Longitudinal study of functional brain networks for processing infant-directed and adult-directed speech during the...

Infant-directed speech (IDS) plays a central role in early communication, initially expressing emotion and later supporting language development. This study examined how the brain's functional network organization responds to infant-directed speech (IDS) versus adult-directed speech (ADS) during early infancy. Electroencephalography (EEG) data were collected from 49 healthy infants at 0, 4, and 9 months as they listened to the same fairy tale spoken in both IDS and ADS. Brain connectivity was assessed using phase lag synchronization across six frequency bands, and network topology was characterized using minimum spanning tree analysis. The delta network showed greater hierarchical and cost-efficient organization in response to IDS, particularly over frontal regions, with these differences becoming more pronounced with age. Over time, network integration increased and shifted toward the left hemisphere. These findings highlight how functional brain networks dynamically adapt to socially relevant speech input, reflecting the evolving communicative function of IDS during the first year of life.