Association between multilingualism and cognitive performance among older adults in rural southern India

INTRODUCTION

Language, thoughts, and social interaction can be considered the key aspects of the development of cognition in humans.^[1] Language acquisition has been studied extensively using techniques such as magnetic resonance imaging,^[2] diffusion tensor imaging,^[3] functional near-infrared spectroscopy^[4], and magnetoencephalography,^[5] which helps in studying the structural and functional changes in the brain associated with language acquisition. However, the direct association between language and cognition is still not established.

The cerebral hemisphere works in complement to each other. Two such areas that are responsible for language are “Broca’s and Wernicke’s areas.” It is known that Broca’s and Wernicke’s areas are the language centers of the brain and are located on the language-dominant hemisphere, which is the left hemisphere in the majority of people. Broca’s area is responsible for speech articulation and Wernicke’s area is primarily involved in language comprehension.^[6,7] When a word is heard or read, the information goes to the cortex, and from there the information goes to Wernicke’s area. Wernicke’s area is important with respect to language comprehension. The information from Wernicke’s area is then passed onto Broca’s area through white matter tracts called the arcuate fasciculus. The damage to any of these specific brain regions or all can result in speech impairment which leads to a condition called aphasia.

Many theories attempt to understand the origin of language development. According to Chomsky (1981), one of the pioneers in the field of linguistics, a child has an innate biological basis for learning a language – language association device. He also described the critical period of time at which language is acquired effortlessly and this critical period is generally before the child attains puberty.^[8,9] However, there will always be a considerable variation in the onset of language acquisition among different people. Despite this, subsequent languages learned after the native language cannot be learned in a way as to achieve native language-like proficiency. The frequency of usage of the language also has an important role with respect to the proficiency with which an individual is able to speak or understand the language.

Multilingualism can be defined as the ability of a person to read, write, or understand an additional language other than their mother tongue.^[10] Multilingualism can strengthen executive functions as it plays a relevant role in inhibiting one language while focusing on the more relevant language. As a result, in a multilingual individual, the language systems tend to be active and competitive.^[11]

Learning a new language affects the neuroplasticity that helps the brain in dealing with the increasing pathological changes before the onset of developing symptoms.^[12] Knowing more than one language have protective effects on dementia and it helps in withstanding the onset symptoms of dementia like mild cognitive impairment (MCI).^[13]

Although there is no clear definition of multilingualism, it is considered an ability of a person to manage more than one language regularly.^[10] Therefore, in this study, a person who can speak, read, or understand more than one language is considered multilingual. The primary objective of this study was to analyze the impact of multilingualism as a protective factor in MCI, which is the prodrome of dementia.

MATERIALS AND METHODS

RESULTS

A total of 3725 participants from the rural cohort were considered for the study. Sociodemographic characteristic profile of monolinguals and multilinguals are provided in Table 1. The cognitive impairment was measured using CDR scores.

The CDR scores of 918 monolinguals and 2807 multilingual were compared with reference to the language category as shown in the Table 2. Out of 918 monolinguals, 794 (86.5%) were healthy and 124 (13.5%) were with MCI. Similarly, among 2807 multilingual participants, 2648 (94.3%) were healthy and 159 (5.7) were with MCI [Figure 1].

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Figure 1:

Distribution of MCI for monolinguals and multilinguals. MCI: Mild cognitive impairment.

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The logistic regression model of CDR scores with reference to the language category was calculated after adjusting for age, gender, occupation, years of education, literacy, and socioeconomic status. The odds ratio is 0.69* 95% CI (0.5-0.9), which implies that monolinguals are more likely to develop MCI, when compared to multilinguals as given in Table 3.

DISCUSSION

This study aimed to analyze the influence of knowing more than one language on the cognitive performance of individuals from rural cohorts. In this study cohort, multilingual performed better in cognitive tasks when compared to monolinguals. The majority of the participants who developed MCI were monolinguals. Therefore, the present study suggests that multilingualism has an advantage over monolingualism.

An individual is considered to be multilingual when he/she can communicate in more than one language which is speaking, reading, writing, or simply understanding the language. Cognitive reserve is maintained in multilingual by the active use of different languages known to the individual.^[19] Since multilingualism has a relevant role in neuroplasticity, it helps in delaying the onset of MCI by coping with changes in the brain. The poor performance of monolinguals in cognitive tasks could be due to the correlation with non-linguistic task-switching ability which might be improved in multilingual allowing for greater cognitive reserve.

A similar study on the influence of bilingualism on the prevalence of dementia and MCI by Papilikar et al.^[20] suggests that bilingualism can act as a potential protective factor in delaying the onset of dementia and MCI. The result of the present study is in contrast with a previous meta-analysis which identified a small advantage in global cognitive performance in bilinguals compared to monolinguals, especially in older adults with MCI.^[21] However, there have also been studies that reported otherwise. One study on the Australian Longitudinal Study of Ageing cohort found that bilinguals had poorer MMSE scores at baseline than monolinguals but the difference was not significant on subsequent follow-ups. However, this study was done on monolingual societies, which might as well imply that they were not active users of their alternative languages.^[22]

The capacity to perceive and comprehend a second language is associated with the subcortical regions (like the basal ganglia) of the brain, which is thought to be activated during verbal fluency tasks.^[23] This might enhance the cognition and sensory processing in multilingual individual, which, in turn, helps them in processing the information better than monolinguals. Therefore, the positive influence on attention and problem-solving tasks due to multilingualism can act as a protective factor in cognitive impairment, thus delaying the onset of disease progression.

India is facing challenges with an increasingly older population in the country. The prevalence of dementia in India is predicted to increase by 20% in 2050.^[24] India has an exceptional language diversity with inhabitants speaking hundreds of different indigenous languages. Therefore, India being a country rich in linguistic diversity, there is always a scope for exploring the associated protective effect of multilingualism as a determinant in cognitive performance. In light of this future, it is very important to study the role of such a relevant potential confounder with the risk of developing dementia.

This is a cross-sectional study involving a large sample size. The cognitive performance was assessed using CDR, which is a widely used tool to assess the severity of dementia. This study has its own limitations with respect to not having adequate information about the proficiency with which the participants understand the language. Although the study shows multilingual advantage, there is an absence of strong evidence to support the same.

Based on our study, some future directions can be offered. First, more cognitive tests can be considered that specifically scores the different language domains like pragmatics, phonology, syntax, morphology and semantics. Second, the role of different basic components of language on cognitive performance can be particularly considered. Furthermore, the age of acquisition, what are the different languages known to the participants and the similarities and differences between the different languages known to them can be important aspects to be looked into.

Although multilingualism alone is not an indicator of cognitive advantage, it can be considered as one of the protective factors against cognitive decline. Further studies have to be conducted to provide firm evidence for the same.

CONCLUSION

The effect of multilingualism on cognition is still an area under research. Previous studies on multilingualism and cognition indicated that knowing more than one language can have an influence on executive functioning. The evidence from our study suggests that multilinguals performed better in cognitive tasks when compared to monolinguals. This indicates that multilingualism essentially strengthens the cognitive reserve. Understanding the neural basis of language processing and acquisition can provide strong evidence for the same.