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No / Area V3A was identified in five human subjects on both a functional and retinotopic basis using functional magnetic resonance imaging techniques. V3A, along with other visual areas responsive to motion, was then targeted for disruption by repetitive transcranial magnetic stimulation (rTMS) whilst the participants performed a delayed speed matching task. The stimuli used for this task included chromatic, isoluminant motion stimuli that activated either the L-M or S-(L+M) cone-opponent mechanisms, in addition to moving stimuli that contained only luminance contrast (L+M). The speed matching task was performed for chromatic and luminance stimuli that moved at slow (2 degrees/s) or faster (8 degrees/s) speeds. The application of rTMS to area V3A produced a perceived slowing of all chromatic and luminance stimuli at both slow and fast speeds. Similar deficits were found when rTMS was applied to V5/MT+. No deficits in performance were found when areas V3B and V3d were targeted by rTMS. These results provide evidence of a causal link between neural activity in human area V3A and the perception of chromatic isoluminant motion. They establish area V3A, alongside V5/MT+, as a key area in a cortical network that underpins the analysis of not only luminance but also chromatically-defined motion.

Afrikaans text / Curriculum and Instructional Studies / M. Ed. (Didaktiek)

INTRODUÇÃO: Os fatores de risco cardiovascular (FRCV) afetam o fluxo sanguíneo cerebral, contribuindo possivelmente para o declínio cognitivo e a emergência da Doença de Alzheimer (DA), a forma mais comum de demência. A tomografia por emissão de pósitrons (positron emission tomography, PET) com fluordesoxiglucose F18 (18F-FDG) é largamente usada para demonstrar o padrão específico de metabolismo cerebral de glicose reduzido em sujeitos com DA e em indivíduos não-demenciados portadores do alelo e4 da apolipoproteína E (APOE e4), o maior fator de risco genético para DA. Entretanto, estudos de PET investigando o impacto dos FRCV no metabolismo cerebral são escassos. OBJETIVO: Examinar se níveis diferentes de FRCV estariam associados com reduções na taxa de metabolismo cerebral de glicose (TMCG), envolvendo as regiões cerebrais afetadas nos estágios iniciais da DA (pré-cúneo e giro do cíngulo posterior, neocórtex parieto-temporal lateral e região hipocampal). MÉTODOS: Nós avaliamos 59 indivíduos cognitivamente preservados (66-75 anos) subdivididos em três grupos de acordo com seu escore para Framingham Coronary Heart Disease Risk (FCHDR) (alto-risco, médio-risco e baixo-risco) para os exames de ressonância magnética (RM) e de PET-FDG. Dados de PET foram corrigidos para os efeitos de volume parcial a fim de evitar efeitos confundidores devido à atrofia cerebral regional. Nós realizamos uma análise de covariância global (ANCOVA) para investigar as reduções de TMCG em associação com os três grupos, comparações entre dois grupos para as diferenças de TMCG pelo teste-t, e índices de correlação linear voxel-a-voxel entre os valores de TMCG e escores FCHDR. Todas as análises incluíram a presença ou a ausência do APOE e4 como covariada confundidora de interesse. RESULTADOS: A investigação ANCOVA de diferenças de TMCG entre os três grupos mostraram significantes diferenças de TMCG somente no giro parahipocampal direito (p=0,032). Nas comparações entre dois grupos, reduções de TMCG significantes foram detectadas no grupo de altorisco comparado ao baixo-risco no pré-cúneo esquerdo (p=0,008) e o giro do cíngulo posterior esquerdo (p=0,007). Focos inesperados de reduções de TMCG no grupo baixo-risco comparado ao grupo alto-risco no giro parahipocampal foram detectados em ambos os hemisférios direito (p=0,001) e esquerdo (p=0,045). Havia também uma significante correlação linear positiva entre valores de TMCG e escores FCHDR no giro parahipocampal em ambos os lados direito (p=0,007) e esquerdo (p=0,025). CONCLUSÃO: Depois de controlar para a presença do APOE 4, nossos achados de hipofunção cerebral regional relacionado a FRCV mantiveram a significância estatística no pré-cúneo e no giro do cíngulo posterior, as duas regiões cerebrais onde comprometimentos funcionais são os mais consistentemente detectados nos estágios incipientes da DA. Isso sugere que os achados de hipometabolismo cerebral similares àqueles vistos nos sujeitos com DA podem ser vistos em associação com a gravidade de FRCV em amostras de indivíduos cognitivamente preservados. Uma possível explicação para o hipermetabolismo relativo no giro parahipocampal nos indivíduos com elevados FRCV seria um viés na seleção da amostra. É possível que nós tenhamos excluídos os sujeitos com os níveis mais graves de risco cardiovascular que teriam exibido os padrões de reduções de TMCG no giro parahipocampal, forçando a seleção de indivíduos que estão para o alto risco cardiovascular, mas que são capazes de exibir mecanismos compensatórios para manter o funcionamento metabólico adequado para as regiões temporolímbicas, as quais são vulneráveis às mudanças microvasculares / INTRODUCTION: Cardiovascular risk factors (CVRF) are known to affect cerebral blood flow, possibly contributing to cognitive decline and to the emergence of Alzheimers disease (AD), the commonest form of dementia. Positron emission tomography (PET) with 18-fluoro-2-deoxyglucose (18FFDG) has been widely used to demonstrate specific patterns of reduced brain glucose metabolism in AD subjects and in non-demented individuals carriers of the apolipoprotein e4 allele (APOE e4), the major genetic risk factor for DA. However, PET studies investigating the impact of CVRF on cerebral metabolism have been scarce to date. OBJECTIVE: To examine whether different levels of CVRF would be associated with cerebral metabolic rate of glucose (CMRgl) reductions, involving brain regions affected in early stages of DA (precuneus and posterior cingulate gyrus, lateral temporalparietal neocortices and hippocampal region). METHODS: We assessed 59 cognitively preserved individuals (66-75 years), subdivided into three groups according to their Framingham Coronary Heart Disease Risk (FCHDR) score (high-risk, medium-risk, and low-risk), both with magnetic resonance imaging (MRI) and FDG-PET scans. PET data were corrected for partial volume effects to avoid confounding effects due to regional brain atrophy. We performed an overall analysis of covariance (ANCOVA) to investigate CMRgl reductions in association with the three groups, two-group comparisons of CMRgl differences by t-tests, and voxelwise linear correlation indices between CMRgl values and FCHDR scores. All analysis included the presence or absence of the APOE 4 allele as a confounding covariate of interest. RESULTS: The ANCOVA investigation of CMRgl differences across the three groups showed significant CMRgl differences only in the right parahippocampal gyrus (p=0.032). In the two-group comparisons, significant CMRgl reductions were detected in the high-risk group compared to the lowrisk group in the left precuneus (p=0.008); and the left posterior cingulate gyrus (p=0.007). Unexpected foci of CMRgl reductions in the low-risk compared to the high-risk group in the parahippocampal gyrus were detected, both on the right (p=0.001) and left (p=0.045) hemispheres. There was also a significant positive linear correlation between CMRgl values and FCHDR scores in the parahippocampal gyrus both for the right (p=0.007) and left (p=0.025) sides. CONCLUSION: After controlling for the presence of the APOE 4 allele, our findings of CVRF-related regional brain hypofunction retained statistical significance in the precuneus and posterior cingulate gyrus, the two brain regions where functional impairments are most consistently detected in incipient stages of AD. This suggests that findings of brain hypometabolism similar to those seen in AD subjects can be seen in association with the severity of CVRF in samples of cognitively preserved individuals. One possible explanation for the relative hypermetabolism in the parahippocampal gyrus in high CVRF individuals would be a bias in the sample selection. It is possible that we have excluded subjects with severest levels of cardiovascular risk who would have displayed patterns of reduced CMRgl in the parahippocampal gyrus, forcing the selection of individuals who are at high cardiovascular risk but are capable of displaying compensatory mechanisms to maintain adequate metabolic functioning in temporolimbic regions vulnerable to microvascular changes

Natural surfaces are usually associated with feature graphs, such as the cortical surface with anatomical atlas structure. Such a feature graph subdivides the whole surface into meaningful sub-regions. Existing brain mapping and registration methods did not integrate anatomical atlas structures. As a result, with existing brain mappings, it is difficult to visualize and compare the atlas structures. And also existing brain registration methods can not guarantee the best possible alignment of the cortical regions which can help computing more accurate shape similarity metrics for neurodegenerative disease analysis, e.g., Alzheimer’s disease (AD) classification. Also, not much attention has been paid to tackle surface parameterization and registration with graph constraints in a rigorous way which have many applications in graphics, e.g., surface and image morphing. This dissertation explores structural mappings for shape analysis of surfaces using the feature graphs as constraints. (1) First, we propose structural brain mapping which maps the brain cortical surface onto a planar convex domain using Tutte embedding of a novel atlas graph and harmonic map with atlas graph constraints to facilitate visualization and comparison between the atlas structures. (2) Next, we propose a novel brain registration technique based on an intrinsic atlas-constrained harmonic map which provides the best possible alignment of the cortical regions. (3) After that, the proposed brain registration technique has been applied to compute shape similarity metrics for AD classification. (4) Finally, we propose techniques to compute intrinsic graph-constrained parameterization and registration for general genus-0 surfaces which have been used in surface and image morphing applications.

Diss. (sammanfattning) Umeå : Umeå universitet, 2009. / Härtill 3 uppsatser. Även tryckt utgåva.

Resting state functional magnetic resonance imaging (fMRI) is currently at the forefront of research on cognition and the brain’s large-scale organization. Patterns of hemodynamic activity that it records have been strongly linked to certain behaviors and cognitive pathologies. These signals are widely assumed to reflect local neuronal activity but our understanding of the exact relationship between them remains incomplete. Researchers often address this using multimodal approaches, pairing fMRI signals with known measures of neuronal activity such as electroencephalography (EEG). It has long been thought that infraslow (< 0.1 Hz) fMRI signals, which have become so important to the study of brain function, might have a direct electrophysiological counterpart. If true, EEG could be positioned as a low-cost alternative to fMRI when fMRI is impractical and therefore could also become much more influential in the study of functional brain networks. Previous works have produced indirect support for the fMRI-EEG relationship, but until recently the hypothesized link between them had not been tested in resting humans. The objective of this study was to investigate and characterize their relationship by simultaneously recording infraslow fMRI and EEG signals in resting human adults. We present evidence strongly supporting their link by demonstrating significant stationary and dynamic correlations between the two signal types. Moreover, functional brain networks appear to be a fundamental unit of this coupling. We conclude that infraslow electrophysiology is likely playing an important role in the dynamic configuration of the resting state brain networks that are well-known to fMRI research. Our results provide new insights into the neuronal underpinnings of hemodynamic activity and a foundational point on which the use of infraslow EEG in functional connectivity studies can be based.

Diss. (sammanfattning) Umeå : Univ., 2005. / Härtill 5 uppsatser.

La mentalisation, ou la capacité d’élaborer des hypothèses sur les états mentaux d’autrui, a fait l’objet de nombreuses études durant les 20 dernières années dans le champ des neurosciences sociales. Toutefois, les bases neurales de cette fonction particulièrement complexe restent mal comprises, notamment en termes de connectivité structurale. Récemment, une organisation anatomo-fonctionnelle en double voie a été proposée. Selon ce modèle, les aspects réflexifs, inférentiels, de la mentalisation seraient sous-tendus par le faisceau cingulaire. Les aspects préréflexifs, identificatoires, seraient médiés, quant à eux, par le complexe faisceau arqué/partie latérale du faisceau longitudinal supérieur (FLS). L’objectif général de ce travail est d’apporter des données originales sur l’organisation anatomo-fonctionnelle du réseau neural impliqué dans la mentalisation basée sur les visages. Pour ce faire, nous avons utilisé comme modèle physiopathologique d’étude le gliome diffus de bas grade. Cette tumeur cérébrale primitive s’avère particulièrement intéressante pour l’étude du rôle de la substance blanche dans la cognition et ce pour deux raisons : (i) les cellules tumorales se propagent préférentiellement le long des fibres blanches ; (ii) l’exérèse chirurgicale est souvent réalisée en condition éveillée avec cartographie fonctionnelle peropératoire pour permettre d’identifier, et ainsi de préserver, les structures fonctionnelles, notamment de substance blanche.Dans une première étude, grâce aux stimulations électriques peropératoires, nous avons pu identifier un vaste réseau cortico-sous-cortical impliqué dans la mentalisation. L’analyse des déconnexions induites par les stimulations de la substance blanche nous a permis de mettre clairement en évidence, et ce pour la première fois, le rôle du faisceau occipito-frontal inférieur (FOFI) tout en confirmant celui du FLS. Dans une deuxième étude, en utilisant des techniques de cartographie lésionnelle chez des patients ayant été opérés, nous avons démontré que les troubles permanents, non compensables, de la mentalisation étaient expliqués par l’atteinte du faisceau arqué. Enfin, dans une dernière étude, en combinant l’imagerie par résonance magnétique fonctionnelle de repos (IRMfr) et les sites corticaux démasqués pendant la chirurgie, nous avons pu générer de véritables cartographies fonctionnelles du réseau cortical de la mentalisation, très similaires à celles observées en imagerie fonctionnelle classique.De façon générale, nos découvertes suggèrent que la mentalisation basée sur les visages reposerait sur l’intégrité d’au moins deux faisceaux associatifs de substance blanche. Elles permettent également de valider l’utilisation combinée de l’IRMfr et des stimulations corticales en tant qu’approche originale pour cartographier les réseaux neurocognitifs.En plus de ces considérations fondamentales, nos résultats ont des implications cliniques, notamment pour la cartographie fonctionnelle peropératoire. Ils permettent en outre de mieux comprendre les pathologies cérébrales caractérisées par un trouble de la mentalisation et une atteinte des voies de substance blanche. / Mentalizing, or the ability of human beings to make assumptions about other people’s mental states, has been the subject of many studies over the last 20 years. The neural bases and especially the white matter connectivity of this complex cognitive function is still poorly understood. Recently, an anatomo-functional organization into two neural pathways has been proposed. According to this model, it is assumed that the reflective, inferential aspects of mentalizing is underpinned by the cingulum. The reflexive, identificatory aspects of mentalizing are thought to be mediated, for their part, by the arcuate fascicle and the lateral part of the superior longitudinal fascicle. The main purpose of this scientific work is to provide original data on the anatomo-functional organization of the neural network involved in the face-based mentalizing. We used as a pathophysiological study model diffuse low-grade gliomas. These primary brain tumors are particularly interesting for the study of the functional role of the white matter for two reasons: (i) the tumor cells propagate preferentially along the white matter fibers; (ii) the surgical resection is often performed in awake condition with intraoperative functional mapping to identify, and thus to preserve functional structures, including the white matter.In our first study, using intraoperative electrical stimulation, we were able to identify a large cortico-subcortical mentalizing network. The analysis of the disconnections induced by the stimulation of the white matter allowed us to clearly highlight, for the first time, the role of the inferior fronto-occipital fascicle. We also confirmed the already established role of the superior longitudinal fascicle in mentalizing. In a second study, using lesion mapping analyses in patients operated on for a diffuse low-grade glioma, we demonstrated that the long-term, non-compensatory mentalizing deficit was explained by the involvement of the arcuate fascicle. Finally, in a third study combining resting-state functional MRI and the cortical sites unmasked during surgery, we were able to identify a large cortical mentalizing networks, which were very similar to those identified by classical task-based functional imaging.In general, our findings suggest that the face-based mentalizing would require the integrity of at least two associative white matter fascicles. They also validate the combined use of resting-state functional MRI and direct cortical stimulations as an original approach to map neurocognitive networks.In addition to these fundamental considerations, our results have also clinical implications, especially regarding the intraoperative functional mapping. They also provide a better understanding of brain pathologies characterized by both mentalizing deficit and white matter impairment.

Afrikaans text / Curriculum and Instructional Studies / M. Ed. (Didaktiek)