Development of the social perception pathway across the third trimester of gestation and perinatal transition.

Babies display social perceptual skills within hours of birth which may indicate that the neural predecessors of such skills have prenatal origins. However, the putative fetal neural infrastructure supporting these skills remains unexplored. Data from 497 participants scanned between 28-44 weeks postmenstrual age were examined to map the development of intrinsic functional connectivity (iFC) within the proto social pathway (pSP), encompassing the superior temporal sulcus (STS), a region implicated in processing multimodal social stimuli later in development, and the proto ventral pathway (pVP), including the fusiform face area (FFA), a region associated with static face processing in older children and adults. IFC was greater than 0 in the bilateral pSP and pVP by 28 weeks and increased significantly in the left and right pSP and left pVP but not in the right pVP between 28 and 44 weeks. By 44 weeks, both pathways exhibited robust right-dominance. By 40 weeks, iFC for the right and left pSP was significantly higher than in the corresponding pVPs. Lastly, the right posterior STS (pSTS) and the right FFA coupling became positive by 40 and 44 weeks and the left pSTS-FFA coupling became negative by 44 weeks. These findings demonstrate that neural architecture supporting social perception later in life is present in the third trimester and undergoes rapid development across the pre- to postnatal transition. The strengthening of intrinsic connectivity, emergence of right-hemisphere dominance, and early differentiation of putative social perception and face-processing circuitry indicate that key features of the social brain begin to assemble before birth, providing a developmental scaffold for later social development.