Brain Structure in Bilingual Compared to Monolingual Individuals with Alzheimer's Disease: Proof of Concept

Bilingualism is increasingly recognized as protective in persons at risk for Alzheimer's disease (AD).

Compare MRI measured brain volumes in matched bilinguals versus monolinguals with AD.

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's D effect sizes were calculated for statistically significant structures. Partial correlations between bilingualism and brain volumes adjusted for age, gender, and TIV.

Bilinguals had higher brain volumes in 37 structures. Statistical significance (p < 0.05) was observed in brainstem (t = 2.33, p = 0.02, Cohen's D = 0.71) and ventral diencephalon (t = 3.01, p = 0.004, Cohen's 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.

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.