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

Article type: Research Article

Authors: Raji, Cyrus A.^{a; 1; *} | Meysami, Somayeh^{b; 1} | Merrill, David A.^{c; d} | Porter, Verna R.^{b; d} | Mendez, Mario F.^{b; c; e}

Affiliations: [a] Mallinckrodt Institute of Radiology, Division of Neuroradiology, Washington University in St. Louis, St. Louis, MO, USA | [b] Department of Neurology, David Geffen School of Medicine at UCLA, Los Angeles, CA, USA | [c] Department of Psychiatry & Biobehavioral Sciences, David Geffen School of Medicine at UCLA, Los Angeles, CA, USA | [d] The John Wayne Cancer Institute and Pacific Neuroscience Institute, Providence and St. Johns Health Center, Santa Monica, CA, USA | [e] V.A. Greater Los Angeles Healthcare System, Los Angeles, CA, USA

Correspondence: [*] Correspondence to: Cyrus A. Raji, MD, PhD, Mallinckrodt Institute of Radiology, Division of Neuroradiology, Washington University in St. Louis, St. Louis, MO, USA. E-mail: [email protected].

Note: [1] These co-authors contributed equally to this work.

Abstract: Background:Bilingualism is increasingly recognized as protective in persons at risk for Alzheimer’s 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’s 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 < 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. 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.

Keywords: Alzheimer’s disease, bilingual, brain structure, Neuroreader

DOI: 10.3233/JAD-200200

Journal: Journal of Alzheimer's Disease, vol. 76, no. 1, pp. 275-280, 2020