The language you are introduced to affects the structure of your brain, influences how you see the world and who you are. But what if you speak two languages?
Can learning a language rewire your brain?
As our species evolved parts of our brain expanded, resulting in more computing power for language. It's what makes us hard-wired for communication. What is perhaps more surprising is how language can shape our brains throughout our lives.
Most of the evidence for this comes from studies of people who are bilingual. Being bilingual offers widespread benefits across a range of complex cognitive tasks and it comes from distinct areas of the brain.
Brain scan studies show that switching between two languages triggers different patterns of brain activity compared with speaking in one language, particularly in the prefrontal cortex. That part of the brain, at the very front of our skulls, is involved in organising and acting on information, including using working memory, reasoning and planning. Other studies show that bilinguals are faster at getting to grips with a new language.
Quadrilinguist Arturo Hernandez, director of the Laboratory for the Neural Bases of Bilingualism at the University of Houston in Texas, says these differences could reflect differences in the architecture of bilingual brains. In other words, learning another language could change how your brain is wired. "It would make sense, if you have had this very different linguistic experience, to see some sort of stable, long-lasting effect," Hernandez says.
It may also make the brain more resilient. Ellen Bialystok at York University in Toronto, Canada, has found that lifelong bilinguals tend to be diagnosed with dementia on average 4.5 years later than monolinguals, and have more white matter, including in their prefrontal cortex. White matter is made of nerve fibres that connect different brain regions, shuttling information back and forth between them. So boosting language skills appears to build more connected brains -- although Bialystok cautions that this still needs to be confirmed.
More evidence for the benefits of second languages came last year from a study of 608 people who had had a stroke. Thomas Bak of the University of Edinburgh, UK, found that of the bilinguals among them, 40 per cent recovered full function, compared with only 20 per cent of monolinguals. Bak speculates that the mental gymnastics involved in speaking several languages could build extra connections that improve function and help cope with damage. "The idea is that if you have a lot of mental exercise, your brain is trained and can compensate better," says Bak.
It is not certain how languages of different and similar linguistic structures are represented. Many studies have found evidence that all the languages that we acquire in the course of our life are represented in one area of the brain. However, other studies have found evidence that a second language is dissociated from the representation of a mother tongue.
Can language influence how you see the world?
Time flows from back to front for English-speakers: we "cast our minds back" to the 1990s, and "hope for good times ahead". It's an example of a cultural concept encoded in language, but can language in turn influence how we think?
Maria Sera is a native Spanish-speaker who grew up believing all squirrels were female. The Spanish word for squirrel, ardilla, is feminine. As a linguist at the University of Minnesota, she has found some substance for her childhood belief. Studies of French and Spanish speakers, whose languages attribute genders to objects, suggest they associate those objects with masculine or feminine properties.
The idea that the language you speak could influence how you think dates back to 1940, when linguist Benjamin Lee Whorf proposed that people whose languages lack words for a concept would not understand it. It was relegated to fringe science until the early 2000s, when a few people began probing a related but more nuanced idea: that language can influence perception.
Greek, for instance, has two words for blue -- ghalazio for light blue and ble for a darker shade. A study found that Greek speakers could discriminate shades of blue faster and better than native English speakers.
"Greeks have two words for blue and are faster at telling shades of blue apart"
Language even seems to affect our sense of space and time. Some peoples, like the Guugu Yimithirr in Australia, don't have words for relative space, like left and right, but do have terms for north, south, east and west. Studies have shown that they tend to be unusually skilled at keeping track of where they are in unfamiliar places. There is also some evidence that the direction in which your first language is written can influence your sense of time, with speakers of Mandarin more likely to think of time running from top to bottom than English speakers. And the language you speak may affect how you perceive others (see "Does your language shape your personality?", right).
More generally, language helps us understand the world by allowing us to categorise things. Children are better at grouping objects if they have already learned the names of the categories they belong to. Conversely, after a stroke, people who have lost language skills can have trouble grouping objects. "It's not that language just affects some high-level reasoning part of the brain," says Gary Lupyan of the University of Wisconsin-Madison. "It's changing our basic perceptual representations."
Does your language shape your personality?
"To have another language is to possess a second soul," Charlemagne is rumoured to have said. He may have been on to something. In the 1960s, sociolinguist Susan Ervin-Tripp of the University of California at Berkeley asked English-Japanese bilinguals to describe what was going on in ambiguous pictures. One person, for example, told a different tale depending on their storytelling language. A picture of a woman leaning against a couch elicited a story in Japanese about a woman contemplating suicide after the loss of her fiancÃ©. The same person, asked to respond at a separate session in English, said the woman was completing a sewing project for a class. "In general, there was more emotion in the Japanese stories," Ervin-Tripp wrote in a description of the experiment. "The switch in language draws with it the cultural baggage associated with that language."
Nairin Ramrez-Esparza at the University of Connecticut asked bilingual Mexicans to rate their personalities using both English and Spanish questionnaires. English responses emphasised openness and extroversion, while Spanish responses were more humble and reserved. "Language is such a powerful thing. It obviously makes you see yourself differently," Ramrez-Esparza says.
According to Shai Danziger of Ben-Gurion University in Israel and Robert Ward of Bangor University in the UK, it can also influence how you think of others. They asked Arabic-Hebrew bilinguals to match Arab and Jewish names with positive or negative trait words by pressing a key. They say participants showed more involuntary positive attitudes towards Jews when tested in Hebrew than when tested in Arabic. Paula Rubio-Fernandez of the University of Oslo, meanwhile, has found that bilingual children perform better on tests that require them to understand a situation from someone else's perspective.
Evidence is mounting that the words we speak and think shape our brains, perceptions, and personalities. Who knows what else? Perhaps our tastes, habits, or values. The door is wide open.