Drawing together reveals how young and old brains build connection

Two strangers sit over one sheet of paper, oil pastels nearby, trying to draw without talking. Their hands move, their eyes follow, and their brains begin responding to each other.

At ETH Zurich, cognitive scientist Ryssa Moffat used that simple scene to study how new relationships form. Moffat, a postdoctoral researcher at the Social Brain Sciences Lab within the Chair of Cognitive and Social Neuroscience, followed pairs of people as they met repeatedly for shared drawing sessions.

The study, published in PLOS Biology, included 61 pairs who met six times across six weeks. Participants came from two age groups: younger adults ages 18 to 35 and older adults ages 70 to 85. The group included 31 cross-generational pairs and 30 same-age pairs.

At the start, the participants did not know each other.

Each session followed the same basic rhythm. First, participants drew individually on separate sheets of paper. Then they drew together twice on a single sheet.

They could decide whether to take turns or draw at the same time. They could talk during the session, but they had to remain silent while drawing.

During each meeting, the researchers recorded brain activity with wearable brain sensors. This allowed participants to move naturally and respond to one another during the task. The setup avoided the stiffness of many lab experiments, where people must sit still or lie inside scanners.

The ETH team focused on brain synchrony. That means the extent to which two people’s brain activity changes in similar ways at the same time.

Moffat was not trying to identify a brain pattern for one feeling, such as liking or irritation. The main question was broader: how does shared activity change the relationship between two brains as people become more familiar?

The key measure was inter-brain synchrony. In a shared task, each person’s brain reacts continuously to the other person’s actions. If similar changes occur in both brains at the same time, researchers describe the brains as synchronized.

Previous studies had suggested that two people’s brain activity often becomes more similar as they become more familiar with each other. Based on that work, the ETH researchers expected synchrony to rise over time as pairs adjusted to one another.

The first result matched expectations in a basic way. In both cross-generational and same-age pairs, brain synchrony was higher when participants drew together than when they drew separately.

Collaboration mattered.

But the longer-term pattern surprised the team. In cross-generational pairs, brain synchrony started higher and then decreased from week to week. In same-age pairs, synchrony started lower and increased across the six weeks.

“In the cross-generational pairs, brain synchrony was higher at the start – and it decreased from week to week,” Moffat shares. “In the same-age pairs, it was the other way round: they started with lower synchrony, which increased over the course of the six weeks.”

The cross-generational pairs still felt closer over time. That made the brain result more interesting, not less.

The finding suggests that growing social closeness does not always mean two brains become more alike in their activity. For Moffat, the study shows that when two people feel closer, their brains do not necessarily “tick” in the same way.

The difference may come from how people learn to understand each other.

Many earlier studies on brain synchrony used a model called “Common Cognitive Processing.” That idea assumes two people sharing an experience process similar stimuli. Their brains respond in similar ways because they are taking in the same thing.

Moffat’s explanation leans toward another model, called “Mutual Prediction.” In this view, interaction depends on learning to anticipate another person’s behavior. One person may ask: What will the other person say next? How will they respond to my suggestion?

That model could help explain the age difference.

“The participants of the same age were mostly students with similar daily routines and quickly found topics they had in common. Younger and older people, on the other hand, first had to work out what they could actually talk about.”

Higher synchrony at the start of cross-generational meetings may not mean the pairs were closer right away. It may mean they were working harder.

For Moffat, that distinction matters.

“Greater brain synchrony can also mean that two people are making a particularly strong effort to understand one another.”

That effort may be strongest early in a relationship, especially when two people come from different generations. They may have fewer obvious shared topics. They may need to watch each other more carefully, adjust more deliberately and search for common ground.

Same-age pairs may begin differently. Peers often find shared ground quickly or already have it. But Moffat suggests their interactions can become more playful over time. They may start surprising each other more in conversation, making prediction harder.

“Peers often find common ground more quickly or already have it. Over time, however, they become more playful, surprising each other in their conversations and thereby making it harder for their counterpart to predict their behaviour.”

In that sense, synchrony is not a simple scoreboard. More synchrony is not always better, and less synchrony does not always mean weaker connection.

A second study in Acta Psychologica examined the same encounters and measurement data from another angle. The researchers looked for recurring patterns of shared brain activity during the meetings.

They identified seven “two-brain states” that stayed remarkably stable throughout the six-week period.

One state stood out. It lasted much longer in intergenerational pairs than in same-age pairs. In this state, synchrony between the two brains was relatively low. But within one person’s brain, there was a strong connection between two areas in that person’s frontal lobe.

The researchers interpreted this cautiously. It may point to a division of roles. The person with stronger internal synchrony may have been more likely to adapt their behavior to the other person.

In most cases, that person was the younger participant. The older participant more often appeared to take a leadership role.

The drawing behavior also fit this pattern. Same-age pairs were more likely to draw at the same time. Intergenerational pairs more often took turns.

The study opens new ground for social brain research by following younger and older people across repeated meetings, rather than studying only one short interaction. It also brings older adults into an area that has often focused on parent-child, teacher-pupil, doctor-patient or romantic relationships.

“Our study is the first to show, over a period of several weeks, how brain activity develops in younger and older people,” Moffat concludes.

The findings could help researchers better understand how strangers become acquaintances, and perhaps friends. They also suggest that joint creative activity can reveal subtle changes in how people coordinate, predict and adapt to one another.

The work does not show that brain synchrony directly measures closeness. Instead, it offers a more careful lesson: building connection may involve both syncing with another person and learning when less effortful coordination is enough.

These studies explore neural and physiological synchronization, social interaction and relationship development beyond the current PLOS Biology paper.

Two-brain states characterize within- and between-brain connectivity during intergenerational collaborative drawing: This companion analysis identified seven recurring brain-connectivity states and evidence for asymmetric adaptation during cross-generational drawing. (Acta Psychologica, 2026)

Cardiac Synchrony During Collaborative Drawing: A Longitudinal Comparison of Same Generation and Intergenerational Dyads: Using the same six-week drawing program, researchers found that self-reports and behavior captured relationship development better than cardiac synchrony. (Annals of the New York Academy of Sciences, 2026)

Brain-to-brain coupling: a mechanism for creating and sharing a social world: This influential review describes how interacting brains can become coupled through communication and shared sensory information. (Trends in Cognitive Sciences, 2013)

Brain-to-brain synchrony tracks real-world dynamic group interactions in the classroom: Portable measurements showed that neural synchrony among students was associated with shared classroom experiences and social dynamics. (Current Biology, 2017)

Interpersonal synchronization of inferior frontal cortices tracks social interactive learning of a song: Hyperscanning experiments demonstrated synchronized frontal brain activity during cooperative interpersonal learning. (NeuroImage, 2012)

Research findings are available online in the journal PLOS Biology.

The original story "Drawing together reveals how young and old brains build connection" is published in The Brighter Side of News.

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