Neural Correlates of Visuomotor Co-regulation in Social Synchronization

: During social activities, people coordinate their movements by exchanging visuomotor information. Interpersonal coordination arises from two complementary processes, involving either voluntary (planned) or spontaneous (emergent) synchronization, whose neurofunctional underpinnings are currently unknown. We investigated the brain correlates of these two synchronization processes during an fMRI finger-tapping task. Thirty participants (17 females, 13 males) were scanned while reproducing a target tempo either synchronizing with (Joint Action, JA) or resisting (Non-interactive, NI) the partner's tapping, whose hand was always visible to the scanned participant. Faster, slower, or equal tempi were used to induce within-dyad tempo discrepancies. Results revealed the emergence of tempo contagion: participants tapped faster in response to their partner's faster taps and vice versa for slower taps. The magnitude of this interpersonal contagion effect was similar across conditions but associated with the activity of different neural structures. Tempo contagion correlated positively with lateral occipitotemporal cortex (LOTc) activations in the JA condition but negatively with cerebellar activations in the NI condition. This suggests that visuomotor information is exploited in opposite ways depending on the task instructions: the LOTc activity contributes to co-regulation to achieve synchronization in JA, whereas the cerebellar activity contributes to preserving individual motor stability in NI, preventing tempo contagion. A negative functional connectivity between the cerebellum and LOTc supports this latter result. These findings have implications for understanding the interplay between planned and emergent synchronization during motor interactions.