Minding the bilingual gap: A systematic review and perspective on EEG-based diagnoses of dementia

Dementia is a highly prevalent neurodegenerative disease, making early diagnosis a key priority for healthcare professionals to ensure timely and targeted care is provided. Electroencephalography (EEG) provides a promising and cost-efficient tool for such early diagnosis. However, existing EEG-based diagnostic protocols often neglect language background in the workflow, despite robust EEG-evidence indicating that lifelong bilingualism reshapes the brain. Leveraging this experience-dependent neuroplasticity, bilingualism has emerged as a protective factor, associated with delaying the onset of dementia by 4–5 years. Given growing evidence that bilinguals might be more protected against dementia, and the prevalence of bi- and multilingualism in the global population, bilingualism should be considered a factor when screening for dementia with EEG techniques. This thesis conducts a systematic literature review (SLR) to evaluate the extent to which bilingualism can be integrated into early EEG-based dementia diagnostics. It synthesizes findings from two domains: (a) the neural correlates of bilingualism in adult EEG studies, and (b) neurophysiological biomarkers used for dementia diagnosis. By systematically examining how EEG patterns associated with bilingualism align with or differ from established dementia EEG-biomarkers, this thesis also offers perspectives on future directions for clinicians and advocates for bilingual-normed references in relevant diagnostic protocols for dementia.