Abstract
This longitudinal study investigated the differential impacts of maternal speech on early socio-communicative development in infants at low likelihood (LL) and elevated likelihood (EL) of autism spectrum disorder (ASD). Using functional near-infrared spectroscopy, we measured cortical responses and connectivity in 6-month-old infants while they listened to their mother's voice and an unfamiliar female voice. LL infants exhibited extensive cortical activation and robust connectivity in temporal and frontal regions, particularly in areas associated with voice processing, reward, and language functions. In contrast, EL infants showed minimal activation and weaker connectivity in these regions. Specifically, LL infants demonstrated significant connectivity between the superior temporal gyrus and the inferior frontal gyrus on the left side and between the orbitofrontal cortex and language areas, facilitating language processing and reward-related responses to maternal speech. These neural patterns were absent in EL infants, highlighting a neural basis for subsequent language delays. Furthermore, many of these reward-related or language-related networks predicted subsequent language development. Our findings underscore the importance of neural sensitivity to familiar human voices, regarding them as rewards that will eventually facilitate the acquisition of speech.