18 years ago, a young woman was born without a part of her brain (the entire left hemisphere) but still has above-average reading skills. Note that the left hemisphere is generally the part of the brain used in language. She also has a slightly above average IQ.
Brain scans (which assess cerebral perfusion using complex molecules labeled with technetium-99m, capable of crossing the blood-brain barrier) revealed that the young woman had more brain tissue involved in reading than what is usually found in the majority of individuals. Tests of his brain activity indicate that the right side of her brain has taken over some of the functions that the left hemisphere usually does, showing that the organ has adapted to compensate for the missing tissue.
The parents of the young woman, known here as C1, noticed that something was out of the ordinary when she was 7 months old already. Most babies stop clenching their thumbs with their fists around this age, but C1 continued to do so with her right hand. It was when C1 was 10 months old that a scintigraphy revealed that there was a pocket of liquid where the left hemisphere of her brain should have been.
C1 has been diagnosed with hemi-hydranencephaly, an extremely rare disease in which a large part of the cerebral cortex is missing. To date, only 9 cases have been reported worldwide.
At the age of 14 months, C1 was enrolled in a research project: a team of scientists, based at the University of Chicago, followed her progress until her 16 years, as well as those of 64 other children with a brain said to be normal (full) and 40 children who had had a stroke in the weeks before or after birth.
Brain compensation that gets worse over time
Their linguistic, reading, spatial and mathematical skills were tested every four months until the age of almost 5 years. At first, C1's language skills were below average compared to developing children of the same age, and her vocabulary was severely limited. But she has improved over the years and developed average speaking skills by the time she was 4 and a half years old.
But C1 did not stop there: she also excelled in other areas. Indeed, when, between 5 and 7 years old, the researchers tested her ability to recognize and reorganize sounds into words, C1 even surpassed her peers! She also achieved exceptional reading results and was "in the upper range, and was significantly better than the group showing typical development," adds Asaridou.
In addition, according to the researchers, C1's language skills do not seem to have developed at the expense of other cognitive skills. Her IQ is in the “medium to high” range, and she has typical spatial skills. C1 is exceptionally good at short-term memory tests, which involve, for example, remembering sequences of numbers.
Scientists were able to learn more about her brain through brain scans. When she was 14, they used functional MRI (fMRI) to study her brain activity while she was listening to stories. Asaridou and his colleagues then compared the results of C1 with those of 30 developing children, generally aged 12 to 14 years.
"C1's pattern of activity looked like what we saw in the left hemisphere of typical developing children," says Asaridou. This proves that the right hemisphere of C1 has adapted to assume some of the functions usually managed by the left side, like language processing for example.
A second series of scans, taken at the same age, revealed that her brain had more white matter (the tissue that connects regions of the brain and allows them to communicate) than what is generally found in a human brain. More specifically: C1 has more white matter in the regions known to be involved in language skills, ranging from sound mapping to articulation through reading.
Asaridou and the other researchers suspect that her environment could have helped her: C1's family is well off, so that her parents could afford, from an early age, to provide her with physical and oral therapies. In addition, C1 has a brother (younger) who is also particularly gifted when it comes to language tests, "which could possibly also be a genetic factor," says Asaridou. "But these are just speculations. This is a complicated case with a unique contribution from different factors. "
At present, C1 is still having difficulty moving the right side of her body but according to the team study her, she seems to be doing well in life in general and has passed her school exams.
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