Social and Physiological Context can Affect the Meaning of Physiological Synchrony

Survival of many species, from insects and birds to human and non-human mammals, requires synchronized activity. Among humans, synchrony occurs even at the level of autonomic functioning; people interacting often show mutual, simultaneous changes in activity of the sympathetic or parasympathetic branches of the autonomic nervous system. Critically, autonomic reactivity predicts many mental states and, when synchronized, may reflect higher-order social processes like affiliation. Here, using data from 134 strangers interacting in pairs, we manipulated two features of social context to test their impact on synchrony in sympathetic and parasympathetic reactivity. Participants completed a knot-tying task within a collective reward ("cooperation") or individual reward ("competition") framework while conversing or not ("talking" condition). Autonomic reactivity varied by features of social context. Synchrony occurred across social contexts in both autonomic branches. We then examined how synchrony predicted affiliation. Sympathetic synchrony alone predicted affiliation yet social context and parasympathetic reactivity moderated associations between parasympathetic synchrony and affiliation. Thus, social and physiological context of parasympathetic synchrony predicted affiliation better than parasympathetic synchrony alone. We argue that social context and the degree of physiological reactivity underlying physiological synchrony, not the mere existence of physiological synchrony, are key to interpreting physiological synchrony as a social process.