by Patrick Lejtenyi, Concordia University

ROIs from the Desikan–Killiany–Tourville cortical atlas (A) and the FreeSurfer subcortical atlas (B). ROIs also include the subiculum and CA1 subfields (not depicted here but located within the hippocampus). Language-related regions are shown in light gray and AD-related regions are shown in dark gray. Credit: Bilingualism: Language and Cognition (2024). DOI: 10.1017/S1366728924000221

Bilingualism has long been known to have cognitive benefits for older adults. Research shows it helps delay the onset of Alzheimer's disease by up to five years compared to monolingual adults. This is one of several lifestyle factors that may contribute to brain resilience as we age.

In a study published in the journal Bilingualism: Language and Cognition, Concordia researchers use neuroimaging methods to examine brain resilience in regions of the brain linked to language and aging.

They found that the hippocampus in bilinguals with Alzheimer's disease was noticeably larger than those who were monolingual when matched for age, education, cognitive function and memory.

"There was greater brain matter in the hippocampus, which is the main region in the brain for learning and memory and is highly affected by Alzheimer's," says the study's lead author, Ph.D. candidate Kristina Coulter. She co-wrote the study with Natalie Phillips, a professor in the Department of Psychology and the Concordia University Research Chair (Tier 1) in Sensory-Cognitive Health in Aging and Dementia.

The researchers compared brain characteristics of monolingual and bilingual older adults who were either cognitively normal, who were in the risk states of subjective cognitive decline or mild cognitive impairment, or who were diagnosed with Alzheimer's.

They found that while there was evidence of hippocampal atrophy between individuals with mild cognitive impairment and Alzheimer's who were monolingual, there was no change in hippocampal volume in bilinguals across the continuum of Alzheimer's development.

"The brain volume in the Alzheimer's-related area was the same across the healthy older adults, the two risk states and the Alzheimer's disease group in the bilingual participants," says Coulter. "This suggests that there may be some form of brain maintenance related to bilingualism."

Localized resilience

Brain maintenance, brain reserve and cognitive reserve are the three components of brain resilience, a concept that refers to the brain's ability to cope with changes associated with aging.

Brain maintenance is the continued ability to maintain its form and function as it ages. Mental stimulation, such as bilingualism, along with a healthy diet, regular exercise, good sleep and good sensory health are believed to help protect the brain from deteriorating.

Brain reserve applies to the size and structure of the brain. Brains with greater reserve can maintain normal functions because of the extra volume or capacity of brain matter even when experiencing damage or atrophy because of aging, including by pathological diseases like Alzheimer's disease.

Cognitive reserve refers to the way a brain can use alternative pathways to maintain functionality even when it has been damaged or experienced shrinkage linked to aging. Brains with greater cognitive reserve can use other parts of the brain than those usually associated with a particular function, such as language or memory, thanks to a lifetime accruing cognitive flexibility.

Coulter notes that they did not find any bilingualism-associated brain reserve in the language-related areas of the brain or cognitive reserve in the Alzheimer's-related areas of the brain.

"Speaking more than one language is one of several ways to be cognitively and socially engaged, which promotes brain health," Phillips says. "This research study was unique in that it was able to look at the potential influence of being bilingual on brain structure across the continuum of dementia risk, ranging from individuals who were cognitively normal, to those who are at higher risk of developing Alzheimer's, to those who actually have the disease."

Future work from these Concordia researchers will delve into whether being multilingual has a similar positive influence on brain networks.

The researchers used data from the Comprehensive Assessment of Neurodegeneration and Dementia Study (COMPASS-ND) and the Consortium for the Early Identification of Alzheimer's disease-Quebec (CIMA-Q) for this study.

More information: Kristina Coulter et al, Bilinguals show evidence of brain maintenance in Alzheimer's disease, Bilingualism: Language and Cognition (2024). DOI: 10.1017/S1366728924000221

Provided by Concordia University