Lifelong bilingualism is associated with delayed dementia onset, suggesting a protective effect on the brain. Here, the authors aim to study the effects of lifelong bilingualism as a dichotomous and continuous phenomenon, on brain metabolism and connectivity in individuals with Alzheimer's dementia.
In the present study, the scientists from Italy and Switzerland modeled bilingualism with two complementary approaches, as either a dichotomous or a continuous phenomenon. They employed FDG-PET to evaluate brain glucose metabolism and brain dysfunction in large series of bilingual and monolingual individuals with AD to investigate the neural effects of lifelong bilingualism.
According to the brain reserve hypothesis, they expected more severe cerebral hypometabolism in the group of bilinguals with AD in comparison to the monolingual AD patients, at comparable levels of dementia severity.
A language background questionnaire measured the level of language use for conversation and reading. Severity of brain hypometabolism and strength of connectivity of the major neurocognitive networks was compared across monolingual and bilingual individuals, and tested against the frequency of second language life-long usage.
Cerebral hypometabolism was more severe in bilingual compared to monolingual patients; severity of hypometabolism positively correlated with the degree of second language use.
The metabolic connectivity analyses showed increased connectivity in the executive, language, and anterior default mode networks in bilingual compared to monolingual patients. The change in neuronal connectivity was stronger in subjects with higher second language use.
The neuroprotective effects of lifelong bilingualism act both against neurodegenerative processes and through the modulation of brain networks connectivity.
These findings highlight the relevance of lifelong bilingualism in brain reserve and compensation, supporting bilingual education and social interventions aimed at usage, and maintenance of two or more languages, including dialects, especially crucial in the elderly people.