Exploring brain synchronization patterns during social interations

We experience the world and connect with others through social interactions. Engaging in activities, such as having a conversation, collaborating on a task, and having an intimate relationship, deeply affects brain activity leading to both coordinated neural activity within an individual's brain (intra-brain synchronization) and between the brains of multiple individuals (inter-brain synchronization).

Researchers study brain synchronizations to understand the neural processes behind social behaviors. This knowledge can help diagnose and treat conditions like social anxiety and communication-related disorders. However, investigations on brain synchronization have primarily focused on groups with strong social ties, such as romantic couples and parents and children.

In a study published in Scientific Reports a team of Japanese researchers show that cooperative interactive tasks between individuals with weak social ties result in more synchronized brain activity compared to individuals with strong ties. In other words, the very opposite of what we thought.

What the researchers say: “Our findings challenge the conventional understanding that stronger social ties predict greater brain synchronization and offer fresh insights into neural networking during social interactions,” the lead researcher said.

The team studied 14 pairs of strangers who met for the first time and 13 acquaintance pairs, in which one participant brought their partner. The participants were given a joint tapping task, where they had to tap a mouse button in opposite rhythms. Each participant wore earphones to hear both their taps and their partner's taps, and they had to anticipate their partner's movements.

Brain activity was captured using electroencephalograph (EEG) electrodes placed on the subjects’ scalps for four tapping conditions: slow tapping with a 0.5-second interval, fast tapping with a 0.25-second interval, tapping freely at their preferred frequency, and tapping coordinated with a metronome at 0.50-second intervals (a pseudo condition). The study investigated how brain signals synchronize across the theta (4–7 Hz), alpha (8–12 Hz), and beta (13–30 Hz) frequency bands.

EEG analysis revealed that pairs of strangers exhibited greater intra-brain synchronization in the theta band, compared to acquainted pairs. Furthermore, binary undirected graphs constructed to represent the connectivity between EEG channels showed that the neural network was more densely connected in strangers than in acquaintances.

“Surprisingly, despite having weaker social ties, stranger pairs demonstrated more robust intra- and inter-brain EEG networks than acquainted pairs,” the lead author of the study commented. This heightened engagement leads to a more efficient transfer of information between closely connected nodes within the neural network.

This finding underscores the importance of weak social ties in shaping social relationships and individual behavior. “By demonstrating that strangers exhibit heightened intra- and inter-brain synchronization, our research highlights the potential of weak ties in fostering new connections and understanding the neural underpinnings of social interactions,” the lead author concluded.

So, what? This is a great example of a study overturning a deeply held assumption. A study done some 15 years ago came to a very similar conclusion about the levels of understanding between people, and therefore, presumably, their brain synchronization. They discovered through analyzing their conversations that those who knew each other well, or who worked together, understood each other less than complete strangers.

The reason for this was that those who thought they knew each other made more assumptions about each other—90% of which (as subsequent research has shown) are wrong. The strangers asked more questions and made fewer assumptions.