Identification of Invariant Sensorimotor Structures as a Prerequisite for the Discovery of Objects

Perceiving the surrounding environment in terms of objects is useful for any general purpose intelligent agent. In this paper, we investigate a fundamental mechanism making object perception possible, namely the identification of spatio-temporally invariant structures in the sensorimotor experience of an agent. We take inspiration from the Sensorimotor Contingencies Theory to define a computational model of this mechanism through a sensorimotor, unsupervised and predictive approach. Our model is based on processing the unsupervised interaction of an artificial agent with its environment. We show how spatio-temporally invariant structures in the environment induce regularities in the sensorimotor experience of an agent, and how this agent, while building a predictive model of its sensorimotor experience, can capture them as densely connected subgraphs in a graph of sensory states connected by motor commands. Our approach is focused on elementary mechanisms, and is illustrated with a set of simple experiments in which an agent interacts with an environment. We show how the agent can build an internal model of moving but spatio-temporally invariant structures by performing a Spectral Clustering of the graph modeling its overall sensorimotor experiences. We systematically examine properties of the model, shedding light more globally on the specificities of the paradigm with respect to methods based on the supervised processing of collections of static images.Comment: 24 pages, 10 figures, published in Frontiers Robotics and A

À propos d’Oppède de Consuelo de Saint-Exupéry

Pourquoi proposer une lecture d'Oppède, ce roman quasi inconnu que Consuelo de Saint-Exupéry publia en 1945 chez Brentano's, et chez Gallimard en 1947 ? Parce que, sous le couvert de la fiction, Consuelo redonne vie à l'expérience originale qui fut celle du " Groupe d'Oppède ", jeunes architectes et artistes réfugiés après 1940 dans le Lubéron. Parce que ce récit, baigné de fantaisie et de gravité, n'est pas exempt d'autodérision et d'humour, ce qui peut le rendre attachant. Mais aussi parce que s'y rencontrent, dès les premières pages, des réminiscences bien apparentes des textes de Saint-Exupéry.Why is it worth reading Oppède, this almost unknown novel by Consuelo de Saint-Exupéry published in 1945 by Brentano's and by Gallimard in 1947 ? Firstly because under the guise of fiction, Consuelo enables the reader to relive the experience of the " Groupe d'Oppède ", young architects and artists who took refuge in the Lubéron after 1940. Secondly because this story, both light-hearted and serious, is peppered with self-derision and humour, which captivates the reader. Last but not least because there are echoes of Saint-Exupéry from the very first pages of this work

The renal cortical interstitium: morphological and functional aspects

The renal interstitial compartment, situated between basement membranes of epithelia and vessels, contains two contiguous cellular networks. One network is formed by interstitial fibroblasts, the second one by dendritic cells. Both are in intimate contact with each other. Fibroblasts are interconnected by junctions and connected to basement membranes of vessels and tubules by focal adhesions. Fibroblasts constitute the "skeleton” of the kidney. In the renal cortex, fibroblasts produce erythropoietin and are distinguished from other interstitial cells by their prominent F-actin cytoskeleton, abundance of rough endoplasmic reticulum, and by ecto-5′-nucleotidase expression in their plasma membrane. The resident dendritic cells belong to the mononuclear phagocyte system and fulfil a sentinel function. They are characterized by their expression of MHC class II and CD11c. The central situation of fibroblasts suggests that signals from tubules, vessels, and inflammatory cells converge in fibroblasts and elicit an integrated response. Following tubular damage and inflammatory signals fibroblasts proliferate, change to the myofibroblast phenotype and increase their collagen production, potentially resulting in renal fibrosis. The acquisition of a profibrotic phenotype by fibroblasts in renal diseases is generally considered a main causal event in the progression of chronic renal failure. However, it might also be seen as a repair proces

Modèles numériques de la stimulation optique de neurones assistée par nanoparticules plasmoniques

La stimulation de neurones par laser émerge depuis plusieurs années comme une alternative aux techniques plus traditionnelles de stimulation artificielle. Contrairement à celles-ci, la stimulation lumineuse ne nécessite pas d’interagir directement avec le tissu organique, comme c’est le cas pour une stimulation par électrodes, et ne nécessite pas de manipulation génétique comme c’est le cas pour les méthodes optogénétiques. Plus récemment, la stimulation lumineuse de neurones assistée par nanoparticules a émergé comme un complément à la stimulation simplement lumineuse. L’utilisation de nanoparticules complémentaires permet d’augmenter la précision spatiale du procédé et de diminuer la fluence nécessaire pour observer le phénomène. Ceci vient des propriétés d’interaction entre les nanoparticules et le faisceau laser, comme par exemple les propriétés d’absorption des nanoparticules. Deux phénomènes princpaux sont observés. Dans certains cas, il s’agit d’une dépolarisation de la membrane, ou d’un potentiel d’action. Dans d’autres expériences, un influx de calcium vers l’intérieur du neurone est détecté par une augmentation de la fluorescence d’une protéine sensible à la concentration calcique. Certaines stimulations sont globales, c’est à dire qu’une perturbation se propage à l’ensemble du neurone : c’est le cas d’un potentiel d’action. D’autres sont, au contraire, locales et ne se propagent pas à l’ensemble de la cellule. Si une stimulation lumineuse globale est rendue possible par des techniques relativement bien maîtrisées à l’heure actuelle, comme l’optogénétique, une stimulation uniquement locale est plus difficile à réaliser. Or, il semblerait que les méthodes de stimulation lumineuse assistées par nanoparticules puissent, dans certaines conditions, offrir cette possibilité. Cela serait d’une grande aide pour conduire de nouvelles études sur le fonctionnement des neurones, en offrant de nouvelles possibilités expérimentales en complément des possibilités actuelles. Cependant, le mécanisme physique à l’origine de la stimulation lumineuse de neurones, ainsi que celui à l’orgine de la stimulation lumineuse assistée par nanoparticules, n’est à ce jour pas totalement compris. Des hypothèses ont été formulées concernant ce mécanisme : il pourrait être photothermique, photomécanique, ou encore photochimique. Il se pourrait également que plusieurs mécanismes soient à l’oeuvre conjointement, étant donné la variété des observations. La littérature ne converge pas à ce sujet et l’existence d’un mécanisme commun aux différentes situations n’a pas été démontrée.----------Abstract For several years, laser light has been used as an alternative means of artificially stimulating neurons. Unlike more traditional methods, this technique does not require a direct interaction with the organic tissue, such as those based on electrical stimulation. In addition, no genetic manipulation is needed, as it is required in optogenetic frameworks. More recently, nanoparticles have been added to the experimental process of light stimulation of neurons. These particles allow for a better spatial control of the method and potentially necessitate smaller fluences to trigger a neuron reaction, thanks to the specific properties of the interaction between a laser light and nanoparticles, such as absorption. This stimulation consists in two main phenomena. In some cases, depolarisation of the neuron membrane occurs, or an action potentiel can even be triggered. In other cases, an inward calcium influx is detected by the fluorescence of a calcium sensitive protein. On the one hand, some of these stimulations are global, which means that a perturbation of the neuron propagates to the whole cell. Action potentials belong to this category of stimulation. On the other hand, some stimulations remain local and do not propagate any further. Whereas a global stimulation with light is relatively well achieved with contemporary methods such as optogenetics, a local stimulation is more difficult to evoke. Nanoparticle assisted light stimulation techniques seem to provide this possibility, which would open new opportunities of experimental studies on the biophysics of neurons. However, the physical mechanism responsible for the light stimulation and the nanoparticle assisted light stimulation of neurons is not yet completely understood. Several hypothesis have been proposed to explain the experimental results : photothermal, photomechanical, or photochemical mechanisms have been mentioned. Furthermore, a simultaneous combination of several of these mechanisms could be responsible for the effect. The existence of a common mechanism for all experiments has not been determined yet in the literature. The most popular assumption is the one of a photothermal mechanism, which seems to be the most likely experimentally. We analyse this possibility and we propose theoretical models to compare numerical calculations to experimental observations. Firstly, we study models based on thermosensitive ion channels. Ion channels are proteins populating the cell membrane and are essential to many biological processes. Several methods exist to evaluate the effect of temperature on ion channels, such as Hodgkin-Huxley models, thermodynamic models and Markov models

MHC antigens in interferon γ (IFNγ) receptor deficient mice: IFNγ-independent up-regulation of MHC class II in renal tubules

MHC antigens in interferon γ (IFNγ) receptor deficient mice: IFNγ-independent up-regulation of MHC class II in renal tubules. MHC class II gene products in parenchymal cells, such as tubular epithelial cells in kidney, may play a role in the regulation of autoimmune reactions. Expression of MHC class II in renal tubular cells is normally very low, but it increases considerably under various pathologic conditions. The predominant role of IFNγ in up-regulation of MHC class II expression has been demonstrated repeatedly. We tested the existence of alternative pathways of MHC class II regulation using IFNγ receptor-deficient (IFNγR-/-) mice. Mutant and wild type mice received 50 µg bacterial endotoxin (LPS) i.p. Four days later the kidneys were removed for immunofluorescence examination. In agreement with published results LPS provoked an increase of immunoreactivity for MHC class I and MHC class II in proximal tubules of wild type mice. While MHC class I up-regulation was strictly IFNγ receptor-dependent, up-regulation of MHC II was still evident in mutant mice, although less than in wild type mice. Since injection of IFNγ induced proximal tubular MHC class II expression in wild type mice but not in IFNγR-/- mice, an alternative signaling pathway for IFNγ does not seem to exist. Thus, up-regulation of MHC class II expression in renal tubules does not necessarily require IFNγ. The markedly patchy pattern of immunofluorescence in IFNγR-/- mice suggests that induction of MHC class II after LPS injection may represent renal injury due to shock