Neural synchrony is shaped by both relationship type and task demands

A new study finds that the alignment of brain activity between two people, known as interpersonal neural synchrony, varies based on their relationship and what they are doing together. The research, published in NeuroImage, found that mother-child pairs tend to have lower synchrony than adult friends or romantic partners, and that passively sharing an experience can sometimes generate more neural alignment than active cooperation.

Scientists have long been interested in how our brains coordinate during social interactions, but research findings have often been difficult to compare. Studies have examined different types of relationships, from strangers to romantic partners, and used a wide range of tasks, from simple cooperation games to open-ended conversations. This variability has made it challenging to build a cohesive understanding of the factors that govern brain-to-brain synchrony.

To address this, a team of researchers from the University of Trento in Italy and the University of Vienna in Austria, led by PhD student Alessandro Carollo and Professor Gianluca Esposito, designed a study to systematically investigate two key dimensions: interpersonal closeness and the level of social interactivity.

“Most neuroscience research on social interaction has relied on highly controlled, artificial tasks where people are tested alone and exposed to social stimuli such as faces or voices on a screen. While this work has deepened our understanding of how the brain processes social information, it tells us little about what happens during real interactions between people,” the researchers told PsyPost.

“In this study, we wanted to explore how the brain supports active coordination and communication in natural settings — across different kinds of relationships, from close friends to romantic partners and mothers with their children. Our goal was to identify the neural mechanisms that allow people to connect with one another in everyday life.”

The researchers recruited 142 pairs of participants, divided into three groups based on their relationship: 70 dyads of close friends, 39 romantic partner dyads, and 33 mother-child dyads. Each pair’s brain activity was recorded simultaneously using a technique called functional near-infrared spectroscopy, or fNIRS. This non-invasive method involves wearing a cap with sensors that use light to measure changes in blood oxygen levels in the brain, providing a proxy for neural activity.

During the experiment, each pair engaged in three distinct activities designed to elicit different levels of interaction. In a passive condition, they watched a short animated video together without speaking. In a structured active condition, they played a cooperative game of Jenga. In an unstructured active condition, they engaged in a five-minute free-form conversation.

The researchers focused on activity in two brain areas on both sides of the brain: the inferior frontal gyrus and the temporoparietal junction. These regions are known to be involved in social cognitive processes like understanding others’ actions and intentions.

First, the team confirmed that the synchrony they observed was meaningful. They compared the brain alignment in the real pairs to that of “surrogate” pairs, created by randomly matching data from individuals who had not actually interacted. The real pairs showed significantly higher neural synchrony, indicating that the alignment was a genuine product of the shared social experience. This effect was particularly strong for connections involving the right inferior frontal gyrus, a brain area associated with action observation and imitation.

“We found that people’s brains do tend to ‘sync up’ when they interact, and that this synchrony is influenced by both who we are interacting with and how,” Carollo and Esposito explained. “Even simple, everyday moments of connection can lead to similar patterns of brain activity among people.”

When examining the effect of relationship type, the study produced an unexpected outcome. The researchers had hypothesized that mother-child pairs, representing a foundational attachment bond, would show the highest levels of synchrony.

Instead, they found that both close friends and romantic partners exhibited significantly higher synchrony than mother-child pairs. This could suggest that the brains of close-knit adults, which are fully mature and have a long history of attuning to social equals, may coordinate more readily. The lower synchrony in mother-child pairs might also reflect ongoing developmental processes in the child’s brain, which is still maturing in its ability to engage in complex social coordination.

The results related to social activity were also contrary to the team’s initial predictions. They had expected that more active and unstructured interactions would require greater neural coordination, leading to higher synchrony. However, the data revealed that across all groups, the passive task of watching a video together produced the highest overall synchrony. The structured cooperative game ranked second, while the unstructured free conversation was associated with the lowest levels of synchrony. This pattern was most clear in the adult-adult pairs.

“We actually expected the opposite pattern regarding interpersonal closeness and social interactivity,” Carollo and Esposito told PsyPost. “We thought that closer relationships and more interactive contexts would show higher levels of brain synchrony. Instead, synchrony was sometimes stronger in less interactive settings, such as when close friends watched a movie together. This suggests that simply sharing an experience, being present together, can promote alignment between brains, even without active communication.”

The researchers suggest that when two people passively observe the same dynamic stimulus, their brains process the information in a similar way and at a similar pace, leading to a strong, stimulus-driven alignment. In more open-ended interactions like conversation, the social signals are less predictable and more complex, potentially leading to less consistent moment-to-moment alignment across the measured brain regions.

“The level of synchrony isn’t always higher in closer or more interactive relationships,” Carollo and Esposito noted. “In some cases, greater alignment may actually reflect the brain’s effort to coordinate during newer or less familiar interactions.”

“It’s tempting to think that higher neural synchrony means ‘better’ communication or a stronger emotional bond, but that’s not always the case. Synchrony reflects coordination at the neural level, not the depth or quality of a relationship. It’s also shaped by factors like attention, task structure, and developmental stage.”

“And importantly, neural synchrony is not a form of telepathy. It doesn’t mean people are literally sharing thoughts. Instead, it likely reflects how the brain aligns with shared rhythms of communication, things like gaze, speech, gestures, and mutual attention, that help us stay ‘in tune’ with and possibly understand each other during social interactions.”

A more detailed analysis showed that the effect of the task depended on the specific brain regions involved. While many brain connections were most synchronized during the passive video-watching task, synchrony between the left inferior frontal gyrus of both participants, and between one person’s left inferior frontal gyrus and the other’s right temporoparietal junction, peaked during the cooperative Jenga game.

This suggests that while passive shared experience drives one form of neural alignment, active, goal-directed cooperation relies on the coordination of a different set of neural pathways involved in joint action and strategic thinking.

“Our results suggest that neural synchrony can act as a kind of ‘neural signature’ of social coordination, much like the behavioral, physiological, or hormonal synchrony seen in earlier studies,” Carollo and Esposito said. “Over time, these brain-to-brain measures could help us better understand how social experiences shape development, relationships, and individual differences in social functioning. Ultimately, our findings reinforce the idea that the human brain is profoundly social. It is wired to respond to, adapt to, and resonate with the dynamics of our interpersonal world.”

The study has some limitations. The data for the adult pairs and mother-child pairs were collected in two different countries using slightly different equipment, though procedures were standardized as much as possible. The study also did not include fine-grained behavioral analysis, which could link specific actions like eye contact or gestures to fluctuations in neural synchrony. The inherent age difference between mother-child pairs and adult pairs also makes it difficult to completely separate the effects of relationship type from developmental factors.

Future research could build on these findings by including other types of relationships, such as non-parental adult-child pairs or child-child friendships, to better isolate the influence of development and interpersonal closeness.

“We hope to contribute to a more standardized framework for studying neural synchrony across labs,” the researchers said. “Future work will look more closely at how synchrony relates to specific relational variables, for instance, co-regulation in mother–child pairs or the quality of friendship among peers. In the longer term, we aim to understand how brain-to-brain alignment functions in larger groups and whether it might predict collective performance in collaborative or team settings.”

The study, “Interpersonal neural synchrony across levels of interpersonal closeness and social interactivity,” was authored by Alessandro Carollo, Andrea Bizzego, Verena Schäfer, Carolina Pletti, Stefanie Hoehl, and Gianluca Esposito.