15 research outputs found
Statistical Physics and Representations in Real and Artificial Neural Networks
This document presents the material of two lectures on statistical physics
and neural representations, delivered by one of us (R.M.) at the Fundamental
Problems in Statistical Physics XIV summer school in July 2017. In a first
part, we consider the neural representations of space (maps) in the
hippocampus. We introduce an extension of the Hopfield model, able to store
multiple spatial maps as continuous, finite-dimensional attractors. The phase
diagram and dynamical properties of the model are analyzed. We then show how
spatial representations can be dynamically decoded using an effective Ising
model capturing the correlation structure in the neural data, and compare
applications to data obtained from hippocampal multi-electrode recordings and
by (sub)sampling our attractor model. In a second part, we focus on the problem
of learning data representations in machine learning, in particular with
artificial neural networks. We start by introducing data representations
through some illustrations. We then analyze two important algorithms, Principal
Component Analysis and Restricted Boltzmann Machines, with tools from
statistical physics
Can grid cell ensembles represent multiple spaces?
The way grid cells represent space in the rodent brain has been a striking discovery, with theoretical implications still unclear. Di\u21b5erently from hippocampal place cells, which are known to encode multiple, environment-dependent spatial maps, grid cells have been widely believed to encode space through a single low dimensional manifold, in which coactivity relations between di\u21b5erent neurons are preserved when the environment is changed. Does it have to be so? Here, we compute \u2013 using two alternative mathematical models \u2013 the storage capacity of a population of grid-like units, embedded in a continuous attractor neural network, for multiple spatial maps. We show that distinct representations of multiple environments can coexist, as existing models for grid cells have the potential to express several sets of hexagonal grid patterns, challenging the view of a universal grid map. This suggests that a population of grid cells can encode multiple non-congruent metric relationships, a feature that could in principle allow a grid-like code to represent environments with a variety of di\u21b5erent geometries and possibly conceptual and cognitive spaces, which may be expected to entail such context-dependent metric relationships
26th Annual Computational Neuroscience Meeting (CNS*2017): Part 3 - Meeting Abstracts - Antwerp, Belgium. 15â20 July 2017
This work was produced as part of the activities of FAPESP Research,\ud
Disseminations and Innovation Center for Neuromathematics (grant\ud
2013/07699-0, S. Paulo Research Foundation). NLK is supported by a\ud
FAPESP postdoctoral fellowship (grant 2016/03855-5). ACR is partially\ud
supported by a CNPq fellowship (grant 306251/2014-0)
Activité de cellules de lieu de l'hippocampe : modélisation et analyse par des méthodes de physique statistique
Place cells in the hippocampus are neurons with interesting properties such as the corre-lation between their activity and the animalâs position in space. It is believed that theseproperties can be for the most part understood by collective behaviours of models of inter-acting simplified neurons. Statistical mechanics provides tools permitting to study thesecollective behaviours, both analytically and numerically.Here, we address how these tools can be used to understand place-cell activity withinthe attractor neural network paradigm, a theory for memory. We first propose a modelfor place cells in which the formation of a localized bump of activity is accounted for byattractor dynamics. Several aspects of the collective properties of this model are studied.Thanks to the simplicity of the model, they can be understood in great detail. The phasediagram of the model is computed and discussed in relation with previous works on at-tractor neural networks. The dynamical evolution of the system displays particularly richpatterns. The second part of this thesis deals with decoding place-cell activity, and theimplications of the attractor hypothesis on this problem. We compare several decodingmethods and their results on the processing of experimental recordings of place cells in afreely behaving rat.Les cellules de lieu de lâhippocampe sont des neurones aux propriĂ©tĂ©s intrigantes, commele fait que leur activitĂ© soit corrĂ©lĂ©e Ă la position spatiale de lâanimal. Il est gĂ©nĂ©ralementconsidĂ©rĂ© que ces propriĂ©tĂ©s peuvent ĂȘtre expliquĂ©es en grande partie par les comporte-ments collectifs de modĂšles schĂ©matiques de neurones en interaction. La physique statis-tique fournit des outils permettant lâĂ©tude analytique et numĂ©rique de ces comportementscollectifs.Nous abordons ici le problĂšme de lâutilisation de ces outils dans le cadre du paradigmedu ârĂ©seau attracteurâ, une hypothĂšse thĂ©orique sur la nature de la mĂ©moire. La questionest de savoir comment ces mĂ©thodes et ce cadre thĂ©orique peuvent aider Ă comprendrelâactivitĂ© des cellules de lieu. Dans un premier temps, nous proposons un modĂšle de cellulesde lieu dans lequel la localisation spatiale de lâactivitĂ© neuronale est le rĂ©sultat dâunedynamique dâattracteur. Plusieurs aspects des propriĂ©tĂ©s collectives de ce modĂšle sontĂ©tudiĂ©s. La simplicitĂ© du modĂšle permet de les comprendre en profondeur. Le diagrammede phase du modĂšle est calculĂ© et discutĂ© en comparaison avec des travaux prĂ©cedents.Du point de vue dynamique, lâĂ©volution du systĂšme prĂ©sente des motifs particuliĂšrementriches. La seconde partie de cette thĂšse est Ă propos du dĂ©codage de lâactivitĂ© des cellulesde lieu. Nous nous demandons quelle est lâimplication de lâhypothĂšse des attracteurs surce problĂšme. Nous comparons plusieurs mĂ©thodes de dĂ©codage et leurs rĂ©sultats sur letraitement de donnĂ©es expĂ©rimentales
Neuropeptides and bacterial interactions: The example of the impact of the C-type natriuretic peptide (CNP) on Pseudomonas aeruginosa biofilm formation
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Host Peptidic Hormones Affecting Bacterial Biofilm Formation and Virulence
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