1,721,002 research outputs found
Bifurcaciones de equilibrios en un modelo no diferenciable para redes competitivas
Get PDFEn este trabajo estudiamos las propiedades de un modelo de redes neuronales conocido como modelocompetitivo lineal por sectores. Nos enfocamos en el caso más sencillo en el que el modelo puede exhibir oscilacionesgeneradas por un ciclo lı́mite: tres nodos interconectados. La presencia de este tipo de no-linealidades relativamentesimples le otorga a la red la capacidad de producir una dinámica compleja, pero a su vez matemáticamente tratable.Fil: Bel, Andrea Liliana. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional del Sur. Departamento de Matemática; ArgentinaFil: Reartes, Walter. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional del Sur. Departamento de Matemática; ArgentinaFil: Rotstein, Horacio G.. New Jersey Institute of Technology; Estados UnidosCongreso de MAtemática Aplicada, Computacional e IndustrialComodoro RivadaviaArgentinaUniversidad Nacional de la Patagonia San Juan BoscoAsociación Argentina de Matemática Aplicada, Computacional e Industria
Frequency filter interactions in network of non-oscillatory cells
No full textResonance refers to the ability of dynamical systems to exhibit a peak in their amplitude response to oscillatory inputs at a preferred (resonant) frequency. In neuronal cir- cuits, resonance is typically measured by using the imped- ance amplitude profile Z defined as the absolute value of the quotient of the Fourier transforms of the output and the input. Resonance has been investigated in single neurons by many authors both experimentally and theoretically (Cichon & Gan, 2015 Apr; Sajikumar et al., 2014 Aug 19). Network resonance has received much less attention. Two important questions are (i) whether and under what condi- tions a network of neurons exhibits resonance in one or more neurons in response to inputs to one or more neurons, and (ii) whether and under what conditions the information is communicated between neurons in a frequency-dependent manner. In this project we address these issues by using a minimal network consisting of two passive cells (linear, non-reso- nant neurons) recurrently connected via graded synaptic inhibition or excitation and receiving oscillatory inputs in either one or the two nodes (Sezener et al., 2021). In order to investigate how network resonance emerges we extend the concept of impedance to nonlinear systems by comput- ing the peak-to-trough amplitudes normalized by the input amplitude. In order to investigate the communication of frequency-dependent information across neurons in the network we borrow the concept of the coupling coefficient from the gap junction literature. The coupling coefficient K, defined as the quotient between the postsynaptic and pre- synaptic membrane potentials of two electrically coupled neurons, is used to measure the strength of the connection in the presence of constant (DC) inputs. Here we extend this metrics to synaptically connected neurons and to the fre- quency domain. Linear networks (linear neurons and linear connectivity) can only show a low-pass filter K profile (K as a function of the input frequency). We show that the pres- ence of the more realistic nonlinear synaptic connectivity can produce band-pass K profiles. We note that the concept of communication of information we use here is different than the standard one used in information theory.Fil: Bel, Andrea Liliana. Universidad Nacional del Sur. Departamento de Matemática; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Unidad de Dirección. Comunicación Institucional; ArgentinaFil: Rotstein, Horacio G.. New Jersey Institute of Technology; Estados Unidos. Rutgers University; Estados Unidos30th Annual Computational Neuroscience MeetingMichiganEstados UnidosOrganization for Computational Neuroscience
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Nonlinearities Shape the Response Patterns to Oscillatory Inputs in a Caricature Electrochemical Cell Model
No full textWe investigate the nonlinear mechanisms of generation of preferred frequency response patterns to oscillatory inputs in a phenomenological (caricature) model that captures the type of nonlinearities present in electrochemical (EC) cells and is simple enough to begin to develop the dynamical systems tools necessary for the understanding of the relationship between the model nonlinearities and the response patterns. Previous work has shown that linearized EC models exhibit resonance (preferred frequency response to oscillatory inputs at a nonzero, resonant, input frequency) in parameter regimes where the stable equilibrium is either a node (no intrinsic oscillations) or a focus (damped oscillations). We use a combination of numerical simulations and dynamical systems tools to understand how the model nonlinearities, partially captured by the geometry of the nullclines in the phase-space diagram, shape the response patterns to oscillatory inputs away from the validity of the corresponding linearization. We develop and adapt an extended version of the classical phase-plane diagram that allows us to track the evolution of the response trajectories and their interaction with the so-called moving nullclines (in response to the oscillatory inputs). We use this approach to explain the mechanisms of generation of nonlinear resonant patterns, the nonlinear amplification/attenuation of these patterns by increasing input amplitudes, and the mechanisms of generation of more complex patterns of mixed-mode-type, where the stationary amplitude response is not uniform across cycles
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Subthreshold amplitude and phase resonance in models of quadratic type: Nonlinear effects generated by the interplay of resonant and amplifying currents
No full textWe investigate the biophysical and dynamic mechanisms of generation of subthreshold amplitude and phase resonance in response to sinusoidal input currents in two-dimensional models of quadratic type. These models feature a parabolic voltage nullcline and a linear nullcline for the recovery gating variable, capturing the interplay of the so-called resonant currents (e.g., hyperpolarization-activated mixed-cation inward and slow potassium) and amplifying currents (e.g., persistent sodium) in biophysically realistic parameter regimes. These currents underlie the generation of resonance in medial entorhinal cortex layer II stellate cells and CA1 pyramidal cells. We show that quadratic models exhibit nonlinear amplifications of the voltage response to sinusoidal inputs in the resonant frequency band. These are expressed as an increase in the impedance profile as the input amplitude increases. They are stronger for values positive than negative to resting potential and are accompanied by a shift in the phase profile, a decrease in the resonant and phase-resonant frequencies, and an increase in the sharpness of the voltage response. These effects are more prominent for smaller values of (larger levels of the time scale separation between the voltage and the resonant gating variable) and for values of the resting potential closer to threshold for spike generation. All other parameter fixed, as increases the voltage response becomes “more linear”; i.e., the nonlinearities are present, but “ignored”. In addition, the nonlinear effects are strongly modulated by the curvature of the parabolic voltage nullcline (partially reflecting the effects of the amplifying current) and the slope of the resonant current activation curve. Following the effects of changes in the biophysical conductances of realistic conductance-based models through the parameters of the quadratic model, we characterize the qualitatively different effects that resonant and amplifying currents have on the nonlinear properties of the voltage response. We identify different classes of resonant currents, represented by h- and slow potassium, according to whether they enhance (h-) or attenuate (slow potassium) the nonlinear effects. Finally, we use dynamical systems tools to investigate the dynamic mechanisms of generation of resonance and phase-resonance. We show that the nonlinear effects on the voltage response (e.g., amplification of the voltage response in the resonant frequency band and shifts in the resonant and phase-resonant frequencies) result from the ability of limit cycle trajectories to follow the unstable (right) branch of the voltage nullcline for a significant amount of time. This is a canard-related mechanism that has been shown to underlie the generation of intrinsic subthreshold oscillations in quadratic type models such as medial entorhinal cortex stellate cells. Overall, our results highlight the complexity of the voltage response to oscillatory inputs in nonlinear models and the roles that resonant and amplifying currents have in shaping these responses
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