Experience-driven neural efficiency and reserve in aging: Evidence from bilingual attentional adaptation

Bilingualism offers a powerful test case for understanding how control systems adapt to sustained, variable attentional demands. Converging evidence across behavioral, structural, functional, and clinical literatures indicates that repeated demands for selection, conflict resolution, and language switching are associated with reorganization of control architecture in ways that are consistent with predictive and reinforcement-learning mechanisms, producing two interdependent outcomes. Efficiency emerges as control is redistributed from metabolically costly frontal regions to posterior and subcortical circuits, potentially supported by cortico-striatal learning, cerebellar calibration, and thalamic coordination. Reserve emerges as white matter tracts strengthen, functional connectivity becomes more integrated, and redundancy develops across distributed networks, enabling rerouting when primary pathways deteriorate. Together, these adaptations provide a candidate account for why bilinguals often show equal or greater neuropathology at diagnosis yet maintain cognition longer, exhibiting delayed, but not prevented, clinical expression of dementia. This article synthesizes evidence across domains to present a candidate mechanistic account of experience-driven neural adaptation and generates explicit testable predictions for longitudinal imaging, multimodal biomarkers, reinforcement-learning signatures, and clinical resilience. More broadly, bilingualism illustrates a general principle: attentional control systems reorganize in response to repeated demands, yielding more efficient and more resilient cognition across the lifespan.