Naudszus, L. A. | Search bioRxiv

bioRxiv2026

Two-brain states during collaborative drawing reflect leader-follower dynamics in intergenerational dyads

Engaging with others in social scenarios can result in the alignment of brain activity between individuals. Dyadic (i.e., hyperscanning) studies typically estimate average region-specific levels of connectivity between brains (as opposed to within brains) across a given task to quantify brain activity alignment. This approach assumes symmetric interactions with equal and mutual adaptation from both dyad members, excluding asymmetric (e.g., leader-follower) contexts. Such approaches also obscure spatial dynamics (i.e., relationship between different brain regions) and temporal dynamics during unfolding interactions. To overcome these challenges, we took a data-driven approach to quantify within- and between-brain connectivity during collaborative drawing among dyads. Specifically, we used sliding windows and Riemannian-geometry-based k-means clustering to identify recurrent two-brain states while 61 dyads drew alone and together at 6 weekly timepoints. Thirty dyads comprised young adults only (same generation) and 31 dyads comprised one older and one younger individual (intergenerational). We identified 7 two-brain states, 3 of which were specific to real (not pseudo) dyads. One two-brain state showed convincing evidence of sensitivity to collaboration context: During collaborative drawing, low-to-medium between-brain connectivity and prominent within-brain connectivity in bilateral IFG in a single dyad member arose for longer periods in intergenerational than same generation dyads (co-occurring with reduced turn-taking behaviour). No two-brain state showed evidence of longitudinal changes across sessions. These findings inform recent accounts of neural dynamics that emphasise the complementary roles of within-brain and between-brain connectivity. Furthermore, they suggest that state-based analyses can inform neural dynamics in a way not captured by traditional analysis techniques. HighlightsO_LITwo-brain states can characterise within- and between-brain connectivity. C_LIO_LISeven two-brain states identified using data-driven approach. C_LIO_LIIntergenerational collaborative drawing linked to asymmetric connectivity. C_LI

neuroscience↗

bioRxiv2025

Cardiac synchrony remains stable across repeated intergenerational encounters but is enhanced during high stakes collaboration

Intergenerational social programs provide opportunities for people of all ages to form new relationships. Furthermore, existing qualitative and behavioural evidence from such programs points to health and wellbeing benefits, yet the physiological consequences of repeated intergenerational encounters remain unknown. A deeper understanding of how such programs shape dyadic physiological responses will illuminate the mechanisms of relationship formation. Across a six-session collaborative drawing program, we tracked cardiac synchrony within 31 intergenerational (older/younger adult) and 30 same generation (younger adult) dyads. Each session dyads completed self-report measures, then drew together and alone, while we recorded participants actions with motion capture and physiological signals (neural and cardiac) using fNIRS. Collaborative behaviour, self-reported social closeness, and interpersonal distance (i.e., proximity) showed group-specific patterns, whereby interpersonal distance emerged as a promising objective measure of relationship development. Cardiac synchrony did not covary with group, task, an interaction thereof or any measure of behaviour or social closeness-yet there was a trending relationship between collaboration while drawing together and cardiac synchrony for intergenerational dyads only. In summary, cardiac synchrony pointed to marginally enhanced arousal during active collaboration between older and younger adults. Relationship development was better characterised, in this study, by behaviour and self-report measures than cardiac synchrony.

physiology↗