Identifying Individual Differences in the Neural Correlates
of Language Processing Using fMRI

Abstract

Mapping language functions in the brain is of profound theoretical and clinical interest. The aim of the current Ph.D. project was to develop an fMRI paradigm to assesses different language processes (i.e., phonological, semantic, sentence processing) and modalities (listening, reading, repetition) in a stimulus-driven manner, keeping non-linguistic task demands to a minimum. Cortical activations and functional connectivity patterns were largely in line with previous research, validating the suitability of the paradigm for localizing different language processes. The first empirical chapter of the thesis investigated sentence comprehension in listening and reading, which elicited largely overlapping activations for the two modalities and for semantic and syntactic integration in the left anterior temporal lobe (ATL). Functional connectivity of the left ATL with other parts of the cortical language network differed between the modalities and processes. The second empirical chapter explored individual differences in brain activity in relation to verbal ability. Results supported the notion of more extended as well as stronger activations during language processing in individuals with higher verbal ability, possibly reflecting enhanced processing. The third empirical chapter further investigated individual differences in brain activity, focusing on lateralization in activity as a fundamental principle of how language processing is functionally organized in the brain. Degrees of left-lateralization differed significantly between language processes and were positively related to behaviorally assessed language lateralization. Furthermore, the results provided new evidence supporting a positive relationship between left-lateralization and verbal ability. The thesis concludes with a discussion of the significance of the results with regard to general principles of brain functioning and outlines potential clinical implications.