1,721,012 research outputs found
Design principles for central pattern generators with preset rhythms
No full textThis article is concerned with the design of synthetic central pattern generators (CPGs). Biological CPGs are neural circuits that determine a variety of rhythmic activities, including locomotion, in animals. A synthetic CPG is a network of dynamical elements (here called cells) properly coupled by various synapses to emulate rhythms produced by a biological CPG. We focus on CPGs for locomotion of quadrupeds and present our design approach, based on the principles of nonlinear dynamics, bifurcation theory, and parameter optimization. This approach lets us design the synthetic CPG with a set of desired rhythms and switch between them as the parameter representing the control actions from the brain is varied. The developed four-cell CPG can produce four distinct gaits: walk, trot, gallop, and bound, similar to the mouse locomotion. The robustness and adaptability of the network design principles are verified using different cell and synapse models
Design of Synthetic Central Pattern Generators Producing Desired Quadruped Gaits
No full textThis paper is concerned with a method for design and analysis of specific neuronal networks, called central pattern generators (CPGs), which produce primary rhythmic patterns in animals. In particular, the paper is focused on synthetic CPGs made up of few basic elements and governing quadrupeds' gaits and gait transitions, under the control of an external drive. The method combines principles of bifurcation theory, geometric properties of symmetry, and numerical analysis based on the recently proposed toolbox CEPAGE. The method is applied to two CPGs, one bio-inspired and one purely synthetic. In both cases, the method provides a way to obtain a desired sequence of gaits by continuously changing a bifurcation parameter related to the external drive
Modeling Rhythm Generation in Swim Central Pattern Generator of Melibe Leonina
Full text linkCentral pattern generators (CPGs) are neural networks to produce a rich multiplicity of rhythmic activity types like walking, breathing and swim locomotion. Basis principles of the underlying mechanisms of rhythm generation in CPGs remain yet insufficiently understood. Interactive pairing experimental and modeling studies have proven to be vital to unlocking insights into operational and dynamical principles of CPGs and support the consensus that the most of essential structural and functional elements in vertebrate and invertebrate nervous systems are shared.
We have developed a family of highly-detailed, biologically plausible CPG models using the extensive data intracellularly recorded from constituent interneurons of the swim CPG of the sea slug {\it Melibe leonina}. We also have deduced fundamental properties needed for the devised Hodgkin-Huxley type neuronal models with specific slow-fast dynamics to become qualitatively and quantitatively similar to biological CPG interneurons and their responses to parameter and external perturbations. We have studied the onset and robustness of rhythmogenesis of network bursting the CPG circuits comprised of tonic spiking interneurons coupled with mixed inhibitory/excitatory, slow chemical synapses. We have shown that the mathematical CPG model can be reduced functionally from an 8-cell circuit to a 4-cell one using the calibration of timing and weights of synaptic coupling between CPG core interneurons.
We demonstrate that the developed mathematical network meets all the experimental fact-checks obtained for the biological Melibe swim CPG from a variety of state-of-the-art experimental studies including dynamic-clamp recordings, external pulses perturbations as well as from its forced behaviors under applications of neuro-blockers such as curare and TTX.
Our model and developed mathematical approaches and computational methodology allow for laying down theoretical foundations necessary for devising new detailed and phenomenological models of neural circuits and for making testable predictions of dynamics of rhythmic neural networks from diverse species.Doctor of Philosophy (PhD)Mathematics and Statistic
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Semidefinite Programming and Stability of Dynamical System
Full text linkIn the first part of the thesis we present several interior point algorithms for solving certain positive definite programming problems. One of the algorithms is adapted for finding out whether there exists or not a positive definite matrix which is a real linear combination of some given symmetric matrices A1,A2, . . . ,Am. In the second part of the thesis we discuss stability of nonlinear dynamical systems. We search using algorithms described in the first part, for Lyapunov functions of a few forms. A suitable Lyapunov function implies the existence of a hyperellipsoidal attraction region for the dynamical system, thus guaranteeing stability
Variations on the Author
Full text link“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
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe 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
Models of Multifunctional Central Pattern Generators: Polyrhythmic Bursting
Full text linkWe demonstrate a motif of three reciprocally inhibitory cells that is able to produce multiple patterns of bursting rhythms. Through the examination of the qualitative geometric structure of two-dimensional maps for phase lag between the cells we reveal the organizing centers of emergent polyrhythmic patterns and their bifurcations, as the asymmetry of the synaptic coupling is varied. The presence of multistability and the types of attractors in the network are shown to be determined by the duty cycle of bursting. This analysis does not require knowledge of the equations that model the system, and so provides a powerful new approach to studying regulatory networks. Thus, the approach is applicable to a variety of biological phenomena beyond motor control
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