Abstract/Summary

In the recent decades a significant amount of research has been dedicated to study of the neurocognitive effects of bilingualism. Although most of the work in this field has been focussed on healthy young adult populations, there has recently been an increased interest in examining bilingualism in the later years of life. This trend is intensified by the discovery that bilingualism may have clinical implications; bilingualism has been shown to considerably delay Alzheimer’s dementia symptom onset and age of formal clinical diagnosis. Episodic memory decline is one of the primary symptoms of dementia. This cognitive function has been linked to bilingualism-related enhancements across the lifespan. The hippocampus, a brain structure crucial for episodic memory function, is also known to be sensitive to bilingualism-induced adaptation, at least in younger populations. The aim of this thesis is to employ a more granular approach to bilingualism, as opposed to more commonly used monolingual vs. bilingual between-groups comparisons, in an investigation of the impact bilingualism might have on declining neurocognition in clinical and healthy ageing. Three studies are presented. The first two studies empirically examine the effects of bilingualism on episodic memory function and the hippocampal structure in healthy older adults and individuals with an MCI diagnosis. Results reveal bilingualism, and especially active engagement in second language use, to offer neuroprotection of the hippocampus in the older age, although behavioural differences may not always be observed. The third study is an epistemological investigation raising the question of whether bilingualism might be a more universal protective factor against cognitive and neural decline in other progressive neurodegenerative diseases, such as Parkinson’s, Huntington’s and multiple sclerosis. This thesis highlights the need to further evaluate the effects of bilingualism by considering it as a generalised neuroprotective factor in clinical ageing, by fusing brain data and behavioural outcomes.