8,205 research outputs found
Poster session at Computational NeuroScience Conference in 2020 - An integrate-and-fire model of narrow band modulation in mouse visual cortex
No full textBMC Neuroscience 2020, 21(Suppl 1):P128
An integrate‐and‐fre model of narrow band modulation in mouse visual cortex
Gamma band neuronal oscillations are involved with sensory processing ubiquitously in the central nervous system. They emerge from the coordinated interaction of excitation and inhibition and are a biological marker of local active network computations [1]. Visual features as contrast and orientation are known to modulate broad band gamma activity in the primary visual cortex (V1) of primates [2]. In mouse V1, however, a narrow band within gamma oscillation was found to display specifc functional sensitivity to visual features [3]. Here we present a network of recurrent excitatory-inhibitory spiking neurons reproducing the gamma narrow band dynamics in mouse V1 observed in [3], building on previous works of our group [4,5]. By combining experimental data analysis and simulations, we show that a proper design of the simulated thalamic input results in the network to exhibit both narrow and broad band gamma activity. We reproduced the spectral and temporal modulations of V1 local feld potentials of awake mice presented with gratings of different contrast levels by approximating the thalamic input rate with two linear functions defned over complementary contrast ranges. We propose a theoretical framework in which the external thalamic drive is responsible for inducing the emergence of broad by triggering cortical resonances and narrow band gamma activity by inducing entrainment to an oscillatory drive. Our results support in particular the hypothesis of a subcortical origin of the narrow gamma band [3]. Our network provides a simple and effective model of contrastinduced gamma activity in rodents V1. The model could be easily extended to reproduce the modulation of V1 gamma activity induced by other visual stimulus features. Moreover, the model could help to investigate network dynamics responsible for pathological dysfunctions of physiological visual information processing in mice.
References
1. Buzsáki G, Wang XJ. Mechanisms of gamma oscillations. Annual Review of Neuroscience. 2012; 35: 203-25.
2. Henrie JA, Shapley R. LFP power spectra in V1 cortex: the graded efect of stimulus contrast. Journal of Neurophysiology. 2005; 94(1): 479-90.
3. Saleem AB, et al. Subcortical source and modulation of the narrowband gamma oscillation in mouse visual cortex. Neuron. 2017; 93(2): 315-22.
4. Mazzoni A, Brunel N, Cavallari S, Logothetis NK, Panzeri S. Cortical dynamics during naturalistic sensory stimulations: experiments and models. Journal of Physiology-Paris. 2011; 105(1-3): 2-15.
5. Mazzoni A, Linden H, Cuntz H, Lansner A, Panzeri S, Einevoll GT. Computing the local feld potential (LFP) from integrate-and-fre network models. PLoS Computational Biology. 2015; 11(12): e1004584
ALBERTO MAZZONI / MARIA CHIARA MALAGUTI. Derecho del comercio internacional: Fundamentos y perspectivas
No full textEste artículo reseña: Alberto Mazzoni / Maria Chiara Malaguti. Derecho del comercio internacional: Fundamentos y perspectivas. Torino, G. Giappichelli Editore, Valencia, Tirant lo Blanch, 2021, 310 pp. ISBN: 978-84-1355-217-
From single neuron activity to network information processing: Simulating cortical local field potentials and thalamus dynamic regimes with integrate-and-fire neurons
No full textCortical and subcortical neural activity has been modeled for decades by means of recurrent networks of integrate and fire neurons (IFN). Such networks have proved to be able to capture a variety of neural functions ranging from sensory processing to short term memory and decision making. Some network scale phenomena, however, were considered too complex to be simulated with simple basic components as IFN. Namely, Local Field Potentials (LFP) were simulated with multi-compartmental models, as IFN lacked the ability to cope with the spatial features of the signal, and thalamic oscillations were modeled with Hodgkin and Huxley and similar neuron models, as IFN were thought not be able to mimic the rebound properties of the neurons of the area. Here we will show instead how it is possible to capture both phenomena with IFN networks. First, in a series of works spanning almost a decade, we were able to build flexible LFP proxies simulating the extracellular signal from IFN network dynamics. We identified several key properties of the neuronal structure, based on the dipolar approximation of LFP generation, and we implemented them in the IFN model. This led to a dimensionality reduction of the system parameters of two order of magnitudes, while capturing almost entirely the LFP dynamic. Actually, the resulting model of LFP is so efficient to be able to reconstruct spiking dynamics from LFP recorded in the primary visual cortex. Second, we were able to reproduce with IFN two dynamic regimes of the thalamus displaying different characteristic oscillations bands and different information processing properties. The key advancement was to highlight the connection between single neuron dynamics and network regimes. Spindle oscillations preventing information transmission to the cortex occur when the neurons fire exclusively because of rebound from inhibition. When the external excitatory inputs are sufficiently strong, instead, thalamocortical relay neurons start firing because of depolarization, weakening spindle oscillations and leading to information transmission. Starting from these results we will discuss the possibility of capturing the whole process of encoding of sensory stimuli by means of a chain of spiking neuron model covering the whole path from peripheral sensors to primary sensory cortex. Building the whole structure with simple and elegant IFN will make the analysis and the comparison with experimental results sharper
Numerical and experimental study of the fatigue life of wheels for industrial vehicles
No full textLa presente ricerca riguarda lo sviluppo di metodi sperimentali per la previsione di vita a fatica di ruote per applicazioni industriali. Ad oggi, gli studi su tale argomento riguardano soprattutto il settore automotive, dove i carichi sulle ruote sono più bassi e le condizioni di utilizzo più uniformi, rispetto al settore industriale. Da qui l’esigenza di sviluppare maggiori conoscenze anche in quest’ultimo settore. Infatti, la continua richiesta di miglioramento delle prestazioni dei veicoli dal punto di vista dei carichi di lavoro, della variabilità di utilizzo e della durata complessiva, potrebbe condurre a situazioni dove gli attuali strumenti di validazione risultino insufficienti.
La prima parte della tesi presenta lo stato dell’arte dei metodi di validazione delle ruote industriali, con particolare riferimento alle prove di fatica eseguite in laboratorio secondo standard riconosciuti. Di queste sono evidenziate le principali criticità, relative soprattutto ad applicazioni non comprese in tali standard di prova, o a casi dove gli elevati carichi richiesti non consentono di completare le prove con tempi e costi accettabili per la pratica industriale. Per ovviare a tali criticità, è proposto un approccio basato sul miglioramento della conoscenza degli spettri di carico in esercizio tramite prove sul campo, e su metodi alternativi di caratterizzazione a fatica del materiale dopo il processo produttivo. L’importanza di questi temi è confermata dall’analisi di un caso di rottura in servizio di una macchina per movimentazione container.
Nella seconda parte della tesi, lo studio si concentra sulla caratterizzazione del comportamento a fatica di un componente, un cerchione per applicazioni agricole, per il quale non esistono attualmente casi di rottura né sul campo né tramite prove a fatica tradizionali. Il metodo usato prevede l’esecuzione di prove a fatica su provini ricavati dal componente, studiati in modo da replicarne le condizioni di massima sollecitazione nei punti critici in condizioni di esercizio. Dai risultati si è ricavata una curva a fatica per il componente che considera anche alcuni aspetti determinati dal processo produttivo, come la rugosità superficiale e l’incrudimento dovuto a deformazione plastica localizzata. Non sembrano essere invece incluse le tensioni residue di compressione che, seppure presenti nel cerchione completo, sono state rilasciate durante la realizzazione dei provini. Data la loro riconosciuta influenza sulla vita a fatica dei componenti strutturali, esse dovrebbero comunque essere valutate nell’analisi complessiva, ad esempio misurandole sul componente finito ed aggiungendole, come tensioni medie, agli spettri di carico misurati nelle prove sul campo.
Il metodo esposto è stato replicato su un cerchione differente, per il quale già esistevano dati di rottura a fatica, verificando l’esistenza di un fattore di scala tra i risultati di durata del componente rispetto a quelli dei singoli provini. L’applicazione dello stesso procedimento a casi simili consentirà di valutare la variabilità di tale fattore di scala e la sua estendibilità ad altri componenti.
In conclusione, le procedure utilizzate in questa ricerca consentono un miglioramento nella progettazione a fatica di ruote per veicoli industriali. Questo può portare allo sviluppo di prodotti più affidabili ed ottimizzati, con riduzione di peso a pari resistenza, e conseguente risparmio energetico, aspetto fondamentale nello sviluppo industriale moderno. Dai risultati ottenuti, sono poi emersi ulteriori argomenti di ricerca, riguardanti l’influenza dei processi produttivi sulla resistenza del materiale e la necessità di definire nuovi standard di prova in laboratorio, per ruote di applicazioni critiche, a partire dall’analisi dei dati acquisiti in condizioni di esercizio.This research deals with the development of experimental methods for the fatigue life evaluation of wheels for industrial applications.
To date, the studies about this topic are mainly related to the automotive industry, where the loads on wheels are lower and the conditions of usage more standardised than in the industrial sector. Hence, the need of improving the knowledge also in this sector. In fact, the continuous request of improving the vehicles performance from the point of view of working loads, variability of usage and life-time duration, could lead to situations where the current design validation methods are insufficient.
The first part of this thesis presents the state of the art of the validation methods for industrial wheels, with particular reference to fatigue lab testing according to approved standards. The most critical aspects of these methods are highlighted, mostly regarding applications not included in any test standard, or cases where the high loads required do not allow fatigue tests to be completed with acceptable time and cost for the industrial practice. To overcome these critical issues, an alternative approach is proposed. It is based on improving the knowledge of the service load spectra through appropriate field tests, and on alternative methods for evaluating the fatigue properties of the material after the production process. The importance of these topics is confirmed by a case of failure analysis of a machine for container handling.
In the second part of this thesis, the study focuses on the evaluation of the fatigue properties of a specific component, a rim for agricultural applications, for which, to date, no fatigue failure has ever happened, neither in field service nor in traditional lab testing. The method used consists in the fatigue testing of section specimens obtained from the component, designed to replicate the maximum stress in the critical points of the full-scale component in service conditions. The results allowed to obtain a fatigue curve for the component, which also considers some aspects related to the production process, such as the surface roughness and the work hardening due to local plastic deformation. However, the compressive residual stresses, which were present in the full-scale rim, were released during the production of the specimens and they seem not considered by this approach. Given their known influence on the fatigue life of structural components, they should be evaluated anyway, in the general analysis. For example, they could be measured on the finished component and added, as mean stresses, to the stress spectra acquired during field tests.
The approach discussed was also applied to a different rim size, for which fatigue failures were already reached through standard testing. This further investigation showed the existence of a scale factor between the fatigue life results of the full-scale component and the ones of the rim section specimens. The further application of the same procedure to similar cases will allow to evaluate the variability of this scale factor and its possible use for other components.
In conclusion, the methods investigated in this research can be used to improve the design against fatigue of wheels for industrial vehicles. That may lead to the development of more reliable and optimised products, with possible weight reduction at the same fatigue strength, and consequent energy saving, which is a fundamental aspect in modern industry. Moreover, further topics for new possible research emerged, regarding the influence of the production process on the fatigue strength of the components and the need of developing new lab test standards, for critical applications, starting from the analysis of field tests data in real service conditions.
The themes discussed and the methods used, here applied to wheels for industrial vehicles, are of general interest in mechanical engineering and can be extended to other structural components
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No full textDataset associated to the article "Transition between functional regimes in an integrate-and-fire network model of the thalamus", by Alessandro Barardi, Jordi Garcia-Ojalvo and Alberto Mazzoni.<br
From neuronal networks to behavior: dynamics of spontaneous activity and onset of movement in the leech
No full textAnimal behavior was once seen as a chain of reactions to stimuli from the environment. From
chemotaxis in bacteria to mammals withdrawing from painful stimuli, most of the actions taken by
animals are clearly driven by external inputs. Reflexes were among the first phenomena to be
studied to have an insight on the dynamics of the nervous system. Later, a step forward was the
discovery of central pattern generators: once a behavior is started by a stimulus, some neuronal
networks are able to maintain it without further inputs from the environment. The nervous system of
all animals, however, is so complex that is displaying a rich dynamics even in the absence of
external inputs or, in a more realistic situation, when no single input is able to drive a clear-cut
reaction. In the same way, at the motor output level, animals keep moving in the absence of evident
stimuli. These spontaneous behaviors are still far from being understood.
Difficult problems are often easier to solve in simple systems. The leech has a relatively simple
nervous system, composed of ~103 neurons disposed in a regular structure, but at the same time
displays a variety of different behaviors. It seems then a good preparation to approach the
spontaneous dynamics problem.
The aim of my PhD research is to describe the spontaneous behavior of the leech and the
spontaneous activity of its nervous system.
A first, necessary step for this study was to develop a method of automatic classification and
analysis of the leech movements. Thanks to this method we described accurately the properties of
the different behaviors: we focused particularly on the largely unknown irregular exploratory
behavior, which is found to display a broad range of oscillation frequencies and displacement
speeds, but with some recurrent movement patterns. Finding the complete list of the leech
spontaneous behaviors, and the probability of the transitions between them, it was possible to
demonstrate that decision making in the leech is a Markovian process.
The spontaneous activity in the isolated leech ganglion was found to be characterized by long-term
correlations and a large variability in bursts size and duration. The same dynamics was observed in
dissociated culture of rat hippocampal neurons, despite the difference in the structure between the
two networks. We studied the effects of pharmacological modulations of inhibitory and excitatory
processes on the spontaneous activity, and the role of single identified motor neurons in spontaneous bursts. Finally we proposed a simple statistical model accounting for experimental
results.
We studied then the spontaneous activity of the leech ganglion when it was connected to the other
ganglia and in the semi-intact moving animal. Inputs received from the head and tail brain caused a
drastic change in the activity of the ganglion, increasing synchronization among neurons and
leading to a regime dominated by very large bursts. By recording at the same the movements of the
leech and its nervous activity it was possible to have a better understanding of the relationship
between the motor neuron bursts and the onset of movements
Can extremism guarantee pluralism?
No full textMany models have been proposed to explain opinion formation in groups of
individuals; most of these models study opinion propagation as the interaction
between nodes/agents in a social network. Opinion formation is a complex
process and a realistic model should also take into account the important
feedbacks that the opinions of the agents have on the structure of the social
networks and on the characteristics of the opinion dynamics. In this paper we
will show that associating to different agents different kinds of
interconnections and different interacting behaviours can lead to interesting
scenarios, like the coexistence of several opinion clusters, namely pluralism.
In our model agents have opinions uniformly and continuously distributed
between two extremes. The social network is formed through a social aggregation
mechanism including the segregation process of the extremists that results in
many real communities. We show how this process affects the opinion dynamics in
the whole society. In the opinion evolution we consider the different
predisposition of single individuals to interact and to exchange opinion with
each other; we associate to each individual a different tolerance threshold,
depending on its own opinion: extremists are less willing to interact with
individuals with strongly different opinions and to change significantly their
ideas. A general result is obtained: when there is no interaction restriction,
the opinion always converges to uniformity, but the same is happening whenever
a strong segregation process of the extremists occurs. Only when extremists are
forming clusters but these clusters keep interacting with the rest of the
society, the survival of a wide opinion range is guaranteed
Entre invention, restauration et vente : la peinture médiévale au début du XXe siècle
No full textMazzoni Gianni, Olivetti Alberto, Redon Odile, Hordynsky-Caillat Lada. Entre invention, restauration et vente : la peinture médiévale au début du XXe siècle. In: Médiévales, n°14, 1988. La culture sur le marché, sous la direction de Yvonne Cazal . pp. 73-90
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