Chinese babies adopted across international borders may not remember the language they heard in their first days, but the words leave a lasting mark on their brains, which respond to Chinese tones more than a decade later, scientists said.
The study published in the Proceedings of the National Academy of Sciences on Monday is the first that employs brain imaging scans to show how we process lost language.
“What is kind of striking is that these traces are there even though they don’t really need them any more,” said co-author Denise Klein of the Montreal Neurological Institute and Hospital at McGill University.
“The brain is responding to the information.”
The study included 48 girls, aged nine to 17. Some were born and raised in a French family, speaking only French. Some were Chinese-born and adopted into French families, and learned to speak only French. Others were fluent in both Chinese and French.
All three groups listened to Chinese language sounds while magnetic resonance imaging scans were taken.
They heard sounds like ma-ma, spoken in slightly different tones. Those with no Putonghua would hear them just as sounds.
However, those with some knowledge of the language would know that depending on the tone, ma could mean mother, hemp, horse or scold.
The children heard three syllable sounds and were asked to press a button to indicate if the final syllables sounded the same .
All the participants responded with high levels of accuracy to the quiz, but only some showed brain activity that indicated recognition, or what the study described as “linguistic relevance”.
The bilingual Chinese-French and the children adopted from China showed brain activity in the right and left hemispheres, while the monolingual French children showed brain activity only in the right hemisphere.
This signifies that those who had heard Chinese as babies were able to tell that the sounds they were hearing were “language, or meaningfully related”, even if they no longer understood them, explained Klein.
Even though they had little if any language ability even when they were adopted, somehow their brains continued to process Chinese sounds as meaningful an average of 12 years later.
Klein described the MRI scans as showing that mental templates set up early in life are not overwritten by new information.
Previous research has shown that babies initially respond to all languages heard in their environment, but slowly they stop responding to foreign tongues and turn their heads mainly when they hear their parents’ language.
The latest research goes further, showing the precise area of brain activity at play, and suggesting “a special status for language input obtained during the first year of development”, said the study.