<p>Inter-brain synchrony has recently emerged as core mechanism of brain functioning. Two approaches distinctly measure cross-brain processes; during live social exchanges or passive observation of social stimuli, but are the two underpinned by similar processes? Guided by the <i>biobehavioral synchrony</i> frame, we utilized hyperscanning EEG and a paradigm developed for the current study to explore the linkage between inter-brain synchrony during <i>Live</i> and <i>Represented</i> social experiences. In Study 1 (n = 130) mother-adolescent dyads engaged in free interaction, coded for behavioral synchrony, and then observed this interaction in separate rooms. Greater neural synchrony across the fronto-temporal inter-brain network emerged during live social participation than passive observation of represented social moments, and the two were inter-related and predicted by behavioral synchrony. Study 2 (n = 54) tested the generalizability of the findings in unfamiliar adults and similarly found linkage between neural synchrony during live and represented experiences, both associated with behavioral synchrony. Shared social experiences create lasting neural synchrony that can be reactivated during subsequent invocation and depends on relationship quality and familiarity. Findings highlight the role of live social moments and their retention in memory in shaping the social brain and have implications for the integration of the third- and second-person perspectives in social neuroscience.</p><p></p>