Dissertations / Theses on the topic 'Connectivity Functions'
To see the other types of publications on this topic, follow the link: Connectivity Functions.
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'Connectivity Functions.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Williams, Kathleen Anne. "Resting State Connectivity in the Rat Brain." Thesis, Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/14059.
Full textAbstract:
Functional MRI is a method of imaging changes in blood oxygenation that accompany neural activity in the brain. A specific area within fMRI studies investigates what the brain is doing when it is not being stimulated. It is postulated that there are distinctly separate regions of the brain that are connected based upon functional relations and that these connected regions synchronously communicate even during rest. Resting state connectivity has become a tool to investigate neurological disorders in humans without specific knowledge of the mechanisms that correlate neural activity with brain metabolism and blood flow. This work attempts to characterize resting state connectivity in the rat brain to establish a model that will help elucidate the relationship between functional connectivity, as measured with fMRI, and brain function. Four analysis techniques, power spectrum estimation, cross correlation analysis, principle component analysis, and independent component analysis, are employed to examine data acquired during a non-stimulation, single-slice, gradient echo EPI sequence in search of functionally connected, spatially distant regions of the rat brain.
2
Taixés, i. Ventosa Jordi. "Connectivity of Julia sets of transcendental meromorphic functions." Doctoral thesis, Universitat de Barcelona, 2011. http://hdl.handle.net/10803/50391.
Full textAbstract:
Newton's method associated to a complex holomorphic function f is defined by the dynamical system Nf(z) = z – f(z) / f'(z). As a root-finding algorithm, a natural question is to understand the dynamics of Nf about its fixed points, as they correspond to the roots of the function f. In other words, we would like to understand the basins of attraction of Nf, i.e., the sets of points that converge to a root of f under the iteration of Nf.
Basins of attraction are actually just one type of stable component or component of the Fatou set, defined as the set of points for which the family of iterates is defined and normal locally. The Julia set or set of chaos is its complement (taken on the Riemann sphere).
The study of the topology of these two sets is key in Holomorphic Dynamics. In 1990, Mitsuhiro Shishikura proved that, for any non-constant polynomial P, the Julia set of NP is connected. In fact, he obtained this result as a consequence of a much more general theorem for rational functions: If the Julia set of a rational function R is disconnected, then R has at least two weakly repelling fixed points.
With the final goal of proving the transcendental version of this theorem, in this Thesis we see that: If a transcendental meromorphic function f has either a multiply-connected attractive basin, or a multiply-connected parabolic basin, or a multiply-connected Fatou component with simply-connected image, then f has at least one weakly repelling fixed point.
Our proof for this result is mainly based in two techniques: quasiconformal surgery and the study of the existence of virtually repelling fixed points.
We conclude the Thesis with an idea of the strategy for the proof of the case of Herman rings, as well as some ideas for the case of Baker domains, which is left as a subject for a future project.
3
Pallarés, Picazo Vicente. "Individual traits versus invariances of cognitive functions: a model-based study of brain connectivity." Doctoral thesis, Universitat Pompeu Fabra, 2019. http://hdl.handle.net/10803/666806.
Full textAbstract:
Es conocido en la literatura de neuroimagen que las redes cerebrales funcionales reflejan rasgos personales. Estas características individuales, podrían interferir al caracterizar la cognición entendida como la manera en que se coordinan las redes para realizar una tarea, como mantener la atención, recordar, o procesar información visual. Cómo estos aspectos individuales coexisten con mecanismos generales es, por tanto, una pregunta clave en investigación sobre conectividad cerebral. Este trabajo estudia la relación entre marcadores de conectividad específicos tanto de sujetos, como de tareas. Se centra en dos escalas temporales distintas: la variabilidad entre sesiones, y las fluctuaciones rápidas producidas durante una sesión de adquisición. Utilizamos técnicas de machine learning para separar cuantitativamente las contribuciones de información del sujeto y del estado cognitivo a la conectividad. La metodología presentada nos permite extraer aquellas redes representativas de ambas dimensiones, así como profundizar en su evolución, sugiriendo las escalas temporales relevantes en la cognición.És conegut en la literatura de neuroimatge que les xarxes cerebrals funcionals reflecteixen trets personals. Aquestes característiques individuals podrien interferir en caracteritzar la cognició entesa com la manera en què les xarxes es coordinen per realitzar una tasca, com mantenir l'atenció, recordar o processar informació visual. Cóm aquests aspectes individuals coexisteixen amb mecanismes generals, és, per tant, una pregunta clau en recerca sobre connectivitat cerebral. Aquest treball estudia la relació entre marcadors de connectivitat específics tant de subjectes, com de tasques. Se centra en dues escales temporals: la variabilitat entre sessions, i les fluctuacions ràpides produïdes durant una sessió d'adquisició. Utilitzem tècniques de machine learning per separar quantitativament les contribucions d'informació del subjecte i de l'estat cognitiu a la connectivitat. La metodologia presentada ens permet extreure aquelles xarxes representatives d'ambdues dimensions, així com aprofundir en la seva evolució, suggerint les escales temporals rellevants en la cognició.
There is consistent evidence in the neuroimaging literature that functional brain networks reflect personal traits. Individual specificity may interfere with the characterization of cognition, in terms of coordination of brain networks to perform a task, such as sustained attention, memory retrieval or visual information processing. How individual traits coexist with invariant mechanisms is, therefore, a key question in brain connectivity research. This work aims to examine the relationship between subject- and task-specific connectivity signatures. It focuses on two different timescales: day-to-day variability and faster fluctuations exhibited within a scanning session. We adopt a machine learning approach to quantitatively disentangle the contribution of subject information and cognitive state to the connectivity patterns. The proposed methodology allows us to extract the specific brain networks that support each of the two dimensions, as well as to delve into their changes over time, suggesting the relevant timescales for cognition.
4
Liu, Xiaojin [Verfasser]. "Multi-modal Parcellation of the Human Striatum: Functions, Clinical Relevance and its Specific Connectivity / Xiaojin Liu." Düsseldorf : Universitäts- und Landesbibliothek der Heinrich-Heine-Universität Düsseldorf, 2021. http://d-nb.info/1239893752/34.
Full text
5
Adar, Maia. "Step-Selection Functions for Modeling Animal Movement -- Case Study: African Buffalo." Scholarship @ Claremont, 2018. http://scholarship.claremont.edu/cmc_theses/1938.
Full textAbstract:
Understanding what factors influence wildlife movement allows landscape planners to make informed decisions that benefit both animals and humans. New quantitative methods, such as step-selection functions, provide valuable objective analyses of wildlife connectivity. This paper provides a framework for creating a step-selection function and demonstrates its use in a case study. The first section provides a general introduction about wildlife connectivity research. The second section explains the math behind the step-selection function using a simple example. The last section gives the results of a step-selection model for African buffalo in the Kavango Zambezi Transfrontier Conservation Area. Buffalo were found to avoid fences, rivers, and anthropogenic land use; however, there was great variation in individual buffalo's preferences.
6
Fuller, Joanne Elizabeth. "Analysis of affine equivalent boolean functions for cryptography." Thesis, Queensland University of Technology, 2003. https://eprints.qut.edu.au/15828/1/Joanne_Fuller_Thesis.pdf.
Full textAbstract:
Boolean functions are an important area of study for cryptography. These functions, consisting merely of one's and zero's, are the heart of numerous cryptographic systems and their ability to provide secure communication. Boolean functions have application in a variety of such systems, including block ciphers, stream ciphers and hash functions. The continued study of Boolean functions for cryptography is therefore fundamental to the provision of secure communication in the future. This thesis presents an investigation into the analysis of Boolean functions and in particular, analysis of affine transformations with respect to both the design and application of Boolean functions for cryptography. Past research has often been limited by the difficulties arising from the magnitude of the search space. The research presented in this thesis will be shown to provide an important step towards overcoming such restrictions and hence forms the basis for a new analysis methodology. The new perspective allows a reduced view of the Boolean space in which all Boolean functions are grouped into connected equivalence classes so that only one function from each class need be established. This approach is a significant development in Boolean function research with many applications, including class distinguishing, class structures, self mapping analysis and finite field based s-box analysis. The thesis will begin with a brief overview of Boolean function theory; including an introduction to the main theme of the research, namely the affine transformation. This will be followed by the presentation of a fundamental new theorem describing the connectivity that exists between equivalence classes. The theorem of connectivity will form the foundation for the remainder of the research presented in this thesis. A discussion of efficient algorithms for the manipulation of Boolean functions will then be presented. The ability of Boolean function research to achieve new levels of analysis and understanding is centered on the availability of computer based programs that can perform various manipulations. The development and optimisation of efficient algorithms specifically for execution on a computer will be shown to have a considerable advantage compared to those constructed using a more traditional approach to algorithm optimisation. The theorem of connectivety will be shown to be fundamental in the provision many avenues of new analysis and application. These applications include the first non-exhaustive test for determining equivalent Boolean functions, a visual representation of the connected equivalence class structure to aid in the understanding of the Boolean space and a self mapping constant that enables enumeration of the functions in each equivalence class. A detailed survey of the classes with six inputs is also presented, providing valuable insight into their range and structure. This theme is then continued in the application Boolean function construction. Two important new methodologies are presented; the first to yield bent functions and the second to yield the best currently known balanced functions of eight inputs with respect to nonlinearity. The implementation of these constructions is extremely efficient. The first construction yields bent functions of a variety of algebraic order and inputs sizes. The second construction provides better results than previously proposed heuristic techniques. Each construction is then analysed with respect to its ability to produce functions from a variety of equivalence classes. Finally, in a further application of affine equivalence analysis, the impact to both s-box design and construction will be considered. The effect of linear redundancy in finite field based s-boxes will be examined and in particular it will be shown that the AES s-box possesses complete linear redundancy. The effect of such analysis will be discussed and an alternative construction to s-box design that ensures removal of all linear redundancy will be presented in addition to the best known example of such an s-box.
7
Fuller, Joanne Elizabeth. "Analysis of Affine Equivalent Boolean Functions for Cryptography." Queensland University of Technology, 2003. http://eprints.qut.edu.au/15828/.
Full textAbstract:
Boolean functions are an important area of study for cryptography. These functions, consisting merely of one's and zero's, are the heart of numerous cryptographic systems and their ability to provide secure communication. Boolean functions have application in a variety of such systems, including block ciphers, stream ciphers and hash functions. The continued study of Boolean functions for cryptography is therefore fundamental to the provision of secure communication in the future. This thesis presents an investigation into the analysis of Boolean functions and in particular, analysis of affine transformations with respect to both the design and application of Boolean functions for cryptography. Past research has often been limited by the difficulties arising from the magnitude of the search space. The research presented in this thesis will be shown to provide an important step towards overcoming such restrictions and hence forms the basis for a new analysis methodology. The new perspective allows a reduced view of the Boolean space in which all Boolean functions are grouped into connected equivalence classes so that only one function from each class need be established. This approach is a significant development in Boolean function research with many applications, including class distinguishing, class structures, self mapping analysis and finite field based s-box analysis. The thesis will begin with a brief overview of Boolean function theory; including an introduction to the main theme of the research, namely the affine transformation. This will be followed by the presentation of a fundamental new theorem describing the connectivity that exists between equivalence classes. The theorem of connectivity will form the foundation for the remainder of the research presented in this thesis. A discussion of efficient algorithms for the manipulation of Boolean functions will then be presented. The ability of Boolean function research to achieve new levels of analysis and understanding is centered on the availability of computer based programs that can perform various manipulations. The development and optimisation of efficient algorithms specifically for execution on a computer will be shown to have a considerable advantage compared to those constructed using a more traditional approach to algorithm optimisation. The theorem of connectivety will be shown to be fundamental in the provision many avenues of new analysis and application. These applications include the first non-exhaustive test for determining equivalent Boolean functions, a visual representation of the connected equivalence class structure to aid in the understanding of the Boolean space and a self mapping constant that enables enumeration of the functions in each equivalence class. A detailed survey of the classes with six inputs is also presented, providing valuable insight into their range and structure. This theme is then continued in the application Boolean function construction. Two important new methodologies are presented; the first to yield bent functions and the second to yield the best currently known balanced functions of eight inputs with respect to nonlinearity. The implementation of these constructions is extremely efficient. The first construction yields bent functions of a variety of algebraic order and inputs sizes. The second construction provides better results than previously proposed heuristic techniques. Each construction is then analysed with respect to its ability to produce functions from a variety of equivalence classes. Finally, in a further application of affine equivalence analysis, the impact to both s-box design and construction will be considered. The effect of linear redundancy in finite field based s-boxes will be examined and in particular it will be shown that the AES s-box possesses complete linear redundancy. The effect of such analysis will be discussed and an alternative construction to s-box design that ensures removal of all linear redundancy will be presented in addition to the best known example of such an s-box.
8
Shin, Jaemin. "Characterization and compensation of physiological fluctuations in functional magnetic resonance imaging." Diss., Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/44862.
Full textAbstract:
Functional magnetic resonance imaging (fMRI) based on blood oxygenation level dependent (BOLD) contrast has become a widespread technique in brain research. The central challenge in fMRI is the detection of relatively small activity-induced signal changes in the presence of various other signal fluctuations. Physiological fluctuations due to respiration and cardiac pulsation are dominant sources of confounding variability in BOLD fMRI. This dissertation seeks to characterize and compensate for non-neural physiological fluctuations in fMRI.
First, the dissertation presents an improved and generalized technique for correcting T1 effect in cardiac-gated fMRI data incorporating flip angle estimated from fMRI dataset itself. Using an unscented Kalman filter, spatial maps of flip angle and T1 relaxation are estimated simultaneously from the cardiac-gated time series. Accounting for spatial variation in flip angle, the new method is able to remove the T1 effects robustly, in the presence of significant B1 inhomogeneity. The technique is demonstrated with simulations and experimental data. Secondly, this dissertation describes a generalized retrospective technique to precisely model and remove physiological fluctuations from fMRI signal: Physiological Impulse Response Function Estimation and Correction (PIRFECT).
It is found that the modeled long-term physiological fluctuations explained significant variance in grey matter, even after removing short-term physiological effects. Finally, application of the proposed technique is observed to substantially increase the intra-session reproducibility of resting-state networks.
9
Rahal, Line. "Imagerie fonctionnelle ultrasonore du cerveau pour l'étude, le suivi et le traitement de la douleur aiguë et chronique." Thesis, Paris Sciences et Lettres (ComUE), 2018. http://www.theses.fr/2018PSLET041.
Full textAbstract:
Ces travaux de thèse visaient à démontrer l’intérêt de l’imagerie fonctionnelle ultrasonore pour la définition et le suivi de traitements thérapeutiques des manifestations douloureuses aiguës et chroniques. Dans le cadre d’un projet commun mêlant physique des ondes, imagerie, neurosciences et douleur, nous avons montré que cette jeune technologie d’imagerie pouvait être appliquée à l’imagerie de la douleur chez le petit animal anesthésié, à différents niveaux du système nerveux.Dans le but d’avoir une anesthésie adaptée, stable, reproductible d’un animal à l’autre, et contenant le moins d’agents modulateurs de la douleur possible, nous avons comparé six protocoles d’anesthésie différents. Cette étude a conclu que l’utilisation d’un mélange de kétamine et de médétomidine était le meilleur compromis pour nos futures expérimentations en douleur.La première étude sur les processus de la douleur s’est concentrée sur le test à la formaline, un modèle bien caractérisé de douleur inflammatoire court terme (1h). En effet, notre souhait était de débuter sur un modèle de douleur aiguë le plus court possible pouvant être réalisé chez l’animal anesthésié. Sur ce modèle, nous n’avons observé aucun changement significatif de connectivité fonctionnelle dans le cerveau des rats injectés. Nous avons alors choisi de nous tourner vers des modèles de douleur inflammatoire plus persistants.La seconde étude de cette thèse a porté sur l’étude des altérations de connectivité fonctionnelle et d’états cérébraux dans deux modèles de douleur inflammatoire : un modèle à court terme, induit par injection unilatérale d’adjuvant de Freund, et un modèle à long terme, qui est la polyarthrite induite par adjuvant (quatre semaines d’inflammation bilatérale). Tandis que nous n’avons pas obtenu de résultats significatifs d’altérations fonctionnelles dans le modèle court terme, le modèle long terme nous a apporté de nombreuses informations sur les altérations du système nerveux central pendant le processus de chronicisation.Enfin, la dernière étude a porté sur l’imagerie fonctionnelle ultrasonore des ganglions trigéminaux, structures du système nerveux périphérique, à la fois petites et profondes. Nous avons cherché à caractériser la réponse vasculaire de ces ganglions suite à des stimulations nociceptives mécaniques et chimiques de la cornée chez le rat anesthésié. Cette étude nous a permis de confirmer les observations obtenues par immunohistochimie du proto-oncogène c-fos et de valider l’imagerie fonctionnelle ultrasonore comme modalité pour l’imagerie de l’activation des ganglions trigéminaux chez le rat anesthésié, pour l’étude de la douleur trigéminaleThose thesis works aimed at demonstrating the value of functional ultrasound imaging for the definition and the tracking of acute and chronic pain therapeutic treatments. As part of a common project intertwining wave physics, imaging, neurosciences and pain, we demonstrated that this young imaging technology can be applied to pain imaging on the anesthetized small animal, at different levels of the nervous system.With the aim of obtaining an adapted anaesthesia, stable, reproducible from one animal to another, and containing as less pain modulating agents as possible, we compared six different anaesthetics protocols. This study was concluded by the use of the ketamine and medetomidine mixture as the best compromise for our future experiments in pain.The first study on pain processes has focused on the formaline test, a well characterized model of short term inflammatory pain (1h). Indeed, our wish was to start with an acute pain model as short as possible which may be performed on the anesthetized animal. With this model, we didn’t observe any significant change of functional connectivity in the brain of the injected rats. We then chose to turn to more ongoing models of inflammatory pain.The second study of this thesis dealt with the study of the functional connectivity and brain states alterations in two models of inflammatory pain: a short term model, induced by unilateral injection of Freund’s adjuvant, and a long term model, which is adjuvant induced polyarthritis (four weeks of bilateral inflammation). While we didn’t obtain significant results of functional alterations in the short term model, the long term model gave us ample information on the central nervous system alterations during the chronification process.Finally, the last study concerns the ultrasound functional imaging of the trigeminal ganglions, peripheral nervous system structures, both small and deeply located. We tried to characterize the vascular response of those ganglions following mechanical and chemical nociceptive stimulations of the cornea on the anesthetized rat. This study allowed us to confirm the observations obtained by immunohistochemistry of the proto-oncogene c-fos and to validate the functional ultrasound imaging as a modality for the imaging of the trigeminal ganglions in the anesthetized rat, for the study of trigeminal pain
10
Senouci, Mustapha. "De l'usage de la théorie des fonctions de croyance dans le déploiement et le contrôle de réseaux de capteurs sans fil." Thesis, Paris Est, 2014. http://www.theses.fr/2014PEST1045.
Full textAbstract:
Cette thèse porte sur les problèmes de déploiement des Réseaux de Capteurs sans Fil (RCsF). Elle suit trois directions principales : (1) le déploiement aléatoire, (2) le déploiement déterministe, et (3) l'auto-déploiement. En premier lieu, nous présentons une étude sur le placement aléatoire des capteurs dans les RCsF et nous élaborons une stratégie pratique de déploiement aléatoire. Ensuite, dans le cadre d'un déploiement déterministe, nous analysons le problème de gestion des imperfections liées à la collecte des données par les capteurs. Nous discutons les modèles de couverture et les algorithmes de placement existants et nous exploitons la théorie de l'évidence pour concevoir des stratégies de déploiement plus efficaces. Enfin, nous explorons les stratégies d'auto-déploiement existantes et nous élaborons un protocole en deux phases, léger et complet, pour assurer une couverture optimisée de la zone contrôlée en utilisant un RCsF mobile. Les résultats obtenus montrent l'efficacité des approches proposée qui ont été étudiées à la fois sur des données synthétiques que sur un test expérimentalThis dissertation is an in-depth investigation of the Wireless Sensor Networks (WSNs) deployment problems that follows three general directions: (1) random deployment, (2) deterministic deployment, and (3) self-deployment. First, we present a survey and taxonomy of random node placement in WSNs and we devise a practical random deployment strategy. Second, we analyze the uncertainty-aware deterministic WSNs deployment problem where sensors may not always provide reliable information. We discuss sensor coverage models and placement algorithms found in the literature and we investigate the evidence theory to design better deployment strategies. We devise evidence-based sensor coverage models and we propose several polynomial-time uncertainty-aware deployment algorithms. Third, we explore the published self-deployment strategies and we devise a lightweight and comprehensive two-phase protocol, for ensuring area coverage employing a mobile WSN. Experimental results based on synthetic data sets, data traces collected in a real deployment, and an experimental test, show that the proposed approaches outperform the state-of-the-art deployment strategies
11
Van, Der Werf Steven Martijn. "Architecture and performance of multi-hop wireless ad-hoc routing protocol (MultiWARP)." Thesis, Curtin University, 2010. http://hdl.handle.net/20.500.11937/1989.
Full textAbstract:
In recent years, a great deal of attention has been given to wireless connectivity solutions that are capable of establishing wireless ad-hoc networks between mobile nodes. Whilst most of these networks are formed using a combination of fixed and mobile infrastructure, completely infrastructure-less networks are thought to become more commonplace in the future. Moreover, this type of network structure seeks to utilise multi-hop connectivity between mobile nodes rather than the traditional single-hop connectivity established between fixed access points.The initial configuration phase and subsequent maintenance phase of a multi-hop wireless ad-hoc network requires the use of appropriate routing functions to exist between the mobile nodes. Therefore, it is essential that a routing protocol capable of determining correct and optimal routing path information in the presence of node mobility and the mobile radio environment be sought. Furthermore, it is beneficial to utilise the limited wireless bandwidth efficiently, such that a routing protocol should be designed specifically in the context of a multi-hop wireless ad-hoc network topology. This can be achieved through employing a non-hierarchical approach and using neighbouring nodes to act as intermediate relay nodes.The proposed routing protocol, called the Multi-hop Wireless Ad-hoc Routing Protocol (MultiWARP), is comprised of both a proactive and reactive routing component, thus forming a hybrid protocol which is able to exploit the benefits of each component. It is shown that manipulating these two components within the context of an awareness region, which divides the network into 2 regions, the routing overhead can be minimised. For the proactive component, the necessary network topology information that must be transmitted between neighbouring nodes is encoded within a routing update (RUPDT) packet. In this study, three alternative RUPDT encoding schemes have been formulated to encode the network topology in an efficient manner to reduce the RUPDT packet size.For the reactive component, a novel covercasting mechanism is designed that minimises the number of route request (RREQ) transmissions required to determine the routing path by utilising existing routing table information. Supplementary techniques are then utilised, such as snooping, route repair, and route optimisation to further optimise performance and minimise the route discovery delay (latency). This same covercasting mechanism is then utilised to efficiently transmit periodic RUPDT packets between neighbouring nodes to maintain routing table validity at each node, without having to resort to flooding which causes the “broadcast storm problem”. In addition, several route selection algorithms are considered which distribute traffic data between the intermediate relay nodes comprising the ad-hoc network.The performance and computational complexity of the proposed hybrid routing protocol is shown by means of computer simulations and theoretical analysis. Various traffic scenarios and topologies are presented to obtain the routing protocol performance metric results, and these are compared with other protocols found in the literature. For a multi-hop wireless ad-hoc network, it is shown that the proposed hybrid routing protocol, MultiWARP, is able to achieve higher average system performance in terms of improved throughput and stability performance when compared to other wireless ad-hoc routing protocols, such as DSR.
12
Jagger, Audreyana. "DEFAULT MODE NETWORK (DMN) AND CENTRAL EXECUTIVE NETWORK (CEN) RESTING-STATE CONNECTIVITY AND THEIR RELATIONSHIP TO HOT AND COOL EXECUTIVE FUNCTIONS IN A MIXED CLINICAL GROUP." OpenSIUC, 2016. https://opensiuc.lib.siu.edu/theses/1916.
Full textAbstract:
The current study explored how hot and cool executive functions (EF) could predict resting-state connectivity of the Default Mode Network (DMN) and Central Executive Network (CEN) in a mixed clinical and typically developing sample of adolescents. It was hypothesized that hot EF would predict a quadratic, inverted U-shaped, relationship between connectivity of the major regions of the DMN: the Posterior Cingulate Cortex (PCC) and the Medial Prefrontal Cortex (MPFC). It also was hypothesized that cool EF would predict a quadratic, inverted U-shaped, relationship between the connectivity of the major regions of the CEN: the right Posterior Parietal Cortex (right PPC) and the right Dorsal Lateral Prefrontal Cortex (right DLPFC). The results suggested that hot EF, specifically emotional regulation, predicted a quadratic relationship in DMN connectivity. However, this relationship was U-shaped instead of an inverted U-shaped. Thus, participants who scored well or poorly in emotional regulation generally had higher connectivity than those with average scores in emotional regulation. There were no significant results between cool EF and the CEN. Additional exploratory analysis suggested that the main hypotheses were not driven or suppressed by group differences. Further exploration observed other brain regions involved in resting-state activity that may play a role in hot or cool EF. Overall, findings support the Internal Mentation Hypothesis of DMN activity and are indicative of a relationship between emotional regulation and DMN resting-state connectivity.
13
Barbalat, Guillaume. "Architecture du contrôle cognitif au sein du cortex cérébral dans la schizophrénie." Phd thesis, Université Claude Bernard - Lyon I, 2009. http://tel.archives-ouvertes.fr/tel-00617958.
Full textAbstract:
Le but de cette thèse est d'investiguer l'organisation fonctionnelle du contrôle cognitif au sein du cortex préfrontal latéral dans la schizophrénie. Chez le sujet sain, Koechlin et coll. (Science, 2003) ont montré que le cortex préfrontal latéral était structuré en une cascade de processus de contrôle allant des régions antérieures aux régions postérieures, intégrant respectivement les informations épisodiques (événements antérieurs) et contextuelles (le contexte immédiat de l'action) au choix de l'action en réponse à un stimulus externe. En utilisant le paradigme expérimental de Koechlin et coll. en IRM fonctionnelle, nous avons investigué l'architecture fonctionnelle du contrôle cognitif au sein du cortex latéral préfrontal chez 15 patients schizophrènes et 14 sujets contrôles appariés. Dans une première étude, nous avons trouvé que les patients schizophrènes présentaient un déficit sélectif du contrôle contextuel associé à une hypoactivation des régions postérieures préfrontales, expliquant la désorganisation du discours et du comportement observés chez ces patients. Par ailleurs, les patients schizophrènes hyperactivaient leurs régions rostrales du cortex préfrontal latéral pendant le contrôle des informations de nature épisodique, ce que nous avons interprété comme une tentative de compensation infructueuse des dysfonctions du contrôle contextuel. Dans une seconde étude, nous avons montré que les patients schizophrènes présentaient également une perturbation du traitement top-down des informations de nature épisodique, liée à une dysconnectivité des régions rostrales vers les régions caudales du cortex préfrontal latéral.
14
Edde, Manon. "Approche multimodale de connectivité fonctionnelle et structurelle pour l’analyse du déclin cognitif au cours du vieillissement : étude au sein de la cohorte des 3Cités." Thesis, Paris Sciences et Lettres (ComUE), 2019. http://www.theses.fr/2019PSLEP011.
Full textAbstract:
Le vieillissement s’accompagne de modifications cérébrales dont l’hétérogénéité expliquerait en partie la variabilité inter-individuelle du déclin cognitif. Ces modifications concernent aussi bien les aspects structurels que fonctionnels. L’imagerie cérébrale multimodale a apporté des éléments de compréhension sur la relation structure-fonction, mais reste peu étudiée dans le cadre du vieillissement. Au cours de ce travail, la connectivité fonctionnelle de repos (CF) et structurelle (CS) prélevées dans l’espace natif ont été explorées chez 120 sujets âgés (cohorte 3C) afin d’étudier leur lien avec les trajectoires cognitives modélisées sur les 12 ans de suivi. Dans notre échantillon, les niveaux de CF inter-hémisphérique élevés sont associés avec les altérations globales du parenchyme cérébral (atrophie de la substance grise et charge lésionnelle de la substance blanche) et avec le déclin en mémoire épisodique. Les paramètres de diffusion corrigés de l’eau libre et extraits du faisceau cingulaire reconstruit par tractographie sont associés au déclin en fluence verbale. D’autre part, une CF élevée et une CS basse entre le cortex cingulaire postérieur ventral (vPCC) et le precuneus A7m sont associés avec le déclin en mémoire épisodique, indépendamment du volume hippocampique. Enfin, les sujets âgés présentent un déficit de réorganisation de l’architecture fonctionnelle de repos à court terme après la réalisation d’une tâche d’apprentissage. Ainsi, le vieillissement cérébral s’accompagne de différents types de modifications de CF (augmentation, diminution, déficit de réorganisation à court terme) offrant ainsi au cerveau un répertoire de réponse plus complexe que la CSAging is associated with changes in the brain, the heterogeneity of which partly explains the inter-individual variability of cognitive decline. These changes concern both the structural and functional aspects. Multimodal brain imaging has provided some insights into the structure-function relationship, but this has been little studied in the context of aging. In this work, functional rest (CF) and structural (CS) connectivity from native space were explored in 120 elderly subjects (cohort 3C) to study their relationship to cognitive trajectories modeled on the 12 years of follow-up. In our sample, elevated interhemispheric CF levels are associated with global changes in cerebral parenchyma (gray matter atrophy and white matter injury burden) and episodic memory decline. The diffusion parameters corrected for free-water, extracted from the cingulum tract are associated with the decline in verbal fluency. On the other hand, high CF and low CS between posterior ventral cingulate cortex (vPCC) and precuneus A7m are associated with episodic memory decline, regardless of hippocampal volume. Finally, the elderly subjects present a deficit of short-term reorganization of the rest-functional architecture after a learning task. Thus, cerebral aging is associated with different patterns of CF changes (increase, decrease, short-term reorganization deficit) thus providing to the brain a more complex response repertoire than CS
15
Kabbara, Aya. "Estimation des réseaux cérébraux à partir de l’EEG-hr : application sur les maladies neurologiques." Thesis, Rennes 1, 2018. http://www.theses.fr/2018REN1S028/document.
Full textAbstract:
Le cerveau humain est un réseau très complexe. Le fonctionnement cérébral ne résulte donc pas de l'activation de régions cérébrales isolées mais au contraire met en jeu des réseaux distribués dans le cerveau (Bassett and Sporns, 2017; McIntosh, 2000). Par conséquent, l'analyse de la connectivité cérébrale à partir des données de neuroimagerie occupe aujourd'hui une place centrale dans la compréhension des fonctions cognitives (Sporns, 2010). Grâce à son excellente résolution spatiale, l'IRMf est devenue l'une des méthodes non invasives les plus couramment utilisées pour étudier cette connectivité. Cependant, l'IRMf a une faible résolution temporelle ce qui rend très difficile le suivi de la dynamique des réseaux cérébraux. Un défi considérable en neuroscience cognitive est donc l'identification et le suivi des réseaux cérébraux sur des durées courtes (Hutchison et al., 2013), généralement <1s pour une tâche de dénomination d'images, par exemple. Jusqu'à présent, peu d'études ont abordé cette question qui nécessite l'utilisation de techniques ayant une résolution temporelle très élevée (de l'ordre de la ms), ce qui est le cas pour la magnéto- ou l'électro-encéphalographie (MEG ou EEG). Cependant, l'interprétation des mesures de connectivité à partir d'enregistrements effectués au niveau des électrodes (scalp) n'est pas simple, car ces enregistrements ont une faible résolution spatiale et leur précision est altérée par les effets de conduction par le volume (Schoffelen and Gross, 2009). Ainsi, au cours des dernières années, l'analyse de la connectivité fonctionnelle au niveau des sources corticales reconstruites à partir des signaux du scalp a fait l'objet d'un intérêt croissant. L'avantage de cette méthode est d'améliorer la résolution spatiale, tout en conservant l'excellente résolution temporelle de l'EEG ou de la MEG (Hassan et al., 2014; Hassan and Wendling, 2018; Schoffelen and Gross, 2009). Cependant, l'aspect dynamique n'a pas été suffisamment exploité par cette méthode. Le premier objectif de cette thèse est de montrer comment l'approche « EEG connectivité source » permet de suivre la dynamique spatio-temporelle des réseaux cérébraux impliqués soit dans une tache cognitive, soit à l'état de repos. Par ailleurs, les études récentes ont montré que les désordres neurologiques sont le plus souvent associés à des anomalies dans la connectivité cérébrale qui entraînent des altérations dans des réseaux cérébraux «large-échelle» impliquant des régions distantes (Fornito and Bullmore, 2014). C'est particulièrement le cas pour l'épilepsie et les maladies neurodégénératives (Alzheimer, Parkinson) qui constituent, selon l'OMS, un enjeu majeur de santé publique. Dans ce contexte, la demande clinique est très forte pour de nouvelles méthodes capables d'identifier des réseaux pathologiques, méthodes simples à mettre en œuvre et surtout non invasives. Ceci est le deuxième objectif de cette thèseThe human brain is a very complex network. Cerebral function therefore does not imply activation of isolated brain regions but instead involves distributed networks in the brain (Bassett and Sporns, 2017, McIntosh, 2000). Therefore, the analysis of the brain connectivity from neuroimaging data has an important role to understand cognitive functions (Sporns, 2010). Thanks to its excellent spatial resolution, fMRI has become one of the most common non-invasive methods used to study this connectivity. However, fMRI has a low temporal resolution which makes it very difficult to monitor the dynamics of brain networks. A considerable challenge in cognitive neuroscience is therefore the identification and monitoring of brain networks over short time durations(Hutchison et al., 2013), usually <1s for a picture naming task, for example. So far, few studies have addressed this issue which requires the use of techniques with a very high temporal resolution (of the order of the ms), which is the case for magneto- or electro-encephalography (MEG or EEG). However, the interpretation of connectivity measurements from recordings made at the level of the electrodes (scalp) is not simple because these recordings have low spatial resolution and their accuracy is impaired by volume conduction effects (Schoffelen and Gross, 2009). Thus, during recent years, the analysis of functional connectivity at the level of cortical sources reconstructed from scalp signals has been of increasing interest. The advantage of this method is to improve the spatial resolution, while maintaining the excellent resolution of EEG or MEG (Hassan et al., 2014; Hassan and Wendling, 2018; Schoffelen and Gross, 2009). However, the dynamic aspect has not been sufficiently exploited by this method. The first objective of this thesis is to show how the EEG connectivity approach source "makes it possible to follow the spatio-temporal dynamics of the cerebral networks involved either in a cognitive task or at rest. Moreover, recent studies have shown that neurological disorders are most often associated with abnormalities in cerebral connectivity that result in alterations in wide-scale brain networks involving remote regions (Fornito and Bullmore, 2014). This is particularly the case for epilepsy and neurodegenerative diseases (Alzheimer's, Parkinson's) which constitute, according to WHO, a major issue of public health.In this context, the need is high for new methods capable of identifying Pathological networks, from easy to use and non-invasive techniques. This is the second objective of this thesis
16
Corell, Hanna. "Applications of ocean transport modelling." Doctoral thesis, Stockholms universitet, Meteorologiska institutionen (MISU), 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-75344.
Full textAbstract:
The advective motion of seawater governs the transport of almost everything, animate or inanimate, present in the ocean and those lacking the ability to outswim the currents have to follow the flow. This makes modelling of advective ocean transports a powerful tool in various fields of science where a displacement of something over time is studied. The present thesis comprises four different applications of ocean-transport modelling, ranging from large-scale heat transports to the dispersion of juvenile marine organisms. The aim has been to adapt the method not only to the object of study, but also to the available model-data sets and in situ-observations. The first application in the thesis is a study of the oceanic heat transport. It illustrates the importance of wind forcing for not only the heat transport from the Indian to the Atlantic Ocean, but also for the net northward transport of heat in the Atlantic. In the next study focus is on the particle-transport differences between an open and a semi-enclosed coastal area on the Swedish coast of the Baltic Sea. The modelled patterns of sedimentation and residence times in the two basins are examined after particles having been released from a number of prescribed point sources. In the two final studies the transport-modelling framework is applied within a marine-ecology context and the transported entities are larvae of some Scandinavian sessile and sedentary species and non-commercial fishes (e.g. the bay barnacle, the blue mussel, the shore crab and the gobies). The effects of depth distribution of dispersing larvae on the efficiency of the Marine Protected Areas in the Baltic Sea are examined. Further, the diversity in dispersal and connectivity depending on vertical behaviour is modelled for regions with different tidal regimes in the North Sea, the Skagerrak and the Kattegat. The spatial scales dealt with in the studies varied from global to a highly resolved 182-metres grid. The model results, excepting those from the global study, are based on or compared with in situ-data.At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Submitted. Paper 3: Submitted. 4: Manuscript.
17
Emeriau, Samuel. "Caractérisation des réseaux multi-sujets en IRMf : apport du clustering basé sur la connectivité fonctionnelle." Thesis, Reims, 2011. http://www.theses.fr/2011REIMS018/document.
Full textAbstract:
La compréhension du fonctionnement cérébral est en constante évolution depuis l’essor des neurosciences.Les nouvelles modalités d’imagerie ont permis de mettre en évidence une architecture de notre cerveau en réseaux complexes. Mon travail a pour but de développer une méthode mettant en évidence les réseaux les plus représentatifs d’un groupe de sujet en IRM fonctionnelle.Dans un premier temps, j’ai développé une méthode de réduction des données basées sur le clustering.J’ai introduit une nouvelle caractérisation de l’information fonctionnelle par le profil de connectivité.Celui-ci permet de réduire le biais induit par le bruit présent au sein des données d’IRM fonctionnelle.De plus ce profil ne nécessite pas d’a priori sur les données contrairement aux méthodesi nférentielles classiques.Dans un deuxième temps, j’ai développé une méthode qui permet l’identification de réseaux communs sur un groupe de sujets tout en prenant en compte les variabilités spatiales et fonctionnelles inter-sujets. Les réseaux obtenus peuvent ensuite être caractérisés par leur distribution spatiale mais également par les liens de connectivités se manisfestant en leur sein.Cette méthode permet également la comparaison des réseaux de différents groupes de sujets et la mise en évidence de l’implication de réseaux différents en fonction de stimulations différentes ou d’un état pathologiqueThe comprehension of cerebral operations is in constant evolution since the rise of the neurosciences.New methods of imagery made it possible to highlight an architecture of our brain in complex networks.The purpose of my work is to develop a method to find the most representative networks of a group of subjects in Functional MRI.In the first step, I developed a method to reduce the fMRI data size based on clustering. I introduced a new characterization of functional information by the profile of connectivity. This one makes it possible to reduce the variance induced by the noise present within the data of Functional MRI.Moreover this profile does not require a priori information on the data contrary to the traditional inferential methods.In the second step, I developed a method to identify common networks on a group of subjects while taking into account of spatial and functional inter-subjects variability. The networks obtained can then be characterized by their spatial organization but also by their inner connectivity links.This method also allows the comparison of the networks of various groups of subjects, making it possible to highlight the implications of different networks according to different stimulations or pathological states
18
Quidé, Yann. "Etat de stress post-traumatique : corrélats cérébraux, neuropsychologiques, biologiques et thérapeutiques." Thesis, Tours, 2013. http://www.theses.fr/2013TOUR4043/document.
Full textAbstract:
L’état de stress post-traumatique (PTSD) est un trouble anxieux, lié au stress, souvent observé chez les soldats revenant de conflits armés, les victimes de guerre ou de catastrophes naturelles, mais qui peut également survenir après exposition à des situations plus « communes » dans les pays occidentaux en temps de paix, tels les accidents de la route ou les agressions sexuelles. Le PTSD est caractérisé par des troubles des fonctions exécutives (attention, mémoire de travail), associés à des anomalies cérébrales morphologiques et fonctionnelles. Cette thèse de doctorat a permis de caractériser les effets morphologiques et fonctionnels des différents traitements actuellement reconnus de première ligne pour les troubles anxieux et le trouble dépressif majeur, indiquant un effet « top-down » de normalisation des aires frontales par les traitements psychothérapiques, alors que les traitements pharmacologiques semblent avoir un effet « bottom-up » de normalisation des aires limbiques. De plus, dans une seconde étude, nous avons montré l’importance de l’étude de réseaux cérébraux impliqués dans la performance de tâches cognitives telles des tâches de mémoire. Ces réseaux se trouvent dérégulés dans la pathologie post-traumatique, conduisant à leur inefficacité, et provoquant une impossibilité pour les patients de pouvoir répondre correctement à la tâche proposée. Finalement, nous avons pu mettre en place un protocole de recherche clinique ambitieux de part son design longitudinal (visite à 1 mois, puis suivi à 6 mois) permettant de comprendre les étapes précoces du développement du PTSD chez des victimes d’agressions sexuelles. Cette étude allie mesures neuropsychologiques des fonctions exécutives, mesures biologiques de l’axe hypothalamo-hypophyso-surrénalien (cortisol salivaire) et des mesures de neuroimagerie structurale (IRM, DTI), fonctionnelle (IRMf, ASL), incluant des mesures de connectivité cérébrale (structurale, fonctionnelle)Posttraumatic stress disorder (PTSD) is an anxiety, stress-related disorder, often seen in soldiers returning from armed conflict, victims of war or natural disasters, but can also occur after exposure to more « common » situations in Western countries, such as motor vehicle accidents or sexual assault. PTSD is characterized by executive functioning impairments (attention, working memory) associated with morphological and functional brain abnormalities. This thesis aimed to characterize the morphological and functional effects of different treatments currently recognized as first line for anxiety disorders and major depressive disorder, indicating a « top-down » effect of normalization of frontal areas for psychotherapeutic treatments, while pharmacological treatments seem to lead to a « bottom-up » normalization effect in limbic areas. In addition, in a second study, we demonstrated the importance of the study of brain networks involved in the performance of cognitive tasks such as memory tasks. These networks are deregulated in PTSD, leading to their inefficiency, and therefore to PTSD patient’s inability to perform the required task correctly. Finally, we have set up an ambitious longitudinal (1 month and 6 months) clinical research protocol, investigating early stages of PTSD development in victims of sexual assault. This study combines neuropsychological measures of executive functions, biological measures of the hypothalamic-pituitary-adrenal axis (salivary cortisol) and measures of structural (MRI, DTI) and functional imaging (fMRI, ASL), including measures of brain connectivity (structural, functional)
19
Radhakrishnan, Rupa M. D. "Altered Functional Activation and Network Connectivity Underlies Working Memory Dysfunction in Adolescents with Epilepsy." University of Cincinnati / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1515514289145094.
Full text
20
Baronnet-Chauvet, Flore. "IRM fonctionnelle au repos après un accident ischémique : de la connectivité fonctionnelle au handicap." Thesis, Paris 6, 2016. http://www.theses.fr/2016PA066229/document.
Full textAbstract:
L’étude des réseaux cérébraux en IRM fonctionnelle au repos est de plus en plus utilisée chez les patients victimes d’accidents vasculaires cérébraux. La majorité des études se sont focalisés sur les déficits moteurs, attentionnels ou phasiques. Dans ce travail, nous avons étudié l’impact du handicap global sur la connectivité fonctionnelle de grands réseaux corticaux à la phase subaiguë d’infarctus cérébraux. Ce travail a porté sur 50 patients ayant subi un premier infarctus sus-tentoriel (29 hommes, 22 AIC gauche, 57 ± 14 ans, délai médian après l’AIC = 4.5 semaines) et 75 témoins (27 hommes, 55 ± 15 ans). Sept réseaux de repos ont été étudiés à partir d’une analyse en graine et nous avons distingué pour chacun les connectivités fonctionnelles interhémisphérique, ipsi et contralésionnelle. Les 22 patients sans handicap (mRS = 0/1) avaient une connectivité normale alors qu’une diminution diffuse et bilatérale était observée chez les 28 patients avec handicap, expliquant 22% de la variance. Les analyses post-hoc ont montré que ces différences s’observaient essentiellement entre les patients sans handicap et ceux avec handicap léger et portaient surtout sur le mode par défaut et un réseau exécutif. Nous avons calculé pour chacun un score d’intégrité de la connectivité fonctionnelle permettant de résumer l’ensemble de ces altérations. Cet outil simple permettait de prédire le handicap résiduel avec une spécificité de 91% et une sensibilité de 86%. Nous avons donc observé une diminution diffuse de la connectivité fonctionnelle des réseaux de repos chez les patients ayant un handicap résiduel, alors qu’une connectivité normale marquait un excellent pronostic fonctionnelResting-state functional MRI is increasingly used to investigate brain networks in stroke patients. Most studies focused specifically on motor, attentional and language deficits. Here we have investigated the relationships between global post-stroke disability and functional connectivity of seven major cortical networks in subacute ischemic stroke patients. We have studied 50 patients with first-ever unilateral hemispheric stroke (29 men, 22 left strokes, 57 ± 14 years) with a median post-stroke delay of 4.5 weeks and 75 healthy volunteers (27 men, 55 ± 15 years). Seven cortical networks were characterized with a seed-based approach and for each network we distinguished inter-hemispheric, ipsi- and contra-lesional functional connectivity. The 22 patients without disability (modified Rankin’s scale 0-1) had normal functional connectivity in all networks whereas the 28 disabled patients had widespread and bilateral decreases in functional connectivity explaining 22 % of the variance. Secondary analyses showed that abnormalities mainly differentiate no disability from mild disability and may predominate in default-mode and top-down control networks. We have computed for each subject a functional connectivity index that summarizes all these abnormalities. This simple tool was strongly predictive of residual disability with a specificity of 91% and a sensitivity of 86%. In conclusion, widespread and bilateral alterations in cortical connectivity occur in disabled subacute stroke patients, whereas normal indicate excellent global outcome
21
Nylén, Jan. "Exploring Ways of Visualizing Functional Connectivity." Thesis, Umeå universitet, Institutionen för tillämpad fysik och elektronik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-141182.
Full textAbstract:
Functional connectivity is a field within neuroscience where measurements of co-activation between brain regions are used to test various hypotheses or explore how the brain activates depending on a given situation or task. After analysis, the underlying data in the field consists of a n by n adjacency matrix where each cell represents a correlation value between two regions in the brain. Depending on the research question the number of regions and matrices incorporated varies and new visualizations are needed in order to portray them. In this thesis the design of an interactive web based visualization tool for functional connectivity was explored through an iterative design process. The design of the tool was based on existing guidelines, interviews and best practices in data visualization as well as an analysis of current visualization solutions used in functional connectivity. The final concept and prototype uses a network plot for functional connectivity called the connectogram as well as a grouped bar graph to provide an intuitive and accessible way of comparing functional connectivity data by interacting with and highlighting networks and specific network data through direct manipulation. Results of qualitative evaluations of a prototype using data from a concurrent scientific project is presented. The prototype was found to be useful, engaging, easily perceivable and offered an easy and quick way of exploring data sets.
22
Goldstone, Aimée. "Functional connectivity of the ageing brain." Thesis, University of Birmingham, 2017. http://etheses.bham.ac.uk//id/eprint/7651/.
Full textAbstract:
This thesis investigated the impact of advancing age on modifying the functional connectivity (FC) of both typical cortical resting-state networks and subcortical structures in the human brain. Furthermore, it explored how any differences in FC may be associated with changes in sleep quality, also thought to be affected by age, and how such interactions may contribute to typical cognitive disruption associated with older age. The results suggest that older age is associated with the heterogeneous, spatially specific re-organisation of resting-state networks (RSNs), as well as indicating gender-specific spatial re-organisation. Investigation of thalamic FC revealed that older adults exhibited greater thalamo-sensory and thalamo-hippocampal FC, which was related to cognitive performance on RT and memory tasks, respectively. Investigation into participant’s sleep patterns provided evidence that sleep quality was more variable amongst the older participants. Furthermore, older adults that slept the longest each night were found to exhibit patterns of thalamic FC which were associated with better cognitive performance, than seen in older shorter sleepers. These results provide preliminary evidence that sleep may be associated with more ‘preferable’ patterns of FC in older adults which may be beneficial for cognitive function.
23
Merz, Susanne. "Functional connectivity in disorders of consciousness." Thesis, University of Aberdeen, 2013. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=211209.
Full textAbstract:
Disorders of consciousness (DoC) are a group of disorders that can occur after severe brain injury. DOC have been subdivided based on behavioural observations into: Coma, lacking any signs of wakefulness or awareness; the vegetative state, showing signs of wakefulness but lacking any signs of awareness; and the minimally conscious state, showing signs of wakefulness and infrequent and irregular signs of awareness. The so-called locked-in syndrome, a state where both wakefulness and awareness are intact, but no communication is possible due to a lack of muscle function, does not belong to the disorders of consciousness. However, it is difficult to distinguish the locked-in syndrome from DoC diagnostically, because consciousness can only be shown through consistent responses to a command and current methods for assessing consciousness rely on behavioural responses. Patients with locked-in syndrome might not be able to move voluntarily at all in the most severe cases. Behavioural assessment would then classify them as unaware. While this is an extreme and rare case, it illustrates the problem behavioural assessment poses. Such assessments are unable to distinguish the effects of impaired muscular control from impaired awareness, when either has reached an extreme level of severity. Brain damage that does not affect consciousness itself can nevertheless affect the results of the behavioural assessment of consciousness. It is then hardly surprising that the diagnosis of DoC is associated with a high level of uncertainty. The advantage of brain imaging methods is that they do not rely on the patients ability to produce a consistent behavioural response. There have therefore been efforts to use the brain imaging methods electroencephalography, positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) to aid diagnosis of disorder of consciousness. PET and fMRI have successfully been used to identify regions of difference in some patients in a DoC. Task-based fMRI has been used to identify intact consciousness, using tasks that require explicit understanding of instructions and wilful modulation of brain activity, but no motor control. One of these tasks consists of periods where the participant imagines playing tennis alternated with periods of rest. The ability to follow this paradigm is evidence of consciousness, and a few patients with a diagnosis of DoC have been shown to be able to do this task. However, the tennis task requires high order processing of the tasks requirements and the majority of patients does not respond to this task. fMRI tasks that test sensory modalities instead of consciousness have been used to show retained brain function even in DoC patients that do not respond to the tennis task. In this work the tennis task and a battery of other tasks including tactile, visual and auditory stimulation, were studied on a group of DoC patients. It was found that none of the patients responded to the task of imagining playing tennis, but retained sensory function could be identified in three out of seven patients. This highlights a strength of fMRI, namely that it can identify retained brain function below the level that is necessary for consciousness. However, the results also show that more than half of the patients studied here, did not show retained brain activation during the fMRI scan. For any of the patients that did not show a response, this can be due to an actual lack of retained brain function, but it can also be due to limitations of the task-based fMRI analysis. The fMRI tasks only test one sensory function at a time, for a short time. Thus a visual fMRI task for example, can only provide information about areas of the brain, that are involved in visual processing. And when vigilance is fluctuating, retained brain function can remain undetected, if vigilance is low during the scan. Functional connectivity analysis is a method to study internal connections between brain areas that is not dependent on an external task. It models the brain as a network of interconnected regions and studies the characteristics of this network. Graph theory is a mathematical field that has found application on many other fields using network analysis, like social sciences, metabolic network modelling or gene network modelling. In fMRI analysis, graph theory has been used to study different phenomena and pathologies and global network properties have been shown reproducibly. The work presented here aims to develop new methods based in graph theory aiding the identification of residual brain integrity. To allow an assessment of the brain network topology and its use in the assessment of residual brain integrity, a novel method was designed based on a graph theoretical measure. The method, termed Cortical Hubs And Related network Topology (CHART) is a two stage procedure. The rst stage identifies statistically significant differences in functional connectivity between two groups, using a measure of the average connectivity of each voxel, the weighted global connectivity. The second stage highlights the topology of the networks associated with those differences. Two fMRI datasets, with different underlying tasks and pathologies were used to test the CHART method. The first dataset was acquired from a group of patients with severe depression. It contrasted the state of the brain before and after successful treatment with electroconvulsive therapy. In this patient group the CHART method was able to identify an area of hyperconnectivity in the depressed state, compared to the treated state. This area of hyperconnectivity was connected to areas that had priorly been shown to be overly connected in the depressed state. The second dataset consisted of DoC patients, that had been extensively assessed behaviourally. Half of the patients were diagnosed to be in a vegetative state, the other half was diagnosed to be in a minimally conscious state. The first stage of CHART identified several areas of difference based on the weighted global connectivity. The second stage highlighted that the observed global differences were due to an overall lack of extended functional connectivity in the vegetative state patients. The addition of a healthy control group in stage two allowed comparison not only between the two DoC groups, but also with the healthy group. In summary it was observed that the spatial extent of the connectivity seen in the minimally conscious group resembles the spatial extent of the connectivity seen in the healthy control group, while the spatial extent of connectivity observed in the vegetative state group was minimal, compared to both healthy and minimally conscious group. Thus the spatial extent of connectivity is a distinguishing property for the vegetative state group studied here. However the first stage of the CHART method is a group based method. In disorders of consciousness, where the underlying pathology is different from case to case, this concept is problematic. Finding a meaningful group of interest is difficult or impossible, because lesions differ in location and extent. Individual differences in connectivity can be expected to be large, and a generalisation of the CHART result might not lead to improved diagnosis for every patient. For diagnosis, the patients individual characteristics must be taken into account. An additional objective of this work was therefore to develop a method to compare a single patient to a group of controls. An approach based on regression modelling was tested but failed to provide the necessary statistical sensitivity to detect impaired connectivity. In conclusion the CHART method developed in this work provides insights into the functional connectivity of a group of DoC patients. To assist diagnosis, further development of a method to compare a single subject to a group of controls will be important.
24
Nauhaus, Ian Michael. "Functional connectivity in primary visual cortex." Diss., Restricted to subscribing institutions, 2008. http://proquest.umi.com/pqdweb?did=1692099811&sid=1&Fmt=2&clientId=1564&RQT=309&VName=PQD.
Full text
25
Ghumman, Sukhmanjit. "Functional connectivity in patients with brain tumours." Mémoire, Université de Sherbrooke, 2018. http://hdl.handle.net/11143/12001.
Full textAbstract:
Abstract: The default mode network of the brain is a set of functionally connected regions associated with introspection and daydreaming. Recent fMRI studies have discovered that the default mode network is often perturbed in the diseased brain. For example, the default mode network is known to be modulated in dementia, ADHD, depression, and schizophrenia, among others. This has led many into believing that this network could have a role in the physiopathology of nervous system disease, or could be a useful marker of brain function. However, very few studies have yet been done which investigate how surgical lesions such as brain tumours affect the default mode network. Consequently, the goal of this project was to characterise the effect of brain tumours on the default mode network based on their location, histological type, and other parameters.Le mode de fonctionement par défaut du cerveau est un réseau cérébral associé à la rêverie et à l’introspection. Des études récentes sur ce réseau ont découvert qu’il est perturbé dans plusieurs pathologies cérébrales. Par example, le mode de fonctionnement par défaut est modulé en démence, TDAH, dépression, schizophrénie et plusieurs autres maladies liés au cerveau. Ceci a mené à l’hypothèse que le mode de fonctionnement par défaut pourrait avoir un rôle dans la physiopathologie des maladies du système nerveux, ou pourrait être un marqueur utile du fonctionnement cérébral. Par contre, très peu d’études ont investigué l’effet de lésions chirurgicaux comme les tumeurs cérébrales sur le mode de fonctionnement par défaut. Par conséquent, le but de ce projet était de caractériser l’importance de l’histologie, de la localisation et de plusieurs autres paramètres de l’effet d’une tumeur cérébrale sur le mode de fonctionnement par défaut.
26
Boisgontier, Jennifer. "Corrélats anatomo - fonctionnels de la vulnérabilité aux troubles du spectre autistique." Thesis, Paris Est, 2016. http://www.theses.fr/2016PESC0074/document.
Full textAbstract:
Les troubles du spectre autistique (TSA) sont des troubles neurodéveloppementaux fortement héritables. En parallèle, la théorie de l'hypoconnectivité fronto – postérieure semble être au coeur de la physiopathologie des TSA. Afin de comprendre la contribution des facteurs de risque familiaux de ce trouble, nous avons conduit conjointement une étude de connectivité anatomique et fonctionnelle chez des parents non atteints de sujets atteints de TSA. Nous avons réalisé une étude de tractographie en cerveau entier afin de comparer les valeurs de l'anisotropie fractionnelle généralisée le long des principaux faisceaux de substance blanche chez 85 sujets adultes : 39 parents non atteints, 18 sujets atteints de TSA comparés à 28 sujets contrôles. Après avoir corrigé pour les tests multiples, nous avons mis en évidence une diminution significative de l'anisotropie fractionnelle généralisée le long du faisceau fronto- occipital inférieur bilatéral chez les parents non atteints, les sujets atteints de TSA en comparaison aux sujets contrôles. Afin de comprendre l'implication fonctionnelle de la dysconnectivité anatomique fronto – occipitale retrouvée en tractographie, nous avons calculé la connectivité fonctionnelle entre les régions fronto – occipitales selon les extrémités du faisceau frontal - occipital inférieur bilatéral. En comparaison à 28 sujets contrôles, nous avons ainsi observé une augmentation significative de la connectivité fonctionnelle fronto - occipitale chez 38 parents non atteints et chez 13 sujets atteints de TSA. Une étude de connectivité fonctionnelle en cerveau entier serait une perspective prometteuse quant à l'interprétation de l'augmentation de la connectivité fronto – occipitale observée. Les anomalies fronto – occipitales montrées chez les parents non atteints, les sujets atteints de TSA pourraient correspondre à la mise en évidence d'un endophénotype dans les TSAAutism Spectrum Disorder (ASD) are neurodevelopmental disorders highly heritable.In parallel, the underconnectivity theory of ASD assumes that fronto-posterior brain disconnectivity is at the core of its pathophysiology. Our goal was to assess long-range structural and functional connectivity in unaffected parents of subjects with ASD to better understand the contributions of familial factors to heightened risk of ASD. We performed a diffusion weighted imaging (DWI) based whole brain tractography to compare generalized fractional anisotropy (gFA) in the main deep long white matter tracts in 85 adults: 39 unaffected parents, 18 probands compared to 28 controls. After corrections for multiple comparisons, we identified a significant decrease in gFA in the bilateral inferior frontal occipital fasciculus (IFOF) in both probands with ASD and unaffected parents when compared to controls. To understand the functional implication of fronto – occipital anatomical disconnectivity, we assessed the functional connectivity between the regions linked by IFOF exhibiting significant alterations in gFA. We also showed that both probands and unaffected parents exhibited a significantly increased functional connectivity between the frontal and occipital regions linked by the IFOF. In order to better understand and extend this interesting results, to evaluate the global functional connectivity of our sample in order to be able to interpret the increase of fronto-occipital functional connectivity would be an important perspective. These findings highlight an altered fronto-occipital connectivity in subjects with ASD and unaffected parents suggesting that fronto-occipital disconnectivity may be an endophenotype of ASD
27
Kopal, Jakub. "Usage de la connectivité pour étudier les (dys)fonctions cérébrales." Thesis, Toulouse 3, 2021. http://www.theses.fr/2021TOU30020.
Full textAbstract:
Nous nous représentons le cerveau comme un réseau complexe de régions structurellement connectées et fonctionnellement couplées. Les fonctions cognitives découlent de l'activité coordonnée de régions corticales distantes. La connectivité est utilisée pour représenter la coopération de régions cérébrales ségréguées et fonctionnellement spécialisées. Qu'il s'agisse de l'analyse des liens anatomiques, des dépendances statistiques ou des interactions causales, la connectivité révèle des aspects fondamentaux du fonctionnement (dys)cérébral. Cependant, l'estimation et l'application de la connectivité posent encore des problèmes. C'est pourquoi cette thèse est consacrée à surmonter ces défis. Le premier défi provient de l'effet néfaste du bruit systématique (comme les mouvements de la tête) sur les estimations de la connectivité. Nous avons proposé un indice qui décrit la qualité de la connectivité et qui peut refléter différents types d'artefacts, d'erreurs de traitement et de pathologie cérébrale, permettant son utilisation étendue dans le suivi de la qualité des données et les investigations méthodologiques. En outre, les altérations de la connectivité jouent un rôle inestimable dans la compréhension des dysfonctionnements cérébraux. En étudiant certains mécanismes de l'épilepsie, nous montrons que la connectivité peut suivre les changements progressifs de la susceptibilité aux crises et identifier les facteurs déterminants de la génération des crises. L'identification des moments critiques de modification de la connectivité pourrait aider à prédire avec succès les crises. Enfin, on ne comprend pas bien comment le cerveau s'adapte aux exigences des tâches cognitives à une échelle de temps rapide. Nous présentons une combinaison d'EEG intracrâniens et de mesures de pointe épileptiques pour étudier la dynamique des réseaux pendant la mémoire de reconnaissance. Il est essentiel de comprendre comment le cerveau fait face dynamiquement aux changements rapides des demandes cognitives pour comprendre les bases neurales de la cognition. En conclusion, l'objectif modeste de cette thèse est de répondre au moins partiellement à certains des nombreux défis auxquels les neurosciences actuelles sont confrontéesWe picture the brain as a complex network of structurally connected regions that are functionally coupled. Brain functions arise from the coordinated activity of distant cortical regions. Connectivity is used to represent the cooperation of segregated and functionally specialized brain regions. Whether it is the analysis of anatomical links, statistical dependencies, or causal interactions, connectivity reveals fundamental aspects of brain (dys)function. However, estimating and applying connectivity still faces many challenges; therefore, this work is devoted to tackling them. The first challenge stems from the detrimental effect of systematic noise (such as head movements) on connectivity estimates. We proposed an index that depicts connectivity quality and can reflect various artifacts, processing errors, and brain pathology, allowing extensive use in data quality screening and methodological investigations. Furthermore, connectivity alterations play an invaluable role in understanding brain dysfunction. Investigating the mechanisms of epilepsy, we show that connectivity can track gradual changes of seizure susceptibility and identify driving factors of seizure generation. Identifying critical times of connectivity changes could help in successful seizure prediction. Finally, how the brain adapts to task demands on fast timescales is not well understood. We present a combination of intracranial EEG and state-of-art measures to investigate network dynamics during recognition memory. Understanding how the brain dynamically faces rapid changes in cognitive demands is vital to our comprehension of the neural basis of cognition. In conclusion, the modest goal of this thesis is to at least partially answer some of the many challenges that current neuroscience is facing
28
Narayanan, Ananth. "Pharmacological Modulation of Functional Connectivity in Neuropsychological Disorders." The Ohio State University, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=osu1353086436.
Full text
29
Fauvet, Maxime. "Mécanismes centraux de contrôle de la motricité saine et altérée : rôle fonctionnel de la dynamique des couplages cortico-musculaires." Thesis, Toulouse 3, 2022. http://www.theses.fr/2022TOU30065.
Full textAbstract:
Le contrôle de l'activité motrice volontaire est un point de discussion important pour les personnes intéressées par le mouvement des êtres humains et qui est partagé entre le domaine de la biomécanique et celui du contrôle moteur exercé au niveau central. Il existe des théories valides qui modélisent les mécanismes mis en jeu, que ce soit au niveau de l'encéphale, de la moelle épinière ou des muscles, pour les deux approches. Cependant, il manque encore à ce jour une théorie unificatrice qui relierait les différents niveaux d'observation en un modèle global du contrôle moteur. C'est dans l'objectif de contribuer à la construction d'une telle théorie que ce projet de thèse a été réalisé en s'appuyant sur l'analyse de la connectivité entre les différentes structures intervenant dans la réalisation d'un mouvement pour mettre en évidence les communications au sein du réseau moteur. Ainsi, les principaux objectifs de ce travail ont été i) de développer une méthode d'analyse de la dynamique de la connectivité, ii) d'appliquer cette méthode à l'étude de la connectivité fonctionnelle à partir de mouvements du coude chez le sujet sain et le patient AVC et iii) d'approfondir les données issues de la connectivité fonctionnelle par des analyses de la dynamique de la connectivité effective. Ce projet de thèse est donc pluridisciplinaire, en se situant au croisement des neurosciences, de la biomécanique et du traitement du signal. Nos résultats montrent que la méthode développée permet l'analyse de la dynamique de la connectivité dans un contexte de variabilité inter et intra-individuelle importante. L'étude comparée des sujets sains et des patients AVC révèle une altération de la connectivité fonctionnelle entre le cortex moteur et les muscles antagonistes au mouvement chez les patients ainsi que des niveaux variables de connectivité au cours du mouvement. Enfin, le développement des méthodes de connectivité effective et la sélection des différents paramètres à appliquer laissent supposer que leur application permettra d'étudier les sens des différents échanges d'informations qui ont lieu pendant un mouvement. L'ensemble des résultats de ce travail révèle que l'inclusion des analyses de la dynamique de la connectivité peut représenter un apport majeur aux théories du contrôle moteur existantes et peut même servir de base à la constitution d'un modèle dynamique reflétant les communications qui relient les différentes structures impliquées dans la génération d'un mouvementThe control of voluntary movement is a most discussed issue for those people interested in how the human locomotion or other daily acts are controlled and find answers in two apparently separate fields of research: biomechanics on the one hand and motor control on the other. Verified theories, which model some of the mechanisms involved in motor control at either muscles or brain levels, exist in both fields. However, we still miss a unifying theory that would bridge the gap existing between biomechanics and motor control and would offer a model including all levels of observation: from central nervous system to muscle activity. The present work has been actually designed to partly answer this issue: we propose to study the dynamics of communications occurring during a movement between the different nodes of the motor network through connectivity analyses. Hence, we pursued three main goals: i) develop a dynamic analysis of connectivity measures, ii) apply this analysis to the comparison of functional connectivity between healthy subjects and stroke patients performing elbow extensions and iii) complete the previous analyses with effective connectivity studies of the same paradigm. Thus, this is a multidisciplinary work involving neurosciences, biomechanics and signal processing. Our results show that high inter-variability and intra-variability are less influential in connectivity analysis with our method. Compared analyses between healthy subjects and stroke patients reveal a specific alteration of functional connectivity between antagonist muscles and motor cortex in stroke patients and varying levels of connectivity measures during movement. Finally, the development of effective connectivity analyses and the associated parameters selection will allow us to figure out the direction of communications within the motor network during movement. The overall results of this work show that the analyses of connectivity dynamics can complete existing motor control theories and provide a basis for the constitution of a new dynamic model including the communications between the nodes of the motor network involved in movement control and finally reunite biomechanics and motor control
30
Rizkallah, Jennifer. "Characterization of neocortical networks from high-resolution EEG : application to disorders of consciousness." Thesis, Rennes 1, 2019. http://www.theses.fr/2019REN1S095.
Full textAbstract:
Le cerveau humain est un réseau complexe. Une fonction cognitive efficace est garantie lorsque le cerveau reconfigure d’une manière dynamique l'organisation de son réseau durant le temps. Les études ont montré que la plupart des troubles cérébraux, y compris les maladies neuro-dégénératives et mentales, se caractérisent par des altérations du réseau cérébral structurel et/ou fonctionnel. Il existe donc une forte demande pour des nouvelles méthodes non invasives, basées sur les réseaux et faciles à utiliser, permettant d'identifier ces réseaux pathologiques. La méthode appelée connectivité de sources en électroencéphalographie (EEG) permet de suivre la dynamique des réseaux cérébraux large échelle avec une excellente résolution temporelle. C’est dans ce contexte que s’inscrivent mes travaux de thèse qui prolongent les développements méthodologiques et cliniques de notre équipe de recherche sur la connectivité fonctionnelle au niveau des sources cérébrales. L’objectif de mes travaux de thèse est double : i) progresser sur les aspects méthodologiques de la méthode connectivité de sources en EEG et ii) utiliser cette méthode dans une application clinique en lien avec les troubles de la conscience. Ma thèse se divise donc en deux grandes parties, avec deux études réalisées dans chaque partie. Dans la première partie (aspects méthodologiques), j’ai abordé, dans une première étude, la capacité de la méthode connectivité de sources en EEG à suivre les altérations dynamiques des réseaux cérébraux durant une tâche cognitive rapide. Puis dans une seconde étude, j’ai testé l’effet du problème de l’étalement spatial des sources sur la reconstruction des réseaux fonctionnels. Dans la deuxième partie (applications cliniques), j’ai analysé les altérations dans les réseaux cérébraux chez les patients souffrant d’un désordre de la conscience, en utilisant une analyse statique pour la première étude et une analyse dynamique pour la deuxième étudeThe human brain is a complex network. Cognitive function is guaranteed when the brain dynamically reconfigures its network organization over time. Studies have showed that most brain disorders, including neurodegenerative and mental diseases, are characterized by changes in the structural and/or functional brain networks. Thus, there is a strong demand for new, non-invasive, network-based and easy-to-use methods to identify these pathological networks. Electroencephalography (EEG) source connectivity method enables the tracking of large scale brain networks dynamics with an excellent temporal resolution. It is in this context that my thesis was carried out. My work here extends the methodological and clinical developments of our research team on functional connectivity at cortical level. The aim of my thesis work is twofold: i) to progress on the methodological aspects of the EEG source connectivity method and ii) to use this method in a clinical application related to the disorders of consciousness. My thesis is divided into two main parts, with two studies realized in each part. In the first part (methodological aspects), I approached, in a first study, the capacity of the EEG source connectivity method to track the brain network dynamic alterations during a fast cognitive task. Then in a second study, I tested the effect of the spatial leakage problem on the reconstructed functional brain networks. In the second part (clinical applications), I analyzed brain networks alterations in patients with disorders of consciousness, using static analysis in the first study and dynamic analysis in the second one
31
Ing, Alex. "Comparing functional connectivity across the whole brain." Thesis, University of Aberdeen, 2014. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=225661.
Full textAbstract:
Functional connectivity MRI (fcMRI) based on the blood oxygen level dependent (BOLD) contrast has become a widely used modality for mapping the brain's functional architecture. In recent years, applications of fcMRI have led to numerous breakthroughs in both clinical research and basic sciences. However, there are a number of unresolved issues associated with fcMRI relating to both the modality itself, and to methods used to analyse fcMRI data. The aim of this thesis was twofold: to develop novel data analysis procedures, and to demonstrate their feasibility in dedicated neuroimaging studies. Subject head movement can act as a significant confound in fcMRI. Investigating this issue, it was found that subject motion can induce significant increases and decreases in functional connectivity across the brain. A novel motion correction method was developed, which proved more effective than standard procedures in the removal of motion induced connectivity changes. The BOLD contrast is not a direct measure of neural activity, it measures the hemodynamic response caused by changes in neural activity, which varies across the brain. The hypercapnic state is often used to calibrate the BOLD signal. This calibration crucially relies on the assumption that hypercapnia does not affect neuronal activity. An investigation into the hypercapnic state revealed that it is associated with both increases and decreases in functional connectivity. Whilst carrying out this investigation, a number of limitations, such as the need for a hypothesis and information loss, were identified in standard data analysis procedures. Three novel methods were developed to address these limitations. The efficacy of these methods was demonstrated in four different neuroimaging studies, which investigated functional connectivity changes induced by hypercapnia, aerobic exercise, hormonal changes across the menstrual cycle, and electroconvulsive therapy treatment in depression.
32
Stringer, Michael S. "Functional connectivity approaches to focal neurological conditions." Thesis, University of Aberdeen, 2016. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=231782.
Full textAbstract:
A wide range of conditions are characterised by focal neurological symptoms, yet the pathophysiolgy often remains poorly understood. This thesis has focussed on applying functional neuroimaging in clinical groups. Migraines with aura are amongst the most common conditions posing a significant burden to sufferers. Elevated connectivity was detected in the visual cortex of migraine with aura patients, potentially complementing one of the leading proposed mechanisms for attacks. Minor strokes patients are also affected by focal symptoms after events which in some cases can be prolonged. Altered connectivity was observed in a number of regions reflecting previous findings for acute stroke. A group of transient ischaemic attack patients were also analysed, revealing subtle differences necessitating further study. Lastly disorders of consciousness pose acute challenges for treatment and ongoing care. Task based imaging was applied to form a more accurate picture of residual cognition. Additionally the correlation between measures derived from resting state data and cerebral glucose consumption was explored.
33
Björnfot, Cecilia. "Multiband functional magnetic resonance imaging (fMRI) for functional connectivity assessments." Thesis, Umeå universitet, Institutionen för fysik, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-149906.
Full textAbstract:
During resting state the brain exhibits synchronized activity within all major brain networks. Using blood oxygen level dependent (BOLD) resting state functional magnetic resonance imaging (fMRI) based detection it is possible to quantify the degree of correlation, connectivity, between regions of interest and assess information regarding the integrity of the inter-regional functional integration. A newly available multiband echo planar imaging (EPI) fMRI sequence allows for faster scan times which possibly allows us to better examine large-scale networks and increase the understanding of brain function/dysfunction. This thesis will assess how the newly developed sequence compares to a conventional EPI sequence for detecting resting state connectivity of canonical brain networks. The data acquisitions were made on a 3 Tesla scanner using a 32 channel head coil. The hypothesis was that the multiband sequence would produce a better result since it has faster sampling rate, thus more data points in its time-series to support the statistical analyses. Using Pearson’s linear correlation between the average time-series (approximately 12 minutes long) within a seed-region and all voxels contained in the image volume, correlation maps where created for each of the eight participants using data normalized to Montreal Neurological Institute (MNI) space. The resting state networks (RSN) were then found by performing a one sample T-test on group level. Six seed-coordinates, based on literature, where used revealing the the homotopic connections in anterior Hippocampus, Motor cortex, Dorsal attention, Visual and the Default mode network (DMN) as well for an anterior-posterior connection in the DMN. By comparing the maximum T-values within the regions for the RSN no systematic difference could be found between the multiband and conventional fMRI data. Further tests were conducted to evaluate if the sequences would differentiate in their results if the acquisition time was shortened, i.e shortening the time-series in the voxels. However no such difference could be established.Importantly, the results are specific to the 32 channel head coil used in the current study. Presumably recently available and improved coil designs could better exploit the multiband technique.
34
Almashaikhi, Talal. "Electrical brain stimulation and human insular connectivity." Thesis, Lyon 1, 2013. http://www.theses.fr/2013LYO10174/document.
Full textAbstract:
Le cortex insulaire est le cinquième lobe du cerveau en charge de l'intégration de nombreuses fonctions cognitives, sous-tendues par une organisation cytoarchitectonique etune connectivité aussi riche que complexe. Ce travail vise à évaluer la connectivité fonctionnelle insulaire du cerveau humain par le biais de stimulation électrique intra-cérébrale et de potentiels évoqués cortico-corticaux (PECC) réalisés chez des patients explorés en stéréoélectroencéphalographie (SEEG) pour une épilepsie partielle réfractaire. Nous avons développé un protocole automatisé permettant destimuler successivement l’ensemble des bipoles d’enregistrement intracérébraux (deux plots contigus d’une même électrode) disponibles chez les patients explorés en SEEG. Deux sériesde 20 stimulations monophasiques d’une durée unitaire de 1 ms et d’une intentisté de 1 mA, étaient délivrés à une fréquence de 0,2 Hz au niveau de chaque bipole (105 en moyenne,produisant un total d’environ 11.000 PECC par patient). Un premier travail a consisté dans lamise au point d’une méthode fiable d’analyse statistique objective des PECC significatifs, encomplement de l’analyse visuelle, sur un échantillon de 33017 enregistrements chez trois patients. L’analyse a porté sur les quatre fenêtres temporelles post-stimulation suivantes: 10-100 ms, 100-300 ms, 300-500 ms, 500-1000 ms. La seconde partie de notre thèse a appliquéces méthodes à l’étude des connections intra-insulaires sur un échantillon de10 patients présentant au moins deux éléctrodes intra-insulaires. La dernière partie de notre travail s’est intéressé aux efférences insulaires sur un échantillon de 11 patients. L’étude des PECC apporte des éléments de connectivité fonctionnelle derésolution spatiale et temporelle inégalée, complémentaires de ceux découlant des techniquesde neuroimagerie. La gestion complexe du volume de données à gérer pour chaque patientpeut être résolu par des procédures d’analyse statistiques automatisée de sensibilité etspécificité satisfaisante. Le pattern des connections intra- et extra-insulaires révélé par cetteapproche permet une meilleure compréhension de la physiologie de l’insula chez l’Homme etdes modalités de propagations des décharges épileptiques impliquant ce lobeThe insular cortex is the fifth lobe of the brain and is in charge of the integration of many cognitive functions, underpinned by a rich cytoarchitectonic organization and a complex connectivity. Our work aims to evaluate the insular functional connectivity of the human brain using intracerebral electrical stimulation and recording of cortico-cortical evoked potentials (CCEPs) in patients investigated with stereoelectroencephalography (SEEG) for refractory partial epilepsy. We first developed an automated protocol to stimulate successively all intracerebral recorded bipoles (two contiguous leads of the same electrode) available in patients undergoing SEEG. Two sets of 20 monophasic stimulation of 1 ms duration and 1mA intensity were delivered at a frequency of 0.2 Hz at each bipole (105 on average, producing a total of about 11,000 recordings per patient). We then develop a reliable and objective statistical method to detect significant CCEPs as a complement to visual analysis, and validate this approach on a sample of 33017 recordings in three patients. The analysis was performed over four distinct post-stimulus epochs: 10-100 ms, 100-300 ms, 300-500 ms, 500-1000 ms. In the second part of our thesis, we applied these methods to the study of intrainsular connections on a sample of 10 patients with at least two intra-insular electrodes. The last part of our work used the same approach to investigate insular efferents in a sample of 11 patients. The study of CCEPs provides novel and important findings regarding the human brain functional connectivity, with unmatched spatial and temporal resolutions as compared to neuroimaging techniques. The complex management of large volume of data in each patient can be solved by automated statistical analysis procedures with satisfactory sensitivity and specificity. The pattern of connections within and outside the insula revealed by this approach provides a better understanding of the physiology of the Human insula as well as of the propagation of epileptic discharges involving this lobe
35
Osher, David Eugene. "Function follows form : how connectivity patterns govern neural responses." Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/81731.
Full textAbstract:
Thesis (Ph. D. in Neuroscience)--Massachusetts Institute of Technology, Dept. of Brain and Cognitive Sciences, 2013.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references.
Connectivity restricts and defines the information that a network can process. It is the substance of information processing that underlies the patterns of functional activity in the brain. By combining diffusion-weighted imaging or DWI, with fMRI, we are able to non-invasively measure connectivity and neural responses in the same individuals and directly relate these two measures to one another. In Chapter 2, I first establish the proof-of-principle that anatomical connectivity alone can predict neural responses in cortex, specifically of face-selectivity in the fusiform gyrus. I then extend this novel approach to the rest of the brain and test whether connectivity can accurately predict neural responses to various visual categories in Chapter 3. Finally, in Chapter 4, I compare and contrast the resulting models, which are essentially networks of connectivity that are functionally-relevant to each visual category, and demonstrate the type of knowledge that can be uncovered by directly integrating structure and function.
by David Eugene Osher.
Ph.D.in Neuroscience
36
Brown, Christopher A. "THE DEFAULT MODE NETWORK AND EXECUTIVE FUNCTION: INFLUENCE OF AGE, WHITE MATTER CONNECTIVITY, AND ALZHEIMER’S PATHOLOGY." UKnowledge, 2017. http://uknowledge.uky.edu/neurobio_etds/18.
Full textAbstract:
The default mode network (DMN) consists of a set of interconnected brain regions supporting autobiographical memory, our concept of the self, and the internal monologue. These processes must be maintained at all times and consume the highest amount of the brain’s energy during its baseline state. However, when faced with an active, externally-directed cognitive task, the DMN shows a small, but significant, decrease in activity. The reduction in DMN activity during the performance of an active, externally-directed task compared to a baseline state is termed task-induced deactivation (TID), which is thought to ‘free-up’ resources required to respond to external demands. However, older adults show a reduced level of TID in the DMN. Recently, it has begun to be appreciated that this decrease in TID may be associated with poorer cognitive performance, especially during tasks placing high demands on executive function (EF). Diminished DMN TID has not only been associated with increasing age but also with multiple age-related neurobiological correlates such as accumulating Alzheimer’s disease (AD) pathology and reductions in white matter (WM) connectivity. However, these biological factors—age, WM connectivity reductions and increasing AD pathology—are themselves related. Based on the literature, we hypothesized that declining WM connectivity may represent a common pathway by which both age and AD pathology contribute to diminished DMN TID. Further, we hypothesized that declines in DMN function and WM connectivity would predict poorer in EF. Three experiments were carried out to test these hypotheses. Experiment 1 tested whether WM connectivity predicted the level of DMN TID during a task requiring a high level of EF. Results from 117 adults (ages 25-83) showed that WM connectivity declined with increasing age, and that this decline in WM connectivity was directly associated with reduced DMN TID during the task. Experiment 2 tested whether declines in WM connectivity explained both age-related and AD pathology-related declines in DMN TID. Results from 29 younger adults and 35 older adults showed that declining WM connectivity was associated with increasing age and AD pathology, and that this decline in WM connectivity was a common pathway for diminished DMN TID associated with either aging or AD pathology. Experiment 3 investigated whether measures of WM connectivity and DMN TID at baseline could predict EF measured using clinically-used tests. Results from 29 older adults from Experiment 2 showed that less DMN TID predicted poorer EF at baseline and diminished WM connectivity at baseline predicted a greater decline in EF after 3 years. Further, WM connectivity explained reductions in EF predicted by baseline AD pathology, as well as further reductions in EF not predicted by baseline AD pathology. Together the results of these studies suggest that WM connectivity is a key pathway for age-related and AD pathology-related patterns of diminished DMN TID associated with poorer EF. Further, WM connectivity may represent a potential therapeutic target for interventions attempting to prevent future declines in EF occurring in aging and AD.
37
Spencer, Matthew. "Evolving complex network models of functional connectivity dynamics." Thesis, University of Reading, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.590143.
Full textAbstract:
Functional connectivity networks describe how regions of the brain interact. The timing, location, and frequency of these interactions inform about memory, decision making, motor movement, affective states, and more. However, while these interactions are well described as networks, these networks, like many others throughout nature, are constantly changing. Complex network evolution poses a highly dimensional problem but also contains much information about the system in question. In this thesis, a recent class of evolving complex network models was explored and extended to capture the functional connectivity dynamics observed in neuronal networks. Functional connectivity was investigated through data- and model-driven techniques at the cellular level, with cultures of cortical neurones on multi-electrode arrays, and at the whole-brain level, with electroencephalography. At the neuronal level, complex spatial dependencies were identified in bursts of excitation and two novel network models, the Starburst model and the Excitation Flow model, are used to capture the resulting functional connectivity. At the whole-brain level, functional connectivity dynamics were used to perform single-trial classification of intentional motor movement. Again, spatiotemporal dependencies were identified and used to present three novel techniques for modelling the network dynamics. The first two techniques decomposed networks into network templates (one model-based and one spectral-based) and modelled the dynamics with hidden Markov models. The final technique was a generalised evolving version of the Starburst model. The hidden Markov model of spectrally decomposed networks was shown to classify motor intentions with an accuracy around 80%. Firstly, this thesis shows that time plays an important role in the production of the complex network topologies observed in functional connectivity, both at the cellular and whole-brain leve1. Further, it is shown that evolving complex network models are very useful tools for modelling these topologies and that the network dynamics can be used to uncover features that are crucial to identifying functional states.
38
Akram, Harith. "Application of MRI connectivity in stereotactic functional neurosurgery." Thesis, University College London (University of London), 2018. http://discovery.ucl.ac.uk/10052005/.
Full textAbstract:
This thesis examines potential applications of advanced MRI-connectivity studies in stereotactic functional neurosurgery. Several new analysis methodologies are employed to: (1) build predictive models of DBS surgery outcome; (2) refine the surgical target and (3) help build a better understanding of the pathogenesis of the treated conditions and the mechanism of action of DBS therapy. The experimental component is divided into three main parts focusing on the following pathologies: (1) Parkinson’s disease (PD), (2) tremor and (3) trigeminal autonomic cephalalgias (TAC). Section I: In the first experiment (chapter 3), resting state fMRI was used to find radiological biomarkers predictive of response to L-DOPA in 19 patients undergoing subthalamic nucleus (STN) DBS for PD. A greater improvement in UPDRS-III scores following L-DOPA administration was characterized by higher resting state functional connectivity (fcMRI) between the prefrontal cortex and the striatum (p=0.001) and lower fcMRI between the pallidum (p=0.001), subthalamic nucleus (p=0.003) and the paracentral lobule. In the second experiment (chapter 4), structural (diffusion) connectivity was used to map out the influence of the hyperdirect pathways on outcome and identify the therapeutic ‘sweet spots’ in twenty PD patients undergoing STN-DBS. Clusters corresponding to maximum improvement in symptoms were in the posterior, superior and lateral portion of the STN. Greater connectivity to the primary motor area, supplementary motor area and prefrontal cortex was predictive of higher improvement in tremor, bradykinesia and rigidity, and rigidity respectively. The third experiment (chapter 5) examined pyramidal tract (PT) activation in 20 PD patients with STN-DBS. Volume of tissue activation (VTA) around DBS contacts were modelled in relation to the PT. VTA/ PT overlap predicted EMG activation thresholds. Sections II: Pilot data suggest that probabilistic tractography techniques can be used to segment the ventrolateral (VL) and ventroposterior (VP) thalamus based on cortical and cerebellar connectivity in nine patients who underwent thalamic DBS for tremor (chapter 6). The thalamic area, best representing the ventrointermedialis nucleus (VIM), was connected to the contralateral dentate cerebellar nucleus. Streamlines corresponding to the dentato-rubro-thalamic tract (DRT) connected M1 to the contralateral dentate nucleus via the dentato-thalamic area. Good response was seen when the active contact’s VTA was in the thalamic area with the highest connectivity to the contralateral dentate nucleus. Section III: The efficacy and safety of DBS in the ventral tegmental area (VTa) in the treatment of chronic cluster headache (CH) and short lasting unilateral neuralgiform headache attacks (SUNA) were examined (chapters 7 and 8). The optimum stimulation site within the VTa that best controls symptoms was explored (chapter 9). The average responders’ deep brain stimulation activation volume lay on the trigemino-hypothalamic tract, connecting the trigeminal system and other nociceptive brainstem nuclei, with the hypothalamus, and the prefrontal and mesial temporal areas.
39
Orban, Csaba. "Amygdala resting state functional connectivity in alcohol dependence." Thesis, Imperial College London, 2016. http://hdl.handle.net/10044/1/59191.
Full textAbstract:
Alcohol dependence is a global societal problem, yet current avenues for its treatment are largely ineffective in slowing its chronic-relapsing trajectory. Animal studies of alcohol dependence have described neuroadaptations in the amygdala that may play a central role in mechanisms of relapse. In this thesis, spontaneous amygdala network function was examined in abstinent alcohol dependent patients (ADP) using functional magnetic resonance imaging within the framework of a multi-site neuroimaging platform: ICCAM. Participants underwent five scans that included baseline, as well as scans under placebo, acute antagonism of μ-opioid, Dopamine D3 (DRD3) and Neurokinin-1 (NK1) receptor systems previously implicated in mechanisms of addiction. At baseline, amygdala – substantia nigra/ventral tegmental area (SN/VTA) resting state functional connectivity (RSFC) was elevated in abstinent ADP, despite widespread grey-matter (GM) volumetric atrophy, in both amygdala and SN/VTA, compared with age-matched healthy controls (HC). The strength of amygdala – SN/VTA RSFC in ADP was primarily associated with years of cumulative alcohol exposure, but not with amygdala or SN/VTA GM volume, length of abstinence, smoking status, or head motion. Amygdala RSFC with other regions showed sensitivity to core clinical features of ADP at baseline. Amygdala – frontoparietal (FPN) RSFC was inversely associated with abstinence length, with ADP in the first two months of abstinence showing significantly reduced amygdala – FPN RSFC compared with HC. Voxelwise comparison of amygdala RSFC between each drug session and placebo, did not reveal differential effects of receptor blockade on ADP and HC. Across both groups, however, the three drugs exhibited both overlapping and differential effects on distinct brain networks. Notably, amygdala RSFC in the superior temporal gyrus showed increases under NK1-antagonism, and decreases under naltrexone compared with placebo. Finally, amygdala – SN/VTA was significantly elevated in ADP relative to HC across all four sessions, suggesting that it may represent a stable neurophysiological feature of alcohol dependence.
40
Savva, Androula. "Assessment of Functional Connectivity Impairment in Rat Brains." Thesis, KTH, Skolan för kemi, bioteknologi och hälsa (CBH), 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-247593.
Full textAbstract:
While the rodent model has long been used in brain research, there exists no standardisedprocessing routine that can be employed for analysis and investigation of disease models. Thepresent thesis attempts to investigate a diseased brain model by implementing a collection ofscripts, combined with algorithms from existing neuroimaging software, and adapting themto the rodent brain, in an attempt to examine when and how monaural canal atresia affectsthe functional connectivity of the brain. We show that it is possible to use software tailoredto the human brain to pre-process the rodent model. Following conventional pipelines andresting state functional MRI (rs-fMRI)-specific strategies, the developed processing routineimplements the most basic steps suggested in literature. On the single-subject level, skullstripping was done using Mialite software, motion correction and distortion correction werebased on FMRIB software library (FSL) algorithms and motion artefacts were removed usingICA-based Automatic Removal Of Motion Artifacts (ICA-AROMA). Following denoising,normalisation to standard space, smoothing and temporal filtering, group level analysis wasperformed. A univariate, hypothesis-driven method and a multivariate, data-driven methodwere used for group comparison and statistical inference. While seed-based correlationanalysis (SCA) did not return any significant results, independent component analysis (ICA) identified two components that show activation in areas of interest.Djurmodeller med gnagare (råtta och mus) har länge använts i hjärnforskning. Men ännu finns det ingen standardiserad rutin för analys och utvärdering av bilddata från sådana sjukdomsmodeller. Detta arbete använder en råttmodell av sjukdomen ensidig hörselgångsatresi, som innebär att yttre hörselgången är igensatt på ena sidan. Detta görs genom att mjukvaruverktyg som utvecklats för att analysera bilddata från magnetkameraundersökning av den mänskliga hjärnan anpassas för att användas på motsvarande bilddata från råtta för att studera hur ensidig hörselgångsatresi påverkar hjärnans funktionella konnektivitet, dvs hur mönstren i hjärnaktivering samvarierar mellan olika delar av hjärnan (rs-fMRI). Vi visar att det är möjligt att använda mjukvara avsedd för människans hjärna för att förbehandla bilder av råtthjärna. Med hjälp av etablerade arbetsflöden och särskilda procedurer för rs-fMRI kunde den utvecklade proceduren implementera de viktigaste stegen i analysen. För varje individ avgränsades hjärnan med programmet Mialite, rörelsekorrigering och korrigering av rumsdistorsion gjordes med FSL, och rörelseartefakter avlägsnades med ICA-AROMA. Sedan brus tagits bort, och bilddata standardiserats till en standardanatomi och genomgått filtrering i rum och tid, gjordes analys på två grupper, med och utan artificiell hörselgångsatresi. En univariat, hypotesdriven metod och en multivariat, data-driven metod användes för gruppjämförelse och statistisk analys. Frö-baserad korrelationsanalys (SCA) gav inga signifikanta resultat, men oberoende-komponent-analys (ICA) påvisade två anatomiska områden med aktivering relaterad till skillnader mellan grupperna.
41
McRae, Kateri Lynne. "Functional and Effective Connectivity of Effortful Emotion Regulation." Diss., The University of Arizona, 2007. http://hdl.handle.net/10150/194032.
Full textAbstract:
Emotion regulation plays an important role in emotional well-being, as well as in the protection against and recovery from mood and anxiety disorders. Previous studies of the functional neuroanatomy of emotion regulation have reported greater activity in prefrontal control-related regions during active regulation. These activations are accompanied by decreases in activity in emotion-responsive regions such as the amygdala and insula. These findings are widely interpreted as consistent with models of cognitive control that implicate top-down, negative influences from prefrontal cortex upon emotion-related processing in other regions. However, no studies to date have used measures of effective connectivity to investigate the likely influence of prefrontal control regions upon emotion-responsive regions in the context of effortful emotion regulation. In the present study, participants alternated between responding naturally to negative emotional stimuli and reinterpreting the negative stimuli with the goal of reducing their experienced negative affect. Functional magnetic resonance imaging (fMRI) was used to measure whole-brain blood-oxygen level dependent signal throughout the task. fMRI data were analyzed using partial least squares (PLS) and structural equations modeling (SEM) to test for differences in effective connectivity between natural and regulated emotional responding. Results indicate that three paths significantly distinguish between regulation and non-regulation negative conditions. The path from inferior frontal gyrus (IFG) to anterior cingulate cortex (ACC) was significantly less positive during regulation than natural responding. In addition, the reciprocal paths between ACC and insula were more negative during regulation than natural responding. Taken as a whole, these changes in effective connectivity are consistent with assumptions of top-down modulation during effortful emotion regulation. In addition, these changes suggest a pivotal role for the influence of IFG upon ACC and the ACC-insula loop in emotion regulation. The processes represented by these changes and implications for future research are discussed.
42
Goparaju, Balaji. "High level motion: neural correlates and functional connectivity." Thesis, Boston University, 2012. https://hdl.handle.net/2144/21157.
Full textAbstract:
Thesis (M.Sc.Eng.) PLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you.This thesis uses functional magnetic resonance imaging (fMRI) data to investigate: 1. The neural substrate of high level visual motion 2. The functional connectivity between a behavioral task and resting state. In chapter 1, we find the neural substrate of a set of psychophysical high level motion tasks. Specifically, we used tasks of visually guided navigation, such as heading from optic flow, landmarks, motion parallax, and collision detection. We also used tasks underlying the ability to perform object recognition from motion cues alone such as 3D Structure From Motion (SFM) and Biological Motion (BM). fMRI data was analyzed with Brain Voyager and activated anatomical areas were delineated using Matlab scripts developed in the laboratory. Several regions within the dorsal visual system elicited significant BOLD activity: the dorsal-occipital (BA19) and parietal lobes (BA 37, 40, 7). The ventral areas (BA 20, 21, 22, 38) showed significant BOLD activity only in BM and SFM and in heading tests using landmarks or motion parallax. We generated a schematic map with the overlapping areas among high level motion tasks, which can aid in diagnosis and rehabilitation of motion deficits in neurological patients. In chapter 2, we computed the functional brain connectivity between the brain areas in a resting state (subject performs no task), and during task (subject performs a visual motion task). In the resting state, we found connectivity using correlations between the posterior cingulate cortex (PCC), precuneus, medial prefrontal cortex (MPFC), lateral parietal cortex, and the hippocampal formation, which have been reported as the default mode network (DMN) since it represents correlated neural activity during a state of rest. We used bivariate correlations to compute functional connectivity using the CONN fMRI toolbox and in-house Matlab scripts. We computed a whole-brain analysis and compared network statistics in both, resting state and during task to investigate measures of integration such as path length and global efficiency, regional measures such as degree (number of connections) and betweenness centrality (number of shortest paths), and global measures such as small-worldness. The DMN and graph theoretical measures connectivity during task was stronger as compared with the resting state. We also computed these measures in task using a similar frequency spectrum as rest (0.009 Hz < f < 0.08 Hz), and in the full frequency spectrum. We find that on the whole, the connectivity measures in the DMN and the graph theoretical measure are stronger in the fullband signal processing analysis as compared to the bandpass version of the analysis.
2031-01-01
43
Lee, Pamela Wen-Hsin. "Mutual information derived functional connectivity of the electroencephalogram (EEG)." Thesis, University of British Columbia, 2007. http://hdl.handle.net/2429/219.
Full textAbstract:
Monitoring the functional connectivity between brain networks is becoming increasingly important in elucidating brain functionality in normal and disease states. Current methods of detecting networks in the recorded EEG such as correlation and coherence are limited by the fact that they assume stationarity of the relationship between channels, and rely on linear dependencies. Here we utilize mutual information (MI) as the metric for determining nonlinear statistical dependencies between electroencephalographic (EEG) channels. Previous work investigating MI between EEG channels in subjects with widespread diseases of the cerebral cortex had subjects simply rest quietly with their eyes closed. In motor disorders such as Parkinson’s disease (PD), abnormalities are only expected during performance of motor tasks, but this makes the assumption of stationarity of relationships between EEG channels untenable. We therefore propose a novel EEG segmentation method based on the temporal dynamics of the cross-spectrogram of the computed Independent Components (ICs). After suitable thresholding of the MI values between channels in the temporally segmented EEG, graphical theoretical analysis approaches are applied to the derived networks. The method was applied to EEG data recorded from six normal subjects and seven PD subjects on and off medication performing a motor task involving either their right hand only or both hands simultaneously. One-way analysis of variance (ANOVA) tests demonstrated statistically significant difference between subject groups. This proposed segmentation/MI network method appears to be a promising approach for EEG analysis.
44
Goldhacker, Markus [Verfasser], and Elmar [Akademischer Betreuer] Lang. "Frequency-resolved dynamic functional connectivity and scale stability of connectivity-states / Markus Goldhacker ; Betreuer: Elmar Lang." Regensburg : Universitätsbibliothek Regensburg, 2017. http://d-nb.info/1124679944/34.
Full text
45
Berkström, Charlotte. "Ecological connectivity in East African seascapes." Doctoral thesis, Stockholms universitet, Systemekologiska institutionen, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-75194.
Full textAbstract:
Coral reefs, seagrass beds and mangroves constitute a complex mosaic of habitats referred to as the tropical seascape. Great gaps exist in the knowledge of how these systems are interconnected. This thesis sets out to examine ecological connectivity, i.e. the connectedness of ecological processes across multiple scales, in Zanzibar and Mafia Island, Tanzania. Paper I examined the current knowledge of interlinkages and their effect on seascape functioning, revealing that there are surprisingly few studies on the influences of cross-habitat interactions and food-web ecology. Furthermore, 50% of all fish species use more than one habitat and 18% of all coral reef fish species use mangrove or seagrass beds as juvenile habitat in Zanzibar. Paper II examined the seascape of Menai Bay, Zanzibar using a landscape ecology approach and studied the relationship between fish and landscape variables. The amount of seagrass within 750m of a coral reef site was correlated with increased invertebrate feeder/piscivore fish abundance, especially Lethrinidae and Lutjanidae, which are known to perform ontogenetic and feeding migrations. Within patch seagrass cover was correlated with nursery species abundance. Paper III focused on a seagrass-dominated seascape in Chwaka Bay, Zanzibar and showed that small-scale habitat complexity (shoot height and density) as well as large-scale variables such as distance to coral reefs affected abundance and distribution of a common seagrass parrotfish Leptoscarus vaigiensis. Paper IV studied the connectivity and functional role of two snappers (Lutjanus fulviflamma and L. ehrenbergii) using stable isotopes (δ15N and δ13C) and found that connectivity between habitats was maintained by ontogenetic and foraging migrations by these species. The thesis concludes that ecological connectivity and multi-habitat usage by fish is a general and important characteristic in the Western Indian Ocean and should be considered in management planning.At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Submitted. Paper 4: Submitted.
46
Twomey, T. "Ventral occipito-temporal cortex function and anatomical connectivity in reading." Thesis, University College London (University of London), 2013. http://discovery.ucl.ac.uk/1417085/.
Full textAbstract:
Previous functional neuroimaging studies of reading in skilled readers, acquired dyslexia and developmental dyslexia have all shown that the left ventral occipito-temporal cortex (vOT) is involved in visual word recognition. Specifically, a region in the left posterior occipito-temporal sulcus lateral to fusiform gyrus and medial to inferior temporal gyrus has been reported to play an important role. However, the precise functional contribution of this area in reading is yet to be fully explored. In this thesis, I empirically evaluated a claim that vOT responds not only to bottom-up processing demands of the visual stimuli but is also influenced by automatic, top-down non-visual processing demands, as proposed by the Interactive Account of vOT functioning. The first part of this thesis investigated the functional properties of vOT during reading, using functional magnetic resonance imaging. In the first project, the top-down influences on vOT were investigated, teasing apart visual and non-visual properties of written stimuli. In the second project, using the Japanese orthography I disentangled a word’s lexical frequency from the frequency of its visual form – an important distinction for understanding the neural information processing in regions engaged by reading and further explored the interactive nature of the vOT responses. The second part then investigated the anatomical basis of these functional interactions between vOT and other cortical regions. I used diffusion-weighted magnetic resonance imaging and tractography, the only method currently available to identify and measure white matter fibre pathways non-invasively and in vivo. My research has demonstrated that vOT integrates bottom-up visual information and top-down predictions from regions encoding non-visual attributes of the stimulus in an interactive fashion. It also illustrated the putative anatomical basis for functional connectivity during reading, which is consistent with the parallel cortical visual pathways seen in other primates. Altogether, the results provide strong support for the Interactive Account.
47
Makewita, Sumedha M. "Investigating the generic information seeking function of organisational decision makers : perspectives on improving organisational information systems." Thesis, University of Southampton, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.246832.
Full text
48
Rieubland, S. C. S. "Functional and anatomical connectivity patterns in the cerebellar cortex." Thesis, University College London (University of London), 2013. http://discovery.ucl.ac.uk/1400297/.
Full textAbstract:
The rules governing synaptic connectivity in neural circuits are still poorly understood. In the cerebellar cortex, the general wiring patterns between different cell types are known, but the precise circuit at the level of individual cells is still unclear. In the molecular layer, thought to be the principal site of cerebellar learning, I investigated three fundamental microcircuits and their connectivity: the network of chemically and electrically coupled inhibitory interneurons, their inhibitory connection to Purkinje cells, and their shared parallel fibre input, which together form a feed-forward inhibitory circuit. I used both electrophysiological and anatomical techniques to probe functional and structural connectivity patterns in these circuits. Optimisation was performed to combine electrophysiological recordings and imaging with a focused ion beam scanning electron microscope. The resulting high-resolution three-dimensional imaging reveals the precise connectivity of hundreds of individual parallel fibres. I found that their connectivity is constrained by volume exclusion rules between presynaptic boutons. These spatial constraints are overcome between directly adjacent interneurons and Purkinje cells, receiving input from a common parallel fibre bouton. Using multiple patch-clamp recordings, I found evidence for specific, non-random connectivity amongst molecular layer interneurons. The electrical and chemical networks are both highly clustered and their overlap is non-random. Inhibitory connections between interneurons are preferentially organized in a feed-forward (or transitive) fashion. I show that individual interneurons can both decrease and increase the inhibition received by Purkinje cells, via an indirect connection through electrically coupled interneurons. A highly specific connectivity pattern supports this control of inhibition of Purkinje cells by the coupled network. To summarize, I investigated the rules governing neural connectivity in the molecular layer: from spatial constraints, via formation of specific connectivity motifs, to the implementation of functional roles. This new information will help shape our understanding of the interactions and computations performed in the cerebellar cortex.
49
Habberfield, Michael William. "Functional connectivity for wildlife populations across spatially complex landscapes." Thesis, State University of New York at Buffalo, 2016. http://pqdtopen.proquest.com/#viewpdf?dispub=10163822.
Full textAbstract:
Integrating animal movement information with the spatial analysis of landscape structure is critical for restoring biological communities in spatially-structured landscapes. This integration can be accomplished by focusing on functional connectivity—a landscape’s potential for the movement of organisms among resource patches—in relation to the spatial and structural connectivity of landscape elements. I carried out three investigations in order to examine how landscape structure interacts with the ecological factors associated with animal movement processes, and thereby produce actionable outcomes for the restoration of wildlife populations. This work combined population- and individual-level data of dispersing wildlife to better resolve the influence of spatial structure on functional connectivity. First, I used a meta-analysis to quantify the relationship between structural and functional connectivity for a broad scope of animal species. Second, I assessed the influence of landscape position and habitat density on colonization, movement, and population dynamics of wood frogs (Lithobates sylvatica) within a network of restored vernal pools. Third, I experimentally evaluated dispersal and habitat selection of green frogs (Lithobates clamitans) within this vernal pool system.
The meta-analysis demonstrated that universal scaling relationships of species and the landscapes they are moving through interact as key drivers mediating the level of functional connectivity afforded to wildlife by structural connectivity. Mark-recapture data revealed rapid colonization of the restored vernal pool network by wood frogs, with subsequently moderate levels of frog movement among neighboring pools. Local pool density interacted with the colonization process and terrestrial habitat availability to limit wood frog productivity within a pool cluster. Experimental dispersal data for green frogs artificially translocated within the pool network showed key differences between movement in familiar and novel environments. Differing movement behaviors and habitat selection patterns indicated that a habitat patch for this species is on the scale of a pool cluster rather than an individual pool. Together, the observed spatial dynamics of these vernal pool amphibians contribute a framework for improving amphibian dispersal modeling, potential responses to rapid environmental changes, and predicting colonization and subsequent population dynamics in restored systems. The results of this dissertation improve our understanding of how spatial structure interacts with organism-specific factors to produce observed patterns of functional connectivity.
50
Joules, Richard Bryan. "Functional connectivity and machine learning for psychiatric drug development." Thesis, King's College London (University of London), 2015. http://kclpure.kcl.ac.uk/portal/en/theses/functional-connectivity-and-machine-learning-for-psychiatric-drug-development(23f2637e-2604-4b82-82e2-619e084cd6d3).html.
Full textAbstract:
The human brain is a complex biological network consisting of spatially separated but functionally integrated regions. Study of functional connectivity gained immense popularity in recent years providing new insight into the mechanisms underlying complex functions and the fundamental organisation of the brain. This has led to the emergence of new techniques for investigating connectivity, such as the application of pattern recognition techniques and the investigation of network dynamics. While highly promising, the application of these new techniques to pharmacological imaging data has not yet been fully explored. In this thesis we apply pattern recognition techniques to functional connectivity measures obtained for pharmacological imaging data to discriminate patterns of whole brain connectivity. Furthermore, we demonstrate that consideration of functional connectivity dynamics provides additional insight into the effect of pharmacological interventions. Specifically, we explore the effects of the N-methyl-D-aspartate receptor antagonist, ketamine, on the connectivity within the human brain. We argue that the investigation of connectivity is a more appropriate tool for the investigation of this compound due to the highly distributed pattern of effects, as compared to traditional approaches investigating amplitude effects. We demonstrate the applicability of pattern recognition techniques for the discrimination pharmacological states using measures of regional connectivity over the whole brain, using network interactions and through the inspection of network dynamics. We expand upon traditional approaches in our investigation, introducing a new approach to investigate network effects and temporal dynamics of connectivity organisation.