Father-infant bonding alters their neural entrainment to mothers’ speech: an fNIRS hyperscanning study

Inter-brain synchrony (IBS) refers to an integrative function across brains between more than two people examined using neuroimaging techniques. Previous studies have mainly focused on synchrony between mothers and infants or children, with fathers being left out. To fill this research gap and understand how paternal roles affect child development, the current study examined the inter-brain coherence (IBC) between 34 dyads of fathers and infants 7-9 months of age using functional near-infrared spectroscopy (fNIRS). There were three conditions: a baseline condition, and two speech perception conditions where the infant and the adult participant jointly listened to mothers telling stories in Cantonese in infant-directed speech (IDS) and adult-directed speech (ADS). Father-infant IBC was compared with stranger-infant IBC in the same experimental settings. Our results found that father-infant IBC was higher in the baseline and ADS conditions but lower in the IDS condition, compared to stranger-infant IBC. Further, stranger-infant dyads showed higher IBC in the IDS condition than in the ADS condition, with no significance in father-infant IBC between the two speech conditions. These results identified different inter-brain connection mechanisms between the two dyads. The IBC pattern in stranger-infant dyads is driven by neural entrainment to mothers’ speech, whereas father-infant IBC is more resistant to mothers’ behaviors in the co-presence of both parents.