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Title: The human medial temporal lobe, brain connectivity, and recognition memory
Author: Rudebeck, Sarah
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2012
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The brain is made up of networks of brain regions that interact through white matter fibre tracts. These pathways are collections of thousands of axons and are vital for the successful functioning of the brain. The recent development of diffusion tensor imaging (DTI) has made it possible to investigate the integrity of these tracts in the human brain, whilst advances in the analysis of functional magnetic resonance imaging (fMRI) data have enabled the functional interaction between brain regions to be assessed. The first aim of this thesis was to investigate one of the main white matter tracts of the medial temporal lobe (MTL), a region of the brain that has been implicated in long-term memory (LTM) functioning. Specifically, the relationship between the microstructural integrity of the fornix, the major efferent of the hippocampus, and recognition memory performance (as assessed by an experimental task) was explored in young adults (Chapter 2). Our results showed that the ability of young adults on recollection, but not familiarity, memory correlated significantly with fornix microstructural integrity. These results speak to theories of MTL function and highlight a role for the hippocampus in recollection. In Chapter 3, it was investigated whether variations in fornix microstructure in young adults are also associated with differences in recall and recognition memory abilities as measured by standard psychometric memory tests. Although aspects of the results from this work converged with those from the first study, an inconsistent pattern of findings was observed overall, perhaps reflecting the relative insensitivity of the standard memory tests used. Next, the consequences of organic brain damage to MTL regions on white matter and resting-state functional connectivity of the brain were investigated in two amnesic patients with focal MTL lesions (Chapter 4). DTI and resting-state fMRI revealed that, compared to age-matched neurologically healthy controls, a patient with gross MTL damage had significant white matter changes in her fornix and right uncinate fasciulus, and also reduced functional connectivity between brain regions associated with the posterior hippocampus resting-state network. Surprisingly, a patient with selective bilateral damage to the hippocampus did not have any significant changes to her resting-state networks or white matter integrity. Finally, a large scale behavioural study was conducted to determine whether a single cognitive training task could be created to improve LTM. This was the first stage of a project designed to determine whether the improvement of LTM via cognitive training is supported by changes in white matter integrity and functional connectivity (Chapter 5). It was found that extensive cognitive training in young adults on a complex spatial working memory task was able to stimulate improvements in recognition memory in some participants. The limitations and implications of the findings from all of the aforementioned studies are considered in the concluding chapter (Chapter 6).
Supervisor: Nobre, Kia ; Lee, Andy Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available