1,721,001 research outputs found
Exploration of epileptic networks by functional ultrasound imaging and electrophysiology
No full textLes épilepsies sont des hyperactivités neuronales pathologiques largement distribuées au sein du système nerveux. Aborder la question de l'organisation spatiotemporelle de ces crises est un premier pas crucial vers la dissection des mécanismes qui les sous-tendent. Alors qu'il existe de nombreux modèles d'hyperactivité épileptiforme, il est plus difficile d'étudier les crises spontanées, qui sont altérées par la sédation. Dans cette thèse, j'ai développé une approche combinant l'électroencéphalogramme (EEG) avec l'imagerie fonctionnelle ultrasonore (fUS), sur le rat mobile. Ainsi, sur un modèle d'épilepsie absence, j'ai pu enregistrer simultanément la survenue des crises et les variations hémodynamiques, marqueurs du métabolisme cellulaire. Le suivi additionnel de l'activité hémodynamique n'avait pas d'effet en soi sur l'occurrence et la durée des crises épileptiques. L'analyse des enregistrements a permis de mettre en évidence des corrélations entre les activités électriques et vasculaires durant les crises. Tandis que le thalamus présentait des zones d'hyperperfusion pendant les crises, le cortex présentait des corrélats variables suivant les aires, avec une hyperémie des aires somato-sensorielles accompagnée parfois d'une baisse de perfusion des tissus adjacents. La sensibilité du fUS a révélé, à partir d'événements uniques, qu'une série de pointe-ondes observée par une électrode EEG ne s'accompagne pas toujours d'une hyperactivité vasculaire au même endroit. Ainsi, cette approche permet de délimiter le contour des aires présentant une activité vasculaire pendant les crises et montre une dichotomie partielle entre les composantes électriques et vasculaires des crises.Epilepsies consist in neuronal hyperactivities distributed across the nervous system that need first to be located in order to later decipher the mechanisms of these pathologies. While there are many models of epileptiform hyperactivity, it is more difficult to study spontaneous seizures, which are altered by sedation. In this thesis, I developed an approach that combines electroencephalography (EEG) and functional ultrasound imaging (fUS), on the mobile rat. Thus, on a model of absence epilepsy, I could record simultaneously the occurrence of seizures and the hemodynamic variations, which reflect cellular metabolism. Seizures were unaltered by the recording protocol, compared to rats with EEG alone. Correlations were observed between electric and vascular activities. The thalamus showed areas of hyperperfusion during seizures. The cortex exhibited different correlates in distinct areas, with hyperaemia in somato-sensory areas, occasionally associated with a decrease in perfusion in adjacent tissue. The sensitivity of fUS, which could resolve blood changes from single occurrences, revealed that series of spike-wave discharges recorded from an EEG electrode were not always associated with vascular hyperactivity in the same region. Thus, this approach can delimit the contour of areas presenting vascular activity during seizures and shows a partial dichotomy between the electric and vascular components of seizures
Responses of cortical circuits to subcortical inputs involved in the modulation of vigilance states
No full textAu cours de cette thèse, j’ai cherché à comprendre comment trois structures impliquées dans la modulation des états vigilance agissaient sur la dynamique du réseau cortical. Les noyaux du thalamus non-spécifique sont impliqués dans le transfert d’informations contextuelles. À l’inverse, les noyaux spécifiques convoient des informations sensorielles vers le néocortex. Ces entrées sensorielles activent fortement les interneurones fast-spiking du cortex qui limite la durée de l’activation du réseau. À l’inverse, mes travaux montrent que les entrées contextuelles entraînent l’activation des interneurones lents, générant une activation prolongée du réseau cortical. D’autre part, je me suis intéressée à la couche VIb du néocortex dont les neurons sont sensibles à deux modulateurs des états de vigilance : l’orexine et à l’acétylcholine. J’ai pu montrer que la couche VIb projette principalement dans les couches corticales infragranulaires où elle pourrait être servir d’amplificateur dépendant de l’orexine des entrées du thalamus non-spécifique. Finalement, j’ai cherché à comprendre si la transmission nicotinique endogène était médiée par une synapse ou par transmission volumique. Pour cela, j’ai comparé les courants nicotinques reçus par les neurones des couches I et VI. Mes travaux mettent en évidence l’existence d’une synapse mixte comprenant des récepteurs α4β2 et α7 dans la couche I et d’une synapse simple comprenant uniquement α4β2 en couche VI. Ces synapses sont activées par la stimulation phasique des neurones cholinergiques. Néanmoins mes résultats suggèrent aussi l’existence de récepteurs α4β2 extra-synaptiques activés par la libération tonique des fibres cholinergiques.During my PhD, I investigated how three structures involved in the modulation of arousal states act on the dynamic of the cortical network. Nuclei of the non-specific thalamus convey information on environmental and behavioral context, whereas specific nuclei relay sensory information to the neocortex. These sensory inputs activate strongly the fast-spiking interneurons of the neocortex that limits response duration of the network. Conversely, I showed that contextual inputs target mainly the slow adapting interneurons allowing a long-lasting activation of the cortical network. I have also been interesting in the layer VIb of the neocortex whose neurons are sensitive to orexin and acetylcholine, two main modulators of the arousal states. I showed that layer VIb projects mainly onto infragranular cortical layers where its activation should act as an orexin-dependent amplifier of the non-specific thalamic inputs. Finally, I tried to decipher whether the endogenous nicotinic transmission is mediated by a synapse or by volume transmission. To do that, I compared nicotinic currents received by layer I interneurons and layer VI pyramidal cells. I showed that nicotinic transmission is likely to be mediated by a mixed synapse comprising α4β2 and α7 receptors in layer I and a simple α4β2 containing synapse in layer VI. These synapses are activated by a phasic stimulation of the cholinergic fibers. However, my results also suggest that a tonic activation of these fibers recruits extra-synaptic α4β2 receptors in both layer I and VI neurons
Control of perineuronal net by the activity of cortical fast-spiking parvalbumin interneurons
No full textLa fermeture des périodes critiques est marquée par deux événements concomitants: la formation d'une matrice extracellulaire spécialisée, le «perineuronal net» (PNN), qui entoure les interneurones à parvalbumine dits fast-spiking (FS-PV) et l'import de l’homéoprotéine OTX2 dans ces neurones. Le PNN apparaît comme un facteur limitant la plasticité des cartes corticales chez l’adulte. La digestion enzymatique de celui-ci permet la réouverture de cette plasticité. L’inhibition spécifique des FS-PV, réinstaure une plasticité corticale élevée chez l’adulte qui pourrait être liée à un changement du PNN. A ce jour le lien entre l’activité des FS-PV et la régulation du PNN chez l’adulte restent inconnus. Ma thèse vise à déterminer : (i) les effets de la manipulation de l’activité des FS-PV sur la densité de PNN dans le cortex visuel de la souris adulte et (ii) si elles expriment les protéines nécessaires au remodelage du PNN. Nous avons montré que l’inhibition chemogénétique ciblée des FS-PV ou des cellules pyramidales voisines réduit fortement le PNN. La surexcitation du réseau n’affecte pas le PNN. Ces résultats combinés à la caractérisation électrophysiologique réalisée par patch-clamp ou par EEG, démontre que la désinhibition du réseau n’est pas à l’origine de la régression du PNN. De plus nos résultats semblent indiquer que chaque cellule FS-PV régule son propre PNN, comme le démontre leur profil d’expression des gènes liés au PNN. En conclusion, ces résultats novateurs montrent qu’une diminution de l’activité des FS-PV directement ou via l’inhibition des cellules pyramidales voisines permet de réduire la densité de PNN chez l’adulte.The closure of the highly plastic period, called critical period, is concomitant with the accumulation of a specialized extracellular matrix, the perineuronal net (PNN), around fast-spiking inhibitory interneurons that express parvalbumin (FS-PV). The PNN limits the plasticity of cortical maps in the adult, and its enzymatic digestion allows the reopening of cortical maps plasticity. The specific inhibition of FS-PV interneurons, reinstates high cortical plasticity, which may be linked to changes in the PNN. To date, the link between FS-PV cell activity and the regulation of PNN density in the adult remains unexplored. My thesis project aims to determine (i) what are the effects of the manipulation of FS-PV activity on PNN density in the primary visual cortex of adult mice and (ii) if FS-PV interneurons express keys proteins to remodel the PNN. We found that targeted chemogenetic inhibition of FS-PV interneurons or of neighboring pyramidal cells strongly reduces the PNN in adult mice. Overexcitation of the network does not affect the PNN. These results combined with electrophysiological characterization performed using patch-clamp or using EEG recordings, show that network disinhibition is not the trigger of PNN regression. Interestingly, our results suggest that each FS-PV cells is able to regulate its own PNN supported by our results of the expression pattern of PNN-related genes found in FS-PV interneurons. To conclude, our results show that a decrease of FS-PV cells activity, directly or through inhibition of nearby pyramidal cells, reduces PNN density in the adult. These results are innovative and deepen our understanding of PNN regulation mechanisms in adults
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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