Can Bilingualism Mechanisms Prevent the Onset of Dementia?

Early Bilingualism May Contribute to Adult Neurogenesis in the Brain and Lead to Better Cognitive Reserves Compared to Monolingual People

    Disease-related cognitive decline caused by Alzheimer's Disease (AD) and other types of Dementia is becoming increasingly prevalent in the aging population as overall lifespans increase, and more people are living longer. It is becoming increasingly clear that meaningful cognitive stimulation is critical in preventing the onset neurodegenerative diseases such as AD. Researchers consistently find that elderly patients actively participating in activities to stimulate their brain, while maintaining and strengthening neuronal connections. Due to the fact that more neural processing is required for bilingual people compared to monolingual people, they often exhibit a greater cognitive reserve and delayed onset of AD. While there is a general consensus among the scientific community that the bilingual brain is functionally different than age-matched monolingual brains, the exact mechanisms underlying early bilingualism are often debated. 

    In the 2016 review article, "Early bilingualism, language attainment, and brain development", Berken et al. compile multiple studies to explore how language development can contribute to lifelong neuroplasticity. By analyzing data from a variety of neuroimaging techniques such as positron emission tomography (PET), structural MRIs, and functional magnetic resonance imaging (fMRI), the researchers determine that the age of acquisition of a second language is strongly associated with brain structure, organization, and function (Berken, 2016). A specific study focuses on fMRI information from simultaneous bilinguals and sequential bilinguals. Simultaneous bilinguals, or individuals who were exposed to language 1 (L1) and language 2 (L2) at the same time exhibit greater neuronal connectivity between the inferior frontal gyrus (IFG) and other neuronal regions associated with language attainment. The data collected from these studies indicates that simultaneously exposing an infant to L2 and L1 results in higher levels of neuroplasticity and more effective neural connectivity. Alternatively, the neuroplasticity of sequential bilinguals is limited, as a second language is introduced after neuronal pathways have already been established for L1.

    A similar review article, "Bilingualism for Dementia: Neurological Mechanisms Associated with Function and Structural Changes in the Brain," Kim et al. (2019) explore the potential mechanisms underlying bilingualism and how they promote neuroplasticity. Due to the complex nature of learning two languages, the hippocampal-dependent process bilingualism promotes the development of new neuronal connections while simultaneously stimulating adult neurogenesis (Kim, 2019). On a molecular level, bilingual adults exhibit increased levels of vascular endothelial growth factor (VEGF). The growth factor VEGF plays a critical role in adult neurogenesis by enhancing hippocampal-dependent memories which in turn reduces the amount of memory loss the individual experiences. Furthermore, researchers determine that elderly bilingual people improves overall functional connectivity of the brain by increasing gray matter (GM) density in the brain. GM density in the hippocampus specifically is decreased by age-related cognitive decline and AD, however, bilingual individuals exhibit higher levels of preserved GM in the brain.

References 

Berken, J. A., Gracco, V. LI ., & Klein, D. (2016). Early bilingualism, language attainment, and

brain development. Neuropsychologia, 98, 220–227.

 Kim, S. (2019). Bilingualism for Dementia: Neurological Mechanisms Associated with Function and Structural Changes in the Brain. Frontiers in Neuroscience.

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