Brain Structure in Bilingual Compared to Monolingual Individuals with Alzheimer\u27s Disease: Proof of Concept.

BACKGROUND: Bilingualism is increasingly recognized as protective in persons at risk for Alzheimer\u27s disease (AD). OBJECTIVE: Compare MRI measured brain volumes in matched bilinguals versus monolinguals with AD. METHODS: This IRB approved study analyzed T1 volumetric brain MRIs of patients with criteria-supported Probable AD. We identified 17 sequential bilinguals (any native language) with Probable AD, matched to 28 (62%) monolinguals on age and MMSE. Brain volumes were quantified with Neuroreader. Regional volumes as fraction of total intracranial volume (TIV) were compared between both groups, and Cohen\u27s D effect sizes were calculated for statistically significant structures. Partial correlations between bilingualism and brain volumes adjusted for age, gender, and TIV. RESULTS: Bilinguals had higher brain volumes in 37 structures. Statistical significance (p \u3c 0.05) was observed in brainstem (t = 2.33, p = 0.02, Cohen\u27s D = 0.71) and ventral diencephalon (t = 3.01, p = 0.004, Cohen\u27s D = 0.91). Partial correlations showed statistical significance between bilingualism and larger volumes in brainstem (rp = 0 . 37, p = 0.01), thalamus (rp = 0.31, p = 0.04), ventral diencephalon (rp = 0.50, p = 0.001), and pallidum (rp = 0.38, p = 0.01). Bilingualism positively correlated with hippocampal volume, though not statistically significant (rp = 0.17, p = 0.26). No brain volumes were larger in monolinguals. CONCLUSION: Bilinguals demonstrated larger thalamic, ventral diencephalon, and brainstem volumes compared to matched monolinguals with AD. This may represent a neural substrate for increased cognitive reserve in bilingualism. Future studies should extrapolate this finding into cognitively normal persons at risk for AD