Neste trabalho as equações fenomenológicas (tetra-dimensionais) de Hodgkin-Huxley [5], para a membrana da fibra do neurônio, são estudadas mediante transformações não-lineares de variáveis. As transformações de variáveis visam estabelecer um processo controlado de redução de variáveis até chegar a um modelo bidimensional com o menor prejuízo quantitativo possível. O objetivo primordial é aprofundar o entendimento da aparente relação das equações de Hodgkin-Huxley com uma versão da equação de 2ª ordem de van der Pol, conhecida na literatura pelos nomes de equação de FitzHugh-Nagumo [83], equação de Nagumo [84] ou equação Bonhoeffer-van der Pol [7]. É proposta também uma nova formulação matemática para o modelo da corrente de potássio. Estas modificações possibilitam a elaboração de uma remodelagem do aspecto e funcionamento interno do circuito equivalente da membrana. Este circuito, além de facilitar as simplificações para comparar as novas equações em relação ao modelo tipo van der pol, apresenta também potencial teórico mais desenvolvido do que o circuito equivalente original de Hodgkin-Huxley, já que ao contrário deste os elementos do novo circuito podem ser mais facilmente reconhecidos e manipulados dentro da teoria usual de circuitos elétricos. Uma primeira conseqüência da concepção do novo circuito, aqui explorada, é a formulação do modelo da membrana na linguagem da mecânica analítica. / The phenomenological four-variable equations of Hodgkin and Huxley [5] for the neuron fiber membrane are studied by means of nonlinear transformations of variables . The purpose is gradually reduce the number of variables to a three and then to a two-dimensional model, with smallest possible deviations from the quantitative properties of the original model. The primary aim is to get better insights into the apparent connect ion between the Hodgkin-Huxley equations and a version of the second order equation of van der Pol, usually called FitzHugh-Nagumo equation [83], or Nagumo equation [84], or Bonhoeffer- van der Pol equation [7]. An alternative formulation for the potassium current is also proposed. The above modifications lead to an alternative circuit model for the nerve membrane. Such circuit helps the comparison with the van der Pol-type model. It exhibits also better theoretical appeal than the original circuit of Hodgkin and Huxley in the sense that the circuit elements are now properly defined in terms of usual electrical circuit theory. An application of the proposed equivalent circuit i s a description of the Hodgkin-Huxley membrane model according to the formalism of analytical mechanics.

Cette étude de science politique s’inscrit dans le prolongement d’une thèse effectuée en littérature comparée, intitulée « Entre littérature et philosophie : l’Homme est-il un animal politique ? Physique de la misanthropie » (dirigée par M. F. Monneyron, soutenue en nov. 2013, publiée chez L’Harmattan). Dans cette analyse, il s’agissait de tenter une ébauche de conceptualisation philosophique de la haine de l’humanité en partant du théâtre de la misanthropie pour voir ensuite si les quelques résultats obtenus pouvaient s’appliquer à la littérature concentrationnaire et aux dystopies, deux autres genres littéraires qui forment le terreau naturel de doctrines et de pratiques misanthropes.Quelles sont les déterminations culturelles (mythologiques, religieuses, artistiques, médiatiques) de la misanthropie et de la misologie ? Comment apprécier leurs impacts dans le champ politique des paroles et des actes ? La misanthropie n’est-elle pas un composé de misogynie et de misandrie ? Peut-elle être érotique et créer des réseaux ? Comment se concrétise-t-elle dans les domaines du travail, de l’économie, de la technique, de la guerre, dans les problématiques afférentes aux minorités ? Et la démocratie peut-elle générer de la misanthropie ? / This sociological study draws on a comparative literature thesis entitled « Entre littérature et philosophie : l’Homme est-il un animal politique ? Physique de la misanthropie » (Between literature and philosophy: is Man a political animal? Physics of misanthropy) (defended in Nov. 2013, published by L’Harmattan). In this analysis, the aim was to try to sketch a philosophical draft of the hatred of humanity based on misanthropic theatre before trying to apply the results thus obtained to concentration camp literature and to dystopias, two other genres which form the breeding-ground of misanthropic doctrines and practices. This first thought process allowed giving form to some powerfully material aspects of misanthropy: its geography, its therianthropic productions, its infantile manifestations, its exanthropic phenomenology and its dietetics.In the present political science thesis, our aim is to identify the cultural determinations of misanthropy and misology (be it mythological, religious, artistic or in the media) before reflecting on the impact they might have on the political field of speech or of deeds. Isn’t misanthropy a compound of misogyny and misandry? Can misanthropy be erotic? How does it appear in the realms of work, economy, technique, war or in the issues relating to minorities? Eventually we will ask ourselves to which extent democracy creates misanthropy.

Zugl.: Diplomarbeit.

Dans ces travaux de thèse, nous nous sommes intéressés à l'influence du bruit synaptique sur la plasticité synaptique dans un réseau de neurones biophysiquement réalistes. Le simulateur utilisé est un système électronique neuromorphique. Nous avons implanté un modèle de neurones à conductances basé sur le formalisme de Hodgkin et Huxley, et un modèle biophysique de plasticité. Ces travaux ont inclus la configuration du système, le développement d'outils pour l'exploiter, son utilisation ainsi que la mise en place d'une plateforme le rendant accessible à la communauté scientifique via Internet et l'utilisation de scripts PyNN (langage de description de simulations en neurosciences computationnelles). / In this work, we have investigated the effect of input noise patterns on synaptic plasticity applied to a neural network. The study was realised using a neuromorphic hardware simulation system. We have implemented a neural conductance model based on Hodgkin and Huxley formalism, and a biophysical model for plasticity. The tasks performed during this thesis project included the configuration of the system, the development of software tools, the analysis tools to explore experimental results, and the development of the software modules for the remote access to the system via Internet using PyNN scripts (PyNN is a neural network description language commonly used in computational neurosciences).

Ces travaux ont été menés dans le cadre du projet européen FACETS-ITN. Nous avons contribué à la simulation de cellules corticales grâce à des données expérimentales d'électrophysiologie comme référence et d'un circuit intégré neuromorphique comme simulateur. Les propriétés intrinsèques temps réel de nos circuits neuromorphiques à base de modèles à conductance, autorisent une exploration détaillée des différents types de neurones. L'aspect analogique des circuits intégrés permet le développement d'un simulateur matériel temps réel à l'échelle du réseau. Le deuxième objectif de cette thèse est donc de contribuer au développement d'une plate-forme mixte - matérielle et logicielle - dédiée à la simulation de réseaux de neurones impulsionnels. / This work has been supported by the European FACETS-ITN project. Within the frameworkof this project, we contribute to the simulation of cortical cell types (employingexperimental electrophysiological data of these cells as references), using a specific VLSIneural circuit to simulate, at the single cell level, the models studied as references in theFACETS project. The real-time intrinsic properties of the neuromorphic circuits, whichprecisely compute neuron conductance-based models, will allow a systematic and detailedexploration of the models, while the physical and analog aspect of the simulations, as opposedthe software simulation aspect, will provide inputs for the development of the neuralhardware at the network level. The second goal of this thesis is to contribute to the designof a mixed hardware-software platform (PAX), specifically designed to simulate spikingneural networks. The tasks performed during this thesis project included: 1) the methodsused to obtain the appropriate parameter sets of the cortical neuron models that can beimplemented in our analog neuromimetic chip (the parameter extraction steps was validatedusing a bifurcation analysis that shows that the simplified HH model implementedin our silicon neuron shares the dynamics of the HH model); 2) the fully customizablefitting method, in voltage-clamp mode, to tune our neuromimetic integrated circuits usinga metaheuristic algorithm; 3) the contribution to the development of the PAX systemin terms of software tools and a VHDL driver interface for neuron configuration in theplatform. Finally, it also addresses the issue of synaptic tuning for future SNN simulation.

No description available.

Thesis (MSc (Biochemistry))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: The Hodgkin-Huxley model, created in 1952, was one of the first models in computational neuroscience and remains the best studied neuronal model to date. Although many other models have a more detailed system description than the Hodgkin-Huxley model, it nonetheless gives an accurate account of various high-level neuronal behaviours. The fields of computational neuroscience and Systems Biology have developed as separate disciplines for a long time and only fairly recently has the neurosciences started to incorporate methods from Systems Biology. Metabolic Control Analysis (MCA), a Systems Biology tool, has not been used in the neurosciences. This study aims to further bring these two fields together, by testing the feasibility of an MCA approach to analyse the Hodgkin-Huxley model. In MCA it is not the parameters of the system that are perturbed, as in the more traditional sensitivity analysis, but the system processes, allowing the formulation of summation and connectivity theorems. In order to determine if MCA can be performed on the Hodgkin-Huxley model, we identified all the discernable model processes of the neuronal system. We performed MCA and quantified the control of the model processes on various high-level time invariant system observables, e.g. the action potential (AP) peak, firing threshold, propagation speed and firing frequency. From this analysis we identified patterns in process control, e.g. the processes that would cause an increase in sodium current, would also cause the AP threshold to lower (decrease its negative value) and the AP peak, propagation speed and firing frequency to increase. Using experimental inhibitor titrations from literature we calculated the control of the sodium channel on AP characteristics and compared it with control coefficients derived from our model simulation. Additionally, we performed MCA on the model’s time-dependent state variables during an AP. This revealed an intricate linking of the system variables via the membrane potential. We developed a method to quantify the contribution of the individual feedback loops in the system. We could thus calculate the percentage contribution of the sodium, potassium and leak currents leading to the observed global change after a system perturbation. Lastly, we compared ion channel mutations to our model simulations and showed how MCA can be useful in identifying targets to counter the effect of these mutations. In this thesis we extended the framework of MCA to neuronal systems and have successfully applied the analysis framework to quantify the contribution of the system processes to the model behaviour. / AFRIKAANSE OPSOMMINMG: Die Hodgkin-Huxley-model, wat in 1952 ontwikkel is, was een van die eerste modelle in rekenaarmagtige neurowetenskap en is vandag steeds een van die bes-bestudeerde neuronmodelle. Hoewel daar vele modelle bestaan met ’n meer uitvoerige sisteembeskrywing as die Hodgkin-Huxley-model gee dié model nietemin ’n akkurate beskrywing van verskeie hoëvlak-sisteemverskynsels. Die twee velde van sisteembiologie en neurowetenskap het lank as onafhanklike dissiplines ontwikkel en slegs betreklik onlangs het die veld van neurowetenskap begin om metodes van sisteembiologie te benut. ’n Sisteembiologiemetode genaamd metaboliese kontrole-analise (MKA) is tot dusver nog nie in die neurowetenskap gebruik nie. Hierdie studie het gepoog om die twee velde nader aan mekaar te bring deurdat die toepasbaarheid van die MKA-raamwerk op die Hodgkin-Huxley-model getoets word. In MKA is dit nie die parameters van die sisteem wat geperturbeer word soos in die meer tradisionele sensitiwiteitsanalise nie, maar die sisteemprosesse. Dit laat die formulering van sommasie- en konnektiwiteitsteoremas toe. Om die toepasbaarheid van die MKA-raamwerk op die Hodgkin-Huxleymodel te toets, is al die onderskeibare modelprosesse van die neurale sisteem geïdentifiseer. Ons het MKA toegepas en die kontrole van die model-prosesse op verskeie hoëvlak, tydsonafhanklike waarneembare sisteemvlak-eienskappe, soos die aksiepotensiaal-kruin, aksiepotensiaal-drempel, voortplantingspoed en aksiepotensiaal-frekwensie, gekwantifiseer. Vanuit hierdie analise kon daar patrone in die proseskontrole geïdentifiseer word, naamlik dat die prosesse wat ’n toename in die natriumstroom veroorsaak, ook sal lei tot ’n afname in die aksiepotensiaal-drempel (die negatiewe waarde verminder) en tot ’n toename in die aksiepotensiaal-kruin, voortplantingspoed en aksiepotensiaalfrekwensie. Deur gebruik te maak van eksperimentele stremmer-titrasies vanuit die literatuur kon die kontrole van die natriumkanaal op die aksiepotensiaaleienskappe bereken en vergelyk word met die kontrole-koëffisiënte vanuit die modelsimulasie. Ons het ook MKA op die model se tydsafhanklike veranderlikes deur die verloop van die aksiepotensiaal uitgevoer. Die analise het getoon dat die sisteemveranderlikes ingewikkeld verbind is via die membraanpotensiaal. Ons het ’n metode ontwikkel om die bydrae van die individuele terugvoerlusse in die sisteem te kwantifiseer. Die persentasie-bydrae van die natrium-, kalium- en lekstrome wat tot die waarneembare globale verandering ná ’n sisteemperturbasie lei, kon dus bepaal word. Laastens het ons ioonkanaalmutasies met ons modelsimulasies vergelyk en getoon hoe MKA nuttig kan wees in die identifisering van teikens om die effek van hierdie mutasies teen te werk. In hierdie tesis het ons die raamwerk van MKA uitgebrei na neurale sisteme en die analise-raamwerk suksesvol toegepas om die bydrae van die sisteemprosesse tot die modelgedrag te kwantifiseer.

Gerald Heard (1889-1971) was an influential figure among the intelligentsia of the 1930s, once described by E.M. Forster as “one of the most penetrating minds in England.” However, he remains an ill-defined footnote, a marginal figure whose influence and reputation, although acknowledged, remains unexamined. This dissertation examines his life and work, and considers the role which Heard, as a generaliser and public intellectual, played in the intellectual landscape of the 1930s. Central to Heard’s philosophy was a belief that society was in need of a spiritual and psychological force which could allow isolated individuals to participate in community with one another. Heard’s solution to bring about this evolution of consciousness would prove to be partly psychological, partly mystical and partly down to the product of a particular way of living. The first chapter outlines Heard’s philosophy in detail. Subsequent chapters are structured so as to provide a loose biographical chronology, each focussing on a different phase of Heard’s career and examining the development of his thought. Running throughout the dissertation is a consideration of Heard’s role as a public intellectual. It was as a popular ‘generaliser’ of thought that Heard found his public, and the limited degree of success he found as a man of action could be seen to be a natural limitation of the role he had constructed for himself. Chapter II focuses on Heard’s time as personal secretary to Sir Horace Plunkett, father of the Irish Co-Operative Movement, and how the ideals of this movement can be seen to inform his developing ideas of human community. Chapter III looks at Heard’s role as a broadcaster with the B.B.C., where he became a noted populariser of science, firmly establishing himself as a public figure and cultural authority. It is arguably this increased public profile which provided Heard with a ‘public’ to whom he could address his ideas. Chapter IV, drawing on archival material from Dartington Hall, considers Heard’s role as a lecturer at Dartington School, and more importantly his first experiment to establish a small ‘group’ for meditation in an attempt to discover the mystical and psychological basis for a co-operative society. Chapter V examines his career as an outspoken pacifist, where he would advance his arguments for a radical reorganisation of society as a practical solution to the question of peace and further attempt to become a man of action.

AbstractThis essay discusses the concepts of eugenics and social caste in Brave New Worldin relation to Aldous Huxley, from a biographical perspective. The essay analyzes how events and personal relationships of Aldous Huxley have influenced the depiction of the concepts social caste and eugenics in his novel Brave New World. Using sources which recount the travels and the personal encounters that Aldous Huxley made throughout his life, this essay makes comparisons and draws conclusions as to how these eventsand relationshipshave affected the depiction of social caste and eugenics in Brave New World

Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal.