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Neurophysiological correlates of bilingual advantage and its contribution to cognitive reserve

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Can learning a language mitigate the impact of Alzheimer’s disease?

Research is starting to reveal the connections between bilingualism, cognitive reserve, and the way the brain functions in older adults.

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Overall, it is estimated that around 10 % of people over 65 years old have Alzheimer’s disease (AD), and this prevalence increases; up to 33 % of people over 85 will be affected. But we are learning more about the role of what is known as cognitive reserve (CR). “In general, CR may be developed by taking part in cognitively stimulating activities. Specifically, high education attainment, work that involves decision-making and judgement, physical exercise, social interaction, learning new skills such as musical instruments and languages, all build up CR,” explains Jesús Cespón, a postdoctoral researcher at the Basque Center on Cognition, Brain and Language. Cespón, whose work on the BILINGUALPLAS project was supported by the Marie Skłodowska-Curie Actions programme, was interested in the last factor. He posed the question: “Does bilingualism strengthen the cognitive system in such a way that can mitigate the impact of AD?”

Measuring the impact of bilingualism on cognitive reserve

Theoretical models state that speaking two or more languages requires a constant inhibition of the non-target language during the time of a conversation. Bilingual and multilingual individuals frequently switch attention from one language to another language to adapt the correct language to a given context. By doing this daily, they train their executive functions. This is revealed by better performances at executive exercises such as the Stroop and Simon tasks. To examine this relationship further, the project recruited adults aged between 60 and 80 from the San Sebastian area, and experiments were carried out in the Center’s lab. The first session consisted of a neuropsychological assessment to estimate CR levels and ensure that they were cognitively healthy. Then participants attended a second session to perform two tasks while an electroencephalographic (EEG) recording was made. Cespón was interested in recording what happens in the brain when task switching, since it mimics the switching that goes on in the brain of a bilingual person when they move from language to language. “Our subjects worked on the Simon and the Spatial Stroop tasks. Both these are known as executive control tasks and are designed to challenge, rather in the way that driving, or shopping does. They provoke contradictory responses, and the ability to switch between the two and come up with the correct response within certain time frames reveal information about a person’s cognitive processes.”

More brain activity in subjects with higher cognitive reserves

The project found that people with high CR performed the task more accurately than those with lower CR. “Event-related brain potentials analysed from the EEG signal showed faster deployment of cognitive processes in high compared to low CR participants,” he explains. Cespón also found that the deployment of brain activity was greater in people with high compared to low CR, which probably indicates higher synchronisation among neural systems.

Significance of public engagement and dissemination

As all too often, it was difficult to recruit participants. “The most important thing is performing public engagement activities because, in general, people are curious about science, but they cannot take part in an experiment if they do not know that such an experiment exists,” notes Cespón. “I had been interviewed in papers and on local radio, so people knew we were researching this area,” he adds. The project was impacted by the COVID crisis, as the age of their subjects placed them in the vulnerable category, so further research is ongoing. “We will recruit 160 older adults, aged between 60 and 80 years, and divided into four groups according to low vs high CR and monolinguals vs bilinguals. We are currently collecting that sample to give complete responses to the questions raised by the BILINGUALPLAS project,” he says.

Keywords

BILINGUALPLAS, bilingualism, cognitive reserve, Alzheimer’s disease, executive control tasks

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