Flanking age: Multilingualism and its role in shaping cognitive decline and neural dynamics.

This study investigates how individual multilingual engagement modulates brain oscillatory activity and cognitive control across the lifespan, using both resting-state and task-based EEG with a Flanker task. We assessed whether degree of multilingual engagement moderates age-related changes in theta and alpha power and examined how these changes impact task-specific neural dynamics and behavioral performance. Higher degree of multilingual engagement was associated with weaker negative correlations between increasing age and resting-state theta and alpha power. Our analyses of task-based data revealed that older participants with higher degree of multilingual engagement exhibited a smaller Flanker congruency effect (CE) and less reliance on alpha suppression. These patterns may show more efficient interference suppression in this group. In contrast, older adults with lower multilingual engagement demonstrated larger CE and greater alpha suppression, reflecting potentially less efficient neural recruitment. Notably, our findings indicate that effects of higher degree of multilingual engagement extend beyond resting-state dynamics. Specifically, they also impact recruitment patterns in response to cognitive control demands across the lifespan supporting the notion of maintenance of cognitive control mechanisms with increasing age. Interestingly, the hypothesized link between resting-state and task-based power was not observed, suggesting a more complex nature of the mechanisms underlying the relationship between baseline and task-specific activity. By examining resting-state and task-based activity in cognitive control (and potential links between them), this study adds to the growing body of evidence on multilingualism as a lifestyle factor that can contribute to healthier cognitive aging through neurocognitive adaptations.