Functional brain adaptations during speech processing in 4-month-old bilingual infants

Language learning is influenced by both neural development and environmental experiences. This work investigates the influence of early bilingual experience on the neural mechanisms underlying speech processing in 4-month-old infants. We study how an early environmental factor such as bilingualism interacts with neural development by comparing monolingual and bilingual infants’ brain responses to speech. We used functional near-infrared spectroscopy (fNIRS) to measure 4-month-old Spanish-Basque bilingual and Spanish monolingual infants’ brain responses while they listened to forward (FW) and backward (BW) speech stimuli in Spanish. We reveal distinct neural signatures associated with bilingual adaptations, including increased engagement of bilateral inferior frontal and temporal regions during speech processing in bilingual infants, as opposed to left hemispheric specialization observed in monolingual infants. This study provides compelling evidence of bilingualism-induced brain adaptations during speech processing in infants as young as four months. These findings emphasize the role of early language experience in shaping neural plasticity during infancy suggesting that bilingual exposure at this young age profoundly influences the neural mechanisms underlying speech processing. Research Highlights This research sheds light on the intricate relationship between language learning, neural maturation, and environmental factors in early infancy. Bilingual infants exhibit unique functional brain adaptations during speech processing as early as 4 months of age. This study underscores the critical role of language experience in shaping the developing brain. These findings have implications for our understanding of language acquisition and neuroplasticity in infants growing up in bilingual environments.