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A new analysis of neuroimaging data has found that individuals with Alzheimer’s disease who speak only one language (monolinguals) have reduced hippocampal volume in the brain. This reduction was not observed in individuals who speak at least two languages (bilinguals). The research was published in Bilingualism: Language and Cognition.
Alzheimer’s disease is a progressive neurodegenerative disorder that results in cognitive decline. It is the most common cause of dementia, particularly in older adults. In the brain, it is characterized by the accumulation of abnormal protein deposits, including amyloid plaques and tau tangles, which disrupt communication between neurons. Over time, these disruptions cause neurons to lose function and die, leading to brain atrophy.
This atrophy is particularly notable in areas related to memory, such as the hippocampus. As the disease progresses, it impairs other cognitive functions, including reasoning, language, and problem-solving. Emotional changes, such as depression, anxiety, or apathy, often accompany cognitive decline. In advanced stages, individuals lose the ability to carry out basic daily activities and recognize loved ones. Ultimately, Alzheimer’s leads to a severe decline in overall brain function and death.
Study author Kristina Coulter and her colleagues sought to explore whether bilingualism (i.e., knowing two languages) might be protective against dementia. Previous research has suggested that having a cognitive reserve can provide some protection against dementia. Cognitive reserve refers to the brain’s ability to adapt and compensate for damage or age-related changes by using alternative neural pathways or strategies.
Cognitive reserve is shaped by lifelong experiences such as education, intellectual engagement, social interaction, physical activity, and mentally stimulating activities that enhance the brain’s resilience and adaptability. Learning a second language might be one such activity. The researchers hypothesized that, if this were the case, bilingual individuals with dementia would show observable structural brain differences. Specifically, they expected bilingual individuals to have greater cortical thickness and volume in language-related areas of the brain compared to monolinguals.
The researchers analyzed data from the Comprehensive Assessment of Neurodegeneration and Dementia Study (COMPASS-ND) of the Canadian Consortium on Neurodegeneration in Aging (CCNA) and the Consortium for the Early Identification of Alzheimer’s disease-Quebec (CIMA-Q). The first dataset included neuroimaging data from 356 individuals with Alzheimer’s disease, while the second dataset included data from 175 individuals with, or at risk for, various types of dementia.
Participants self-reported their native language and the number of languages they spoke. Individuals who reported speaking two or more languages were considered bilingual. Participants also underwent magnetic resonance imaging of their brains.
Among monolingual participants, 71% reported speaking English. Among bilingual participants, the most commonly spoken languages were English (38%) and French (39%). Of the bilingual participants, 68% reported speaking two languages, 22% knew three languages, and the remaining participants spoke between four and seven languages. Additionally, 11% of monolinguals and 32% of bilinguals were immigrants.
Brain imaging data revealed that individuals diagnosed with diseases known to lead to dementia tended to have lower gray matter volume and cortical thickness across different brain areas. Bilingual individuals did not exhibit signs of cognitive reserve in language-related regions of the brain. However, monolingual older adults with Alzheimer’s disease showed reduced hippocampal volume—a reduction that was not observed in bilingual older adults with Alzheimer’s.
“Although bilingualism was not associated with brain reserve in language-related areas, nor with cognitive reserve in AD-related areas [Alzheimer’s disease-related areas], bilingualism appears to confer reserve in the form of brain maintenance in AD,” the study authors concluded.
The study sheds light on the brain changes in dementia and their relationship to language knowledge. However, it is important to note that the study design does not allow for cause-and-effect conclusions to be drawn from the results.
The paper “Bilinguals show evidence of brain maintenance in Alzheimer’s disease” was authored by Kristina Coulter, Natalie A. Phillips, and the CIMA-Q and COMPASS-ND groups.