How does the human brain learn to read and how is it transformed by this new means of accessing language, which no longer involves the ears but the eyes? For one year, 10 children in their first year of primary school came to NeuroSpin every two months to help researchers from the Institut Frédéric-Joliot, the CNRS and the Collège de France unravel this mystery. The children looked at images of objects, houses, faces, bodies, and also words and letters while in an MRI. Their task was then to press a button as quickly as possible when "Charlie" the comic book character appeared.

Each of these image categories activated a specialized visual region, as in adults. And as for the words? In some children, by the end of November, a region that responded more to words than to other images became visible: the "letter box". This took longer for other children, and the response from this region was proportional to their reading performance. One year later, once the reading of familiar words had become automatic, only the "letter box" and the region where letters are converted into sounds (in the temporal regions of oral language) persisted, in the left hemisphere.

Once reading had become automatic in the children, the researchers sought to turn back time and study what these regions did in each child, particularly the "letter box", before specializing in reading. Does learning to read displace specializations already acquired for other visual categories, or does the "letter box" emerge from a region that is still "free" of any specialization? The research team verified the second hypothesis, and also found that the development of reading in the left hemisphere (the hemisphere for oral language) blocks the development of the region that responds to faces in that hemisphere, in contrast to what happens in the right hemisphere. This competition between words and faces on the left, and not on the right, results in an increase in hemispheric asymmetry among readers, in comparison to illiterates and dyslexics as observed in previous studies.

We are therefore teaching children to read at a moment of plasticity in this region, which increases its response to faces in the natural environment. Thus, the educational process has spontaneously discovered the windows of plasticity offered by the human brain's timeframe of maturation, in order to enable effective learning.

These results were the subject of a press release.