2,379 research outputs found
Association between structural connectivity and generalized cognitive spectrum in alzheimerâs disease
Modeling disease progression through the cognitive scores has become an attractive challenge in the field of computational neuroscience due to its importance for early diagnosis of Alzheimerâs disease (AD). Several scores such as Alzheimerâs Disease Assessment Scale cognitive total score, Mini Mental State Exam score and Rey Auditory Verbal Learning Test provide a quantitative assessment of the cognitive conditions of the patients and are commonly used as objective criteria for clinical diagnosis of dementia and mild cognitive impairment (MCI). On the other hand, connectivity patterns extracted from diffusion tensor imaging (DTI) have been successfully used to classify AD and MCI subjects with machine learning algorithms proving their potential application in the clinical setting. In this work, we carried out a pilot study to investigate the strength of association between DTI structural connectivity of a mixed ADNI cohort and cognitive spectrum in AD. We developed a machine learning framework to find a generalized cognitive score that summarizes the different functional domains reflected by each cognitive clinical index and to identify the connectivity biomarkers more significantly associated with the score. The results indicate that the efficiency and the centrality of some regions can effectively track cognitive impairment in AD showing a significant correlation with the generalized cognitive score (R = 0.7)
How Acute and Chronic Alcohol Consumption Affects Brain Networks: Insights from Multimodal Neuroimaging
Backgroundâ
Multimodal imaging combining 2 or more techniques is becoming increasingly
important because no single imaging approach has the capacity to elucidate all clinically relevant
characteristics of a network.
Methodsâ
This review highlights recent advances in multimodal neuroimaging (i.e., combined
use and interpretation of data collected through magnetic resonance imaging [MRI], functional
MRI, diffusion tensor imaging, positron emission tomography, magnetoencephalography, MR
perfusion, and MR spectroscopy methods) that leads to a more comprehensive understanding of
how acute and chronic alcohol consumption affect neural networks underlying cognition, emotion,
reward processing, and drinking behavior.
Resultsâ
Several innovative investigators have started utilizing multiple imaging approaches
within the same individual to better understand how alcohol influences brain systems, both during
intoxication and after years of chronic heavy use.
Conclusionsâ
Their findings can help identify mechanism-based therapeutic and
pharmacological treatment options, and they may increase the efficacy and cost effectiveness of
such treatments by predicting those at greatest risk for relapse
Data-Driven Sequence of Changes to Anatomical Brain Connectivity in Sporadic Alzheimer's Disease
Model-based investigations of transneuronal spreading mechanisms in neurodegenerative diseases relate the pattern of pathology severity to the brainâs connectivity matrix, which reveals information about how pathology propagates through the connectivity network. Such network models typically use networks based on functional or structural connectivity in young and healthy individuals, and only end-stage patterns of pathology, thereby ignoring/excluding the effects of normal aging and disease progression. Here, we examine the sequence of changes in the elderly brainâs anatomical connectivity over the course of a neurodegenerative disease. We do this in a data-driven manner that is not dependent upon clinical disease stage, by using event-based disease progression modeling. Using data from the Alzheimerâs Disease Neuroimaging Initiative dataset, we sequence the progressive decline of anatomical connectivity, as quantified by graph-theory metrics, in the Alzheimerâs disease brain. Ours is the first single model to contribute to understanding all three of the nature, the location, and the sequence of changes to anatomical connectivity in the human brain due to Alzheimerâs disease. Our experimental results reveal new insights into Alzheimerâs disease: that degeneration of anatomical connectivity in the brain may be a viable, even early, biomarker and should be considered when studying such neurodegenerative diseases
Sparse reduced-rank regression for imaging genetics studies: models and applications
We present a novel statistical technique; the sparse reduced rank regression (sRRR) model
which is a strategy for multivariate modelling of high-dimensional imaging responses and
genetic predictors. By adopting penalisation techniques, the model is able to enforce sparsity
in the regression coefficients, identifying subsets of genetic markers that best explain
the variability observed in subsets of the phenotypes. To properly exploit the rich structure
present in each of the imaging and genetics domains, we additionally propose the use of
several structured penalties within the sRRR model. Using simulation procedures that accurately
reflect realistic imaging genetics data, we present detailed evaluations of the sRRR
method in comparison with the more traditional univariate linear modelling approach. In
all settings considered, we show that sRRR possesses better power to detect the deleterious
genetic variants. Moreover, using a simple genetic model, we demonstrate the potential
benefits, in terms of statistical power, of carrying out voxel-wise searches as opposed to
extracting averages over regions of interest in the brain. Since this entails the use of phenotypic
vectors of enormous dimensionality, we suggest the use of a sparse classification
model as a de-noising step, prior to the imaging genetics study. Finally, we present the
application of a data re-sampling technique within the sRRR model for model selection.
Using this approach we are able to rank the genetic markers in order of importance of association
to the phenotypes, and similarly rank the phenotypes in order of importance to
the genetic markers. In the very end, we illustrate the application perspective of the proposed
statistical models in three real imaging genetics datasets and highlight some potential
associations
Resting-state functional connectivity-based biomarkers and functional MRI-based neurofeedback for psychiatric disorders: a challenge for developing theranostic biomarkers
Psychiatric research has been hampered by an explanatory gap between
psychiatric symptoms and their neural underpinnings, which has resulted in poor
treatment outcomes. This situation has prompted us to shift from symptom-based
diagnosis to data-driven diagnosis, aiming to redefine psychiatric disorders as
disorders of neural circuitry. Promising candidates for data-driven diagnosis
include resting-state functional connectivity MRI (rs-fcMRI)-based biomarkers.
Although biomarkers have been developed with the aim of diagnosing patients and
predicting the efficacy of therapy, the focus has shifted to the identification
of biomarkers that represent therapeutic targets, which would allow for more
personalized treatment approaches. This type of biomarker (i.e., theranostic
biomarker) is expected to elucidate the disease mechanism of psychiatric
conditions and to offer an individualized neural circuit-based therapeutic
target based on the neural cause of a condition. To this end, researchers have
developed rs-fcMRI-based biomarkers and investigated a causal relationship
between potential biomarkers and disease-specific behavior using functional MRI
(fMRI)-based neurofeedback on functional connectivity. In this review, we
introduce recent approach for creating a theranostic biomarker, which consists
mainly of two parts: (i) developing an rs-fcMRI-based biomarker that can
predict diagnosis and/or symptoms with high accuracy, and (ii) the introduction
of a proof-of-concept study investigating the relationship between normalizing
the biomarker and symptom changes using fMRI-based neurofeedback. In parallel
with the introduction of recent studies, we review rs-fcMRI-based biomarker and
fMRI-based neurofeedback, focusing on the technological improvements and
limitations associated with clinical use.Comment: 46 pages, 5 figure
Assessing early white matter predictors of syntactic abilities in post-stroke aphasia using HARDI-based tractography
La recherche de prĂ©dicteurs dâhabilitĂ©s langagiĂšres en aphasie post-accident vasculaire cĂ©rĂ©bral (AVC) basĂ©s sur la matiĂšre blanche a rĂ©cemment vu un Ă©lan. Cela a Ă©tĂ© motivĂ© par lâĂ©mergence du modĂšle Ă double-voie oĂč des faisceaux de matiĂšre blanche dorsaux et ventraux jouent un rĂŽle important dans le langage, ainsi que par lâavĂšnement de la tractographie basĂ©e sur lâimagerie par rĂ©sonance magnĂ©tique (IRM) de diffusion permettant lâĂ©tude in-vivo des faisceaux de matiĂšre blanche et de leurs propriĂ©tĂ©s structurelles. Les caractĂ©ristiques structurelles et la charge lĂ©sionnelle des faisceaux de matiĂšre blanche ont permis de prĂ©dire les troubles langagiers dans la phase chronique dans quelques Ă©tudes. Cependant, les prĂ©dicteurs aigus de matiĂšre blanche des habilitĂ©s syntaxiques en aphasie post-AVC chronique sont mĂ©connus.
Lâexploitation de la tractographie dans lâĂ©tude des faisceaux langagiers de matiĂšre blanche a Ă©tĂ© limitĂ©e par plusieurs dĂ©fis mĂ©thodologiques, dont la difficultĂ© de reconstruire des faisceaux ayant une architecture complexe. Des progrĂšs mĂ©thodologiques ont Ă©tĂ© rĂ©cemment introduits afin dâadresser ces limites, dont le plus important est la tractographie basĂ©e sur lâimagerie Ă haute rĂ©solution angulaire (« HARDI »). Cependant, la fiabilitĂ© test-retest de la reconstruction et des propriĂ©tĂ©s structurelles dâune approche de tractographie HARDI de pointe nâa pas encore Ă©tĂ© Ă©valuĂ©e.
Le premier article de cette thĂšse visait Ă Ă©valuer la fiabilitĂ© test-retest de la reconstruction et des propriĂ©tĂ©s structurelles (anisotropie fractionnelle, FA; diffusivitĂ© moyenne, axiale et radiale, MD, AD, RD; nombre dâorientations de fibres, NuFO; volume du faisceau; longueur moyenne des « streamlines ») de faisceaux langagiers majeurs (arquĂ©, infĂ©rieur fronto-occipital, infĂ©rieur longitudinal, uncinĂ©, AF, IFOF, ILF, UF) obtenus avec une approche de tractographie HARDI de pointe. La majoritĂ© des mesures de propriĂ©tĂ©s structurelles ont montrĂ© une bonne ou excellente fiabilitĂ©. Ces rĂ©sultats ont des implications importantes pour lâutilisation dâune telle approche pour lâĂ©tude des faisceaux langagiers de matiĂšre blanche, car ils renforcent la confiance dans la stabilitĂ© des reconstructions et les propriĂ©tĂ©s structurelles obtenus avec la tractographie HARDI.
Le second article de cette thĂšse visait Ă dĂ©terminer si et quelles propriĂ©tĂ©s structurelles (FA, AD, volume du faisceau), et la charge lĂ©sionnelle, de lâAF et lâUF gauches dans la phase aigĂŒe (†3 jours), obtenus avec lâapproche de tractographie HARDI utilisĂ©e dans le premier article, prĂ©disent les habilitĂ©s syntaxiques dans le discours spontanĂ© en aphasie post-AVC chronique (â„ 6 mois). Des rĂ©gressions multiples ascendantes ont rĂ©vĂ©lĂ© que le volume de lâAF prĂ©dit la production des verbes, la complexitĂ© des phrases et la complexitĂ© de la structure argumentale du verbe. Le volume de lâUF a amĂ©liorĂ© la prĂ©diction de cette derniĂšre. Ces rĂ©sultats indiquent que le volume semble ĂȘtre un bon prĂ©dicteur prĂ©coce des habilitĂ©s syntaxiques dans le discours spontanĂ© en aphasie post-AVC chronique.
Mis ensemble, les rĂ©sultats de cette thĂšse soulignent lâutilitĂ© dâune approche de tractographie HARDI de pointe et son potentiel pour le dĂ©veloppement futur de biomarqueurs prĂ©coces pouvant amĂ©liorer le pronostic de patients ayant une aphasie post-AVC chronique. Cela pourrait promouvoir lâoptimisation des soins et le dĂ©veloppement de thĂ©rapies pour le bienfait des patients et leurs familles.The search for white matter predictors of language abilities in post-stroke aphasia has gained momentum in recent years. This growing interest has been driven by the emergence of the dual-stream framework where dorsal and ventral white matter bundles play an important functional role in language, as well as the advent of diffusion magnetic resonance imaging (MRI)-based tractography which allows the in-vivo investigation of white matter bundles and their structural properties. Structural characteristics, as well as the lesion load, of white matter bundles have been previously found to predict language impairments in the chronic phase. However, little is known about acute white matter predictors of syntactic abilities in chronic post-stroke aphasia.
Leveraging tractography to study white matter language bundles has been limited by several methodological challenges, such as the difficulty of reconstructing white matter bundles with a complex fiber architecture. A number of methodological advances have been introduced fairly recently to address these limitations, the most important of which is the advent of tractography based on High Angular Resolution Imaging (HARDI). However, the test-retest reliability of the reconstruction and structural properties of a state-of-the-art HARDI-based tractography pipeline has not been previously assessed.
The first article of the present thesis aimed to assess the test-retest reliability of the reconstruction and structural properties (fractional anisotropy, FA; mean, axial, radial diffusivity, MD, AD, RD; number of fiber orientations, NuFO; bundle volume; mean length of streamlines) of major white matter language bundles (arcuate, inferior fronto-occipital, inferior longitudinal, and uncinate fasciculi, AF, IFOF, ILF, UF) obtained using a state-of-the-art HARDI-based tractography pipeline. Most measures of structural properties showed good to excellent test-retest reliability. These findings have important implications for the use of such a pipeline for the study of white matter language bundles, as they increase our confidence that the reconstructions and structural properties obtained from the tractography pipeline are stable and not due to random variations in measurement.
The second article of the thesis aimed to determine whether and which structural properties (FA, AD, bundle volume), as well as the lesion load, of the left AF and UF in the acute phase post-stroke (†3 days), obtained with the same state-of-the-art HARDI-based tractography pipeline used in the first article, predict syntactic abilities in connected speech in chronic post-stroke aphasia (â„ 6 months). Forward multiple regressions revealed that the left AFâs volume predicted the percentage of verbs produced, the structural complexity of sentences, as well as verb-argument structure complexity. The left UFâs volume improved the prediction of verbs with a complex argument structure. These findings indicate that the bundle volume may be a good early predictor of syntactic ability in connected speech in chronic post-stroke aphasia.
Overall, the findings of this thesis highlight the usefulness of a state-of-the-art HARDI-based tractography approach and its potential for the future development of early biomarkers that could improve the prognosis and personalized care of patients with chronic post-stroke aphasia. This would promote the optimization of patient care and the development of therapies for the benefit of patients and their families
Developmental neurocognitive pathway of psychosis proneness and the impact of cannabis use
Cette thĂšse fait la promotion dâune nouvelle approche ciblant le risque de psychose qui consiste Ă identifier les enfants et les jeunes adolescents de la communautĂ© appartenant Ă diffĂ©rentes trajectoires dĂ©veloppementales dâexpĂ©riences psychotiques. Une identification trĂšs prĂ©coce du risque de psychose chez des jeunes de la communautĂ© pourrait ainsi diminuer la pĂ©riode oĂč les symptĂŽmes cliniques ne sont pas traitĂ©s, mais aurait Ă©galement le potentiel de prĂ©venir efficacement lâĂ©mergence de symptĂŽmes avĂ©rĂ©s, et ce, si les facteurs de risque sont identifiĂ©s.
Ătant donnĂ© que la consommation de cannabis sâavĂšre un important facteur de risque de la psychose et le contexte actuel oĂč les Ă©tats en sont Ă rĂ©viser leurs politiques de rĂ©glementation du cannabis, il sâavĂšre primordial de mieux comprendre comment la consommation peut mener Ă la psychose chez les individus vulnĂ©rables.
Tout dâabord, jâai investiguĂ© la sĂ©quence temporelle entre la consommation de cannabis et les expĂ©riences psychotiques chez une population de 4000 adolescents, suivis pendant 4 ans, au moment de lâadolescence oĂč les deux phĂ©nomĂšnes sâinitient. Ensuite, jâai examinĂ©, chez des adolescents suivant une trajectoire de vulnĂ©rabilitĂ©, le rĂŽle dâun moins bon fonctionnement cognitif ainsi que celui dâune exacerbation des symptĂŽmes anxieux et dĂ©pressifs comme mĂ©diateurs du lien entre cannabis et risque de psychose. Enfin, jâai investiguĂ© la prĂ©sence de marqueurs neurocognitifs prĂ©coces (fonctionnels et structurels) qui seraient associĂ©s Ă lâĂ©mergence de symptĂŽmes psychotiques chez des adolescents, et explorĂ© si la consommation de cannabis pourrait modĂ©rer lâampleur de ces marqueurs.
Les donnĂ©es proviennent de deux cohortes longitudinales suivant des adolescents de la population gĂ©nĂ©rale, lâĂ©tude Co-Venture (n=4000, ĂągĂ©s de 12 ans, suivis annuellement pendant 4 ans) et lâĂ©tude de neuroimagerie IMAGEN (n=2200, ĂągĂ©s de 14 ans, suivis pendant 2 ans), ainsi quâun sous-Ă©chantillon de lâĂ©tude Co-Venture ayant complĂ©tĂ© des mesures de neuroimagerie (n=151, ĂągĂ©s de 12 ans, suivis annuellement pendant 4 ans).
Les rĂ©sultats ont montrĂ© que la consommation de cannabis prĂ©cĂ©dait systĂ©matiquement lâaugmentation des expĂ©riences psychotiques, et non lâinverse. Chez les jeunes suivant une trajectoire de vulnĂ©rabilitĂ©, la relation entre la consommation de cannabis et le risque de psychose Ă©tait davantage expliquĂ©e par une augmentation des symptĂŽmes de dĂ©pression et dâanxiĂ©tĂ©. Une rĂ©duction du volume de lâhippocampe et de lâamygdale en combinaison avec une hyperactivitĂ© de ces mĂȘmes rĂ©gions en rĂ©ponse Ă des expressions neutres Ă©taient tous associĂ©s Ă lâĂ©mergence de symptĂŽmes psychotiques. Or, la consommation de cannabis nâa pas exacerbĂ© les altĂ©rations structurelles observĂ©es chez les adolescents rapportant des expĂ©riences psychotiques.
Ces rĂ©sultats ont mis en Ă©vidence le rĂŽle primordial dâun hyperfonctionnement du systĂšme limbique pouvant mener Ă lâattribution aberrante dâune importance Ă©motionnelle aux stimuli de lâenvironnement, et ce, chez des adolescents vulnĂ©rables. Il semble que le mĂ©canisme par lequel la consommation de cannabis mĂšne Ă lâĂ©mergence de symptĂŽmes cliniques passe par son influence sur les symptĂŽmes de dĂ©pression et dâanxiĂ©tĂ© ainsi que leurs mĂ©canismes neuronaux sous-jacents dâune hypersensibilitĂ© au stress. Enfin, de par ces rĂ©sultats, cette thĂšse permet de contribuer au dĂ©veloppement de nouvelles interventions visant Ă rĂ©duire la demande de cannabis chez des adolescents vulnĂ©rables.Following the worldwide initiative on intervening early in clinical high-risk individuals for psychosis, this thesis promotes a novel approach to identify those at risk for psychosis by studying children and adolescents from the community who report different trajectories of subclinical psychosis symptoms (i.e., psychotic-like experiences) without the confounds of iatrogenic effects such as major social and cognitive impairments. Early identification from this approach may not only reduce harm by shortening the duration of untreated symptoms, but may also have the capacity to prevent the emergence of clinically validated symptoms, particularly if early risk factors can be identified.
Considering the long-standing notion that cannabis misuse is an important risk factor for psychosis and that jurisdictions around the world are currently revising their cannabis regulatory policies, there is a need to better understand how cannabis use may lead to psychosis in vulnerable youths.
This thesis examined different mechanisms that may explain the complex relationship between cannabis use and psychosis risk. I first explored the temporal sequence between cannabis use and self-reported psychotic-like experiences in a population-based sample of 4000 adolescents, over a 4-year period when both phenomena have their onset. Second, in vulnerable youths, I investigated the role of impaired cognitive functioning as well as increased affective and anxious symptoms as mediators of the cannabis-to-psychosis relationship. And third, I explored the presence of early neurocognitive markers (both functional and structural) associated with the emergence of psychotic symptoms, and how cannabis use moderates these markers.
Two longitudinal cohorts from the general population, the Co-Venture Study (n=4000, aged 12 years old, followed annually for 4 years) and the neuroimaging IMAGEN Study (n=2200, aged 14 years old, followed for 2 years), as well as the neuroimaging subsample from the Co-Venture Study (n=151, aged 12 years old, followed annually for 4 years) were used.
It was found that an increase in cannabis use always preceded an increase in reported psychotic-like experiences throughout adolescence, but an increase in psychotic-like experiences rarely predicted an increase in cannabis use. Then, in vulnerable adolescents, the cannabis-to-psychosis risk relationship was better explained by increases in depression and anxiety symptoms relative to changes in cognitive functioning. It was demonstrated that reduced hippocampus and amygdala volumes, combined with hyperactivity of the same regions during neutral cues processing were associated with the emergence of psychotic symptoms in young adolescents reporting psychotic-like experiences. However, cannabis use did not exacerbate the structural alterations observed in youths with psychotic-like experiences.
These findings have improved our understanding of the relationship between cannabis use and vulnerability to psychosis. They have also highlighted the important role of an impaired limbic network leading to an aberrant emotional salience attribution in vulnerable adolescents. Although cannabis use did not exacerbate brain structural alterations observed in vulnerable youths, it appears that cannabis will more likely interfere with depression and/or anxiety symptoms and their associated brain mechanisms underlying vulnerability to stress in the path towards psychosis risk. This thesis may inform the development of new evidence-based interventions that reduce demand for cannabis among vulnerable youths
ACTIVATED CARBON NANOFIBERS FROM RENEWABLE (LIGNIN) AND WASTE RESOURCES (RECYCLED PET) AND THEIR ADSORPTION CAPACITY OF REFRACTORY SULFUR COMPOUNDS FROM FOSSIL FUELS
Dementia is a condition in which higher mental functions are disrupted. It currently affects an estimated 57 million people throughout the world. Dementia diagnosis is difficult since neither anatomical indicator nor functional testing are currently sufficiently sensitive or specific. There remains a long list of outstanding issues that must be addressed. First, multimodal diagnosis has yet to be introduced into the early stages of dementia screening. Second, there is no accurate instrument for predicting the progression of pre-dementia. Third, non-invasive testing cannot be used to provide differential diagnoses. By creating ML models of normal and accelerated brain aging, we intend to better understand brain development. The combined analysis of distinct imaging and functional modalities will improve diagnostics of accelerated decline with advanced data science techniques, which is the main objective of our study. Hypothetically, an association between brain structural changes and cognitive performance differs between normal and accelerated aging. We propose using brain MRI scans to estimate the cognitive status of the cognitively preserved examinee and develop a structure-function model with machine learning (ML). Accelerated aging is suspected when a scanned individualâs findings do not align with the usual paradigm. We calculate the deviation from the model of normal aging (DMNA) as the error of cognitive score prediction. Then the obtained data may be compared with the results of conducted cognitive tests. The greater the difference between the expected and observed values, the greater the risk of dementia. DMNA can discern between cognitively normal and mild cognitive impairment (MCI) patients. The model was proven to perform well in the MCI-versus-Alzheimerâs disease (AD) categorization. DMNA is a potential diagnostic marker of dementia and its types
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