Dans ces travaux de thèse, nous nous sommes intéressés à l'infuence 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 scientique via Internet et l'utilisation de scripts PyNN (langage de description de simulations en neurosciences computationnelles).

Ce sujet de recherche a pour principaux objectifs la réalisation d'une bibliothèque de fonctions électroniques analogiques intégrées réalisant les opérations mathématiques présentes dans les modèles des canaux ioniques des neurones et l'évaluation des éléments de cette même bibliothèque. Ce travail se poursuit par la conception d'un système démonstrateur basé sur un circuit intégré analogique neuromimétique utilisant la bibliothèque d'opérateurs pour que ce même circuit intégré puisse être utilisé dans de nouvelles expériences mettant en oeuvre la technique hybride. En fonction des performances du circuit, il a été aussi étudié la faisabilité de son utilisation pour le développement d'un outil d'extraction des paramètres d'une cellule nerveuse, voire même d'un mini-réseau composé de moins d'une dizaine de neurones, par la technique d'optimisation.

The purpose of this thesis work is to model the gate control theory, which explains the modulation of pain signals, with a motivation of finding new possible targets for pain treatment and to find novel control algorithms that can be used in engineering practice. The difference of the current study from the previous modeling trials is that morphologies of neurons that constitute gate control system are also included in the model by which structure-function relationship can be observed. Model of an excitable neuron is constructed and the response of the model for different perturbations are investigated. The simulation results of the excitable cell model is obtained and when compared with the experimental findings obtained by using crayfish, it is found that they are in good agreement. Model encodes stimulation intensity information as firing frequency and also it can add sub-threshold inputs and fire action potentials as real neurons. Moreover, model is able to predict depolarization block. Absolute refractory period of the single cell model is found as 3.7 ms. The developed model, produces no action potentials when the sodium channels are blocked by tetrodotoxin. Also, frequency and amplitudes of generated action potentials increase when the reversal potential of Na is increased. In addition, propagation of signals along myelinated and unmyelinated fibers is simulated and input current intensity-frequency relationships for both type of fibers are constructed. Myelinated fiber starts to conduct when current input is about 400 pA whereas this minimum threshold value for unmyelinated fiber is around 1100 pA. Propagation velocity in the 1 cm long unmyelinated fiber is found as 0.43 m/s whereas velocity along myelinated fiber with the same length is found to be 64.35 m/s. Developed synapse model exhibits the summation and tetanization properties of real synapses while simulating the time dependency of neurotransmitter concentration in the synaptic cleft. Morphometric analysis of neurons that constitute gate control system are done in order to find electrophysiological properties according to dimensions of the neurons. All of the individual parts of the gate control system are connected and the whole system is simulated. For different connection configurations, results of the simulations predict the observed phenomena for the suppression of pain. If the myelinated fiber is dissected, the projection neuron generates action potentials that would convey to brain and elicit pain. However, if the unmyelinated fiber is dissected, projection neuron remains silent. In this study all of the simulations are preformed using Simulink.

The work in this thesis concerns mechanisms of excitability of neurons. Specifically, it deals with how neurons respond to input, and how their response is controlled by ion channels and other active components of the neuron. I have studied excitability in two systems of the nervous system, the hippocampus which is responsible for memory and spatial navigation, and the peripheral C–fibre which is responsible for sensing and conducting sensory information to the spinal cord. Within the work, I have studied the role of excitability mechanisms in normal function and in pathological conditions. For hippocampus the normal function includes changes in excitability linked to learning and memory. However, it also is intimately linked to pathological increases in excitability observed in epilepsy. In C–fibres, excitability controls sensitivity to responses to stimuli. When this response becomes enhanced, this can lead to pain. I have used computational modelling as a tool for studying hyperexcitability in neurons in the central nervous system in order to address mechanisms of epileptogenesis. Epilepsy is a brain disorder in which a subject has repeated seizures (convulsions) over time. Seizures are characterized by increased and highly synchronized neural activity. Therefore, mechanisms that regulate synchronized neural activity are crucial for the understanding of epileptogenesis. Such mechanisms must differentiate between synchronized and semi synchronized synaptic input. The candidate I propose for such a mechanism is the fast outward current generated by the A-type potassium channel (KA). Additionally, I have studied the propagation of action potentials in peripheral axons, denoted C–fibres. These C–fibres mediate information about harmful peripheral stimuli from limbs and organs to the central nervous system and are thereby linked to pathological pain. If a C–fibre is activated repeatedly, the excitability is altered and the mechanisms for this alteration are unknown. By computational modelling, I have proposed mechanisms which can explain this alteration in excitability. In summary, in my work I have studied roles of particular ion channels in excitability related to functions in the nervous system. Using computational modelling, I have been able to relate specific properties of ion channels to functions of the nervous system such as sensing and learning, and in particular studied the implications of mechanisms of excitability changes in diseases. / <p>QC 20102423</p>

Dans ces travaux de thèse, nous nous sommes intéressés à l'in fluence 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 con figuration 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).

The aim of this thesis is to analyse two novels written by Aldous Huxley an anti-utopian novel Brave New World (1932) and a utopian novel Island (1963). The examination of both Huxley´ s works is based on the analysis of literary genres. The thesis outlines difficulties concerning a precise definition of the terms "utopia," "anti-utopia," and "dystopia." The genesis of the genres is also briefly mentioned. The thesis also deals with both common and distinct features of the genres. Because of the purpose of the analysis regarding Brave New World and Island, the thesis includes Huxley´ s other works (essays and novels), dystopian novels Nineteen Eighty Four by George Orwell and We by Yevgeny Zamyatin and a utopian novel Men Like Gods by H. G. Wells.

A well documented laboratory setup, leech preparation process, and bio-potential data recording process are needed. Repeatability and quality data recordings are essential and thus dictate the requirements of the laboratory setup and processes listed above. Advances in technology have both helped and hindered this development. While very precise equipment is required to record the low voltage bio-potentials, noisy electronic equipment and wires surrounding the work area provide high levels of interference. Proper laboratory setup and data recording processes, however, limit the unwanted interference. Quality data can only be recorded from a properly handled and prepared leech subject. Proper setup and procedures result in quality recordings which lend a clean signal for furthering the understanding of nerve functionality. The electrophysiology lab at California Polytechnic State University in San Luis Obispo is an example of a proven lab setup for high quality signal capture.

Neuroprosthetics is at the intersection of neuroscience, biomedical engineering, and physics. A biocompatible neuroprosthesis contains artificial neurons exhibiting biophysically plausible dynamics. Hybrid systems analysis could be used to prototype such artificial neurons. Biohybrid systems are composed of artificial and living neurons coupled via real-time computing and dynamic clamp. Model neurons must be thoroughly tested before coupled with a living cell. We use bifurcation theory to identify hazardous regimes of activity that may compromise biocompatibility and to identify control strategies for regimes of activity desirable for functional behavior. We construct real-time artificial neurons for the analysis of hybrid systems and demonstrate a mechanism through which an artificial neuron could maintain duty cycle independent of variations in period.

In this study, the manipulations of history and language in the dystopias of &ldquo / Nineteen Eighty-Four&rdquo / by George Orwell, &ldquo / We&rdquo / by Yevgeni Zamyatin and &ldquo / Brave New World&rdquo / by Aldous Huxley are examined. The principal aim of this investigation is to demonstrate that in these imaginary societies absolute stability is achieved through the manipulations of these two domains. The thesis argues that if the domains of history and language are not taken under control, they are to provide the subjects with the standard of comparisons which would enable them to realize that they are in fact dominated. However, once these domains are manipulated, they are transformed into the means of the dystopian rulers for mentally impoverishing people in a way that they would not be capable of conceiving the flaws within the system and therefore, would not attempt to challenge the order or require a change. In this sense, it is proposed that the subjects of these closed societies, who are formed as a result of the reshaping of history and language, would lack the mental capabilities to identify their subjection and behave automatically in the manner that is imposed on them by the political order. Moreover, in this study, the relationship of the genre dystopia with political theory is explored / it is indicated that dystopias are not only literary works, but rather they are also texts of social criticism containing certain warnings about the future course of events. Relying on this argument, it is claimed that such an invasion of the minds by the control over history and language in our three dystopias is the exaggerated version of the ideological relationships of the individuals to these two realms in the contemporary societies. Thus, having in mind that in the dystopias examined here the manipulations of history and language are the preconditions of the use of other realms (such as religion, sexuality and science), it is concluded that these texts enable modern individuals to see that in order to maintain a critical distance with the established political and social order, the multiplicity of linguistic resources and knowledge of history are very crucial.

Dans un contexte où l'usage de circuits neuromimétiques se généralise au sein des neurosciences, nous étudions ici leur intégration au sein de réseaux adaptatifs. Les circuits mis en oeuvre se basent sur un modèle proche de la biologie résolu en continu et en temps réel. Les calculs relatifs à l'adaptation du réseau sont réalisés en numérique temps réel, logiciel et/ou matériel. La partie logicielle est assurée par un ordinateur interfacé à travers le bus PCI, tandis que la partie matérielle utilise des EPGAS. Trois générations sont présentés avec une analyse critique sur leur utilisation comme système de simulation de réseau neuronal.