by Ji Wook Kim
figures by Abagail Burrus

While 92% of primary and secondary students in Europe learn a foreign language, only 20% of primary and secondary school students in the U.S. study a foreign language. In an ever more international era, these numbers are shocking. There is a debate whether foreign language education is beneficial, but many would agree that bilingualism helps individuals communicate with a diverse group of people and even gives advantages in the job market. A research conducted by a group in Concordia University adds another reason why bilingualism should be encouraged–cognitive benefits.

Beginning with sounds

The younger we are, the faster we learn new languages–the fastest language learners in the world are babies. When and how do infants start learning language? Surprisingly, the learning process is thought to start before we are born. 

The premature auditory system develops at around 33 weeks into pregnancy, so a fetus is capable of listening by then. Not only can a fetus listen, but they also respond differently to different sounds in language. Neuroscientists measured a brain blood flow patterns of preterm infants (born between 28 and 32 weeks into pregnancy) listening to different sounds. They found that the brain of preterm infants exhibits distinct blood flow patterns in response to different phonemes, a sound unit of language (e.g., ga versus ba). This illustrates that babies can discern different sounds very early in development, which is a key to learning a language. 

Babies raised in a bilingual environment are exposed to two languages. To understand whether these babies can discern and process both languages early in development, a group of researchers examined two groups of 11-month-old babies: “monolingual infants” who had no regular exposure to languages other than English, and “bilingual infants” who had a regular exposure to Spanish and English through interactions with native speakers from birth. 

The researchers measured the activity of different parts of the brain that responded to Spanish and English. Monolingual infants showed different patterns of brain activities in response to Spanish and English; many parts of the brain showed weaker activity in response to Spanish than to English. In contrast, bilingual infants’ brains exhibited a similar pattern of activity in response to Spanish and English words. Hence, before they reach their first birthday, before they can even speak fluently, babies exposed to two languages hear speech sounds differently than their monolingual peers.

Figure 1: Bilingual and monolingual infants’ brain response to Spanish and English. Bilingual infants’ brains show a similar pattern of activity in response to Spanish and English (Top), whereas monolingual infants’ brains show weaker pattern of activity in response to Spanish (Bottom).

Critical period of learning language

Unfortunately, it is harder to become bilingual as we age. Unlike babies, adults have difficulty learning a new language. It takes much more time and effort to become fluent, and even then, it’s hard to reach native-level proficiency. It is widely believed that a ‘critical period’, a point when one’s ability to learn a new language dramatically drops, exists for language learning. Yet, there is no consensus on at precisely what age the critical period occurs. 

A recent study performed at MIT suggests that the critical period may end in late adolescence. The authors aimed to understand how language learning changes with age, focusing on the ability to discern grammatically incorrect sentences. To measure a statistically meaningful result, several hundred thousand participants were needed, which was a huge obstacle for the study. The group turned to Facebook as a solution to this problem; they came up with a grammar quiz and spread the link via Facebook. 

Importantly, they also asked participants to provide demographic information, which included their native language, the age of first exposure to English, and current age. The quiz went viral, was shared more than 300,000 times on Facebook, and drew 680,333 participants. The researchers found that the ability to learn a new language drops significantly at around 17 years of age. While the biological reason for the critical period is yet to be understood, many scientists suggest that age-related changes in brain plasticity–the brain’s ability to change and adapt as a result of experience–may be the underlying factor.

Bilingualism may provide cognitive benefits

Growing evidence suggests that bilingualism provides cognitive benefits. For example, life-long bilinguals are better at inhibitory control, the ability to ignore irrelevant information during a task. In a Stroop test, a test designed to assess inhibitory control, people are asked to name the color of a word printed with colorful ink. The color can be the same as or different from the meaning of the word. A 2015 study found that bilinguals performed better than monolinguals when the color and word did not match, showing that bilinguals were less distracted by irrelevant information (i.e., the meaning of the word). Also, bilinguals were shown to be better at managing a complex task and switching attention to goal-relevant information. 

Figure 2: Stroop test. In a Stroop test, people are asked to name the color of all words presented. On the first trial, the color and the meaning of the word correspond to each other. On the second trial, the color and the meaning of the word are different. The time it takes to name the color of all words in each trial are compared. (Word sets adopted from this link. Clock icon was made by Freepik from www.flaticon.com).

One of the most recent and striking discoveries is that bilingualism may delay the onset of Alzheimer’s disease. Alzheimer’s disease involves memory loss and other cognitive disabilities that develop slowly and get worse over time. Numerous studies have found that the onset of Alzheimer’s disease is delayed by 4-5 years in bilingual Alzheimer’s disease patients when compared to monolingual Alzheimer’s disease patients regardless of sex, lifestyle, education, and occupation. 

To examine the role of the brain in this phenomenon, a research group used magnetic resonance imaging (MRI) to compare the brains of monolingual and life-long bilingual Alzheimer’s disease patients. They found that bilingual Alzheimer’s disease patients had thicker and denser brain regions related to language and, more importantly, cognitive control. Patients with thicker cognitive control brain regions tended to remember autobiographical events better, suggesting that bilingualism may help patients maintain some degree of memory function. Yet, whether a bilingualism directly causes a delay of Alzheimer’s disease onset remains to be discovered.

Figure 3: Bilingual and monolingual Alzheimer’s disease patients’ brains are different. Brain regions responsible for cognitive control are thicker and denser in bilingual Alzheimer’s disease patients (Top) than in monolingual Alzheimer’s disease patients (Bottom).

With the advent of big data analysis and brain imaging technology, we are now slowly understanding the biology of language acquisition and its effects on cognitive health. Many studies on the cognitive benefits of bilingualism from infancy suggests that bilingualism in children should be encouraged, yet only 20% of K-12 students in the U.S. take foreign language classes. Although most colleges in the U.S. now have a foreign language requirement of some sort, learning a language in adulthood is harder because students are likely already past the critical period. Giving young children an exposure to foreign languages, either in school or at home, could lead to cognitive benefits that will last their entire life.


Ji Wook Kim is a second-year PhD student in the Biological and Biomedical Sciences program at Harvard Medical School.

Abagail Burrus is a fourth-year Organismic and Evolutionary Biology Ph.D. candidate who studies elaiophore development at Harvard University.

Cover image: “Facts about Languages” by Elaine_Smith is licensed under CC0 1.0

For More Information:

  • To learn more about how bilingual environment affects baby’s brain, check out this TED Talk
  • To learn more about cognitive benefits of bilingualism, check out this TED-Ed video

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