Le présente mémoire fournit des nouvelles évidences montrant la modulation de l’excitabilité neuronale intrinsèque et synaptique, et la conséquence de cette modulation sur l’activité neuronale durant à la fois, les oscillations lentes du sommeil, et les crises électrographiques in vivo chez des animaux anesthésiés. Nous effectuons des enregistrements intracellulaires simultanés de neurones corticaux et des potentiels de champs locaux au niveau du gyrus suprasylvien à l’intérieur du cortex associatif pariétal (aires : 5, 7 et 21). Nous suggérons que la fluctuation de la concentration extracellulaire du calcium durant les oscillations lentes du sommeil module à la fois, l’excitabilité intrinsèque et synaptique des neurones corticaux, ainsi par conséquent, elle module affecte la relation d’input-output de ces neurones.

L’apparition durant les oscillations lentes du sommeil, des crises de type Lennex-Gastaut qui sont générées corticalement, nous a permet d’étudier les propriétés spatio-temporelles des ondes paroxysmiques rapides associées avec ce type de crises. Nous suggérons que les ondes paroxysmiques rapides apparaissent comme des oscillations quasi-indépendantes même dans les localisations corticales voisines, suggérant leur origine focal.

The present memoir provides new evidences showing the modulation of intrinsic and synaptic excitability of cortical neurons, and the consequence of this modulation on neuronal activity during both slow sleep oscillations and electrographic seizures in vivo in anaesthetized animals. We performed simultaneous recordings of cortical neurons with local field potentials in suprasylvian gyrus within parietal associative cortex (area 5, 7 and 21). We suggest that the fluctuation of extacellular calcium concentration during slow sleep oscillations, modulates both intrinsic and synaptic excitability cortical neurons, thus by consequence modulates the input-output relationship of these neurons.

The occurrence during slow-wave sleep of cortically generated Lennox-Gastaut type of seizures admits us to study the spatio-temporal properties of paroxysmal fast runs associated with this type of seizures. We suggest that fast runs appeared as quasi-independent oscillations even in neighbouring cortical locations suggesting their focal origin.

The following memoir is presented in the form of two principal scientific articles. One of them is submitted for publication in Journal of Physiology and the other one is submitted to the Journal of Neurophysiology. The articles are precedes by a general introduction, which describes the theoretical context and experimental strategies of the studies described in the articles including one part of an article to which I contributed as coauthor and which is published in European Journal of Neuroscience titled: Modulation of synaptic transmission in neocortex by network activities. A general conclusion finalizes the memoir with the presentation of a communes concepts linked the results of these articles. The bibliography used for both introduction and conclusion, is presented at the very end of the memoir. Since the articles have been submitted to different scientifics journals, the format of bibliographical citations changes from one to another.

I would like to use this occasion to express my gratitude to my memoir supervisor Dr. Igor Timofeev for the opportunity of working in his laboratory. Without his critics, discussions, corrections and support the present study would not have been possible.

I also would like to thank my colleagues Sylvain Crochet, who in parallel with my superviser, teached me to do electrophysiological experiments and analysis, Sylvan Chauvette for his unvaluable contribution to our common publications and Josée Seigneur for her general help.

Finally, I would like to thank Mr. Pierre Guiguère, Denis Drolet and all my colleagues for their technical and moral support in every moment.