Typescript (photocopy). / Digitized by Kansas Correctional Industries

The anterior thalamic nuclei (ATN) are a critical part of an extended hippocampal system that supports key elements of episodic memory. Damage or disconnection of the ATN is a component of clinical conditions associated with severe anterograde amnesisa such as the Korsakoff’s syndrome, thalamic stroke, and neurodegenerative disorders. Previous studies have demonstrated that the ATN and hippocampus are often interdependent, and that ATN damage can result in ‘covert pathology’ in ostensibly healthy distal regions of the extended hippocampal system. Adult male rats with neurotoxic bilateral ATN lesions or sham surgery were post-operatively housed in an enriched environment or standard housing after a lesion-induced spatial working memory deficit had been established. These rats were retested on cross-maze and then trained in radial-arm maze spatial memory tasks. Other enriched rats received pseudo-training only after the enrichment period. The detailed neuromorphology of neurons was subsequently examined in the hippocampal CA1. Soma characteristics were also examined in the retrosplenial granular b cortex and the prelimbic cortex. In Experiment 1, ATN lesions produced clear deficits in both the cross-maze and radial-arm maze tasks and reduced hippocampal CA1 dendritic complexity, length, and spine density, while increasing the average diameter of the dendrites. Post-operative enrichment reversed the ATN lesion-induced deficits in the cross-maze and radial-arm maze, and returned CA1 basal and apical spine density to a level comparable to that of sham standard housed trained rats. The sham enriched rats exhibited improved radial-arm maze performance and increased CA1 branching complexity and spine density in both basal and apical arbors compared to sham standard housed rats. The neuromorphological changes observed in the enriched ATN and sham rats may be in part responsible for the spatial working memory improvements observed. Experiment 2 provided support for this contention by demonstrating that the CA1 spine changes were explicitly relevant to spatial learning and memory, because trained enriched sham and ATN rats had increased spines, particularly in the basal tree when compared to closely comparable pseudo-trained enriched rats. Interestingly, spatial memory training increased the numbers of both thin and mushroom spines, whereas enrichment was only associated with an increase in thin spines. In Experiment 3, ATN lesions increased cell body size in layer II of the retrosplenial granular b cortex, whereas enrichment decreased cell body size in layer V of this region. Neither ATN lesions nor enrichment had any effect on cell body morphology in the prelimbic cortex. The current research provides some of the strongest evidence to date of ATN and hippocampal interdependence within the extended hippocampal system, and provides the first evidence of neuromorphological correlates of recovery after ATN lesions.

La contribution de ce travail de thèse s'inscrit au sein d'un domaine multidisciplinaire regroupant le traitement automatique du langage naturel, l'indexation dans un système d'information documentaire et l'organisation des connaissances autour de l'information écrite. Sa particularité consiste en la mise à disposition d'outils pour le traitement automatique de l'information.<br />L'objectif est de construire une Plate-forme d'analyse morpho-syntaxique pour l'indexation automatique et la recherche d'information. Elle est composée d'un noyau d'indexation automatique (processus d'indexation) qui utilise le modèle des syntagmes nominaux comme descripteurs de l'information textuelle. Ces syntagmes sont organisés selon une approche Logique Intensionnelle/Extensionnelle (processus de classification des connaissances) qui permet d'ordonner les objets d'une classe et de distinguer les classes de connaissances. A la base de cette dernière propriété, nous construisons notre approche pour la recherche d'information (processus de recherche d'information). <br />Cette Plate-forme d'analyse dans sa logique de fonctionnement sera un outil d'investigation orienté vers l'organisation et la gestion des connaissances écrites.<br />Dans notre recherche, cet aspect sur l'organisation des connaissances a été conduit dans le but de faire émerger les propriétés linguistiques et le traitement du langage dans une pratique expérimentale sur l'indexation automatique documentaire. Nous avons montré la nécessité de coordonner d'autres sources et stratégies dans l'exploration de ces propriétés. Il s'agit du mode de raisonnement et de la technique d'exploitation des objets du discours spécifiques à la gestion des connaissances (comme étape préalable à la recherche d'information).<br />Ces deux derniers aspects (mode et technique) intégrés dans le processus de la présentation et de l'organisation du syntagme nominal offrent des scénarii pertinents pour la recherche d'informations.