Causal relationship between multilingualism and dementia

You have an important meeting scheduled for tomorrow morning and you have to be at your presentable best. You prepare well in advance and keep your best pair of shirt and trousers ready the night before, just to avoid any panic or confusion later. The day finally arrives and you jump straight out of bed and head directly to the bathroom. You start to change into your smartest attire after a nice shower, but something really unforeseen unfolds, and you struggle with something you least expected – something as simple and rudimentary as being able to button your shirt. This is one of the hallmarks of patients with dementia.

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Current estimates suggest that a significant proportion of the Indian populace is at a high risk of contracting some form of dementia by the time they turn sixty. Some experts even suggest that the current aging population of our country is like a “ticking time bomb waiting to explode”. While the physiology and pathology associated with dementia is thought to be due to a form of characteristic neurodegeneration, it seems that there is more to it than what meets the eye. In recent times, it has been observed that certain individuals with these distinct neurodegenerative pathologies, can still function and operate at normal levels. By digging deeper, it was observed that these individuals all had one thing in common – they were all polyglots i.e., they spoke more than one language. What is even more surprising is that individuals who spoke only one language showed much higher levels of cognitive deficit, but their characteristic neuropathology was much less pronounced when compared to their bilingual or multilingual counterparts. For instance, the amount of gray matter in multilinguals was found to be significantly lower due to the progressive neurodegeneration that accompanies dementia. However, their cognitive functioning was remarkably better than age matched monolinguals. This has spurred great interest amongst neurologists and neuroscientists alike, who believe that being able to speak multiple languages grants an individual with a much higher cognitive reserve.

Cognitive reserve or CR, refers to the ability of the brain to respond to various after effects of natural brain aging, an existing pathology, or any other mental or physical insult in the form of neurodegeneration. The cognitive response is ideally adaptive in nature and this cognitive reserve is what grants this adaptability; allowing one to function normally in terms of cognition and other tasks that require executive function. Thus, someone with a lower cognitive reserve would be more susceptible to the effects of aging, pathology etc. However, this cognitive reserve is not fixed or immutable – It is malleable and is prone to change. Prenatal genetic exposure and other socio-economic factors such as occupation, IQ, levels of higher education etc. can contribute significantly in order to increase or decrease one’s CR. Thus, CR is dependent on several such underlying factors apart from the ability to speak multiple languages. The cognitive reserve therefore represents a much more dynamic and plastic model of mental processes that can adapt and respond to any insult or damage. However, this does not imply that the CR is only invoked upon receiving some form of abuse. It could already be in place and be dependent on how much insult one receives for these adaptive mechanisms to come into effect dynamically. Unfortunately, there are no direct methods of measuring CR but there are three broad methods to help quantify and measure CR. These include socio-behavioural proxies, the residual approach and functional imaging.

Socio-behavioural proxies include factors such as physical activity, IQ, occupation, languages spoken etc. These are stated to be more formative in nature, i.e., they may be contributing to the development of the CR. However, taking the shared contribution of these factors into consideration might be misleading since each of the factors could be affecting the CR in their own unique and distinct ways. As a result, proxies of this kind make the problem much more complex and harder to tackle.

Though there are no existing forms of treatment for dementia available, it is paramount that we explore every possibility that helps delay the onset of the symptoms. In recent times, the ability to speak multiple languages has come up time and again and studies are being conducted that are trying to establish a causal relationship between multilingualism and dementia. Thus, being a polyglot and knowing several languages can help you find your way around this fairly scary world figuratively, and quite literally as well.

Written by Devangshu Nandi, NGSF Intern 2021, M.Sc Cognitive Sciences, IIT Gandhinagar.

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