Oberhuber, Marion; (2017) Examining phonological processing in the healthy and damaged brain. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

In this thesis I explore the neural signature of different types of speech sound processing, in the healthy brain and after damage through stroke. The first two Experiments applied a newly developed fMRI language paradigm in healthy controls to study phonological retrieval from speech, orthography and semantics. This showed that there are at least two types of phonological processing that can be dissociated on a neuronal level. Bilateral superior temporal gyri were associated with processing auditory (phonological) representations of speech, consistent with the notion of input to phonology. In contrast, left putamen and precentral cortex/pars opercularis were associated with pre-articulatory activity, and thus with outputs from phonology. The validation of the results in a separate, larger sample increased confidence that these findings are robust rather than false positives. Experiment 3 was concerned with examining the role of a “key player” in phonological processing, which revealed that different parts of the supramarginal gyrus differ in their response profile during a set of language tasks. This is in accordance with cytoarchitectural and connectivity studies demonstrating the structural variability of the region, and has implications for prior imaging studies considering the supramarginal gyrus as a uniform entity in the phonological network. The final experiment revealed that the loss of supramarginal gyrus through stroke has inconsistent effects on language abilities, possibly due to other brain regions or white matter tracts that were damaged in some patients but not in others. It also showed that additional brain regions were recruited in patients compared to controls, which might reflect compensatory brain activation that supports recovery. Taken together, this work proposes a new way of interpreting phonological effects, in particular within the supramarginal gyrus, and new insights into how the brain supports phonological processing after stroke-induced damage.

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