A better understanding of tumour heterogeneity is central for accurate diagnosis, targeted therapy and personalised treatment of glioblastoma patients. This thesis aims to investigate whether pre-operative multi-parametric magnetic resonance imaging (MRI) can provide a useful tool for evaluating inter-tumoural and intra-tumoural heterogeneity of glioblastoma. For this purpose, we explored: 1) the utilities of habitat imaging in combining multi-parametric MRI for identifying invasive sub-regions (I & II); 2) the significance of integrating multi-parametric MRI, and extracting modality inter-dependence for patient stratification (III & IV); 3) the value of advanced physiological MRI and radiomics approach in predicting epigenetic phenotypes (V). The following observations were made: I. Using a joint histogram analysis method, habitats with different diffusivity patterns were identified. A non-enhancing sub-region with decreased isotropic diffusion and increased anisotropic diffusion was associated with progression-free survival (PFS, hazard ratio [HR] = 1.08, P < 0.001) and overall survival (OS, HR = 1.36, P < 0.001) in multivariate models. II. Using a thresholding method, two low perfusion compartments were identified, which displayed hypoxic and pro-inflammatory microenvironment. Higher lactate in the low perfusion compartment with restricted diffusion was associated with a worse survival (PFS: HR = 2.995, P = 0.047; OS: HR = 4.974, P = 0.005). III. Using an unsupervised multi-view feature selection and late integration method, two patient subgroups were identified, which demonstrated distinct OS (P = 0.007) and PFS (P < 0.001). Features selected by this approach showed significantly incremental prognostic value for 12-month OS (P = 0.049) and PFS (P = 0.022) than clinical factors. IV. Using a method of unsupervised clustering via copula transform and discrete feature extraction, three patient subgroups were identified. The subtype demonstrating high inter-dependency of diffusion and perfusion displayed higher lactate than the other two subtypes (P = 0.016 and P = 0.044, respectively). Both subtypes of low and high inter-dependency showed worse PFS compared to the intermediate subtype (P = 0.046 and P = 0.009, respectively). V. Using a radiomics approach, advanced physiological images showed better performance than structural images for predicting O6-methylguanine-DNA methyltransferase (MGMT) methylation status. For predicting 12-month PFS, the model of radiomic features and clinical factors outperformed the model of MGMT methylation and clinical factors (P = 0.010). In summary, pre-operative multi-parametric MRI shows potential for the non-invasive evaluation of glioblastoma heterogeneity, which could provide crucial information for patient care.

No description available.

Différentes méthodes ayant pour objectif une utilisation optimale d'antennes radio-fréquences spécialisées en imagerie par résonance magnétique sont développées et validées. Dans un premier temps, il est démontré qu'une méthode alternative de combinaison des signaux provenant des différents canaux de réception d'un réseau d'antennes mène à une réduction significative du biais causé par la présence de bruit dans des images de diffusion, en comparaison avec la méthode de la somme-des-carrés généralement utilisée. Cette réduction du biais engendré par le bruit permet une amélioration de l'exactitude de l'estimation de différents paramètres de diffusion et de diffusion tensorielle. De plus, il est démontré que cette méthode peut être utilisée conjointement avec une acquisition régulière sans accélération, mais également en présence d'imagerie parallèle. Dans une seconde perspective, les bénéfices engendrés par l'utilisation d'une antenne d'imagerie intravasculaire sont étudiés. Suite à une étude sur fantôme, il est démontré que l'imagerie par résonance magnétique intravasculaire offre le potentiel d'améliorer significativement l'exactitude géométrique lors de mesures morphologiques vasculaires, en comparaison avec les résultats obtenus avec des antennes de surface classiques. Il est illustré qu'une exactitude géométrique comparable à celle obtenue grâce à une sonde ultrasonique intravasculaire peut être atteinte. De plus, plusieurs protocoles basés sur une acquisition de type balanced steady-state free-precession sont comparés dans le but de mettre en évidence différentes relations entre les paramètres utilisés et l'exactitude géométrique obtenue. En particulier, des dépendances entre la taille du vaisseau, le rapport signal-sur-bruit à la paroi vasculaire, la résolution spatiale et l'exactitude géométrique atteinte sont mises en évidence. Dans une même optique, il est illustré que l'utilisation d'une antenne intravasculaire permet une amélioration notable de la visualisation de la lumière d'une endoprothèse vasculaire. Lorsque utilisée conjointement avec une séquence de type balanced steady-state free-precession utilisant un angle de basculement spécialement sélectionné, l'imagerie par résonance magnétique intravasculaire permet d'éliminer complètement les limitations normalement engendrées par l'effet de blindage radio-fréquence de l'endoprothèse. / Specific methods for an optimal use of specialized magnetic resonance radiofrequency coils are developed and validated. First, an improved combination of signals from the different channels of an array coil is shown to lead to a significant reduction of the noise bias in diffusion images, in comparison to the generally accepted sum-of-squares combination method. This reduction of the noise bias is demonstrated to greatly improve the accuracy of the estimated diffusion and diffusion tensor parameters, both for a standard non-accelerated acquisition and when parallel imaging is used. In a second scope, the benefits arising from the use of an intravascular imaging antenna are investigated. Using a phantom study, it is demonstrated that intravascular magnetic resonance imaging offers the potential to improve the geometrical accuracy of morphological vascular measurements in comparison to standard surface magnetic resonance imaging and that a geometrical accuracy comparable to the one obtained using intravascular ultrasound can be reached. Several protocols based on a balanced steady-state free-precession sequence are compared in order to highlight the relations between several acquisitions parameters and the achieved geometrical accuracy. In particular, important relations between the vessel size, the vessel wall signal-to-noise ratio, the in-plane resolution and the achieved accuracy are illustrated. In a similar manner, the use of an intravascular antenna is demonstrated to be highly beneficial for an improved in-stent lumen visualization. When used with a balanced steady-state free-precession acquisition with a carefully chosen flip angle, intravascular magnetic resonance imaging can effectively eliminate the hindering aspect of the radiofrequency shielding effect caused by the presence of the vascular stent.

Os seios maxilares constituem cavidades multifuncionais que apresentam íntima relação como elementos dentários súpero-posteriores e/ou o osso alveolar desta região, tornando-os susceptíveis a infecções de origem odontológica; ou, mediante a presença de sinusopatias de diversas naturezas, resultando em insucesso de procedimentos de abordagem direta destes ou em áreas adjacentes. O estudo imaginológico das cavidades dos seios maxilares previamente a procedimentos odontológicos na região dos seios maxilares é indispensável para garantir-se a evolução pós-operatória favorável. A anatomia complexa destas cavidades requer o uso de ferramentas tridimensionais, como a tomografia computadorizada e a ressonância magnética. Recentemente, novas modalidades técnicas, objetivando otimizar o diagnóstico por ressonância magnética, tem sido investigadas em processos patológicos diversos, incluindo aqueles que podem acometer os seios maxilares. Uma dessas modalidades, é o estudo qualitativo e quantitativo da difusibilidade das moléculas de água, que propõe-se a descrever características celulares e funcionais de tecidos, sob o ponto de vista imaginológico. Essencialmente, a ideia do estudo da celularidade e fisiologia dos tecidos é distinguir processos patológicos diferentes, provendo hipóteses diagnósticas acuradas. Não obstante, existem poucos estudos que analisam as doenças inflamatórias e infecciosas dos seios maxilares, que são as afecções mais usuais nestas cavidades. Assim sendo, o objetivo primordial deste estudo foi analisar os valores quantitativos dos coeficientes de difusibilidade das moléculas de água (ADC) em grupos de alterações imaginológicas nos seios maxilares que correspondem à sinais imaginológicos de sinusopatias inflamatórias e/ou infecciosas, afim de verificar se existem diferenças significativas entre estes valores que poderiam auxiliar no diagnóstico por meio da ressonância magnética. Para desenvolver este objetivo, foram analisados 98 seios maxilares de pacientes que realizaram exames de ressonância magnética, classificando as alterações observáveis nesta cavidade em 4 grupos: presença de espessamento da mucosa sinusal, pólipos ou cistos, nível hidroaéreo, presença de conteúdo de sinal heterogêneo em imagens ponderadas em T2 associado a erosões ósseas e presença de calcificações distróficas. Os valores de ADC foram aferidos nos seus respectivos mapas de ADC. Diferenças estatisticamente significativas foram verificadas comparando-se os 4 grupos; ademais, os seios maxilares foram classificados de acordo com o grau de acometimento destas alterações em: ausência de opacificação, totalmente opacificado, parcialmente opacificado e presença de espessamento da mucosa sinusal. Verificou-se que o grau de opacificação mais prevalente na amostra estudada foi o parcialmente opacificado. Os valores de ADC do espessamento da mucosa sinusal são estatisticamente menores do que os dos demais grupos, indicando menor difusibilidade das moléculas de água do espessamento em relação às demais alterações. Concluiu-se que é possível utilizar os valores de ADC na diferenciação do espessamento da mucosa sinusal das demais alterações dos seios maxilares. / The maxillary sinuses are multifunctional cavities closed related with upper- posterior teeth and / or this region alveolar bone, which can lead to susceptibility to sinusal dental origin infections; or, due to the sinus disease, leading to failure in sunuses direct approach or in adjacent areas procedures. The imaging study of maxillary sinus cavities prior to procedures in the region of the maxillary sinuses is indispensable to ensure favorable postoperative evolution. The complex anatomy of these cavities requires the use of three-dimensional tools, such as computed tomography and magnetic resonance imaging. Recently, new technical modalities aiming to optimize the diagnosis by magnetic resonance have been investigated in diverse pathological processes, including those that can affect the maxillary sinuses. One of these modalities is the qualitative and quantitative study of the diffusibility of water molecules, which proposes to describe celularity and functional characteristics of tissues from an imaginary point of view. Essentially, the idea cellularity and tissue physiology study is to distinguish different pathological processes, providing accurate diagnostic hypotheses. Nevertheless, there are few studies that analyze the inflammatory and infectious diseases of the maxillary sinuses, which are the most common affections in these cavities. Thus, the main objective of this study was to analyze the quantitative values of the water molecule diffusibility coefficients (ADC) in groups of imaging alterations in the maxillary sinuses that correspond to signs of inflammatory and / or infectious sinusopathies, in order to verify if there are any significant differences between these values that could aid in the diagnosis through magnetic resonance imaging. To develop this objective, 98 maxillary sinuses of patients that underwent magnetic resonance imaging were evaluated. The maxillary sinuses were classified according to the inflammatory / infectious changes detected in 4 groups: presence of sinus mucosal thickening, polyps or cysts, air-fluid levels, T2 weighted heterogeneous signal associated with erosions and the presence of dystrophic calcifications. The ADC values were measured on their respective ADC maps. Statistically significant differences were observed comparing the 4 groups; In addition, the maxillary sinuses were classified according to the degree of involvement of these alterations in: absence of opacification, totally opacified, partially opacified and presence of mucous thickening. It was verified that the most prevalent degree of opacification in the studied sample was partially opacified. ADC values of the sinus mucosa thickening are statistically lower than those of the other groups, indicating less diffusibility of the thickening water molecules in relation to the other alterations. It was concluded that it is possible to use the ADC values in the differentiation of the mucous thickening of the other alterations of the maxillary sinuses.

Il est de plus en plus reconnu que les connexions du cerveau jouent un rôle important sur la fonction cérébrale, en particulier les fonctions cognitives supérieures comme le langage. Cependant l’imperfection des techniques traitant les connexions macroscopiques humaines a empêché l’avancement de nos connaissances sur l'anatomie des faisceaux. Nous nous appuyons ainsi aujourd’hui essentiellement sur la littérature du XIXème siècle. Les définitions des trajets et des connexions anatomiques de nombreux faisceaux sont constamment débattues. En utilisant l'imagerie de diffusion, nous réévaluons les anatomies des faisceaux clés dans une grande cohorte saine. Nous utilisons une nouvelle approche de segmentation des faisceaux qui vise à reproduire la méthode introduite par les dissectionistes. Celle-ci définit un tract comme l’ensemble des fibres passant par une même tige, minimisant ainsi l’a priori sur leurs terminaisons. Nous nous concentrons sur les faisceaux d'association des capsules externe et extrême, notamment les faisceaux occipito-frontal inférieur (FOFI) et unciné (FU) impliqués dans le circuit du langage ventral. Nous passons en revue la littérature sur ces tracts, fournissons des descriptions détaillées de leurs connectivités anatomiques et donnons un nouvel éclairage sur leur asymétrie et organisation interne. Dans une première étude, nous confirmons que les deux faisceaux ont de plus vastes projections dans le cortex qu'on ne le pensait, et nous présentons de nouveaux résultats concernant les branches asymétriques des faisceaux. Dans une deuxième étude, nous étudions en profondeur le FU et ses sous composantes. Nous résolvons un débat d’un siècle en exhibant clairement sa frontière avec le FOFI et nous identifions pour chaque sous composante des caractéristiques anatomiques distinctives y compris des asymétries. Ces résultats apportent un éclairage nouveau sur le FOFI et le FU qui sera crucial pour démêler leurs rôles multifonctionnels. / The importance of the brain’s connections for cerebral function is increasingly emphasized especially for higher cognitive functions like language. But the imperfection of the techniques used to address the human macroscopic connections has prevented the advancement of our knowledge on the anatomy of fibre pathways. Thus we rely heavily on XIXth century literature. Controversy surrounding the anatomical course and connections of many fibre pathways persists. Using diffusion imaging, we reevaluate the anatomies of key pathways in a large healthy cohort. We use a novel tract segmentation approach that aims to reproduce the method introduced by dissectionists – defining a tract as all fibers passing through a stem, thus minimizing a priori on their terminations. We focus on the association pathways of the external and extreme capsules, namely the inferior fronto-occipital (IFOF) and uncinate fasciculi (UF), implicated in the ventral language circuitry. We review the literature on these tracts, provide detailed descriptions of their connectional anatomies and present new insights regarding their asymmetry and internal organization. In a first study, we confirm that both tracts have more extensive projections within the cortex than previously thought and present new results regarding asymmetrical tract branches. In a second study we further investigate the UF including its subcomponents. We resolve a century old debate by clarifying its elusive boundary with the IFOF and reveal the distinctive anatomical features including asymmetry patterns of each subcomponent. These results shed new light on the IFOF and UF and will be crucial for disentangling their multifunctional roles.

Différentes méthodes ayant pour objectif une utilisation optimale d'antennes radio-fréquences spécialisées en imagerie par résonance magnétique sont développées et validées. Dans un premier temps, il est démontré qu'une méthode alternative de combinaison des signaux provenant des différents canaux de réception d'un réseau d'antennes mène à une réduction significative du biais causé par la présence de bruit dans des images de diffusion, en comparaison avec la méthode de la somme-des-carrés généralement utilisée. Cette réduction du biais engendré par le bruit permet une amélioration de l'exactitude de l'estimation de différents paramètres de diffusion et de diffusion tensorielle. De plus, il est démontré que cette méthode peut être utilisée conjointement avec une acquisition régulière sans accélération, mais également en présence d'imagerie parallèle. Dans une seconde perspective, les bénéfices engendrés par l'utilisation d'une antenne d'imagerie intravasculaire sont étudiés. Suite à une étude sur fantôme, il est démontré que l'imagerie par résonance magnétique intravasculaire offre le potentiel d'améliorer significativement l'exactitude géométrique lors de mesures morphologiques vasculaires, en comparaison avec les résultats obtenus avec des antennes de surface classiques. Il est illustré qu'une exactitude géométrique comparable à celle obtenue grâce à une sonde ultrasonique intravasculaire peut être atteinte. De plus, plusieurs protocoles basés sur une acquisition de type balanced steady-state free-precession sont comparés dans le but de mettre en évidence différentes relations entre les paramètres utilisés et l'exactitude géométrique obtenue. En particulier, des dépendances entre la taille du vaisseau, le rapport signal-sur-bruit à la paroi vasculaire, la résolution spatiale et l'exactitude géométrique atteinte sont mises en évidence. Dans une même optique, il est illustré que l'utilisation d'une antenne intravasculaire permet une amélioration notable de la visualisation de la lumière d'une endoprothèse vasculaire. Lorsque utilisée conjointement avec une séquence de type balanced steady-state free-precession utilisant un angle de basculement spécialement sélectionné, l'imagerie par résonance magnétique intravasculaire permet d'éliminer complètement les limitations normalement engendrées par l'effet de blindage radio-fréquence de l'endoprothèse. / Specific methods for an optimal use of specialized magnetic resonance radiofrequency coils are developed and validated. First, an improved combination of signals from the different channels of an array coil is shown to lead to a significant reduction of the noise bias in diffusion images, in comparison to the generally accepted sum-of-squares combination method. This reduction of the noise bias is demonstrated to greatly improve the accuracy of the estimated diffusion and diffusion tensor parameters, both for a standard non-accelerated acquisition and when parallel imaging is used. In a second scope, the benefits arising from the use of an intravascular imaging antenna are investigated. Using a phantom study, it is demonstrated that intravascular magnetic resonance imaging offers the potential to improve the geometrical accuracy of morphological vascular measurements in comparison to standard surface magnetic resonance imaging and that a geometrical accuracy comparable to the one obtained using intravascular ultrasound can be reached. Several protocols based on a balanced steady-state free-precession sequence are compared in order to highlight the relations between several acquisitions parameters and the achieved geometrical accuracy. In particular, important relations between the vessel size, the vessel wall signal-to-noise ratio, the in-plane resolution and the achieved accuracy are illustrated. In a similar manner, the use of an intravascular antenna is demonstrated to be highly beneficial for an improved in-stent lumen visualization. When used with a balanced steady-state free-precession acquisition with a carefully chosen flip angle, intravascular magnetic resonance imaging can effectively eliminate the hindering aspect of the radiofrequency shielding effect caused by the presence of the vascular stent.

Os seios maxilares constituem cavidades multifuncionais que apresentam íntima relação como elementos dentários súpero-posteriores e/ou o osso alveolar desta região, tornando-os susceptíveis a infecções de origem odontológica; ou, mediante a presença de sinusopatias de diversas naturezas, resultando em insucesso de procedimentos de abordagem direta destes ou em áreas adjacentes. O estudo imaginológico das cavidades dos seios maxilares previamente a procedimentos odontológicos na região dos seios maxilares é indispensável para garantir-se a evolução pós-operatória favorável. A anatomia complexa destas cavidades requer o uso de ferramentas tridimensionais, como a tomografia computadorizada e a ressonância magnética. Recentemente, novas modalidades técnicas, objetivando otimizar o diagnóstico por ressonância magnética, tem sido investigadas em processos patológicos diversos, incluindo aqueles que podem acometer os seios maxilares. Uma dessas modalidades, é o estudo qualitativo e quantitativo da difusibilidade das moléculas de água, que propõe-se a descrever características celulares e funcionais de tecidos, sob o ponto de vista imaginológico. Essencialmente, a ideia do estudo da celularidade e fisiologia dos tecidos é distinguir processos patológicos diferentes, provendo hipóteses diagnósticas acuradas. Não obstante, existem poucos estudos que analisam as doenças inflamatórias e infecciosas dos seios maxilares, que são as afecções mais usuais nestas cavidades. Assim sendo, o objetivo primordial deste estudo foi analisar os valores quantitativos dos coeficientes de difusibilidade das moléculas de água (ADC) em grupos de alterações imaginológicas nos seios maxilares que correspondem à sinais imaginológicos de sinusopatias inflamatórias e/ou infecciosas, afim de verificar se existem diferenças significativas entre estes valores que poderiam auxiliar no diagnóstico por meio da ressonância magnética. Para desenvolver este objetivo, foram analisados 98 seios maxilares de pacientes que realizaram exames de ressonância magnética, classificando as alterações observáveis nesta cavidade em 4 grupos: presença de espessamento da mucosa sinusal, pólipos ou cistos, nível hidroaéreo, presença de conteúdo de sinal heterogêneo em imagens ponderadas em T2 associado a erosões ósseas e presença de calcificações distróficas. Os valores de ADC foram aferidos nos seus respectivos mapas de ADC. Diferenças estatisticamente significativas foram verificadas comparando-se os 4 grupos; ademais, os seios maxilares foram classificados de acordo com o grau de acometimento destas alterações em: ausência de opacificação, totalmente opacificado, parcialmente opacificado e presença de espessamento da mucosa sinusal. Verificou-se que o grau de opacificação mais prevalente na amostra estudada foi o parcialmente opacificado. Os valores de ADC do espessamento da mucosa sinusal são estatisticamente menores do que os dos demais grupos, indicando menor difusibilidade das moléculas de água do espessamento em relação às demais alterações. Concluiu-se que é possível utilizar os valores de ADC na diferenciação do espessamento da mucosa sinusal das demais alterações dos seios maxilares. / The maxillary sinuses are multifunctional cavities closed related with upper- posterior teeth and / or this region alveolar bone, which can lead to susceptibility to sinusal dental origin infections; or, due to the sinus disease, leading to failure in sunuses direct approach or in adjacent areas procedures. The imaging study of maxillary sinus cavities prior to procedures in the region of the maxillary sinuses is indispensable to ensure favorable postoperative evolution. The complex anatomy of these cavities requires the use of three-dimensional tools, such as computed tomography and magnetic resonance imaging. Recently, new technical modalities aiming to optimize the diagnosis by magnetic resonance have been investigated in diverse pathological processes, including those that can affect the maxillary sinuses. One of these modalities is the qualitative and quantitative study of the diffusibility of water molecules, which proposes to describe celularity and functional characteristics of tissues from an imaginary point of view. Essentially, the idea cellularity and tissue physiology study is to distinguish different pathological processes, providing accurate diagnostic hypotheses. Nevertheless, there are few studies that analyze the inflammatory and infectious diseases of the maxillary sinuses, which are the most common affections in these cavities. Thus, the main objective of this study was to analyze the quantitative values of the water molecule diffusibility coefficients (ADC) in groups of imaging alterations in the maxillary sinuses that correspond to signs of inflammatory and / or infectious sinusopathies, in order to verify if there are any significant differences between these values that could aid in the diagnosis through magnetic resonance imaging. To develop this objective, 98 maxillary sinuses of patients that underwent magnetic resonance imaging were evaluated. The maxillary sinuses were classified according to the inflammatory / infectious changes detected in 4 groups: presence of sinus mucosal thickening, polyps or cysts, air-fluid levels, T2 weighted heterogeneous signal associated with erosions and the presence of dystrophic calcifications. The ADC values were measured on their respective ADC maps. Statistically significant differences were observed comparing the 4 groups; In addition, the maxillary sinuses were classified according to the degree of involvement of these alterations in: absence of opacification, totally opacified, partially opacified and presence of mucous thickening. It was verified that the most prevalent degree of opacification in the studied sample was partially opacified. ADC values of the sinus mucosa thickening are statistically lower than those of the other groups, indicating less diffusibility of the thickening water molecules in relation to the other alterations. It was concluded that it is possible to use the ADC values in the differentiation of the mucous thickening of the other alterations of the maxillary sinuses.

L'exercice aérobique (AE) est associé à de nombreuses modifications fonctionnelles et anatomiques dans le cerveau humain. Par exemple, il a été démontré que l'EA modulait l'excitabilité corticale et la neurochimie immédiatement après l'exercice. Les effets d'une activité physique répétée et soutenue sur les fonctions cérébrales restent toutefois mal compris. En effet, peu de données sont disponibles permettant de déterminer si les personnes ayant une bonne condition physique présentent des modifications persistantes de l'excitabilité corticale et du métabolisme cérébral malgré les changements rapportés dans la matière grise et la matière blanche. Dans la présente étude, 20 personnes sédentaires en bonne santé (< 2 heures/semaine d'activité physique) ont été comparées à 20 personnes actives (> 6 heures/semaine d'activité physique) sur la base de mesures de l'excitabilité corticale (rMT, courbe I/O, SICI, ICF) et de la concentration de métabolites (GABA, Glx, NAA) dans la représentation corticale de la main droite. L'épaisseur corticale de la représentation du cortex moteur primaire de la main droite et la densité apparente des fibres de la voie corticospinale (CST) ont également été évaluées. L'aptitude cardiorespiratoire (VO2max) était significativement plus élevée chez les athlètes que chez les sédentaires, ce qui n'était pas le cas de l'indice de masse corporelle. Aucune différence entre les groupes n'a été constatée en ce qui concerne les mesures du rMT, du SICI et de l'ICF. Les valeurs de la courbe I/O étaient significativement plus élevées et la courbe I/O était plus prononcée chez les individus actifs. Aucune différence significative n'a été observée pour l'épaisseur corticale, la concentration de métabolites et les valeurs de diffusion de la CST. La pente de la courbe I/O était positivement corrélée à la VO2max. Les présentes données suggèrent que des niveaux élevés de capacité aérobique sont associés à une excitabilité corticale accrue dans la représentation de la main du cortex moteur primaire. / Aerobic exercise is associated with widespread functional and anatomical modifications in the human brain. For example, AE has been shown to modulate cortical excitability and neurochemistry immediately after exercise. The effects of repeated and sustained physical activity on brain function, however, remain poorly understood. Indeed, little is known about whether individuals with high levels of fitness display persistent modifications in cortical excitability and brain metabolism despite reported changes in grey and white matter. In the present study, 20 healthy sedentary individuals (< 2 hours/week AE) were compared to 20 active individuals (> 6 hours/week AE) on measures of cortical excitability (rMT, I/O curve, SICI, ICF) and metabolite concentration (GABA, Glx, NAA) in the cortical representation of the right hand. Cortical thickness of the primary motor cortex representation of the right hand and corticospinal tract (CST) apparent fiber density (AFD) were also assessed. Cardiorespiratory fitness (VO2max) was significantly higher in athletes compared to sedentary individuals whereas body mass index was not. No group differences were found on measures of rMT, SICI and ICF. I/O curve values were significantly higher, and the I/O curve was steeper in active individuals. No significant differences were observed between the groups for cortical thickness, metabolite concentration and CST diffusion values. I/O curve slope was positively correlated with VO2max. The present data suggest that high levels of aerobic fitness are associated with increased cortical excitability in the hand representation of the primary motor cortex.

En plus de la triade de symptômes caractérisant l’autisme, ce trouble neurodévelopmental est associé à des particularités perceptives et motrices et, au niveau cérébral, par une connectivité atypique entre les différentes régions du cerveau. Au niveau anatomique, un des résultats les plus communs est la réduction du corps calleux. Toutefois, des effets directs de cette altération anatomique sur l’intégrité et l’efficacité du transfert interhémisphérique restent à être démontrés. Pour la présente thèse, trois différentes études investiguent différents aspects du traitement de l’information visuomotrice : le transfert interhémisphérique entre les régions bilatérales motrices et visuelles, la vitesse de traitement perceptif, et les habiletés motrices visuellement guidées. Dans la première étude, le paradigme visuomoteur de Poffenberger a été utilisé pour mesurer le temps de transfert interhémisphérique (TTIH). L’imagerie par résonnance magnétique fonctionnelle (IRMf) et structurale ainsi que l’imagerie de diffusion ont aussi été utilisées pour étudier les réseaux cérébraux impliqués dans la tâche de Poffenberger. Les autistes ont été comparés à un groupe d’individus à développement typique. La deuxième étude avait pour but d’investiguer la vitesse de traitement perceptif en autisme. Dans la troisième étude, deux tâches motrices (Purdue et Annett) ont été utilisées pour examiner la nature et l’importance des déficits moteurs. La tâche de Purdue inclut deux conditions bimanuelles utilisées comme indice additionnel d’intégration interhémisphérique. Dans les études 2 et 3, le groupe d’autistes a aussi été comparé à un groupe d’individus Asperger afin de voir si, et comment, les deux sous-groupes peuvent être distingués en ce qui concerne le traitement visuel et les déficits moteurs. Aucune différence entre les groupes n’a été observée en termes de TTIH. Les résultats de l’étude IRMf révèlent des différences d’activations corticales en lien avec la tâche de Poffenberger. Dans les groupes d’autistes et de typiques, l’efficacité de la communication interhémisphérique était associée à différentes portions du corps calleux (frontales/motrices chez les typiques, postérieures/visuelles chez les autistes). De façon globale, les résultats de cette étude démontrent un patron atypique de transfert interhémisphérique de l’information visuomotrice en autisme, reflétant un rôle plus important des mécanismes visuels dans le comportement sensorimoteur possiblement en lien avec une réorganisation cérébrale. Les résultats des études comportementales 2 et 3 indiquent que les autistes excellent dans la tâche mesurant la vitesse de traitement perceptif alors que les Asperger accomplissent la tâche à des niveaux similaires à ceux des typiques. La nature des déficits moteurs diffère aussi entre les deux sous-groupes; la dextérité et la coordination bimanuelle est affectée chez les individus Asperger mais pas chez les autistes, qui eux sont plus atteints au niveau de la rapidité unimanuelle. Les sous-groupes d’autistes et de syndrome d’Asperger sont caractérisés par des profils cognitifs différents dont les particularités perceptives et motrices font partie intégrante. / In addition to the triad of symptoms characterizing autism, this neurodevelopmental condition is characterized by visual and motor atypicalities and, at the cerebral level, by atypical connectivity between the different brain areas. Anatomically, one of the most replicated finding is a reduction of the corpus callosum. However, evidence of a direct effect of the corpus callosum reductions on integrity and efficiency of interhemispheric transfer is lacking. Three different studies were designed to investigate different aspect of visuo-motor processing: interhemispheric transfer between bilateral motor and visual brain areas, perceptual processing speed, visually guided motor performance. In the first study, the visuo-motor Poffenberger paradigm was used to measure interhemispheric transfer time (IHTT). Structural and functional magnetic resonance imaging (fMRI) and diffusion tensor imaging (DTI) were also used to study the brain networks involved in the Poffenberger task. Autistics were compared to typically developing individuals. The second study investigates whether perceptual processing speed (Inspection Time task) is atypical in autism. In the third study, two visually-guided motor tasks (the Purdue pegboard and Annett peg moving task) were used to verify the nature and magnitude of motor deficits. The Purdue task includes two bimanual conditions used as additional measures of interhemispheric communication integrity. Moreover, in studies 2 and 3, behavioral differences between autistic and Asperger individuals were investigated in order to see if and how the two subgroups can be distinguished in terms of perceptual processing and motor deficits. No group difference was observed in terms of IHTT. The fMRI results reveal a different pattern of cortical activations associated to the Poffenberger task. In the autism and typical groups, the efficiency of interhemispheric communication was associated with different portions of the corpus callosum (frontal/premotor in typicals, posterior/visual in autistics). These results demonstrate an atypical pattern of interhemispheric visuo-motor information transfer, possibly reflecting a more prominent role of visual mechanisms guiding sensorimotor behavior in autism, related to cerebral reorganizations. Results of the behavioral studies indicate that autistics have an excellent visual processing speed while Asperger individuals performed like typicals. Motor impairments also differed between the two subgroups; dexterity and bimanual coordination was impaired in Asperger individuals but not in autistics, who presented more difficulties in unimanual conditions. Autism and Asperger subgroups are characterized by different cognitive profiles in which visual processing and motor deficits are important factors.

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