Ministère de l'Éducation nationale. Direction des Bibliothèques de France. Instructions sommaires sur l'organisation et le fonctionnement des bibliothèques publiques...

Comprend : Conservation des documents

Temporal dynamics of auditory what and where processing in humans

Recent evidence suggests the human auditory system is organized,like the visual system, into a ventral 'what' pathway, devoted toidentifying objects and a dorsal 'where' pathway devoted to thelocalization of objects in space w1x. Several brain regions have beenidentified in these two different pathways, but until now little isknown about the temporal dynamics of these regions. We investigatedthis issue using 128-channel auditory evoked potentials(AEPs).Stimuli were stationary sounds created by varying interaural timedifferences and environmental real recorded sounds. Stimuli ofeach condition (localization, recognition) were presented throughearphones in a blocked design, while subjects determined theirposition or meaning, respectively.AEPs were analyzed in terms of their topographical scalp potentialdistributions (segmentation maps) and underlying neuronalgenerators (source estimation) w2x.Fourteen scalp potential distributions (maps) best explained theentire data set.Ten maps were nonspecific (associated with auditory stimulationin general), two were specific for sound localization and two werespecific for sound recognition (P-values ranging from 0.02 to0.045).Condition-specific maps appeared at two distinct time periods:;200 ms and ;375-550 ms post-stimulus.The brain sources associated with the maps specific for soundlocalization were mainly situated in the inferior frontal cortices,confirming previous findings w3x. The sources associated withsound recognition were predominantly located in the temporal cortices,with a weaker activation in the frontal cortex.The data show that sound localization and sound recognitionengage different brain networks that are apparent at two distincttime periods.References1. Maeder et al. Neuroimage 2001.2. Michel et al. Brain Research Review 2001.3. Ducommun et al. Neuroimage 2002.

Contemporary engagements within corridors of the past: temporal elasticity, graffiti, and the materiality of St. Rock Street, Barcelona

In a medieval Barcelonan side-street, urine, rubbish, and a bewildering array of graphic imagery splatters the narrowing walls between two major thoroughfares. A contemporary conflict between residents, unknown artists and others is played out using banners, bottles, stickers, posters, stencils, spray paint, and bodily substances. In this shadowed liminality, local and global debates are superimposed upon substructures constructed from disease, prostitution, and the Saint of the Plague. The continuing urban struggle constitutes temporal statements of dirt and purity, violence and humour, dominance and resistance, death and salvation. Like the renovated facades masking the crumbling remains of structures long neglected, the government’s literal whitewashing of the art is a temporal cover-up of a discursive symptom stretching from deeply embedded preconditions. However, from his niche in the angular bend of the alley bearing his name, the statue of St. Rock remains unblinkingly staring, raised above the contestations expressed below.

Interhemispheric coupling between the posterior sylvian regions impacts successful auditory temporal order judgment.

Accurate perception of the temporal order of sensory events is a prerequisite in numerous functions ranging from language comprehension to motor coordination. We investigated the spatio-temporal brain dynamics of auditory temporal order judgment (aTOJ) using electrical neuroimaging analyses of auditory evoked potentials (AEPs) recorded while participants completed a near-threshold task requiring spatial discrimination of left-right and right-left sound sequences. AEPs to sound pairs modulated topographically as a function of aTOJ accuracy over the 39-77ms post-stimulus period, indicating the engagement of distinct configurations of brain networks during early auditory processing stages. Source estimations revealed that accurate and inaccurate performance were linked to bilateral posterior sylvian regions activity (PSR). However, activity within left, but not right, PSR predicted behavioral performance suggesting that left PSR activity during early encoding phases of pairs of auditory spatial stimuli appears critical for the perception of their order of occurrence. Correlation analyses of source estimations further revealed that activity between left and right PSR was significantly correlated in the inaccurate but not accurate condition, indicating that aTOJ accuracy depends on the functional decoupling between homotopic PSR areas. These results support a model of temporal order processing wherein behaviorally relevant temporal information--i.e. a temporal 'stamp'--is extracted within the early stages of cortical processes within left PSR but critically modulated by inputs from right PSR. We discuss our results with regard to current models of temporal of temporal order processing, namely gating and latency mechanisms.

Organisation of genetic variation in multinucleate arbuscular mycorrhizal fungi

Les Champignons Endomycorhiziens Arbusculaires (CEA) forment une symbiose racinaire avec environ 80% des espèces connues de plantes vasculaires. Ils occupent une position écologique très importante liée aux bénéfices qu'ils confèrent aux plantes. Des études moléculaires effectuées sur des gènes ribosomaux ont révélé un très grand polymorphisme, tant à l'intérieur des espèces qu'entre celles-ci. Ces champignons étant coenocytiques et multinucléés, l'organisation de cette variabilité génétique intraspécifique pourrait avoir différentes origines. Ce travail se propose d'examiner l'organisation et l'évolution de cette variabilité. Sur la base de fossiles, l'existence des CEA remonte à au moins 450 millions d'années. Cette symbiose peut donc être considérée comme ancienne. Les premières données moléculaires n'indiquant pas de reproduction sexuée, une hypothèse fut élaborée stipulant que les CEA seraient des asexués ancestraux. La première partie de cette thèse (chapitre 2) met en évidence l'existence de recombinaison dans différents CEA mais montre également que celle-ci est insuffisante pour purger les mutations accumulées. La reproduction étant essentiellement asexuée, on peut prédire que les nombreux noyaux ont probablement divergé génétiquement. En collaboration avec M. Hijri nous avons pu vérifier cette hypothèse (chapitre 2). Dans le chapitre 3 j'ai cherché à comprendre si le polymorphisme était également présent dans une population naturelle du CEA Glomus intraradices au niveau intraspécifique, ce qui n'avait encore jamais été examiné. En comparant les empreintes génétiques d'individus obtenus chacun à partir d'une spore mise en culture, j'ai clairement démontré que d'importantes différences génétiques existent entre ceux-ci. Un résultat similaire, portant sur des traits quantitatifs d'individus de la même population, a été trouvé par A. Koch. Les deux études en ensemble montre que le polymorphisme génétique dans cette population est suffisamment grand pour être important au niveau écologique. Dans le chapitre 4, j'ai cherché a examiner le polymorphisme des séquences du gène BiP au sein d'un individu. C'est la première étude qui examine la diversité génétique du génome de CEA avec un autre marqueur que l'ADN ribosomique. J'ai trouvé 31 types de séquences différentes du gène BiP issu d'un isolat de G. intraradices mis en culture à partir d'une seule spore. Cette variation n'était pas restreinte à des zones sélectivement neutres du BiP. Mes résultats montrent qu'il y a un grand nombre de variants non-fonctionnels, proportionnellement au faible nombre de copies attendues par noyau. Ceci va dans le sens d'une partition de l'information génétique entre les noyaux.<br/><br/>Arbuscular mycorrhizal fungi (AMF) are root symbionts with about 80% of all known species of vascular land plants. AMF are ecologically important because of the benefits that they confer to plants. Molecular studies on AMF showed that rDNA sequences were highly variable between species and within species. Because AMF are coenocytic and multinucleate there are several possibilities how this intraspecific genetic variation could be organized. Therefore, the organization and evolution of this variation in AMF were investigated in the present work. Based on fossil records the AMF symbiosis has existed for 450 Million years and is therefore considered ancient. First molecular data indicated no evident sexual reproduction and gave rise to the hypothesis that AMF might be ancient asexuals. The first part of this thesis (Chapter 2) shows evidence for recombination in different AMF but also indicates that it has not been frequent enough to purge accumulated mutations. Given asexual reproduction, it has been predicted that the many nuclei in AMF should diverge leading to genetically different nuclei. This hypothesis has been confirmed by an experiment of M. Hijri and is also included in chapter 2 as the results were published together. In chapter 3 I then investigated whether intraspecific genetic variation also exists in a field population of the AMF Glomus intraradices. Comparing genetic fingerprints of individuals derived from single spores I could clearly show that large genetic differences exist. A similar result, based on quantitative genetic traits, was found for the same population by A. Koch. The two studies taken together show that the genetic variation observed in the population is high enough to be of ecological relevance. Lastly, in chapter 4, I investigated within individual genetic variation among BiP gene sequences. It is the first study that has analyzed genetic diversity in the AMF genome in a region of DNA other than rDNA. I found 31 sequence variants of the BiP gene in one G. intraradices isolate that originated from one spore. Genetic variation was not only restricted to selectively neutral parts of BiP. A high number of predicted non-functional variants compared to a likely low number of copies per nucleus indicated that functional genetic information might even be partitioned among nuclei. The results of this work contribute to our understanding of potential evolutionary strategies of ancient asexuals, they also suggest that genetic differences in a population might be ecologically relevant and they show that this variation even occurs in functional regions of the AMF genome.

Variabilitat temporal i espacial en l'acumulació del sediment fi al riu Isàbena (Conca del Segre)

En aquest treball s’ha estudiat la variabilitat temporal i espacial en l’acumulació de sediment fi a la llera del riu Isàbena (Conca de l’Ebre) al llarg d’un any (1 de Juny de 2007 al 31 de maig de 2008) així com la seva relació amb l’arribada de sediments a l’embassament de Barasona, amb el mètode directe de camp, en aquest cas el cilindre de resuspensió. Aquesta tècnica s’ha aplicat a quatre seccions ubicades al tram baix de l’Isàbena. Amb les dades obtingudes, s’ha analitzat la dinàmica de les acumulacions a les diferents estacions de l’any, tractant de trobar patrons característics.