examining MRIs of the brains of bilingual people

Perfectly mastering Shakespeare’s and Molière’s languages, and even more so Shakespeare’s and Confucius’, is a rare and enviable ability. But how do the brains of bilingual people process the two languages? In his Essays (1580), Montaigne wrote, “There is the name and the thing: the name is a voice which denotes and signifies the thing. (…) It is a foreign part, attached to the thing and outside of it.”

A French team was therefore interested in how written names, independently of things, are encoded by a bilingual brain in each of the two languages. The authors dissected the reading process in the brains of 21 English-French and 10 English-Chinese bilingual individuals. They used a very precise scalpel: the 7-Tesla functional MRI at the NeuroSpin center at CEA (INSERM-CNRS-Université de Paris-Saclay). Their work was published on April 5 in the journal Science Advances.

“Reading is a two-step process,” explained Professor Laurent Cohen, a neuroscientist at the Institut du Cerveau (Brain Institute) in Paris (Pitié-Salpêtrière Hospital, AP-HP), who coordinated the study with Stanislas Dehaene, director of NeuroSpin and professor at the Collège de France. In the first step, the brain’s visual system recognizes letters and their order. In the second, this data is transmitted to the language system, which provides access to the meaning and sounds of the words read.”

Left temporal lobe

The researchers explored the first stage, which takes place in the “visual word form area,” a small area located in the left temporal lobe. This area, “no bigger than a fingernail,” according to Cohen, is activated 150 to 200 milliseconds following the presentation of a written word. In the case of a stroke located there, patients lose their ability to read because they can no longer recognize letters. Could this area have a deeper specialization in the recognition of letters and letter sequences in different languages, the authors wondered?

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While lying in the MRI machine, the participants were asked to look at a series of images on a screen. At the same time, the researchers scanned the small subregions activated by these visual stimuli, within visual word form area. Occasionally, participants had to press a button when they saw a star appear, to keep their attention alert.

In a first experiment, they were presented with images (faces, bodies, houses, tools, checkerboards, etc.), numbers and words in each of the two languages. In a second experiment, they were series of letters or fragments of Chinese characters (logograms) that generally did not correspond to real words. The frequency of each character, however, and that of the sequences of two or four characters, within these “words” were carefully chosen to match the frequencies found in real words, to varying degrees.

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