Bilingualism reduces associations between cognition and the brain at baseline, but does not show evidence of cognitive reserve over time

Studies suggest that bilingualism may be associated with better cognition, but the role of active bilingualism, the daily use of two languages, on cognitive trajectories remains unclear. One hypothesis is that frequent language switching may protect cognitive trajectories against effects of brain atrophy. Here, we examined interaction effects between language and brain variables on cognition among Hispanic participants at baseline (N = 153) and longitudinally (N = 84). Linguistic measures included self-reported active Spanish–English bilingualism or Spanish monolingualism. Brain measures included, at baseline, regions of gray matter (GM) thickness strongly correlated with cross-sectional episodic memory and executive function and longitudinally, tissue atrophy rates correlated with episodic memory and executive function change. Active Spanish–English bilinguals showed reduced association strength between cognition and gray matter thickness cross-sectionally, β=0.303, p < .01 but not longitudinally, β=0.024, p = 0.105. Thus, active bilingualism may support episodic memory and executive function despite GM atrophy cross-sectionally, but not longitudinally.