Algorithmic adjustment of neural field parameters

Revisiting neural-field calculation maps in the discrete case, we propose algorithmic mechanisms allowing to choose a right set of parameters in order to both (i) guaranty the stability of the calculation and (ii) tune the shape of the output map. These results do not ``prove'' the existence of stable bump solutions, this being already known and extensively verified numerically, but allow to calculate algorithmically the related parameters. The results apply to scalar and vectorial neural-fields thus allowing to bypass the inherent limitations brought by mean frequency models and also take the laminar structure of the cortex or high-level representation of cortical computations into account. We obtain an easy to implement procedure that guaranty the convergence of the map onto a fixed point, even with large sampling steps. Furthermore, we report how rectification is the minimal required non-linearity to obtain usual neural-field behaviors. We also propose a way to control and tune these behaviors (filtering, selection, tracking, remanence) and optimize the convergence rate. This applies to both non parametric profiles, i.e. adjusting the weight values directly, or to parametric profiles and thus adjusting their parameters (e.g. Mexican-hat profiles). Beyond these algorithmic results, the idea of studying neural computations as discrete dynamical systems and not only the discretization of a continuous system is emphasized here. The outcome is shared as an open-source plug-in module, called EnaS (http://enas.gforge.inria.fr), to be used in existing simulation software

On asynchronous dynamic neural field computation

The hallmark of most artificial neural networks is their supposed intrinsic parallelism where each unit is evaluated concurrently to other units in a distributed way. However, if one gives a closer look under the hood, one can soon realize that such a parallelism is an illusion since most implementations use what is referred to as synchronous evaluation. The present article propose to consider different evaluation methods (namely asynchronous evaluation methods) and to study their properties in some restricted but illustrative cases

On practical neural field parameters adjustment

ISBN : 978-2-9532965-0-1Revisiting CNFT calculation maps in both the discrete and continuous temporal cases, we propose a set of results allowing to choose the right set of parameters in order to both (i) guaranty the stability of the calculation and (ii) tune the shape of the output's map. With such parameters it appears that large sampling steps can be used, speeding up overall calculation. Furthermore, we report experimenting the fact that rectification is the only required non-linearity and formalize the use of this simplified but efficient mechanism. The outcome is shared as an open-source plug-in module to be used in existing simulation software

How Gibbs distributions may naturally arise from synaptic adaptation mechanisms. A model-based argumentation

This paper addresses two questions in the context of neuronal networks dynamics, using methods from dynamical systems theory and statistical physics: (i) How to characterize the statistical properties of sequences of action potentials ("spike trains") produced by neuronal networks ? and; (ii) what are the effects of synaptic plasticity on these statistics ? We introduce a framework in which spike trains are associated to a coding of membrane potential trajectories, and actually, constitute a symbolic coding in important explicit examples (the so-called gIF models). On this basis, we use the thermodynamic formalism from ergodic theory to show how Gibbs distributions are natural probability measures to describe the statistics of spike trains, given the empirical averages of prescribed quantities. As a second result, we show that Gibbs distributions naturally arise when considering "slow" synaptic plasticity rules where the characteristic time for synapse adaptation is quite longer than the characteristic time for neurons dynamics.Comment: 39 pages, 3 figure

Neurosmart, une histoire de cerveau et de passionné·e·s de science

We propose a participatory science outreach approach allowing us to co-construct with our audiences resources aimed at understanding and demystifying the most disruptive results obtained regarding human brain by the conjunction of computer science, applied mathematics and neuroscience (computational neuroscience). The context is that of science and technology with a heavy societal impact, for which there is a strong need to allow everyone to build models of representation of these results and to forge an enlightened citizen's vision on these subjects.We rely here on our experience in sharing scientific culture on these subjects and our ability to create large diffusion content and resources, easy to appropriate and to operate.We propose to discover the models of the cerebral functions at the origin of our sensorimotor and vital cognitive behaviors (instinctive and motivated behavior, selection of embodied action, emotional decision-making or not, sites of self-awareness, etc. ) through :- a course of evolving content each time giving minimal key ideas on these subjects, also showing the simple use of mathematical concepts,- a Web-application (3D visualization of the brain in synergy with multi-media content and explanatory texts) with the possibility of interacting with the content. e.g., quizzes.The implementation is a free and open code, easily reusable by anyone with basic computing skills.This is also in itself a tool for learning the code, in addition to the acquisition of skills in integrative neuroscience, and it is a lever for co-creation.On propose la mise en place d’une démarche de médiation scientifique participative pour permettre de co-construire avec nos publics des ressources visant à comprendre et démystifier les résultats les plus disruptifs concernant le cerveau humain obtenus par la conjonction de l’informatique, mathématiques appliquées et des neurosciences (neurosciences computationnelles).Le contexte est celui de sciences et technologies à lourd impact sociétal avec un besoin fort de permettre à chacune et chacun de se construire des modèles de représentation de ces résultats et de se forger une vision citoyenne éclairée sur ces sujets. On s’appuie ici sur notre expérience en matière de partage de culture scientifique sur ces sujets et notre capacité à créer des contenus et des ressources, à forte diffusion, faciles à s’approprier et à faire fonctionner.On propose de découvrir les modèles des fonctions cérébrales à l’origine de nos comportements sensori-moteurs et cognitifs vitaux (comportement instinctif et motivé, sélection de l’action incarnée, prise de décision émotionnelle ou non, siège de la conscience de soi, …) à travers :- un parcours de contenus évolutifs donnant à chaque fois des idées clés minimales sur ces sujets, en montrant aussi l’utilisation simple de notions mathématiques, - une Web-application (visualisation 3D du cerveau en synergie avec des contenus multi-médias et des textes explicatifs) avec la possibilité d’interagir avec les contenus, par exemple un quiz.L’implémentation est un code libre et ouvert, facilement réutilisable par toute personne initiée à l’informatique.Cela constitue aussi en soi un outil d’apprentissage du code, en plus de l’acquisition de compétences en neuroscience intégrative, et c’est un levier de co-création

Simulation numérique des liaisons microstructure-anisotropie du matériau bois à ses différentes échelles d'hétérogénéité

Numerical simulation of the relation between the microstructure and the anisotropy of wood on various levels of inhomogeneity. The highly anisotropic character of the viscoelastic behavior of the wood material, commonly noted on the global level of its use, is essentially due to aspect ratios and spatial orientations of the constituants of wood, observed on three levels of its inhomogeneity. This specific morphology is reproduced here, through the inclusion-matrix model which is applied on the micro, meso and finally global scales. To analyze the resulting anisotropy, a new coefficient has been proposed. The evolution of this coefficient, from scale to scale, is evaluated. The influence of the aspect ratio of various constitutive phases is emphasized for the three levels of inhomogeneity. To perform the simulations, a new numerical tool has been developed which takes into account the specific properties of wood material. A short description of this tool is presented here.Le caractère fortement anisotrope du comportement viscoélastique du matériau bois constaté à l'échelle de son utilisation, résulte essentiellement des paramètres de formes et de l'orientation des constituants mécaniques rencontrés à ses trois échelles d'hétérogénéités. Une description morphologique du matériau, s'appuyant sur le couple inclusion-matrice est proposée pour chaque niveau d'hétérogénéité. Elle amènera de l'échelle nanoscopique à l'échelle macroscopique. L'analyse des anisotropies s'effectuera par un coefficient construit pour l'occasion. Une étude de l'évolution de ce coefficient est réalisée pour chaque échelle. La part essentielle que prennent les paramètres de formes des différentes phases constitutives dans l'anisotropie du matériau est mise en évidence, pour chaque niveau d'hétérogénéité. Pour effectuer les simulations, un outil a été développé pour répondre aux particularités du bois. Une description rapide de ce modèle est présentée

Experimental observations about the influence of the cutting conditions in high speed machining of Ti-6Al-4V Titanium alloy

This work presents experimental observations about the influence of the cutting conditions on orthogonal high speed turning in presence of instabilities. Specially, the influences of the machine tool dynamic characteristics, modified by changes of the tool-holder's length, are examined. Following this, in order to excite the system during machining, the cutting conditions were chosen for assuring chatter and segmented chip apparition. The machining tests were carried out on Ti-6Al-4V Titanium alloy samples, using a L$_{8}$ fractional Taguchi experiment. This method permitted to identify and compare the cutting conditions' effects on the machining process, minimizing the number of tests