Background: The prevalence of adolescent obesity has increased drastically in the last few decades, spurring research examining causes and consequences of this chronic health condition. Neuroimaging techniques are being used to determine possible neural correlates of obesity that could help inform research in this field. However, the research among adolescents is not as abundant and findings so far are contradictory. This study sought to examine the association of the shape and volume of subcortical brain structures involved in reward processing with weight status in adolescent females. Additionally, this study sought to determine if the shape and volume of these structures were correlated with the Power of Food Scale (PFS), a self-report measure of food reward sensitivity. Method: The shape and volume of the nucleus accumbens (NAc) and amygdala were examined in 89 adolescent females ranging from normal weight to obese. MR scans were acquired using a high-resolution T1-weighted (MPRAGE) sequence. Shape was estimated using Large Deformation Diffeomorphic Metric Mapping. Seemingly unrelated regression models (SUM) were used for both brain structures with shape and volume as outcome variables and zBMI as the predictor variable. Pairwise correlation coefficients were determined for PFS score and both regions of interest (ROI). Results: SUM results revealed that zBMI was significantly associated with the shape of the left amygdala (β = -1.1, p<.021, 95% confidence interval [CI] = -2.02, -.16). When we controlled for age on the relationship between zBMI and left amygdala shape, we found the following partial correlation: r = -.24, p = .03. The PFS was found to have weak correlations with the volume and shape of the right NAc that approached significance (r = .20, p = .06; r = .19, p = .08, respectively). Conclusions: Our study suggests that there is an association between higher zBMI and aberrations in the shape of the left amygdala. We did not find associations between zBMI and the shape of our other reward-related ROIs, nor did we find any associations with zBMI and ROI volume. These findings suggest that variation in the shape of certain ROIs implicated in reward processing is associated with weight status in adolescents. Our findings also suggest that the shape and volume of the NAc could be a neural correlate of the PFS warranting further investigation. These findings may elucidate an important neural link between weight status and reward processing that could help to inform obesity research in adolescents.

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Shame is a self-conscious emotion that characterizes the life of all individuals. It arises when a moral violation occurs and the person is judged negatively by others for a way of being that does not correspond to the standards of society. Although over the years it has been widely treated from a theoretical point of view, there are few attempts in the literature to approach it scientifically by psychologists and neuroscientists. Using an integrated approach, based on neuroimaging, behavioral and neuropsychological investigations, in this thesis we aimed to investigate what are the cognitive mechanisms through which shame operates and what are its neural bases. After an initial theoretical introduction in which a novel model of shame functioning is proposed, two behavioral studies are presented in which an innovative experimental paradigm of shame elicitation has been validated and tested. Subsequently, the single-case of a patient with rare bilateral amygdala damage has been described. Since this region is notoriously crucial for emotional aspects, we tested the possibility that an amygdala injury could also lead to deficits in perception and recognition of shame. Afterward, to investigate if shame had its own specific neural activation map, a meta-analysis on functional studies in the literature that investigated the neural bases of shame and guilt (another self-conscious emotion) has been carried out. Finally, given the heterogeneity of the paradigms included in the meta-analysis, we run an fMRI study using our novel paradigm in order to detect shame neural signal. In general, by combining different methodologies, this work allowed us to approach shame from different perspectives, from simple elicitation and behavioral measurement to its neural basis. This has added a piece of knowledge in the field of affective neuroscience regarding a moral emotion (i.e. shame) that is fundamental to individual well-being within our society.

Myelin facilitates efficient neural signal transmission along axons. While predominantly present in white matter, myelin is also found in smaller amounts in the outermost layer of gray matter, known as the cortex, as well as deep subcortical structures. Quantitative magnetic resonance imaging (qMRI) metrics, including longitudinal relaxation rate (R1), can report myelin levels in vivo, although these measures are often estimated and can vary depending on pulse sequences and acquisition parameters used to collect the data. Multi-site approaches can increase the statistical power and ecological validity of studies by recruiting participants from larger and more diverse samples, but considerable variability has previously been reported in qMRI estimates of myelin computed using data from different MRI scanners. Here, we assessed intra- and inter-vendor variability in R1 maps acquired at three sites using scanners from two manufacturers, General Electric (GE) and Siemens. Two ‘traveling heads’ scans, where a participant visits and completes a scan at each site, were acquired to directly assess site effects independent of biological variability. Histogram-based site-specific scaling factors determined from the ‘traveling heads’ scans were then applied to harmonize the main dataset. Before site correction, comparable inter- and intra-vendor differences were observed in both the main dataset and the ‘traveling heads’ scans. Our method of harmonization reduced the inter-site variability considerably, while remaining sensitive to age effects in R1. We then characterized age trajectories of R1 across the whole brain using linear regressions. In the age range of 16-36, age was significantly associated with mean R1s of bilateral putamen, left pallidum, and left amygdala, in line with past research. Cortical analyses also replicated earlier findings, with higher age associations in regions of the motor and lateral frontal cortices. The findings contribute to the growing research in multi-site harmonization, while providing normative estimates and trajectories of whole-brain R1s that can be referred to in future clinical studies. / Thesis / Master of Science (MSc) / Myelin is crucial for efficient signal transmission in nerve cells, and advancements in magnetic resonance imaging (MRI) have allowed us to indirectly estimate myelin levels in the brain. Collaborative multi-site investigations have become increasingly popular due to their ability to recruit larger and more diverse samples, making their findings more generalizable to the public. However, differences in scanner hardware and configurations across sites can introduce site-dependent biases to MRI scans. In this thesis, we found considerable inter-site variability in our whole-brain MRI-based estimate of myelin based on longitudinal relaxation rate (R1). We thus developed a method that can remove unwanted site-dependent differences from images by comparing repeated scans across sites. Using the corrected data, we showed how myelin amounts in different brain structures changes with age during early adulthood. Overall, we highlight the importance of carefully considering site-specific differences in multi-site MRI data and characterized how myelin changes with age in young adults.

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Thèse de doctorat présenté en vue de l'obtention du doctorat en psychologie - recherche intervention, option neuropsychologie clinique (Ph.D) / Selon les dernières estimations mondiales, plus de 43,3 millions d’individus seraient atteints d’une privation visuelle. Autrement dit, l’aptitude de ces individus à percevoir visuellement le monde et les détails qui le composent est presque ou totalement nulle. Bien que privés de l’un des sens les plus importants, ces derniers parviennent à s’adapter et interagir, de façon remarquable, avec l’environnement, et ce, en s’appuyant principalement sur leurs sens préservés. La navigation dans l’espace, la localisation et l’identification d’objets ou de personnes ainsi que la lecture ne sont que quelques exemples permettant d’illustrer la compensation comportementale réalisée par l’entremise des autres canaux sensoriels chez les individus atteints de cécité. L’accomplissement fructueux de telles activités nécessite certes un apprentissage chez les individus aveugles, mais permet également de mettre en lumière qu’au-delà d’une différence de perception visuelle, l’adaptation à une existence vécue dans l’obscurité la plus complète occasionne des changements dans le traitement de l’information en provenance des autres modalités sensorielles. Ces transformations comportementales, issues principalement de la réorganisation cérébrale occasionnée par un déficit perceptif, constitue un sujet d’intérêt pour la communauté scientifique depuis de nombreuses années. Bien que l’apparition des techniques d’imagerie cérébrale non-invasives a permis d’élucider jusqu’à présent de nombreux mystères concernant l’incroyable capacité du cerveau à se modifier sous l’effet de l’expérience, de nombreuses questions demeurent sans réponse. Ainsi, les articles composant cette thèse ont pour objectif principal de contribuer à l’état des connaissances actuelles concernant la réorganisation cérébrale chez les individus atteints de cécité, tant au niveau fonctionnel que structurel, et ce, afin de mieux saisir les répercussions de ces changements cérébraux sur le comportement des non-voyants. Plus particulièrement, nous avons souhaité investiguer l’impact de la privation visuelle précoce sur les régions cérébrales impliquées dans traitement des informations chimiosensorielles (olfactives et trigéminales). Pour ce faire, nous avons d’abord souhaité préciser les mécanismes de réorganisation cérébrale de type structurel prenant place au sein des régions traitant l’information de nature olfactive auprès d’aveugles congénitaux, et ce en comparaison à leurs pairs voyants. L’article 1 de cette thèse révèle que les individus aveugles présentent de multiples altérations cérébrales dans les régions composant le système olfactif. Bien que les aveugles congénitaux inclus dans notre étude présentent des volumes significativement réduits au niveau des bulbes olfactifs, du cortex orbitofrontal et du complexe parahippocampique, leurs performances olfactives, mesurées à l’aide d’épreuves standardisées, demeurent comparables à celles obtenues chez leurs pairs voyants. Nos résultats supportent ainsi la présence d’une réorganisation intramodale au sein du système olfactif chez les aveugles congénitaux, laquelle n’ayant aucune incidence mesurable sur leurs performances olfactive. D’autre part, nous avons souhaité explorer, par le biais de l’imagerie par résonnance magnétique fonctionnelle, si, tout comme pour le traitement de stimuli auditifs et tactiles, les régions habituellement dévolues au traitement visuel participaient, chez l’individu atteint cécité au traitement particulier d’une odeur. Plus précisément, l’article 2 de cette thèse révèle que les aveugles congénitaux sollicitent davantage leur cortex occipital que leurs pairs voyants lors d’une tâche de localisation d’odeurs. Toutefois, lorsque ces mêmes odeurs doivent être identifiées, aveugles et voyants présentent des niveaux d’activité cérébrales comparable dans les régions occipitales. Nos résultats supportent ainsi la présence d’un recrutement intermodal lors du traitement chimiosensoriel de différentes odeurs. Mis ensemble, ces résultats contribuent à une meilleure appréciation des changements cérébraux à la suite d’une privation visuelle, notamment en ce qui concerne les régions impliquées dans le traitement des informations de nature chimiosensorielle. Cette thèse doctorale s’inscrit de façon intéressante au sein des théories de la compensation comportementale présente chez l’individu aveugles, de même que les mécanismes sous-tendant la neuroplasticité structurelle et fonctionnelle des systèmes sensorielles. / According to the latest global estimates, more than 43.3 million people suffer from visual deprivation. In other words, the ability of these individuals to visually perceive the world and the details that compose it is almost or totally absent. Although deprived of one of the most important senses, they manage to adapt and interact with their environment, and this, by relying mainly on their remaining senses. Navigating in space, locating and identifying objects or people, and reading are just few examples that illustrate the behavioral compensation achieved through other sensory channels among individuals living with blindness. The successful accomplishment of such activities certainly requires learning or adaptation. However, it also highlights that beyond a difference in visual perception, adaptation to an existence lived in complete darkness causes changes in the processing of information from other sensory modalities. These behavioral transformations, resulting from the cerebral reorganization caused by a perceptual deficit, have been a subject of interest in the scientific community for many years. Although the emergence of non-invasive brain imaging techniques has, so far, elucidated many mysteries concerning the incredible capacity of the brain to change under the effect of experience, many questions remain unanswered. Thus, the articles included in this thesis have the main objective of contributing to the current knowledge of cerebral reorganization found in individuals living with blindness. More specifically, we wanted to investigate the impact of early visual deprivation on brain regions involved in the processing of chemosensory information (olfactory and trigeminal). To do this, we first evaluated the structural cerebral reorganization taking place among congenitally blind individuals within the olfactory regions. The first study of this thesis reveals that blind individuals present multiple cerebral alterations in the regions composing the olfactory system. More precisely, we found that congenitally blind individuals present significantly reduced olfactory bulb volume, as well as reduction in grey matter density in the orbitofrontal cortex and the parahippocampal complex. Despite this, their olfactory performances, measured using standardized tests, remain comparable to those obtained by their seeing counterparts. Therefore, our results support the presence in congenitally blind individuals of an intramodal reorganization within the olfactory system, which has no measurable impact on their olfactory performance. Through functional magnetic resonance imaging, we wanted to explore if regions that are usually devoted to visual processing are in congenitally blind individuals engaged for the processing of different components of an odor (i.e. olfactory and trigeminal components). More specifically, compared to their sighted counterparts, we found stronger activation in the occipital cortex of blind individuals during our odor localization task. However, when identifying the same odorants, blind and sighted individuals show comparable levels of brain activity in the occipital regions. Our results thus support the presence of cross-modal recruitment during the chemosensory processing of odors. Taken together, these results contribute to a better appreciation of cerebral changes following visual deprivation, particularly in regions involved for the processing of chemosensory information. In an interesting way, the results of this doctoral thesis fit some of the theories stated for blind individuals, such as the structural and functional neuroplasticity of sensory systems.

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