When Do We Fall in Neural Synchrony With Others?

Kelong Lu; Ning Hao


Soc Cogn Affect Neurosci. 2019;14(3):253-261. 

In This Article

Abstract and Introduction


This study aimed to investigate the situation in which interpersonal brain synchronization (IBS) occurs during a collaborative task and examined its trajectory over time by developing a novel functional near-infrared spectroscopy (fNIRS)-based hyperscanning paradigm. Participants were asked to perform a collaborative task in three-person groups where two of the members are real participants and one is a confederate. Compared to dyads between real participants and confederates, real-participant pairings showed greater cooperation behavior and IBS between bilateral dorsolateral prefrontal cortex. And, IBS and cooperation increased over time in real-participant pairings, whereas they remained low and constant in dyads with the confederate. These findings indicate that IBS occurs between individuals engaging in interpersonal interaction during a collaborative task, during which both IBS and cooperatively interpersonal interaction tend to increase over time.


The evolution of human society necessitates social interaction among individuals. The complex and large-scale social interaction in human society was suggested as one of the special features that distinguishes our mankind from other species (Adolphs, 2003; Dunbar, 2009). Considering the importance of social interaction, plenty of studies have been conducted to unveil the underlying mechanism of social interaction, especially the neural mechanism. Most of the neuroimaging studies in this field investigated the neural correlates related to social cognition by measuring brain activity of one individual per time (Montague et al., 2002). Although this kind of typical paradigm could help identify and characterized neural activities related to social cognition, the valuable information of the dynamic interaction among multiple brains was neglected.

To unveil the dynamic neural interaction among multiple individuals, the multi-brain neuroimaging technique was resurrected and renamed as 'hyperscanning technique' (Montague et al., 2002). Thereafter, increasing hyperscanning studies emerged in the field of social interaction (Funane et al., 2011; Cui et al., 2012; Holper et al., 2012; Jiang et al., 2012; Dikker et al., 2017; Dai et al., 2018; Goldstein et al., 2018; Lu et al., 2018; Xue et al., 2018; Lu et al., 2019). Most of these studies revealed enhanced interpersonal brain synchronization (IBS) between individuals while they were engaged in social interaction contexts. To explain the emergence of the IBS between individuals in interpersonal interaction situations, two typical hypotheses were proposed: cooperative interaction hypothesis and similar task hypothesis. The cooperative interaction hypothesis suggests that the IBS indicates that individuals are engaged in cooperatively interaction, whereas the similar task hypothesis suggests that the IBS merely indicates that individuals are working on the similar task.

Some studies provided evidence for the cooperative interaction hypothesis by showing that IBS emerged during cooperatively interpersonal interaction, such as group humming (Osaka et al., 2014), guitar playing (Lindenberger et al., 2009; Müller et al., 2013), cooperative button press (Cui et al., 2012; Pan et al., 2017), coordinated walking (Ikeda et al., 2017), group communication (Jiang et al., 2012; Nozawa et al., 2016; Liu et al., 2017) and group creativity problem solving (Lu et al., 2018; Xue et al., 2018). Besides, researchers have also successfully tracked the IBS underlies teaching–learning interactions which was associated with teaching–learning performance (Dikker et al., 2017; Pan et al., 2018; Zheng et al., 2018). All of this indicated that the IBS between individuals might reflect that individuals were cooperatively interacting with each other. However, several studies supported the similar task hypothesis (Nummenmaa et al., 2012; Abrams et al., 2013; Kawasaki et al., 2013). In each of these studies, although individuals performed the similar tasks solely, enhanced IBS between individuals was still observed. For instance, the participants were instructed to watch several films depicting unpleasant, neutral and pleasant emotions in a fixed order individually while being scanned with fMRI. Although there was no interaction between participants, enhanced IBS was still observed (Nummenmaa et al., 2012). Since interpersonal interaction between individuals scarcely occurred, the enhanced IBS could not be attributed to the interpersonal interaction between individuals. Alternatively, it was supposed that the enhanced IBS might reflect that individuals were just engaged in the similar tasks.

In the current study, we aimed to explore the situation in which IBS occurs during a collaborative task to seek evidence that supports the cooperative interaction hypothesis over the similar task hypothesis and examine its trajectory over time. We developed a novel paradigm in which three people—two of them are participants, one is a confederate—interact while using functional near-infrared spectroscopy (fNIRS)-based hyperscanning technique, which allows for the comparison of IBS between two real participants pairings and control dyads. During the collaborative task, the confederate pretended to perform the task. In fact, the confederate was asked to recall and report prepared task-related ideas merely. In other words, although the confederate was working on the same task as other partners, he was not engaged in any cooperatively interpersonal interaction with others. Hence, according to the cooperative interaction hypothesis, we hypothesized that the IBS between the two real participants should be higher than that of the control dyads in the three-person group (dyads with confederate). However, according to the similar task hypothesis, we hypothesized that there might be no significant differences in IBS among different dyads in the group. Besides, although without any precise hypothesis, we expected to examine the trajectory of the IBS over time, which might help understand the relationship between IBS and interpersonal interaction process more thoroughly.