Mapping the unconscious maintenance of a lost first language

Significance Using functional MRI we examined the unconscious influence of early experience on later brain outcomes. Internationally adopted (IA) children (aged 9–17 years), who were completely separated from their birth language (Chinese) at 12.8 mo of age, on average, displayed brain activation to Chinese linguistic elements that precisely matched that of native Chinese speakers, despite the fact that IA children had no subsequent exposure to Chinese and no conscious recollection of that language. Importantly, activation differed from monolingual French speakers with no Chinese exposure, despite all participants hearing identical acoustic stimuli. The similarity between adoptees and Chinese speakers clearly illustrates that early acquired information is maintained in the brain and that early experiences unconsciously influence neural processing for years, if not indefinitely. Optimal periods during early development facilitate the formation of perceptual representations, laying the framework for future learning. A crucial question is whether such early representations are maintained in the brain over time without continued input. Using functional MRI, we show that internationally adopted (IA) children from China, exposed exclusively to French since adoption (mean age of adoption, 12.8 mo), maintained neural representations of their birth language despite functionally losing that language and having no conscious recollection of it. Their neural patterns during a Chinese lexical tone discrimination task matched those observed in Chinese/French bilinguals who have had continual exposure to Chinese since birth and differed from monolingual French speakers who had never been exposed to Chinese. They processed lexical tone as linguistically relevant, despite having no Chinese exposure for 12.6 y, on average, and no conscious recollection of that language. More specifically, IA participants recruited left superior temporal gyrus/planum temporale, matching the pattern observed in Chinese/French bilinguals. In contrast, French speakers who had never been exposed to Chinese did not recruit this region and instead activated right superior temporal gyrus. We show that neural representations are not overwritten and suggest a special status for language input obtained during the first year of development.