INTRODUCTION
CORTEX
Extant research proposes that functional brain networks reconfigure in response to changes in one's environment (Fries, The current study aimed to examine this question by probing between‐brain and within‐brain coupling during a movement synchronization paradigm. Interpersonal synchrony requires coordination of movement over time of two or more interacting individuals (Chartrand & Lakin, Synchronization frequently emerges spontaneously, when there is no explicit social goal of alignment, as evident in unintentional synchronization of body gestures and facial expressions (Chartrand et al., As attaining synchronization requires making predictions regarding the other's movement as well as continuous observation and updating of predictions (Wolpert et al., Error monitoring has been linked to brain activity of the anterior cingulate cortex (ACC), dorsal medial prefrontal cortex (dmPFC), and insula (Carter et al., In addition to the error monitoring system, previous neuroimaging studies on synchronization focused on the inferior frontal gyrus (IFG), a core region of observation–executions system, as it is commonly active both when an action is performed and when it is passively observed (Rizzolatti & Craighero, While during intentional synchrony cognitive efforts are primarily invested in attempting to become attuned to others, to minimize errors, during free movement efforts are focused on self‐movement and less on the other's movement (Marton‐Alper et al., Some support for the idea of a potential trade‐off between connectivity of within versus between brain networks may be found in studies characterizing the dynamics of topological brain networks of segregation (high connectivity within specialized networks) and integration (connections between specialized networks; Deco et al., Here, our goal was to determine whether interpreting network organization in terms of between‐ and within‐brain networks could explain successful movement synchronization. We scanned dyads with fNIRS while they performed an open‐ended movement task (Reiss et al., (a) 