Neural processing of speech envelopes from different languages and post-stimulation functional connectivity in newborns: an fNIRS study.

Abstract

Speech envelopes convey low-frequency temporal structure, including speech rhythm and prosody, and provide important cues for early speech processing in newborns. However, how the newborn brain processes speech envelopes and how brief exposure to them affects post-stimulation neural activity remain unclear. Using a mixed design with language condition as a between-subjects factor and resting-state time as a within-subjects factor, we assigned 73 newborns from Mandarin-speaking environments to a Mandarin group (n = 25), a French group (n = 23), or an English group (n = 25). Functional near-infrared spectroscopy (fNIRS) was used to record hemodynamic signals during stimulation with the corresponding speech envelopes and during resting-state periods before and after stimulation, allowing us to examine task-related activation patterns and changes in resting-state neural activity. All three speech envelopes elicited neural responses in frontotemporal regions, indicating that the newborn frontotemporal system can process both native-language envelopes and rhythmically distinct nonnative envelopes. Comparisons of the pre- and post-stimulation resting states further revealed a significantly strengthened frontotemporal functional connectivity network in the Mandarin group, without corresponding changes in the amplitude of local spontaneous activity. These findings suggest that the neural effects of brief exposure to speech envelopes may persist into the post-stimulation resting period and are primarily expressed as enhanced functional coordination across brain regions. Such post-stimulation network changes may reflect the newborn brain's brief retention of heard speech and, with continued language exposure, facilitate the gradual stabilization and maturation of early language networks, supporting subsequent speech processing and language learning.