The Bilingual Brain

January 28, 2020

Written by: Sarah Reitz

 

Language is an extraordinarily complex tool. Specific rules exist on many levels, from speech sounds and syllables to grammar and sentence structure, and learning these rules takes years of daily practice to master. While learning one language is difficult enough, roughly half of the world’s population is fluent in two or more languages, and this number is only growing1. Now, neuroscience research is showing that the benefits of speaking more than one language extend far beyond the ability to communicate with more people. But how does being bilingual (or multilingual) affect the brain?

 

Increased executive function

Because language is so complex, it requires a wide network of brain regions. The brain must be able to remember and produce thousands of words and the sounds they make, then string these words together into sentences. It must also be able to listen to another person speaking the language and interpret what they are communicating. Speaking a language really is a whole-brain workout!

This workout is only intensified when the brain must keep track of this crucial information for more than one language. While switching between languages appears effortless for bilinguals, research shows that their language processing actually recruits more of the brain compared to monolinguals. Language comprehension in monolinguals involves areas on the left side of the brain, including the supramarginal gyrus and inferior frontal gyrus, regions in the frontal and temporal lobes of the brain2. However, language comprehension in bilinguals is more complicated, involving both words within one language that sound similar (within-language competition) and words from different languages that sound similar (between-language competition). When facing between-language competition, additional brain regions are activated, including the right dorsolateral prefrontal cortex, caudate, and putamen2. This recruitment of additional brain regions, including greater use of the right half of the brain, is the bilingual brain’s way of monitoring each language, allowing it to focus on the language currently being spoken while suppressing the other language to prevent the person from speaking in the wrong language at the wrong time.

Many of the additional regions recruited by bilinguals for between-language competition, like the prefrontal cortex, are also involved in executive function, a set of skills that gives the brain the ability to concentrate on what is important while ignoring irrelevant information. It comes as no surprise then that bilingual children and adults are consistently shown to have increased executive function compared to monolinguals3, almost certainly due to their constant management of multiple languages. This enhanced executive function applies to tasks other than language processing, enhancing working memory and allowing bilinguals to more rapidly switch their focus from a processed stimulus or task to a new, more relevant one4. Interestingly, this enhanced ability to concentrate is stronger in people who became bilingual at a young age.

 

Increased gray and white matter

Being bilingual not only changes how the brain processes language, it also alters the physical structure of the brain. One way speaking multiple languages changes that brain is by increasing the density of gray matter in certain regions of the brain. Gray matter is made up of neuronal cell bodies, so the denser the gray matter, the more neurons it contains. Unsurprisingly, bilinguals show increased gray matter in many language processing areas of the brain, including the left inferior parietal lobe5. The increase in gray matter is strongest in people who became bilingual before the age of 5, suggesting the bulk of this structural change occurs during early development.

Additionally, the ability to speak more than one language affects white matter in the brain, a fatty substance that covers axons. Messages are sent from neuron to neuron via axons, and white matter allows these messages to be transmitted more quickly and efficiently. As we age, the brain’s ability to maintain white matter decreases. However, being bilingual slows down this white matter decline, allowing neurons to continue communicating in the most efficient way6.

 

Delayed onset of dementia

These increases in gray and white matter, along with enhanced executive function experienced by bilinguals is the likely explanation behind an incredible finding: bilinguals with dementia develop symptoms significantly later (about 4 years!) than monolinguals, regardless of income or literacy level (other factors known to influence dementia onset)7.

Typically, as the brain deteriorates from dementia, cognitive decline rapidly follows, leading to symptoms such as memory loss, confusion, and reduced concentration. Astonishingly however, a bilingual person suffering from the same level of physical brain deterioration as a monolingual person shows fewer cognitive deficits. Researchers think this may be due to the bilingual brain’s enhanced executive control and ability to use alternative brain networks, developed from a lifetime of toggling between two languages. So, while speaking multiple languages doesn’t prevent dementia, it appears to delay symptom onset, giving people the ability to live with the disease longer before affecting their independence.

The bilingual brain is also more likely to recover from a stroke compared to the monolingual brain. In a study of over 600 stroke patients, 40.5% of bilinguals recovered normal cognition, while only 19.6% of monolinguals recovered8.

 

As the number of bilingual people in the world continues to grow, scientists are learning more and more about how this cognitively demanding skill impacts the brain. Studying the bilingual brain will hopefully give us a better understanding into how the brain organizes speech and communication. Additionally, studying the exact neuroscience underlying the enhanced dementia and stroke outcomes of bilinguals may one day be able to improve cognitive health outcomes in many more patients.

 

 

 

 

 

Image References:

Cover image by Mohamad Hassan from Pixabay

 

References:

1) Grosjean, F (2010) Why are people bilingual? Bilingual: Life and Reality. Cambridge, Mass: Harvard University Press.

2) Marian V, et al. (2017) Bilingual cortical control of between- and within-language competition. Sci Rep. 7:11763

3) Morales J, et al. (2013) Working memory development in monolingual and bilingual children. Psychology 114(2):187-202

4) Grundy JG, et al. (2017) Sequential congruency effects reveal differences in disengagement of attentions for monolingual and bilingual young adults. J Cognition. 163:42-55

5) Mechelli A, et al. (2004) Neurolinguistics: Structural plasticity in the bilingual brain. Nature. 431(7010):757

6) Luk G, et al. (2011) Lifelong bilingualism maintains white matter integrity in older adults. J Neurosci. 31(46):16808-13

7) Alladi S, et al. (2013) Bilingualism delays age at onset of dementia, independent of education and immigration status. Neurology. 81(22):1938-44

8) Alladi S, et al. (2016) Impact of bilingualism on cognitive outcome after stroke. Stroke. 47(1):258-61

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