The Bilingual Brain

Humans have the ability to learn multiple languages. Studying bilingual brains offers scientists an opportunity to analyze physical changes in the brain and alterations in how the brain works as a result of some behavior, known as structural and functional plasticity. I recently wrote an article where I discuss plasticity, the ability of our brain to modify its connections in response to experience. Here, I discuss some scientific findings of the bilingual brain.

Is the bilingual brain structurally different?

Figure 1. Structural reorganization in the bilingual brain. Mechelli et. al., 2004.

To answer this question, Andrea Mechelli and collaborators at the Wellcome Department of Imaging Neuroscience, imaged the brains of English-Italian bilinguals. They divided their bilingual cohort into early and late bilinguals. Early bilinguals were those that learned a second language before the age of 5 years and late bilinguals learned a second language between the age of 10 and 15 years. Their study found that bilinguals had greater gray-matter density in the inferior parietal cortex compared to monolinguals. Gray matter is different from white matter in that it contains a greater amount of cell bodies, whereas white matter contains more myelinated axons, which convey messages between cells. The inferior parietal cortex is a brain area involved in language, among other functions concerned with interpretation of sensory information. Early bilinguals showed greater gray-matter density in the same area compared to late bilinguals and in those who had higher proficiency in the second language. In addition, they showed that the effect was decreased with age, meaning the older one is when learning a second language, the less the increase of gray matter density in this particular brain area (Mechelli, 2004).

Is the bilingual brain functionally different?

Figure 2. Spatial distribution of the most informative voxels coding for Language 1(red) and Language 2(blue), and their overlap (yellow). Lateral occipital cortex (LOC; inferior/middle occipital cortex), fusiform gyrus (FusiG), lateral temporal cortex (LTC; superior/middle temporal gyri), temporoparietal cortex (TPC; supramarginal/angular gyri/inferior parietal lobule), and lateral prefrontal cortex (LPFC; inferior/middle frontal gyri), superior parietal lobule/precuneus). Xu et. al., 2017.

Brain imaging technology offers a window into the human brain as it performs tasks. There are some limitations to this, for example, fMRI provides information of blood flow in the brain, but it cannot offer high-resolution information of the activity of individual neurons. This is one reason why answering this question has been challenging. To get around this limitation, Xu and collaborators used functional magnetic resonance imaging (fMRI) and multivariate pattern analysis (MVPA), which allows the identification of patterns of neural activation. In their study, English-Chinese bilinguals were instructed to follow a task that involved implicitly reading words in both languages. The task asked the participants to press a key when two consecutive words had the same meaning in different languages. Because the task did not ask the participants to read the word out loud but they had to read the words obligatorily, the researchers were able to interpret their brain activity at different time points depending on the language of each word.  Xu and colleagues found that different languages were processed in similar brain regions, but their patterns of response were different. This indicates that although activation of overlapping brain areas occurs, different neural representations of each language may be necessary for bilingual speakers to be able to use each language separately (Xu, 2017).  

Does being bilingual offer cognitive advantages?

This has been an ongoing debate in the field of linguistics. Throughout the twentieth century, researchers thought that bilingualism led to cognitive disadvantage at an early age, arguing that children exposed to multiple languages led to confusion. However, important considerations were ignored. For example, researchers did not take into account socioeconomic status, age, and degree of bilingualism. Since these issues were identified, other researchers have taken on the task to test for cognitive abilities in bilinguals, controlling for important factors such as age, sex, and socioeconomic status. Recent research in the late twentieth century and early twenty-first century has revealed that bilingualism may offer some advantages. Studies have shown that bilinguals outperform monolinguals in executive function tasks (Bialystok, 1999). One example is the Stroop task, where color words are presented in different color ink, and the participant must name the color ink ignoring the written word. Below is an example of the Stroop task, try saying the color of each word without paying attention to the written text. Compare the time it takes you to complete the task for each of the two boxes. 

Additionally, research has shown that bilingualism may delay cognitive decline associated with aging. On the flip side, studies have also shown that bilinguals possess a disadvantage in verbal processing (Antoniou, 2019).  The debate is ongoing on whether bilingualism offers cognitive advantages and numerous studies take opposite stances. In the future, avoiding generalizations and controlling for different factors is of extreme importance to adequately analyze acquired data and reach conclusions.

Is the ability to learn a new language uniquely human?

Up until a few years ago, it was understood that the ability to learn a different language and be able to use it in social interactions was uniquely human. In 2014, scientists in San Diego developed a study to analyze if whales were able to learn a “different” language: dolphin. Contextually, bottlenose dolphins and killer whales emit similar vocalizations. However, killer whales have a higher proportion of pulsed calls and dolphins produce more click trains and whistles. The researchers found an opportunity to ask this question by analyzing the vocalizations of three killer whales that were regularly exposed to bottlenose dolphins. They compared the vocalizations emitted by the three whales to those that had no exposure to bottlenose dolphins. They learned that the three whales regularly exposed to dolphins had a higher proportion of click trains and whistles compared to whales housed with other whales. In particular, one killer whale unexpectedly learned to imitate artificial chirps, a skill that was previously taught to the dolphins (Musser, 2014). Does this mean that killer whales are capable of learning dolphin? Maybe, but certainly, killer whales’ brains, akin to human brains, possess vocal plasticity.

Conclusion

Recent advances in technology and ways to interpret brain imaging data will allow scientists to dive deeper into the structural and functional differences between the bilingual and monolingual brain. In the meantime, it is never too late to celebrate your brain’s plasticity and learn a second language, your future self might thank you for delaying cognitive decline associated with aging. 

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