Drosophila melanogaster encounter periods of increased temperature or decreased oxygen in its native environment. One consequence of these environmental stresses is increased production of reactive oxygen species that damage major molecules within cells. Another consequence is that flies fall into a protective coma where biological functions are minimized to conserve energy expenditures. This biological phenomenon is called spreading depression. The overarching aim of this project is to determine if methionine sulfoxide reductases affect entrance or exit from the protective coma induced by acute thermal stress. The data revealed that complete deficiency of Msr in young flies causes a faster induction of the coma. In both young and old flies, Msr does not affect average recovery time but does affect the pattern of recovery from coma. Entrance into the coma is age dependent with young flies maintaining activity longer than before entering into the coma as compared to old flies. / by Karin Schey. / Thesis (M.S.)--Florida Atlantic University, 2012. / Includes bibliography. / Mode of access: World Wide Web. / System requirements: Adobe Reader.

A teoria de redes complexas se consolidou nos últimos anos, graças ao seu potencial como ferramenta versátil no estudo de diversos sistemas discretos. É possível enumerar aplicações em áreas tão distintas como engenharia, sociologia, computação, linguística e biologia. Tem merecido atenção, por exemplo, o estudo da organização estrutural do cérebro, tanto em nível microscópico (em nível de neurônios) como regional (regiões corticais). Acredita-se que tal organização visa otimizar a dinâmica, favorecendo processos como sincronização e processamento paralelo. Estrutura e funcionamento, portanto, estão relacionados. Tal relação é abordada pela teoria de redes complexas nos mais diversos sistemas, sendo possivelmente seu principal objeto de estudo. Neste trabalho exploramos as relações entre aspectos estruturais de redes neuronais e corticais e a atividade nas mesmas. Especificamente, estudamos como a interconectividade entre o córtex e o tálamo pode interferir em estados de ativação do último, considerando-se o sistema tálamo-cortical do gato bem como alguns modelos para geração de rede encontrados na literatura. Também abordamos a relação entre a morfologia individual de neurônios e a conectividade em redes neuronais, e consequentemente o impacto da forma neuronal em dinâmicas atuando sobre tais redes e a eficiência das mesmas no transporte de informação. Como tal eficiência pode ter como consequência a facilitação de processos maléficos às redes, como por exemplo, ataques causados por vírus neurotrópicos, também exploramos possíveis correlações entre características individuais dos elementos que formam as redes complexas e danos causados por processos infecciosos iniciados nos mesmos. / Complex network theory has been consolidated along the last years, owing to its potential as a versatile framework for the study of diverse discrete systems. It is possible to enumerate applications in fields as distinct as Engineering, Sociology, Computing, Linguistics and Biology, to name a few. For instance, the study of the structural organization of the brain at the microscopic level (neurons), as well as at regional level (cortical areas), has deserved attention. It is believed that such organization aims at optimizing the dynamics, supporting processes like synchronization and parallel processing. Structure and functioning are thus interrelated. Such relation has been addressed by complex network theory in diverse systems, possibly being its main subject. In this thesis we explore the relations between structural aspects and the activity in cortical and neuronal networks. Specifically, we study how the interconnectivity between the cortex and thalamus can interfere in activation states of the latter, taking into consideration the thalamocortical system of the cat, along with networks generated through models found in literature. We also address the relation between the individual morphology of the neurons and the connectivity in neuronal networks, and consequently the effect of the neuronal shape on dynamic processes actuating over such networks and on their efficiency on information transport. As such efficiency can consequently facilitate prejudicial processes on the networks, e.g. attacks promoted by neurotropic viruses, we also explore possible correlations between individual characteristics of the elements forming such systems and the damage caused by infectious processes started at these elements.

Le lobe temporal est classiquement divisé en deux systèmes fonctionnels: la voie visuelle ventrale et le système mnésique temporal médial. Cependant, cette séparation fonctionnelle a été remise en question par plusieurs études suggérant que le lobe temporal médial serait mieux compris comme une extension de la voie visuelle ventrale hiérarchiquement organisée. Le but de cette thèse était d’étudier le rôle perceptivo-mnésique du lobe temporal médial. Nous avons ainsi voulu tester à l’aide d’enregistrement électro-encéphalographiques intracérébraux (SEEG) si : (i) les régions médiale, ventrale et latérale du lobe temporal pouvaient être regroupées dans des ensembles fonctionnellement distincts et, (ii) quelles régions étaient à l’interface de ces ensembles fonctionnels. Pour répondre à ces questions, nous avons étudié la connectivité effective dérivée de potentiels évoqués cortico-corticaux issus de stimulations électriques de faible intensité et de basse fréquence (0.5mA, 1Hz, 4ms) réalisées chez 16 patients atteints d’épilepsies pharmaco-résistantes temporale ou temporo-occipitale, lors de leur évaluation pré-chirurgicale par la surveillance à long terme des activités intracérebrales électro-encéphalographiques. Onze régions d'intérêt ont été délimitées au sein du lobe temporal en fonction de repères anatomiques tels que les gyri et sulci. Un modèle de connectivité effective au sein du lobe temporal a été extrait, basé sur les caractéristiques électrophysiologiques des potentiels évoqués cortico-corticaux, telles que les occurrences, amplitudes et latences des pics de la première composante du potentiel évoqué. Le modèle a été discuté du point de vue d’une organisation fonctionnelle globale du fait de la non-indépendance de ses caractéristiques électrophysiologiques. L’amplitude et la latence des potentiels évoqués ont montré des distributions de probabilité cohérente avec les observations de transfert d'informations cognitive. La théorie des graphes nous a fourni des algorithmes pouvant extraire les caractéristiques pertinentes du réseau, telles que la centralité des régions, leur ségrégation fonctionnelle ou les voies d’interaction entre les sous-ensembles fonctionnels des régions du lobe temporal. En particulier, le cortex rhinal est apparu comme la structure la plus centrale du lobe temporal alors que le gyrus temporal supérieur était la moins centrale. Le lobe temporal médial a pu être ségrégué en un ensemble fonctionnel à part entière. Le pôle temporal est apparu comme une zone de convergence et de transfert de l’information provenant des structures du lobe temporal latéral vers les structures médiales. Le gyrus fusiforme antérieur a montré des caractéristiques d’interface duale de convergence d’afférences néocorticales et de rétrocontrôle issu des structures médiales. Par ailleurs, l'hippocampe a montré un rôle d’amplificateur du signal des afférences néocorticales passant par l’amygdale et le cortex rhinal, pour être redistribuée vers les structures limbiques. L’hippocampe postérieur se comportait comme une voie de sortie des structures médiales modulant le gyrus parahippocampique postérieur de manière quasi-unidirectionnelle. Notre étude fournit un modèle régional ou macroscopique du transfert de l’information électro-physiologique au sein du lobe temporal humain. Nos résultats ont été discutés à la lumière des modèles cognitifs actuels de ‘complétion de l’information’ et du ‘binding temporel’ / The temporal lobe is conventionally divided into two functional systems: the ventral visual pathway and the medial temporal mnemonic system. However, this functional separation has been questioned by several studies suggesting that the medial temporal lobe would be better understood as an extension of the ventral visual pathway hierarchically organized. The aim of this thesis was to study the perceptive-mnestic role of the medial temporal lobe. We have tested using intracerebral EEG recordings (SEEG) if (i) the medial, lateral and ventral regions of the temporal lobe could be grouped into functionally distinct modules and, (ii) which areas were at the interface of these functional modules. To answer these questions, we studied the effective connectivity derived from cortico-cortical evoked potentials elicited by electrical stimulations from low intensity, low frequency (0.5mA, 1Hz, 4ms) conducted in 16 patients with drug-resistant temporal or temporo-occipital epilepsies at their pre-surgical long-term monitoring of intracerebral electroencephalographic activity. Eleven regions of interest were defined within the temporal lobe based on anatomical landmarks such as gyri and sulci. We built an effective connectivity model within the temporal lobe, based on the electrophysiological characteristics of cortico-cortical evoked potentials, such as the occurences, latencies and amplitudes of the peaks of the first component of the evoked potential. The model was discussed from the perspective of a global functional organization due to the non-independence of its electrophysiological characteristics. The amplitude and latency of the evoked potentials showed consistent probability distributions with the information transfer in cognitive observations. Graph theory has provided algorithms that can extract the relevant characteristics of the network, such as the centrality of the regions, their functional segregations or the ways of interaction between functional subsets of the regions within the temporal lobe. In particular, the rhinal cortex appeared as the most central structure of the temporal lobe whereas the superior temporal gyrus appeared as the less central. The medial temporal lobe could be segregated as a functional module by itself. The temporal pole appeared as a convergence area of the information transfer from the lateral temporal lobe structures to the medial structures. Anterior fusiform gyrus acted as a dual interface of convergence of neocortical afferences and feedback from medial structures. Furthermore, the hippocampus behaved as an amplifier of neocortical afferent signal passing through the amygdala and the rhinal cortex, and redistributed this amplification to the limbic structures. The posterior hippocampus acted as a way out of the medial structures modulating the posterior parahippocampal gyrus in a almost unidirectional manner. Our study provides a regional or macroscopic model of the transfer of electro-physiological information within the human temporal lobe. Our results were discussed in line with current cognitive models of 'pattern completion' and 'temporal binding'

L'objectif de ce travail est de modéliser la formation, la maintenance et la réorganisation des cartes corticales somesthésiques en utilisant la théorie des champs neuronaux dynamiques. Un champ de neurones dynamique est une équation intégro-différentiel qui peut être utilisée pour décrire l'activité d'une surface corticale. Un tel champ a été utilisé pour modéliser une partie des aires 3b de la région du cortex somatosensoriel primaire et un modèle de peau a été conçu afin de fournir les entrées au modèle cortical. D'un point de vue computationel, ce modèle s'inscrit dans une démarche de calculs distribués, numériques et adaptatifs. Ce modèle s'avère en particulier capable d'expliquer la formation initiale des cartes mais aussi de rendre compte de leurs réorganisations en présence de lésions corticales ou de privation sensorielle, l'équilibre entre excitation et inhibition jouant un rôle crucial. De plus, le modèle est en adéquation avec les données neurophysiologiques de la région 3b et se trouve être capable de rendre compte de nombreux résultats expérimentaux. Enfin, il semble que l'attention joue un rôle clé dans l'organisation des champs récepteurs du cortex somato-sensoriel. Nous proposons donc, au travers de ce travail, une définition de l'attention somato-sensorielle ainsi qu'une explication de son influence sur l'organisation des cartes au travers d'un certain nombre de résultats expérimentaux. En modifiant les gains des connexions latérales, il est possible de contrôler la forme de la solution du champ, conduisant à des modifications importantes de l'étendue des champs récepteurs. Cela conduit au final au développement de zones finement cartographiées conduisant à de meilleures performances haptiques / The aim of the present work is the modeling of the formation, maintenance and reorganization of somatosensory cortical maps using the theory of dynamic neural fields. A dynamic neural field is a partial integro-differential equation that is used to model the cortical activity of a part of the cortex. Such a neural field is used in this work in order to model a part of the area 3b of the primary somatosensory cortex. In addition a skin model is used in order to provide input to the cortical model. From a computational point of view the model is able to perform distributed, numerical and adaptive computations. The model is able to explain the formation of topographic maps and their reorganization in the presence of a cortical lesion or a sensory deprivation, where balance between excitation and inhibition plays a crucial role. In addition, the model is consistent with neurophysiological data of area 3b. Finally, it has been shown that attention plays a key role in the organization of receptive fields of neurons of the somatosensory cortex. Therefore, in this work has been proposed a definition of somatosensory attention and a potential explanation of its influence on somatotopic organization through a number of experimental results. By changing the gains of lateral connections, it is possible to control the shape of the solution of the neural field. This leads to significant alterations of receptive fields sizes, resulting to a better performance during the execution of demanding haptic tasks

Le terme de neurodéveloppement dans son acception la plus large renvoie à l'ensemble des processus permettant le développement du système nerveux depuis les étapes les plus précoces de sa formation in utero jusqu'aux étapes plus tardives de maturation à l'adolescence aboutissant au système nerveux adulte. Les travaux de ces quarante dernières années ont conduit à proposer un modèle neurodéveloppemental des troubles psychiatriques, notamment schizophréniques, sur la base d'arguments génétiques, épidémiologiques et d'imagerie. Ce modèle propose que l'apparition de la maladie soit liée à une/des anomalie(s) dans les processus de formation (neurodéveloppement précoce) et de maturation (neurodéveloppement tardif) du système nerveux, sous l'effet combiné de facteurs génétiques et environnementaux. Dans ce contexte, ce travail de thèse vise à préciser les effets des anomalies neurodéveloppementales sur les troubles psychiatriques, notamment schizophréniques à travers l'étude de différents marqueurs. La première étude a pour objectif d'étudier les corrélations entre deux marqueurs du développement cérébral précoce : un marqueur clinique (les signes neurologiques mineurs) et un marqueur en imagerie (la sulcation du cortex cérébral) dans une population de sujets atteints de schizophrénie. Une corrélation entre ces deux marqueurs est mise en évidence : l'index de sulcation est d'autant plus faible que les sujets présentent des signes neurologiques mineurs significatifs. Notre conclusion est que l'étude combinée de différents marqueurs peut permettre d'isoler des sous-groupes de patients ayant eu des atteintes neurodéveloppementales précoces plus marquées. La deuxième étude a pour objectif de caractériser l'effet de différents marqueurs d'anomalies neurodéveloppementales précoces sur le fonctionnement cognitif de sujets atteints de schizophrénie. L'effet sur le contrôle exécutif (mesuré par la tâche du Trail Making Test) de marqueurs cliniques (signes neurologiques mineurs, latéralisation manuelle) et en imagerie (sulcation du cortex cingulaire antérieur et élargissement des ventricules ventraux) est mesuré en recherchant les effets principaux et les interactions entre chaque marqueur. Nous trouvons des interactions entre différents marqueurs, avec principalement un effet de sommation non-linéaire. Notre interprétation est que les différents marqueurs reflètent des atteintes distinctes, bien que toutes précoces, du développement cérébral avec un effet final commun sur les fonctions exécutives. La troisième étude a pour objectif de préciser la spécificité de la sulcation comme marqueur d'anomalies neurodéveloppementales précoces à travers son étude dans une population de sujets adultes présentant un trouble du spectre autistique (TSA), pathologie débutant dès la petite enfance, en lien évident avec des atteintes neurodéveloppementales précoces. Des anomalies de sulcation du cortex cingulaire antérieur, similaires à celles observées chez les patients atteints de troubles schizophréniques, sont détectées chez les patients présentant un TSA. Ces résultats sont en faveur d'anomalies neurodéveloppementales précoces partagées entre différentes pathologies psychiatriques : les modifications de la sulcation corticale sont spécifiques non pas d'un trouble donné mais de la précocité des atteintes. En conclusion, nous proposons que l'étude des anomalies neurodéveloppementales soit intégrée dans une approche dimensionnelle en psychiatrie. / The term neurodevelopment in its broadest sense refers to all of the processes encompassing development of the nervous system from the earliest stages of formation in utero to later stages of maturation during adolescence to produce the fully functional adult nervous system. Work over the last thirty years has led to a neurodevelopmental model of human psychiatric disorders, including schizophrenia, based on genetic, epidemiological and imaging evidence. This model asserts that disease is fundamentally linked to or develops from abnormality(s) in the formation processes (early neurodevelopment) and maturation (late neurodevelopment) of the nervous system due to a combination of genetic and environmental factors. In this context this thesis aims to clarify the effects of neurodevelopmental abnormalities on psychiatric disorders, including schizophrenia, through the study of different markers. The first study aims to investigate correlations between markers of early brain development: a clinical marker (neurological soft signs) and an imaging marker (sulcation of the cerebral cortex) in a population of subjects with schizophrenia. A correlation between these two markers is presented: the sulcation index was found to be lower in subjects that had significant neurological soft signs. We concluded that the combined study of different markers may help to isolate subgroups of patients with greater early neurodevelopmental damage. The second study aims to characterize effects of different markers of early neurodevelopmental abnormalities on cognitive functioning in patients with schizophrenia. Effects on executive control (as measured by the Trail Making Test) were correlated with clinical markers (neurological soft signs, handedness) and imaging (sulcation of the anterior cingulate cortex and enlargment of the ventricles). We found interactions between different markers with a mainly non-linear summation effect. Our interpretation is that different markers reflect separate insults, though all early, on brain development with a common final effect on executive function. The third study aims to clarify the specificity of sulcation as a marker of early neurodevelopmental abnormalities by studying a population of adult subjects with autism spectrum disorder (ASD), a patholody beginning in early childhood and linked with evidence of early neurodevelopmental damage. Sulcation abnormalities of the anterior cingulate cortex, similar to those observed in patients with schizophrenia are detected in patients with ASD. These results suggest early neurodevelopmental abnormalities are shared by different psychiatric disorders and that changes in cortical sulcation are not specific to a given disorder but the early damage. In conclusion, we suggest that the study of neurodevelopmental abnormalities should be integrated into a dimensional approach in psychiatry.

Establishment and maintenacne of a polarized axis is essential for all organisms. Cells can either change their shape in response to extracellular cues or maintain a stable polarity axis via landmarks defined in relation to internal cues. In the fission yeast Schizosaccharomyces pombe,microtubules regulate cortical cell polarity together with the landmark protein Tea1. Tea1 is transported to cell tips on microtubule plus-­‐ends and deposited upon microtubule contact with the membrane. Although Tea1 has been shown to interact with several binding-­partners, Tea1 anchoring at the cell tip depends mostly on the membrane-­associated protein, Mod5. Tea1 and Mod5 accumulate in clusters at the cell tip in a mutually dependent manner. I used a combination of live-­‐cell imaging, FRAP (Fluorescence Recovery After Photobleaching) and computational modeling to dissect the dynamics of the Tea1-­‐Mod5 interaction. I have shown that although Tea1 is stably associated with the cell tip, Mod5 is mobile within the cell tip. I proposed a model in which Tea1 is stable at the cell tip due to self-­‐polymerization and association in the form of a cluster-­‐network. In the model, the role of Mod5 in the cluster-­‐network is to facilitate the formation of Tea1-­‐Tea1 interactions. Moreover, in the model, Mod5 is restricted to the cell tip due to iterative binding to and release from the Tea1 cluster-­‐network. The properties of the proposed Tea1 cluster-­‐ network might contribute to the behavior of Tea1 as a polarity landmark. I hypothesized that Tea1 transfer from the microtubules to the cell tip was regulated by phosphorylation. Tea1 phosphorylated residues were mapped using mass spectroscopy (MS), and identified to be mostly enriched within a central region of the protein. Using a combination of mutagenic analysis and live-­‐cell imaging I demonstrate that Tea1 phosphorylation might be required for its dissociation from the cluster-­‐network at the cell tip. This suggests that Tea1 interactions within the cluster network are phospho-­‐regulated by one of the several tip-­‐localized kinases. It has been shown in other organisms and in this thesis that comparison among MS samples requires quantitative MS methodologies. Thus, I developed a robust SILAC (Stable Isotope Labeling in Cell Culture) method to perform quantitative MS in S. pombe. As a proof-­‐of-­‐principle of the method I performed a proteome-­‐wide comparison between the late G2 and the G1/S transition of the cell cycle. The cell cycle proteome-­‐wide analysis not only quantified variation in expression levels of cell cycle regulated proteins but also identified novel cell cycle regulated proteins. It has been previously shown that Tea1, Tea3 and Mod5 can interact simultaneously, with each pair interacting independently of the third protein. I describe here a Mod5 mutagenic analysis screen designed to separate Tea1 and Tea3 binding site on Mod5. The Mod5-­‐mutants obtained from this analysis indicate that the Tea3-­‐Mod5 interaction may play a role in cell polarity establishment. Moreover, although Tea3 is non-­‐essential for the cluster-­‐network formation, Tea3 might be important for its compaction, which may be particularly important during de novo formation of cell polarity.

How do circuits in the mammalian cerebral cortex encode properties of the sensory environment in a way that can drive adaptive behavior? This question is fundamental to neuroscience, but it has been very difficult to approach directly. Various computational and theoretical models can explain a wide range of phenomena observed in the primary visual cortex (V1), including the anatomical organization of its circuits, the development of functional properties like orientation tuning, and behavioral effects like surround modulation. However, so far no model has been able to bridge these levels of description to explain how the machinery that develops directly affects behavior. Bridging these levels is important, because phenomena at any one specific level can have many possible explanations, but there are far fewer possibilities to consider once all of the available evidence is taken into account. In this thesis we integrate the information gleaned about cortical development, circuit and cell-type specific interactions, and anatomical, behavioral and electrophysiological measurements, to develop a computational model of V1 that is constrained enough to make predictions across multiple levels of description. Through a series of models incorporating increasing levels of biophysical detail and becoming increasingly better constrained, we are able to make detailed predictions for the types of mechanistic interactions required for robust development of cortical maps that have a realistic anatomical organization, and thereby gain insight into the computations performed by the primary visual cortex. The initial models focus on how existing anatomical and electrophysiological knowledge can be integrated into previously abstract models to give a well-grounded and highly constrained account of the emergence of pattern-specific tuning in the primary visual cortex. More detailed models then address the interactions between specific excitatory and inhibitory cell classes in V1, and what role each cell type may play during development and function. Finally, we demonstrate how these cell classes come together to form a circuit that gives rise not only to robust development but also the development of realistic lateral connectivity patterns. Crucially, these patterns reflect the statistics of the visual environment to which the model was exposed during development. This property allows us to explore how the model is able to capture higher-order information about the environment and use that information to optimize neural coding and aid the processing of complex visual tasks. Using this model we can make a number of very specific predictions about the mechanistic workings of the brain. Specifically, the model predicts a crucial role of parvalbumin-expressing interneurons in robust development and divisive normalization, while it implicates somatostatin immunoreactive neurons in mediating longer range and feature-selective suppression. The model also makes predictions about the role of these cell classes in efficient neural coding and under what conditions the model fails to organize. In particular, we show that a tight coupling of activity between the principal excitatory population and the parvalbumin population is central to robust and stable responses and organization, which may have implications for a variety of diseases where parvalbumin interneuron function is impaired, such as schizophrenia and autism. Further the model explains the switch from facilitatory to suppressive surround modulation effects as a simple by-product of the facilitating response function of long-range excitatory connections targeting a specialized class of inhibitory interneurons. Finally, the model allows us to make predictions about the statistics that are encoded in the extensive network of long-range intra-areal connectivity in V1, suggesting that even V1 can capture high-level statistical dependencies in the visual environment. The final model represents a comprehensive and well constrained model of the primary visual cortex, which for the first time can relate the physiological properties of individual cell classes to their role in development, learning and function. While the model is specifically tuned for V1, all mechanisms introduced are completely general, and can be used as a general cortical model, useful for studying phenomena across the visual cortex and even the cortex as a whole. This work is also highly relevant for clinical neuroscience, as the cell types studied here have been implicated in neurological disorders as wide ranging as autism, schizophrenia and Parkinson’s disease.

L’objectif de cette thèse est de développer des modèles mathématiques de perception visuelle basés sur des architectures corticales et de les appliquer pour reproduire des expériences phénoménologiques ainsi que pour traiter des images naturelles. Nous nous concentrons sur les tâches de vision de bas niveau et nous sommes intéressés par le problème du groupement et de l’individuation des unités perceptives. Nous ferons face au problème de la reconstruction des figures illusoires et de la détection des vaisseaux rétiniens dans les images optiques. Ensuite, nous considérerons le problème du codage et du décodage de l’activité cérébrale du cortex visuel obtenue par Imagerie par Résonance Magnétique fonctionnelle (IRMf). Ceci permet d’estimer la structure du cortex d’un patient spécifique et éventuellement de reconstruire le stimulus visuel de l’activité IRMf, dans une stratégie “de lecture du cerveau”. La distinction entre notre approche et l’état de la littérature consiste à utiliser des modèles neuromathématiques du cortex comme connaissance a priori pour régulariser la structure estimée. Même si c’est un objectif à long terme, nous proposons une première approche pour améliorer les résultats dans ce domaine. L’ensemble du travail de cette thèse a été développé en tenant compte des résultats de la phénoménologie de la perception et des résultats de la neurophysiologie. Dans le domaine de la phénoménologie de la perception, au début du siècle dernier, la théorie de la psychologie de la Gestalt a défini l’intégration des contours et en particulier Wertheimer [1938], Kohler [1947], Kofka [1935] ont défini le regroupement des lois de perception. Celles-ci sont cruciales dans la construction d’objets visuels : les éléments avec des caractéristiques en commun peuvent être regroupés pour former un nouvel objet visuel plus grand. Des expériences psychophysiques ont été proposées pour mesurer les paramètres quantitatifs de ces lois. Un intérêt particulier de cette thèse est le concept de champ d’association introduit par Field et al. [1993] lequel code différents principes de la Gestalt (dont la bonne continuation et la proximité).Ces auteurs ont montré que la co-linéarité de stimulus et la co-circularité jouent un rôle important dans la caractéristique du groupement. Leur étude a montré comment les chances de percevoir un chemin curviligne étaient élevées si l’orientation de ses éléments était tangente à ce chemin. D’autre part, en neurophysiologie, une grande quantité d’expériences confirment que le problème du groupement et de détection des contours est effectué par le cortex visuel primaire (V1) [Hubel, 1995]. Un cadre mathématique, basé sur les instruments différentiels, a été introduit pour formaliser ces résultats. Les premiers modèles géométriques sont dus à Koenderink and van Doorn... / The objective of this thesis is to develop mathematical models of visual perception based on cortical architectures and to apply them to reproduce phenomenological experiments and to process natural images. We primarly focus on low level vision tasks and in particular we are interested in the problem of grouping and of individuation of perceptual units. In this setting we will face the problem of the reconstruction of illusory figures and the detection of retinal vessels in optical images. Then we consider the problem of encoding and decoding of the fMRI signal from in vivo acquired brain activity of visual cortex. This allows to estimate the structure of the cortex of a specific human patient and eventually to reconstruct the visual stimulus from fMRI activity, in a so called “brain reading” strategy. The difference between our approach and the state of the art literature consists in using previously defined neuromathematical models of the cortices as a-priori knowledge to regularise in vivo estimated structure. Even if it is a long term objective, we propose a first approach to improve the results in this field. The entire work of this thesis has been developed taking into account results from phenomenology of perception and results of neurophysiology.In the field of the phenomenology of perception, at the beginning of the last century, the theory of the Gestalt psychology [Wertheimer, 1938, Kohler, 1947, Kofka, 1935] defined the integration of contours and in particular they defined grouping laws underlying perception. These are crucial in the construction of visual objects: points with characteristics in common can be grouped together to form a new visual object. Many psychophysical experiments have been proposed to measure the quantitative parameters of these laws. A particular interest of this thesis is the concept of association fields introduced by Field et al. [1993] which encodes different Gestalt principles (as good continuation, proximity). They showed that stimulus co-linearity and co-circularity play an important role for the feature of grouping. Their study showed how chances of perceiving the curvilinear path were high if the orientation of its features was the one tangent at that point and collapsed as their relative orientation deviated from being tangent...

La magnéto-encéphalographie (MEG) mesure l´activité cérébrale avec un excellent décours temporel mais sa localisation sur la surface corticale souffre d´une mauvaise résolution spatiale. Le problème inverse MEG est dit mal-posé et doit de ce fait être régularisé. La parcellisation du cortex en régions de spécificité fonctionnelle proche constitue une régularisation spatiale pertinente du problème inverse MEG. Nous proposons une méthode de parcellisation du cortex entier à partir de la connectivité anatomique cartographiée par imagerie de diffusion. Au sein de chaque aire d´une préparcellisation, la matrice de corrélation entre les profils de connectivité des sources est partitionnée. La parcellisation obtenue est alors mise à jour en testant la similarité des données de diffusion de part et d´autre des frontières de la préparcellisation. C´est à partir de ce résultat que nous contraignons spatialement le problème inverse MEG. Dans ce contexte, deux méthodes sont développées. La première consiste à partitionner l´espace des sources au regard de la parcellisation. L´activité corticale est alors obtenue sur un ensemble de parcelles. Afin de ne pas forcer les sources à avoir exactement la même intensité au sein d´une parcelle, nous développons une méthode alternative introduisant un nouveau terme de régularisation qui, lorsqu´il est minimisé, tend à ce que les sources d´une même parcelle aient des valeurs de reconstruction proches. Nos méthodes de reconstruction sont testées et validées sur des données simulées et réelles. Une application clinique dans le cadre du traitement de données de sujets épileptiques est également réalisée. / Magnetoencephalography (MEG) is a functional non-invasive modality which provides information on the temporal succession of cognitive processes with an excellent time resolution. Unfortunately, spatial resolution is limited due to the ill-posed nature of the MEG inverse problem for estimating source currents from the electromagnetic measurement. Cortex parcellation into regions sharing functional features constitutes a relevant spatial regularization. We propose a whole cortex parcellation method based on the anatomical connectivity mapped by diffusion MRI. Inside areas of a preparcellation, the correlation matrix between connectivity profiles is clustered. The cortex parcellation is then updated testing the similarity of diffusion data on both sides of pre-parcellation boundaries. MEG inverse problem is constrained from this result. Two methods have been developed. The first one is based on the subdivision of source space regarding the parcellation. The cortical activity is obtained on a set of parcels and its analysis is simplified. Not to force sources to have exactly the same value inside a cortical area, we develop an alternative method. We introduce a new regularization term in the MEG inverse problem which constrain sources in a same region to have close values. Our methods are applied on simulated and real subjects. Clinical application is also performed on epileptic data. Each contribution takes part of a pipeline whose each step is detailed to make our works reproducible.

A teoria de redes complexas se consolidou nos últimos anos, graças ao seu potencial como ferramenta versátil no estudo de diversos sistemas discretos. É possível enumerar aplicações em áreas tão distintas como engenharia, sociologia, computação, linguística e biologia. Tem merecido atenção, por exemplo, o estudo da organização estrutural do cérebro, tanto em nível microscópico (em nível de neurônios) como regional (regiões corticais). Acredita-se que tal organização visa otimizar a dinâmica, favorecendo processos como sincronização e processamento paralelo. Estrutura e funcionamento, portanto, estão relacionados. Tal relação é abordada pela teoria de redes complexas nos mais diversos sistemas, sendo possivelmente seu principal objeto de estudo. Neste trabalho exploramos as relações entre aspectos estruturais de redes neuronais e corticais e a atividade nas mesmas. Especificamente, estudamos como a interconectividade entre o córtex e o tálamo pode interferir em estados de ativação do último, considerando-se o sistema tálamo-cortical do gato bem como alguns modelos para geração de rede encontrados na literatura. Também abordamos a relação entre a morfologia individual de neurônios e a conectividade em redes neuronais, e consequentemente o impacto da forma neuronal em dinâmicas atuando sobre tais redes e a eficiência das mesmas no transporte de informação. Como tal eficiência pode ter como consequência a facilitação de processos maléficos às redes, como por exemplo, ataques causados por vírus neurotrópicos, também exploramos possíveis correlações entre características individuais dos elementos que formam as redes complexas e danos causados por processos infecciosos iniciados nos mesmos. / Complex network theory has been consolidated along the last years, owing to its potential as a versatile framework for the study of diverse discrete systems. It is possible to enumerate applications in fields as distinct as Engineering, Sociology, Computing, Linguistics and Biology, to name a few. For instance, the study of the structural organization of the brain at the microscopic level (neurons), as well as at regional level (cortical areas), has deserved attention. It is believed that such organization aims at optimizing the dynamics, supporting processes like synchronization and parallel processing. Structure and functioning are thus interrelated. Such relation has been addressed by complex network theory in diverse systems, possibly being its main subject. In this thesis we explore the relations between structural aspects and the activity in cortical and neuronal networks. Specifically, we study how the interconnectivity between the cortex and thalamus can interfere in activation states of the latter, taking into consideration the thalamocortical system of the cat, along with networks generated through models found in literature. We also address the relation between the individual morphology of the neurons and the connectivity in neuronal networks, and consequently the effect of the neuronal shape on dynamic processes actuating over such networks and on their efficiency on information transport. As such efficiency can consequently facilitate prejudicial processes on the networks, e.g. attacks promoted by neurotropic viruses, we also explore possible correlations between individual characteristics of the elements forming such systems and the damage caused by infectious processes started at these elements.