Cognitive reserve is thought to prevent cognitive decline and delay neurodegeneration. Recent data suggest that lifelong bilingualism may act through cognitive reserve to delay the onset of dementia by ∼4.5 y. The authors studied brain metabolism, a direct index of synaptic function and density, and neural connectivity to shed light on the effects of bilingualism in vivo in Alzheimer’s dementia. Eighty-five patients with probable Alzheimer’s dementia and matched for disease duration (45 German-Italian bilingual speakers and 40 monolingual speakers) participated in the study. Bilingual individuals were on average 5 y older than their monolingual peers. Cerebral hypometabolism was more severe in the group of bilingual individuals with Alzheimer’s dementia. However, metabolic connectivity analysis showed an increased connectivity in the executive control and the default mode networks in the bilingual, compared with the monolingual, Alzheimer’s disease patients. The degree of lifelong bilingualism (i.e., high, moderate, or low use) was significantly correlated to functional modulations in crucial neural networks, suggesting both neural reserve and compensatory mechanisms. The authors suggest that lifelong bilingualism acts as a powerful cognitive reserve proxy in dementia and exerts neuroprotective effects against neurodegeneration.
Perani D, Farsad M, Ballarini T, Lubian F, Malpetti M, Fracchetti A, Magnani G, March A, Abutalebi J: The impact of bilingualism on brain reserve and metabolic connectivity in Alzheimer’s dementia. Proc. Natl. Acad. Sci. USA 114(7): 1690-1695 (2017).