic selection model criteria, we sought to determine the fiber tracts associated with electrophysiological, behavioral and clinical features of attentional functions.ResultsWe identified three main tracts: the anterior thalamic radiation (ATR), the Superior Longitudinal Fasciculus (‘parietal endings’) (SLFp) and Superior Longitudinal Fasciculus (‘temporal endings’) (SLFt). ADHD symptoms severity was associated with lower fractional anisotropy (FA) within the ATR. In addition, individuals with relatively higher FA in SLFp compared to SLFt showed faster and more accurate behavioral responses to MPH. Furthermore, the same parieto-temporal FA gradient explained the effects of MPH on beta modulation: subjects with ADHD exhibiting higher FA in SLFp compared to SLFt also displayed greater effects of MPH on beta power during response preparation.ConclusionsBased on MPH’s modulatory effects on striatal dopamine levels, our data suggest that the behavioral deficits and aberrant oscillatory modulations observed in ADHD depend on a structural connectivity imbalance within the SLF, caused by a diffusivity gradient in favor of temporal rather than parietal, fiber tracts.

scholarly journals Accumbofrontal tract integrity is related to early life adversity and feedback learning

2021 ◽  
Author(s):  
Bryan V. Kennedy ◽  
Jamie L. Hanson ◽  
Nicholas J. Buser ◽  
Wouter van den Bos ◽  
Karen D. Rudolph ◽  
...  
Keyword(s):  
White Matter ◽  
Early Life ◽  
Structural Connectivity ◽  
Poor Mental Health ◽  
Reward Learning ◽  
Behavioral Alterations ◽  
White Matter Tracts ◽  
Early Life Adversity ◽  
Feedback Learning ◽  
Corticostriatal Circuit

AbstractAbuse, neglect, exposure to violence, and other forms of early life adversity (ELA) are incredibly common and significantly impact physical and mental development. While important progress has been made in understanding the impacts of ELA on behavior and the brain, the preponderance of past work has primarily centered on threat processing and vigilance while ignoring other potentially critical neurobehavioral processes, such as reward-responsiveness and learning. To advance our understanding of potential mechanisms linking ELA and poor mental health, we center in on structural connectivity of the corticostriatal circuit, specifically accumbofrontal white matter tracts. Here, in a sample of 77 youth (Mean age = 181 months), we leveraged rigorous measures of ELA, strong diffusion neuroimaging methodology, and computational modeling of reward learning. Linking these different forms of data, we hypothesized that higher ELA would be related to lower quantitative anisotropy in accumbofrontal white matter. Furthermore, we predicted that lower accumbofrontal quantitative anisotropy would be related to differences in reward learning. Our primary predictions were confirmed, but similar patterns were not seen in control white matter tracts outside of the corticostriatal circuit. Examined collectively, our work is one of the first projects to connect ELA to neural and behavioral alterations in reward-learning, a critical potential mechanism linking adversity to later developmental challenges. This could potentially provide windows of opportunity to address the effects of ELA through interventions and preventative programming.

scholarly journals More highly myelinated white matter tracts are associated with faster processing speed in healthy adults

NeuroImage ◽  
2018 ◽  
Vol 171 ◽  
pp. 332-340 ◽  
Author(s):  
Sidhant Chopra ◽  
Marnie Shaw ◽  
Thomas Shaw ◽  
Perminder S. Sachdev ◽  
Kaarin J. Anstey ◽  
...  
Keyword(s):  
White Matter ◽  
Processing Speed ◽  
Healthy Adults ◽  
White Matter Tracts
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