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Neuroimaging studies of the distributed semantic system and its disruption in disease

Mummery, Catherine Jane; (2000) Neuroimaging studies of the distributed semantic system and its disruption in disease. Doctoral thesis (Ph.D), UCL (University College London). Green open access

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This thesis investigates the neural correlates of semantic processing using a variety of language tasks while scanning normal subjects and patients with positron emission tomography. The aims were to (i) describe the general semantic network; (ii) investigate the internal architecture of semantic memory by examining variations in activation for different types of task or knowledge; (iii) study disruption of the network in patients with focal cognitive deficits. In normals, the semantic network comprised the left anterior and inferolateral temporal lobe, inferior frontal lobe and temporo-parietal junction. Studies were performed to examine differential neural responses for categories of knowledge, and showed that the predominant segregation within the semantic system was due to knowledge type rather than due to object domain. The precise contribution of regions comprising the semantic network was explored using differing explicit and implicit semantic tasks. Disruption of the semantic network was then investigated in patients with semantic dementia, who have a selective semantic associative deficit and anomia. Structural analysis showed a striking correlation between semantic deficit and degree of atrophy in the anterolateral temporal lobe. Functional analysis suggested that the anterior temporal lobes were being activated abnormally, possibly in an attempt to compensate for the damage, while the posterior inferior temporal lobe failed to activate despite being structurally intact. A patient with fronto-parietal lobe damage was also studied; results confirmed the importance of temporal regions for semantic processing and suggested that the inferior frontal lobe was not necessary for task performance. The results suggest differential roles for regions within the distributed semantic system. For example, the anterior temporal lobe may act as a 'convergence' region, integrating multimodal representations into a unique concept. Secondly, results show that the conjunction of neuropsychology and neuroimaging allows more precise definition of the roles of regions involved in semantic processing.

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: Neuroimaging studies of the distributed semantic system and its disruption in disease
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Thesis digitised by ProQuest.
Keywords: Biological sciences
URI: https://discovery.ucl.ac.uk/id/eprint/10103708
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