Sensory neurons assemble to form networks that process inputs coming from the senses. Through synaptic connections neurons interact and create complex dynamical states in response to these inputs. Networks with different connectivity patterns are thought to display different states and therefore subserve different computational goals. In this thesis, we mainly study brain rhythms, a dynamical state that occurs in various neural structures. Rhythms are emergent oscillations that typically occur in homogeneous recurrent networks, whose neurons have identical properties and are densely interconnected. Many sensory systems comprise neurons with opposite ON and OFF responses to inputs. We show that homogenous recurrent networks fail to sustain rhythms when ON and OFF neurons are present in equal proportions. This happens even when the network is subjected to spatially correlated inputs, which are known to promote synchronized oscillations. In this context, we adapted the so-called linear response theory to include networks containing ON and OFF neurons with different intrinsic properties. In this asymmetric case, oscillations can be recovered. A simpler approach is to segregate the ON and OFF populations, thus producing two oscillating subnetworks. The dynamics of purely feedforward networks are studied next. These networks are composed of two or more populations. The populations are connected in a serial fashion, but neurons are unconnected within the populations. This connectivity scheme is drastically different from the fully recurrent network. Yet, this network is shown to display oscillatorylike properties when subjected to spatially correlated stimulation under certain conditions. We also find that this network can implement various types of gain control, depending on the noise in the system and the strength of synaptic interactions. These results establish some unexpected links between feedforward and recurrent networks. Along the way, we apply our results and conclusions to a well-characterized sensory network, the electrosensory system of weakly electric fish.

No description available.

Controlled Exposure Experiments revealed lesions in the statocysts of four cephalopod species of the Mediterranean Sea (Sepia officinalis, Loligo vulgaris, Illex coindetii and Octopus vulgaris), when exposed to relatively low intensity low frequency sounds. The analysis was performed through: scanning (SEM) and transmission (TEM) electron microscopy techniques of the whole inner structure of the cephalopod statocysts, especially on macula and crista; SEM of the epidermal lines of cephalopod hatchlings; and proteomic studies (2DE/MALDI –MS) of the statocyst’s endolymph. All exposed adult individuals presented the same lesions and the same incremental effects over time, consistent with a massive acoustic trauma observed in land species that were exposed to much higher intensities of sound. Immediately after exposure, the damage was observed in the macula statica princeps (msp) and in the crista sensory epithelium. Kinocilia on hair cells were either missing or were bent or flaccid. A number of hair cells showed protruding apical poles and ruptured lateral plasma membranes, most probably resulting from the extrusion of cytoplasmic material. Hair cells were also partially ejected from the sensory epithelium, and spherical holes corresponding to missing hair cells were visible in the epithelium. The cytoplasmic content of the damaged hair cells showed obvious changes, including the presence of numerous vacuoles and electron dense inclusions not seen in the control animals. The appearance of these lesions became gradually more pronounced in individuals after 12, 24, 48, 72, and 96 hours. Special attention was given to validate these findings with control animals that were caught, maintained and sequentially sacrificed following the same protocol as the exposed individuals. The statocyst ultrastructure was therefore revisited and a comparative analysis was carefully conducted to assess the lesions triggered by the exposure to noise This study also presents preliminary results of the sound effects on epidermal lines of cephalopod hatchlings. The lesions, consistent with an acoustic trauma, were identic in the three species that were exposed, but their evolution over time, in opposition with what was observed in the statocysts, were different, suggesting that the animal size and metabolic response might play a role in a possible recovery process. The analysis of noise effects in the statocyst endolymph by proteomic techniques was only conducted on Sepia officinalis. The presence of differential staining of gels from control and subjected to sound exposure individuals demonstrate that the injuries could be related to a possible physiological imbalance that would affect the protein levels of the endolymph. The lesions and findings described here are new to cephalopod pathology. Given that lowfrequency noise levels in the ocean are increasing (e.g. due to shipping, offshore industry, and naval maneuvers), that the role of cephalopods in marine ecosystems is only now beginning to be understood, and that reliable bioacoustic data on invertebrates are scarce, the present study and future investigations will bring an important contribution to the sustainable use of the marine environment. / Després de sotmetre'ls a experiments d'exposició controlada a sons de baixa intensitat i baixa freqüència es van observar lesions en els estatocists de quatre espècies de cefalòpodes de la mar Mediterrània (Sepia officinalis, Loligo vulgaris, Illex coindetii i Octopus vulgaris). L'anàlisi es va realitzar per mitjà de de microscòpia electronica d'escombratge (SEM) i de transmissió (TEM) de tota l'estructura interna de l'estatocist dels cefalòpodes, especialment en la màcula i en la crista, per SEM de les línees epidèrmiques de les larves dels cefalòpodes i per tècniques de proteòmica (2DE/MALDI-MS), de l'endolimfa de l'estatocist. Tots els estatocists d'individus adults de cefalòpodes exposats presentaven les mateixes lesions i aquests efectes eren més greus a mesura que passava el temps després de l'exposició als sons. Tots els animals exposats al soroll van mostrar lesions consistens amb trauma acústic massiu observat en altres espècies terrestres que havien estat exposades a intensitats molt més altes de so. Immediatament després de l'exposició, es van observar danys a la macula statica princeps (msp) i en l'epiteli sensorial de la crista. Els quinocilis de les cèl·lules ciliades desapareixien o es doblegaven i es tornaven flàccids. Un nombre important de cèl·lules ciliades mostraven els pols apicals sobresortint de l'epiteli sensorial, així com el trencament de les membranes plasmàtiques laterals, molt probablement com a resultat de l'extrusió de material citoplasmàtic. Les cèl·lules ciliades també van ser parcialment expulsades de l'epiteli sensorial deixant visibles forats esfèrics en el mateix. El contingut citoplasmàtic de les cèl·lules ciliades danyades va mostrar canvis obvis, com ara la presència de nombrosos vacúols i inclusions electrodenses que no es veien en els animals control. L'aparició d'aquestes lesions es va tornar gradualment més pronunciada en els individus analitzats després de 12, 24, 48, 72 i 96 hores. Es van validar curosament aquests resultats per mitjà de la comparació amb els animals control que van ser capturats, mantinguts i sacrificats de forma seqüencial seguint el mateix protocol que els individus exposats. La ultraestructura de l'estatocist va ser revisada i es va dur a terme un curós anàlisi comparatiu per tal d'avaluar les lesions provocades per l'exposició al soroll. Aquest estudi també presenta els resultats preliminars dels efectes del so en les línies epidèrmiques de cefalòpodes recent nascuts. Les lesions, consistens amb trauma acústic, eren idèntiques en les tres espècies que van ser exposades, però la seva evolució en el temps, en oposició amb el que es va observar en els estatocists, era diferent, cosa que suggereix que la grandària dels animals i la resposta metabòlica podria tenir influència en un possible procés de recuperació. L'avaluació dels efectes en l'endolimfa de l'estatocist per tècniques de proteòmica es va dur a terme només en Sepia officinalis. La presència de taques diferencials en els gels dels individus control i els sotmesos a exposició a so demostren que les lesions podrien estar relacionades amb un possible desequilibri fisiològic que tindria repercusions en els nivells proteics de l'endolimfa. Les lesions descrites aquí són noves pel que fa a la patologia dels cefalòpodes. Atès que els nivells de soroll de baixa freqüència a l'oceà estan augmentant (per exemple, a causa del transport, la indústria petrolera i les maniobres navals), que el paper dels cefalòpodes en els ecosistemes marins només ha començat a ser entès recentment, i que les dades bioacústiques fiables sobre els invertebrats són escasses, el present estudi i les investigacions futures aportaran una important contribució a l'ús sostenible del medi marí.

The current human-created division between the natural and built environments has exacerbated environmental problems because nature has been designed as and, consequently, is seen as an Other to be utilized and manipulated at will. Exploring this disconnected relationship between humans and nature, as well as its origin and its effect on building occupants and the environment, is thus a necessary part of this project. The primary concern, however, centers on how we can establish a relationship with the natural environment through interior design to help foster ecological design practices and positive environmental behaviors that move beyond sustainability, resulting in a positive human-nature relation while supporting a coevolutionary perspective. Specifically, this investigation utilizes biophilic design as a solution to the division. The product is an adaptively reused structure that houses a mixed-use, multi-unit residential development, which explores the creation of human-nature connections through direct, indirect, and symbolic means.

The current human-created division between the natural and built environments has exacerbated environmental problems because nature has been designed as and, consequently, is seen as an Other to be utilized and manipulated at will. Exploring this disconnected relationship between humans and nature, as well as its origin and its effect on building occupants and the environment, is thus a necessary part of this project. The primary concern, however, centers on how we can establish a relationship with the natural environment through interior design to help foster ecological design practices and positive environmental behaviors that move beyond sustainability, resulting in a positive human-nature relation while supporting a coevolutionary perspective. Specifically, this investigation utilizes biophilic design as a solution to the division. The product is an adaptively reused structure that houses a mixed-use, multi-unit residential development, which explores the creation of human-nature connections through direct, indirect, and symbolic means.

Les projections corticales de retour conduisent l'information vers des relais de traitement de l'information plus précoces. Elles sont essentielles pour la perception sensorielle. En ce qui concerne l'olfaction, l'information sensorielle est constituée d'une multitude de molécules odorantes, et c'est ce mélange complexe qui pénètre dans la cavité nasale. En fonction du contexte, c'est une partie ou une autre de cet ensemble de molécules qui va être importante d'un point de vue comportemental. Les signaux corticaux de retour permettraient de focaliser son attention sur les odeurs pertinentes de l'environnement. Au cours de mon doctorat, j'ai étudié le rôle de la signalisation inhibitrice GABAergique dans ces retours corticaux vers le bulbe olfactif, le premier relais de l'information olfactive. La première partie de mon travail a mis en évidence une modulation métabotropique GABAergique du retour cortical excitateur. Nos expériences caractérisent ensuite l'effet produit par cette modulation sur le bulbe olfactif. Nous avons ainsi démontré que la signalisation GABAergique au niveau de retours corticaux change de manière profonde la réponse du bulbe olfactif aux stimuli olfactifs. Dans un deuxième temps, j'ai trouvé que le cortex olfactif envoie non seulement des projections de retour excitatrices, mais aussi des retours inhibiteurs. Des expériences précisent ensuite la localisation de ce retour GABAergique, ainsi que son impact sur le bulbe olfactif. Nous avons notamment observé qu'en manipulant l'activité de ces fibres GABAergiques, nous pouvions modifier le comportement olfactif. / Cortical feedback conducts information towards earlier relays of information processing. It is instrumental for sensory perception. In the olfactory system, odorants are never experienced in isolation by the nose, and they might be meaningful to the animal or not depending on the context. Feedback inputs onto early processing stages are poised to permit selective attention to the relevant odorants in the olfactory scene. During my thesis work, I focused on understanding the key role that inhibitory GABAergic signaling plays in the cortical feedback to the olfactory bulb in mice.The first part of my work started with the discovery of excitatory transmission between cortical feedback inputs and the olfactory bulb is modulated by metabotropic receptors for GABA. Next, the impact of this regulation on the olfactory bulb network was investigated. We found that GABAergic signaling at cortical feedback axons profoundly changes the response of the olfactory bulb output cells to odor stimulation. In the second part of my thesis, I found that the cortical projections to the olfactory bulb not only comprises of excitatory components, but also inhibitory components. The precise origin of this GABAergic feedback was then determined and its impact on the olfactory bulb network is currently assessed. In particular, we observed that manipulating the activity of this GABAergic feedback perturbs olfactory behavior.

This master’s thesis is focused on sensory systems and analysis of such signals. In the frst part, a theoretical analysis of each sensory system is conducted. Followingly, appropriate flters were used to process these signals. The last part of this thesis deals with the analysis of measured data.

This master’s thesis is focused on sensory systems and analysis of such signals. In the frst part, a theoretical analysis of each sensory system is conducted. Followingly, appropriate flters were used to process these signals. The last part of this thesis deals with the analysis of measured data.

No description available.

Comme tous les marsupiaux, l’opossum Monodelphis domestica nait dans un état très immature – glabre, aveugle, sourd – mais doit grimper sur le ventre de la mère pour trouver une tétine à laquelle il s’accroche afin de poursuivre son développement. Pour ce faire, il rampe à l’aide de ses membres antérieurs, qui sont mobiles contrairement aux membres postérieurs, et se dirige vers une tétine qu’il avale partiellement. Des sens céphaliques sont nécessaires pour qu’il trouve la tétine et s’y accroche. Le toucher est un des sens qui est fonctionnel dès la naissance. Ce sens repose sur des cellules spécialisées qui ont la propriété de percevoir des déformations mécaniques des tissus et d’y répondre en déclenchant l’activation de fibres nerveuses. Cette propriété s’appelle mécanotransduction et est rendue possible par la présence de récepteurs moléculaires à la surface des cellules dont la tâche est de réagir aux stimuli mécaniques afin de provoquer la réponse. Peu de ces récepteurs ont été formellement identifiés et caractérisés. Toutefois, Piezo2 est un canal transmembranaire retrouvé dans une vaste gamme de mécanorécepteurs et qui joue un rôle crucial dans la perception du toucher, en plus d’être impliqué dans la vestibulation (sens de l’équilibre) et l’audition. Le rôle de Piezo2 a surtout été étudié chez des mammifères euthériens matures. Peu d’études ont porté sur son expression développementale, et aucune ne concernait les marsupiaux. L’objectif principal de cette thèse était de décrire l’expression de Piezo2 au niveau de la tête d’opossums en développement. L’expression du gène a été examinée par RT-PCR et hybridation in situ, alors que la présence de la protéine a été démontrée par immunohistochimie. La RT-PCR montre une expression de l’ARNm de Piezo2 à tous les âges à partir de la naissance jusqu’au 21e jour postnatal (P21). L’immunohistochimie n’a pas permis de mettre en évidence Piezo2 dans la peau faciale ni chez les nouveau-nés ni chez l’adulte. Cependant, Piezo2 est présent dans l’oreille interne dès la naissance. Dans le vestibule, le marquage Piezo2 est observé sous la forme de disques à la surface de l’épithélium dans la macule utriculaire dès la naissance et dans la macule sacculaire et les crêtes ampullaires à P7. Ces disques ont une morphologie similaire à ceux formés par l’accumulation d’actine où se développent les cils des cellules ciliées, ce qui permet de penser que Piezo2 se trouve à la surface des cellules ciliées présomptives. Dans la cochlée, la protéine est aussi présente sur toute la surface apicale de l’organe de Corti présomptif. Avec l’âge, le patron de marquage se restreint à la surface des cellules ciliées externes, dont les trois rangées sont visibles à P11. À P14, les disques de marquage Piezo2 sont bien nets dans tous les organes sensoriels de l’oreille interne. Du marquage Piezo2 a aussi été observé dans la membrane tectoriale de la cochlée et les membranes otolithiques des macules vestibulaires, ce qui suggère qu’il joue un rôle dans le développement de ces structures acellulaires. Ces résultats suggèrent que Piezo2 n’est pas impliqué dans la mécanosensation tactile faciale à la naissance et pourrait jouer un rôle mineur dans le toucher chez l’opossum. L’expression de Piezo2 dans l’oreille interne indique qu’une forte maturation des cellules ciliées a lieu au cours de la 1re semaine postnatale dans la macule utriculaire et lors de la 2e semaine pour les autres organes sensoriels vestibulaires. Les cellules ciliées cochléaires auraient une maturation un peu plus tardive, au cours de la 2e semaine postnatale. La forte présence de Piezo2 dans l’épithélium cochléaire dès la naissance, alors que les cellules ciliées sont encore indifférenciées, suggère que cette molécule pourrait jouer un rôle dans la différenciation cellulaire. En résumé, cette étude montre que Piezo2 n’est pas impliqué dans la mécanosensation précoce chez l’opossum, mais qu’il joue un rôle dans le développement de la vestibulation et de l’audition. / Like most marsupials, the opossum Monodelphis domestica is born in a very immature state, ie. blind, glabrous and deaf. To pursue its development and growth, the newborn crawls with its forelimbs on its mother’s belly to find a teat where it attaches. Cephalic senses are needed to find the teat and trigger the attachment. Touch is one of the senses, which depends on mechanoreceptors, sensory cells capable of perceiving the mechanical changes in tissues and to transmit them as neural inputs, a process called mechanotransduction. Of the few molecular receptors underlying mechanotransduction identified so far, Piezo2 is the best candidate. It is a mechanosensitive cation channel found in a wide variety of mechanoreceptors and plays a crucial role in the perception of touch, as well as having been linked to the vestibular and auditory vestibular systems. While having been well characterized in mature eutherian mammals, few studies have looked at its role during ontogenesis and none were done in marsupials. The main objective of this thesis was to describe the developmental expression of Piezo2 in the head of the opossum. Gene expression was examined by RT-PCR and in situ hybridization, while the presence of the protein was demonstrated by immunohistochemistry. RT-PCR has shown that gene expression of Piezo2 is present from birth (postnatal day 0, P0) until P21. Immunohistochemistry did not reveal the presence of Piezo2 in cephalic skin tissues at any stage from birth to adulthood. However, Piezo2 is present in the inner ear from birth onwards. In the vestibular labyrinth, disk-shaped patches of Piezo2 labeling are present in the utricular macula at P0 and can be observed at P7 in the saccular macula and in the crista ampullaris. In all these sensory organs, Piezo2 labeling is similar to that of disk-shaped patches of actin accumulation where the stereocilia of hair cells develop. This suggests that Piezo2 is located at the surface of the hair cells in the inner ear. In the auditory system, the protein is present over the surface of the whole presumptive organ of Corti at P0. With age, Piezo2 labeling was restricted to the apical surface of the outer hair cells by P11. At P14, numerous discs are present in all the sensory organs of the inner ear and the only difference with P21 seems to be an increase in their number. Piezo2 labeling was also observed in the tectorial membrane of the cochlea and the otolithic membranes of the macula, suggesting that it plays a role in the development of these acellular structures. These results indicate that Piezo2 is not involved in skin facial mechanosensation at birth in the opossum and may be less important in the perception of touch in marsupials than in eutherians. The pattern of expression of Piezo2 in the vestibular system suggests that the maturation of the hair cells is important during the first postnatal week in the utricular macula and during the second postnatal week in the other vestibular sensory organs. The hair cells in the organ of Corti are maturating more during the late second postnatal week. Moreover, the strong expression of Piezo2 in the undifferentiated cochlear epithelium during the first postnatal weeks suggests that it may play a role in the differentiation of the cells of the organ of Corti of the opossum Monodelphis domestica. In summary, this study highlights that Piezo2 is not involved in early mechanosensation in opossums but plays a role in the development of both the vestibular and auditory systems.