Languages that people are exposed to at a young age form circuits in the brain that the body does not forget, even if the individual does. 

The existence of this buried information persists after childhood, possibly for life, according to research from the Montreal Neurological Institute and Hospital and the McGill University Department of Psychology. The study, published Nov. 17 online in the Proceedings of the National Academy of Sciences, found that Chinese children ages 9–17 who were adopted by French parents displayed unconscious recognition of their birth language in a functional MRI scan.

“When children are born, essentially their brains are [blank slates] when it comes to language learning,” said Fred Genesee, co-author of the study and a professor emeritus in the Department of Psychology at McGill University in Montreal. 

Until about seven or eight months of age, children have the ability to distinguish speech sounds in their birth language and in various others, Genesee said. After that, the ability to detect sounds that are not useful in their native tongue decreases. For example, Genesee said the words “lot” and “rot” are indistinguishable to a native Japanese speaker because the sounds that correspond with the letters “l” and “r” do not change the meaning of a word in Japanese.

The brain increasingly exposed to one language becomes perceptually attuned, hardwiring itself to perceive the tones and contrasts from a particular pattern of speech rather than retaining an open-door policy, according to Genesee.

While in the fMRI scanner, participants heard either monosyllabic Chinese pseudo-words—units of speech that sound like Chinese to non-native speakers but are actually meaningless—or hummed versions of the same words, according to the study. These words also included lexical tone, a distinctive pitch associated with a syllable in a word that, if shifted up or down, can alter the meaning of that word. Both the Chinese children who were adopted by French parents but did not speak Chinese and a group of Chinese-French bilinguals called upon the left temporal region of the brain—which is associated with the top-down processing of learned linguistics—when they heard the Chinese pseudo-words during the experiment.

Genesee said young children use this top-down process when learning language. The brain scans confirmed that study participants exposed to Chinese at a young age were able to subconsciously recognize the pseudo-words and lexical contrasts they heard. 

“It’s quite well established in the literature, and we’ve known for a very long time, that the best way to become fluent in a language is to learn it when you’re very young,” said Amanda Woodward, professor in the Department of Psychology at the University of Chicago. 

Woodward cited Noam Chomsky, known as the “father of modern linguistics,” who proposed that language is innate in young children. 

“We come into the world expecting to find language,” Woodward said. “[Chomsky] was interested in the grammatical structure of language. He was essentially saying that we are innately prepared to acquire the abstract rules of grammar.”

The adoptees exposed to Chinese in their first year of life were perceiving neurocognitive traces of Chinese in small units, Genesee said. Those who were not exposed to Chinese at that age could only perceive that information as sound, not in any linguistic manner.

The left hemisphere of the brain is usually activated when people engage in language processing, he said. The right hemisphere is more associated with processing sounds in a non-linguistic fashion. People without training in a particular language would not perceive these sounds as words.

According to Lara Pierce, first author of the study and a doctoral candidate at McGill University, there is much debate in the literature about whether early language experiences are overwritten in the brain after long periods of disuse or if the established neurolingual pathways just become too difficult to access.

“These findings suggest the latter and may begin to tell us something important about neural plasticity and what the brain is doing during this early developmental time,” Pierce said in an email.

Researchers have yet to determine whether developing neural pathways for a certain language or sound contrast at a young age makes it any easier to learn that language or a similar one later in life, Genesee said. 

“So laying a new pattern on top of that old pattern is harder when the two patterns are very different,” he said. “Somebody I was talking to said it’s sort of like these are ghosts in your brain that are formulated when you’re young and they’re always in the background.”