Abstract/Summary

The effects of bilingualism on the brain are often investigated in isolation, despite brain structure, function, and cognition being interdependent factors. The cognitive effects of bilingualism are often inconsistent, suggesting that the tasks used may not be sensitive enough to measure its impact effectively. This thesis aimed to bridge the gap between the cognitive and functional effects of bilingualism using elements of task-free and task-based experimental designs. A literature review revealed that the cognitive effects of bilingualism occur in two primary domains: language and executive function, which are supported by functional networks containing overlaps in the brain regions involved. Using a task-driven resting-state electroencephalography design, a continuous measure of bilingualism, and non-linear statistics, we conducted three studies to investigate the impact of the demands of separate cognitive domains and bilingual experience on functional connectivity. The first study examines bilingual brain function at rest and following a domain-general artificial grammar learning task and found whole-brain bilingualism-modulated post-task connectivity, including greater posterior and left temporal connectivity at higher levels of bilingualism. The second study examines the impact of task demands in the language domain, finding that level of bilingualism significantly impacts connectivity between left hemisphere language network regions. Finally, the third study assessed the impact of executive function domain task demands, revealing bilingualism-induced modulations to connections from occipital to central and temporal regions. The results of these studies show differential bilingualism-induced modulations to functional connectivity by cognitive domain. Overall, this thesis highlights the importance of cognitive context on bilingual brain function, leading to modulations in connectivity dependent on the task demands. Crucially, the results revealed that bilingualism also impacts neural reorganisation in the short-term, and that these adaptations are often non-linear in nature. These findings are discussed regarding their implications for current models and theories in the field.