Lifelong Bilingualism as a Method of Delaying the Onset of Dementia

By: Samhitha Maddu

Dementia is a cognitive disorder associated with memory loss, cognitive reasoning, behavior, and judgment impairment and affects around 55 million individuals worldwide and 6.7 million Americans (World Health Organization, 2023; 2023 Alzheimer's Disease, Facts and Figures, 2023). While its development is typically associated with age (65+), it is not a natural part of aging and does not affect all persons of old age. There are currently no effective pharmacological treatments to combat the development of this disorder, prompting researchers to begin looking towards non-pharmacological alternatives that target the stimulation of mental activity and promote cognitive reserve. Among these alternatives, bilingualism has been shown to be an effective way to enhance cognitive reserve and delay the onset of dementia. Researchers have specifically found lifelong bilingualism, where someone speaks two languages consistently, from a young age, to be particularly beneficial. This article explores how bilingualism can help delay dementia and why it is beneficial.

To understand how bilingualism and dementia are related, we must first understand how dementia develops in relation to cognitive reserve and gray matter. Dementia refers to the general damage and/or loss of neurons and neural connections. Common types of dementia, such as Alzheimer’s disease (AD), frontotemporal dementia (FTD), and vascular dementia along with other several risk factors lead to the loss of gray matter. These conditions are differentiated by the area of the brain affected, manifestation of symptoms, and pathological processes. 

Gray matter is a tissue that largely forms the outer layer of the brain and contains all of the neuralconnections and synapses. Gray matter develops throughout adolescence,  typically expanding in volume until age 8 and increasing in density until age 20  (Mercadante & Tadi, 2023). When an individual develops dementia, the neurons in the graymatter will die and eventually lead to “cerebral atrophy” (the decrease/loss of tissue in the brain). It is natural to undergo cerebral atrophy while aging, however dementia accelerates the process.Furthermore, as neurons and synapses die, they cannot be regenerated. In addition to clinical presentation, imaging studies such as MRI (Magnetic Resonance Imaging) of the brain and PET (Positron Emission Tomography) imaging are useful in diagnosing dementia (Fig 1).

Figure 1: Images of FDG PET CT and MRI brain, in three different rows  show normal, AD and FTD respectively. Normal Brain MRI volume and normal FDG activity (row 1), and AD shows atrophy of parietal lobes posteriorly with corresponding decreased FDG activity on PET CT (row 2). Whereas FTD illustrates decreased volume and FDG activity on frontal lobes (anterior parts of the brain, row 3). Source: Radiology Assistant(2024).

 Cognitive reserve is the brain’s ability and agility to process tasks and show resilience to any neuropathological damage of the brain. Thus researchers directed their attention towards cognitive activities that help increase cognitive reserve. There are several ways to improve cognitive reserve, however, one of the most efficient ways is to engage the brain in mental stimulation.

 Bilingualism has proven to improve the brain’s executive and visual-spatial abilities (Estanga et al., 2017) and increase cognitive reserve. Individuals with higher cognitive reserve can completely offset the symptoms of progressive brain disease and continue to function effectively (Harvard Health Publishing, 2023). A study by Schweizer and colleagues (2012) found that bilingual individuals with Alzheimer’s had more significant brain atrophy than their monolingual counterparts at the same disease stage but had a delayed onset of cognitive decline.

Bilingualism offers a cognitive advantage by requiring the brain to switch between languages, which activates the dorsolateral prefrontal cortex (DLPFC), an area associated with executive control (Hernandez et al., 2000). This language-switching process involves focusing on words, sounds, grammar, and concepts, ultimately enhancing attention and other executive functions. According to Bialystok et al. (2007), lifelong bilingualism promotes mental flexibility, improves information processing, and aids in adapting to changes effectively.

Despite promising findings, researchers have also identified several limitations in studying the impact of bilingualism on dementia. Differences in language, culture, socio-economic status, educational background, dementia types, and behaviors can all influence cognitive abilities and cognitive reserve, thus complicating the analysis (Brini & et al., 2020). Around the world, researchers often use different study designs and methods that will result in variability and inconsistencies in results in comparison. Factors such as sample size, cultural contexts, age groups, and cognitive assessment tools further contribute to inconsistencies. As short-term studies are insufficient to demonstrate long-term benefits, future research must focus on longitudinal studies with standardized protocols to ensure generalized and reliable findings. 

Bilinguals with neurodegenerative brain diseases show a delayed onset of symptoms and are prone to a lesser extent of associated cognitive deficits. The effects of lifelong bilingualism on brain metabolism and connectivity are proven to be a more continuous phenomenon. Current evidence supports that learning and using more than one language supports healthy aging and can be beneficial for cognitive aging and reserve. While more research must be conducted to fully understand the impact of bilingualism on brain health, it is essential to develop a standardized study design that includes participants from diverse racial, ethnic, and regional backgrounds along with similar forms of dementia etiologies to reduce the variability in the results. Researchers must consider global disparities in socio-economic status and behavior when developing these standardized methodologies to ensure that findings are as accurate as possible.

REFERENCES

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Brini, S., Sohrabi, H. R., Hebert, J. J., Forrest, M. R., Laine, M., Hämäläinen, H., ... & Fairchild, T. J. (2020). Bilingualism is associated with a delayed onset of dementia but not with a lower risk of developing it: a systematic review with meta-analyses. Neuropsychology review, 30, 1-24.

Estanga, A., Ecay-Torres, M., Ibañez, A., Izagirre, A., Villanua, J., Garcia-Sebastian, M.,  & Martinez-Lage, P. (2017). Beneficial effect of bilingualism on Alzheimer's disease CSF biomarkers and cognition. Neurobiology of Aging, 50, 144-151.

Harvard Health Publishing. (2023, January 6). What is Cognitive Reserve? - Harvard    Health. Harvard Health. https://www.health.harvard.edu/mind-and-mood/what-is-cognitive-reserve

Hernandez, A. E., Martinez, A., & Kohnert, K. (2000). In search of the language switch: An fMRI study of picture naming in Spanish–English bilinguals. Brain and language, 73(3), 421-431.

Mercadante, A.,& Tadi, P. (2023, July 24). Neuroanatomy, Gray Matter. PubMed;       StatPearls  Publishing.  https://www.ncbi.nlm.nih.gov/books/NBK553239/.

‌Schweizer, T. A., Ware, J., Fischer, C. E., Craik, F. I., & Bialystok, E. (2012). Bilingualism as a contributor to cognitive reserve: Evidence from brain atrophy in Alzheimer’s disease. Cortex, 48(8), 991-996.

World Health Organization. (2023, March 15). Dementia. World Health Organization.

https://www.who.int/news-room/fact-sheets/detail/dementia

IMAGE REFERENCES

Dementia - Role of MRI (2022); Radiology Assistant.