Alternative brain connectivity underscores age-related differences in the processing of interactive biological motion.

Rapidly recognizing and understanding others' social interactions is an important ability that relies on deciphering multiple sources of information; for example, perceiving body information and inferring others' intentions. Despite recent advances in characterizing the brain basis of this ability in adults, its developmental underpinnings are virtually unknown. Here, we used fMRI to investigate which sources of social information support superior temporal sulcus (STS) responses to interactive biological motion (i.e. 2 interacting point-light human figures) at different developmental intervals in human participants (of either sex): Children show supportive functional connectivity with key nodes of the mentalizing network, while adults show stronger reliance on regions associated with body- and dynamic social interaction/biological motion processing. We suggest that adults employ efficient action-intention understanding via body and biological motion information, while children show a stronger reliance on hidden mental-state inferences as a potential means of learning to better understand others' interactive behavior. SIGNIFICANCE STATEMENT: Recognizing others' interactive behavior is a critical human skill that depends on different sources of social information (e.g. observable body-action information, inferring others' hidden mental-states etc.). Understanding the brain-basis of this ability, and characterizing how it emerges across development are important goals in social neuroscience. Here, we used fMRI to investigate which sources of social information support interactive biological motion processing in children (6-12 years) and adults. These results reveal a striking developmental difference in terms of how wider-brain connectivity shapes functional responses to interactive biological motion that suggests a reliance on distinct neuro-cognitive strategies in service of interaction understanding (i.e. children and adults show a greater reliance on explicit and implicit intentional inference, respectively).