Bilingual Experience Modulates Brain–Cognition Relationships in Aging: Evidence from the HABS-HD Cohort

Bilingualism has been proposed to confer advantages in cognitive aging, yet the neural mechanisms underlying any such advantages remain debated. In a pre-registered analysis of cross-sectional and longitudinal data from elders in the HABS-HD cohort, we asked whether bilingualism affects three measures of brain structure (total brain volume, hippocampal volume and white-matter lesions) and/or moderates the relationship between brain structure and two measures of cognition (executive function and episodic memory). Overall, we found no significant differences between bilinguals and monolinguals in their baseline brain structure or subsequent change in brain structure, suggesting that a life of bilingualism does not affect Brain Reserve or Brain Maintenance in old age. However, bilingualism did moderate the baseline relationship between total brain volume and executive function, and between hippocampal volume and episodic memory, such that these cognitive functions were less dependent on these brain measures in bilinguals. This suggests that bilingualism functions as a form of Cognitive Reserve. Further, exploratory analyses showed that the effects of bilingualism on hippocampal volume, and on its relationship with episodic memory, might differ according to clinical dementia status. In summary, our findings suggest that bilingualism is associated with altered brain–cognition relationships, rather than with preservation of brain structure.