Brain Plasticity and Language Learning

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A substantial body of work has shown that exposure to the sounds of language in the first year of life are critical for language development. My lab has been instrumental in exploring the effect of early linguistic experience on brain organization and neuroplasticity, to develop insights into universals of languages and how they are represented in the brain. We have capitalized on the unique situation of international adoptees (IA) to probe neural correlates of language, showing that the templates of the first language remain in the brain decades later, after abrupt loss of that language in infancy. What is not yet known, is what purpose these templates serve. Do sound patterns learnt early in life influence later language learning (e.g., when relearning that language)? Are neural patterns fixed or flexible, and how do they relate to individual differences in learning? In this Discovery Grant, we address these knowledge gaps with new experiments using controlled pre-post training approaches, and more naturalistic longitudinal training to link changes in the brain to learning outcomes. State-of-the-art behavioural and neuroimaging methods (MEG, fMRI tasks, resting-state fMRI, structural brain imaging) will be used to assess responses from brainstem to cortex, from acoustic encoding to higher-order language processing, in the same individuals, allowing for comprehensive understanding of language processing across linguistic levels and their interdependencies. We will compare IA, born in China but now speak exclusively French, to tightly matched groups with different language pairings (English-French, Mandarin-French) and simultaneous versus sequential language learners, to disentangle the impact of number of languages learned, types of language pairings, and age of learning on the brain. The first experiments focus on language experiential differences between groups in relation to learning phonetics and prosody, asking whether templates of a birth language, Mandarin, aid relearning of the language later in life, as well as where in the brain this information is encoded and if this changes with training. The second thread of experiments focus on how generalisable early perceptual language experience is to more global language processing, and predispositions related to language learning outcomes. Our analyses focus not only on how language experience impacts the brain, but also on identifying pre-training predictors or biomarkers of language learning success. We expect the results from these studies to shed light on how the brain changes in response to training, leading to advances in language-education policies and practices in Canada. Future work will also extend our focus to other situations of language attrition and re-learning (e.g., heritage languages of Canada). Overall, the proposed experiments advance my research program that aims to elucidate fundamental neurobiological mechanisms underlying speech and language acquisition.