Soutenance de thèse Jérémy GARDETTE

Résumé de la thèse: The medial temporal lobe (MTL) is a set of interconnected structures located on the medial face of the temporal lobe, which include the hippocampus and perirhinal cortex. Numerous results have challenged the view that these regions constitute a module exclusively dedicated to declarative memory. A different type of models thus emerged, built around the notion of representation. Further, an approach termed representational-hierarchical (RH) proposes to decompose cognitive processes into representations and operations. In this view, the representation is the key factor determining the engagement of a given MTL region in a cognitive process, independently of the operation. The present thesis aimed to assess the predictions of the RH model, and to investigate how its principles of functional organisation interact with (1) the long-axis of the hippocampus, and (2) hemispheric lateralisation. We first investigated, in two behavioural studies (N=66 and N=76), how the process of recollection can be broken down into a representation and an operation, using a partial-cue image reconstruction paradigm. Our results showed that it is possible to isolate pattern-completion of scenes and objects, but that additional cognitive mechanisms can be confounded depending on task instructions. In a subsequent fMRI study (N=51), we replicated the previously-reported result that the hippocampus is specifically engaged in pattern-completion of scenes; whereas the perirhinal cortex was more recruited by object processing. We also extended it to additional operations (i.e., visual-discrimination and familiarity-based memory), thereby supporting the RH view of the MTL: the preferential engagement of the hippocampus and perirhinal cortex in scene and single object representations, respectively, is independent of the operation. In addition, our results revealed that the specialisation of the hippocampus was not equivalent in its posterior and anterior segments, which rather supports a specialisation of the hippocampus long-axis depending on the resolution of the representation processed. This constitutes an extension of the RH principles within the hippocampus. Finally, we assessed the hemispheric lateralisation of representational specialisation as operationalised through perceptual manipulations. To this end, we tested patients who underwent left or right MTL surgery for drug-resistant epilepsy in a visual-discrimination task. Perceptual-complexity dependant impairments were found in case of right, but not left, MTL damage. Taken together, our findings are in favour of the RH view of the MTL; they also highlight the diversity of features that characterise a given representation, thereby opening new questions for future research.

PhD Supervisor: Pascal Hot, Université Savoie Mont-Blanc

Composition du Jury:
Pascal HOT, PROFESSEUR DES UNIVERSITÉS, Université de Savoie Mont-Blanc - Directeur de thèse
Christine BASTIN, MAITRE DE RECHERCHE, Université de Liège - BELGIQUE - Rapporteure
Francis EUSTACHE, PROFESSEUR DES UNIVERSITÉS, Université de Caen - Rapporteur
Emmanuel BARBEAU, DIRECTEUR DE RECHERCHE, CNRS Occitanie Ouest - Examinateur
Christopher MOULIN, PROFESSEUR DES UNIVERSITÉS, Université Grenoble Alpes - Examinateur
Morgan BARENSE, PROFESSEUR, Université de Toronto - CANADA - Examinateur
Stéphane ROUSSET, Maître de conférence, Université Grenoble Alpes - Membre invité