How Brain Activity Changes as Strangers Become Friends

Led by cognitive scientist Ryssa Moffat, a postdoctoral researcher at the Social Brain Sciences Lab within the Chair of Cognitive and Social Neuroscience at ETH Zurich, the investigation sought to answer what happens in the brain during collaborative relationship-building. The study involved 61 pairs who met six times over a six-week period. Participants were split into two demographics: a younger age group aged 18 to 35 and an older group aged 70 to 85. This cohort formed 31 cross-generational pairs and 30 same-age pairs. At each session, participants drew individually and then collaborated on a single sheet of paper while wearing mobile brain-scanning technology that recorded their neural activity without restricting natural movement.

For decades, standard models of social neuroscience—often termed “Common Cognitive Processing”—assumed that shared experiences cause two brains to process identical stimuli and thus mirror each other more closely as familiarity grows. However, Moffat’s findings challenge this direct synchronization hypothesis. In same-age pairs, neural synchrony began at lower levels and increased steadily across the six-week timeline as participants found common ground. Conversely, cross-generational pairs exhibited high neural synchrony during initial meetings, which then progressively declined week by week despite participants reporting a subjective increase in personal closeness.

“In the cross-generational pairs, brain synchrony was higher at the start—and it decreased from week to week,” Moffat notes. To account for this divergence, the research team points toward a “Mutual Prediction” model. Rather than simply reacting passively to identical inputs, individuals actively attempt to anticipate their counterpart’s next move, adjustment, or verbal comment. Because same-age participants—largely university students—shared similar daily routines and cultural references, they easily established conversational footing. Intergenerational pairs faced a wider gap in life experiences, requiring intense, effortful neural synchronization early on just to comprehend one another. Once rapport was established, that heavy cognitive calibration eased.

Further granularity emerged in a companion study published in Acta Psychologica. By evaluating recurring patterns of shared neural activity termed “two-brain states,” researchers observed that intergenerational pairs frequently spent extended periods in a state characterized by lower inter-brain synchrony paired with high internal synchronization within the individual frontal lobes. According to study interpretations, this asymmetry reflects a clear division of roles: younger adults predominantly adapted their drawing behavior, while older adults stepped into leadership positions. Same-age pairs, by contrast, displayed more simultaneous drawing habits.

This work marks a significant shift in social brain research, a field that historically focused on parent-child, teacher-pupil, or romantic dynamics while largely bypassing the aging brain. Ultimately, Moffat’s research demonstrates that “ticking alike” is not a mandatory prerequisite for forging human bonds. Brain activity is fundamentally dynamic, fluctuating continuously to meet the communicative demands, generational differences, and predictive challenges inherent in human relationships.

*Disclaimer: The information provided in this article is for educational and scientific communication purposes only and does not constitute medical advice. Always consult with a qualified healthcare provider regarding any medical condition, diagnosis, or treatment plan.*