In our increasingly global society, bilingualism - or the ability to speak two languages - is on the rise. How the brains of bilingual people differ from their monolingual counterparts is an emerging area of research.
Attitudes toward bilingualism have changed significantly in the past 50 years. Gone are the days when using a second language in the home was frowned upon, labeled as confusing for children and supposedly holding back their development.
Instead, the number of bilinguals has been rising steadily. Data from the United States Census Bureau show that between 2009 and 2013, around 20.7 percent of people over the age of 5 spoke a language other than English at home.
This number has more than doubled since 1980, when it stood at 9.6 percent.
With a rising number of bilingual people comes increased research into the science that underpins this skill. Do the brains of bilinguals differ from those of monolinguals? And do bilinguals have the edge over monolinguals when it comes to cognitive functioning and learning new languages?
As a member of a bilingual household, I was keen to investigate.
A 2015 review in the journal Seminars in Speech and Language explains how bilingual children develop their language skills, dispelling commonly believed myths.
According to authors Erika Hoff, a professor of psychology at Florida Atlantic University in Boca Raton, and Cynthia Core, an associate professor of speech, language and hearing science at the George Washington University in Washington, D.C., newborns can distinguish between different languages.
They are also capable of developing vocabulary in two languages without becoming confused. When bilinguals mix words from different languages in one sentence - which is known as code-switching - it is not because they cannot tell which word belongs to which language.
Interestingly, children seem to naturally develop an understanding of who in the house speaks which language early on, and they will often choose the correct language to communicate with a particular individual - a phenomenon I have witnessed with my daughter, who is exposed to both German and English.
Mixing languages does not seem to hold bilingual children back from learning both languages, but it takes longer to learn two languages than to learn one. While there is a tendency on the whole for bilinguals to lag behind monolinguals in their language development, this isn't true for all children.
Scientists are now starting to unravel the mysteries of the bilingual brain and shed light on the advantages that having this skill may bring.
Viorica Marian - a professor of communication sciences and disorders at Northwestern University in Evanston, IL - and colleagues published a study last month in the journal Scientific Reports, investigating which areas of the brain are involved in language control.
The research involved 16 bilingual individuals who had been exposed to Spanish from birth and to English by the time they were 8 years old.
Prof. Marian explains in the paper that "[b]ilinguals' ability to seamlessly switch between two distinct communication systems masks the considerable control exerted at the neural level."
In fact, when a bilingual person hears words in one language, the other language also becomes activated. Scientists think that the brains of bilinguals adapt to this constant coactivation of two languages and are therefore different to the brains of monolinguals.
In her study, Prof. Marian also sought to clarify which brain regions are involved when bilinguals are faced with words that sound similar. In monolinguals, this "phonological" competition occurs only between words from the same language.
But bilinguals have similar-sounding words from their second language added into the mix.
In monolingual people, areas in the frontal and temporal language regions - more specifically, the left supramarginal gyrus and the left inferior frontal gyrus - are activated when faced with phonological competition.
The study results show that different areas of the brain are needed to cope with phonological competition from within the same language, compared with between-language competition.
"We found," Prof. Marian explains, "that the size and type of the neural network that bilinguals recruited to resolve phonological competition differed depending on the source of competition."
"When competition occurred between two languages, bilinguals recruited additional frontal control and subcortical regions, specifically the right middle frontal gyrus, superior frontal gyrus, caudate, and putamen, compared to competition that occurred within a single language."
Prof. Viorica Marian
She concludes that "[t]hese findings demonstrate the considerable neural plasticity that enables bilinguals to process speech in spite of linguistic competition from multiple sources."
Neural plasticity, or the brain's ability to adapt to the environment and new experiences, is crucial in cognitive functioning. Do bilinguals, therefore, have an advantage when it comes to cognitive function?
Ellen Bialystok, a professor of psychology at York University in Toronto, Canada, and her team study the effect of bilingualism and cognitive function using a combination of behavioral and neuroimaging methods.
Prof. Bialystok told me that "[t]he cognitive functions that have been shown to be impacted by bilingualism largely concern attention - the ability to focus attention on relevant information and shift attention as needed."
"This attentional control," she explained, "is one of the most central aspects of cognitive function throughout life and is a big part of cognitive decline with aging. Therefore, anything that boosts these attention systems has the potential to also sustain cognitive function in older age."
Medical News Today reported on a study in 2013 that showed that bilinguals - even those who are illiterate - developed symptoms of dementia significantly later than monolingual individuals. These results are echoed in Prof. Bialystok's research.
"We attribute these protective effects to better maintained attentional control that has been developed through the ongoing use of attention needed to manage selection between two jointly-activated languages."
Prof. Ellen Bialystok
A paper written by Prof. Bialystok's group and published in the journal Cognition earlier this year investigated the ability of bilinguals to switch from one task to the next - a skill that serves as an indicator of cognitive functioning.
First study author John Grundy, Ph.D. - a postdoctoral research fellow in the laboratory of Prof. Bialystok - writes that the "experience of bilingual infants that requires them to pay attention to multiple sources of input within various linguistic contexts makes it adaptive for them to rapidly disengage attention from stimuli once they are processed so that attention can be re-engaged to currently relevant stimuli."
In three studies involving a total of 145 bilingual and 126 monolingual individuals, participants completed a test to study their ability to switch between types of stimulus displays wherein different responses were required.
The results show that bilinguals were faster at disengaging their attention from one trial so that they could focus on the next trial when a different response was required.
As this ability contributes to life-long cognitive health, bilinguals may be at a clear advantage.
But while there is plenty of evidence showing that cognitive decline is slower in bilinguals, do they also have an advantage when it comes to learning additional languages?
From bilingual to polyglot
Earlier this week, Sarah Grey - an assistant professor in the Department of Modern Languages and Literatures at Fordham University in New York City, NY - reported in the journal Bilingualism: Language and Cognition that bilingual individuals learn new languages more quickly than monolinguals.
For their study, Prof. Grey and colleagues taught bilingual Mandarin and English speakers and monolingual English speakers an artificial language called Brocanto2.
Using electroencephalogram analysis, the team found clear differences in the brain waves of both groups when they were listening to sentences in the language.
Bilingual people showed a brainwave pattern called P600 by the end of the first day of training. This pattern is specifically found when individuals process their own language. The monolingual group only started to display the P600 brain waves by the end of the 1-week training session.
"We [...] find that bilinguals appear to learn the new language more quickly than monolinguals," explains Prof. Grey.
"Now, with this small study, we have novel brain-based data that points toward a distinct language-learning benefit for people who grew up bilingual."
Prof. Sarah Grey
Studying the brains of bilingual people is a complex task. As no two individuals are alike, no two bilinguals are either.
However, an increasing interest in the topic, coupled with an increasing number of bilinguals in our society, means that researchers are starting to get to the bottom of how this ability affects the brains and life-long cognitive abilities of those, such as my daughter, blessed with the skill.