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Le rôle des connaissances préalables dans l'apprentissage en mémoire déclarative : une étude dans l'amnésie, le vieillissement et la maladie d'Alzheimer

Abstract : The experimental study of human memory has had two historic moments in the last sixty years. 1957 marks the discovery of the role of the medial temporal lobes in conscious learning. 1997 marks the discovery of two systems of declarative memory, namely episodic and semantic memories. These major breakthroughs are owed to clinical case studies in neuropsychology. This thesis follows on from the neuropsychological tradition: its genesis owes everything to a patient suffering from an atypical form of developmental amnesia, the patient KA. The starting point of this work was a thorough neuropsychological study of this patient. Two striking findings shortly arose. First, despite lifelong amnesia, KA had acquired exceptional levels of knowledge about the world. Second, remaining explicit learning abilities were restricted to meaningful, not meaningless, memoranda. As a consequence, we have investigated two research pathways in that thesis. First, we aimed at better characterizing preserved learning abilities and brain structure of the patient KA. Second, our goal was to explore how prior knowledge affects new declarative learning or, put simply, how do we learn what we know? In a first series of behavioural and neuroimaging experiments, we have shown in this patient a severe and selective damage of the whole extended hippocampal system, but preserved subhippocampal structures (entorhinal, perirhinal and parahippocampal cortex). The patient suffers from severe episodic amnesia, but we bring striking evidence for supranormal semantic knowledge as well as normal explicit learning skills. These skills were, however, restricted to familiar stimuli, that is, stimuli carrying pre-experimental knowledge. In a second series of behavioural and neuroimaging experiments, we explored the hypothesis that prior knowledge can facilitate new learning in declarative memory, even in aging or in situations where structures of the medial temporal lobe are or injured, as in amnesia or Alzheimer's disease. Our results suggest the existence of processes allowing fast learning in declarative memory, independently of the hippocampal system, and that are sensitive to the presence of pre-existing representations in long-term memory. Such learning processes appear to be selectively affected by Alzheimer's disease at the pre-dementia stage, in relation to a lack of activation of subhippocampal regions. In contrast, healthy elderly were able to rely on these learning processes to compensate for the decline in associative memory associated with aging. This work lends support to the models postulating a functional dissociation with respect to learning in declarative memory. It indeed strengthens recent neurocognitive and computational accounts that suggest a rapid neocortical learning path under certain circumstances. It highlights the dynamics of learning in declarative memory and in particular the fundamental entanglement between "knowing" and "remembering". What I know profoundly impacts what I will remember. The present thesis points towards new cognitive tools for the diagnosis of Alzheimer's disease. It further brings evidence that medial temporal lesions differentially impact learning depending on the status of the memoranda in long-term memory, which sheds a new light on material-specific effects in amnesia. Our work speaks for a thorough consideration of whether the contents of events have prior representations within long-term memory, and to further better characterize their nature if we are to better understand learning mechanisms. It also brings additional clues for a deeper understanding of how learning and memory can be preserved in aging. More generally, it contributes to a better understanding of the factors determining successful learning, with a focus on how retrieval and acquisition processes overlap during learning. Such findings have potential applications in the educational field.
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Submitted on : Wednesday, June 24, 2020 - 4:26:11 PM
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Pierre-Yves Jonin. Le rôle des connaissances préalables dans l'apprentissage en mémoire déclarative : une étude dans l'amnésie, le vieillissement et la maladie d'Alzheimer. Neurosciences. Université Paul Sabatier - Toulouse III, 2019. Français. ⟨NNT : 2019TOU30104⟩. ⟨tel-02880185⟩