White, J; (2007) Dissociating the lesion sites that cause difference types of speech production difficulties. Doctoral thesis , UCL (University College London).

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Abstract

Spoken language ability is one of the most complex functions the brain performs, and sets humans apart from other animals. Loss of language ability following brain injuries such as stroke is devastating. The aim of this study was to examine the extent to which lesion site detected by magnetic resonance imaging (MRI) can predict language performance following stroke. Voxel-based morphometry (VBM) analysis was used to find correlations between language performance and brain lesions. The gray matter images of 94 stroke patients and 64 healthy controls (all of whom were right handed) and their language test scores in eight single-word language CAT tests (Comprehensive Aphasia Test) were included in the analysis. Multiple regression was performed at every voxel of the brain to find those voxels where gray matter density was low and behavioural performance was poor The results of our VBM analyses showed that acquired speech production deficits were most likely following lesions to any of the following brain regions: the left frontal orbitalis, left insula (anterior and posterior), left caudate nucleus, left thalamus, and right cerebellum. Lexical phonological retrieval was more impaired if the damage was restricted to the left ventral frontal areas, extending into the anterior insula, and the caudate nucleus, while sublexical phonological retrieval was more impaired if damage was restricted to the left posterior insula and left thalamus. This double dissociation between the anterior and the posterior insula has not been reported previously. The results also showed that phonological short-term memory is more dependent upon the left supramarginal gyrus, consistent with previous functional imaging studies of healthy subjects. Once these task-specific effects had been accounted for, there remained a large area of the posterior frontal cortex where damage impairs performance of all eight speech language tasks.

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