  Mother-child interaction is highly dynamic and reciprocal. Switching roles in
these back-and-forth interactions serves as a crucial feature of reciprocal
behaviors while the underlying neural entrainment is still not well-studied.
Here, we designed a role-controlled cooperative task with dual EEG recording to
study how differently two brains interact when mothers and children hold
different roles. When children were actors and mothers were observers,
mother-child inter-brain synchrony emerged within the theta oscillations and
the frontal lobe, which highly correlated with children's attachment to their
mothers. When their roles were reversed, this synchrony was shifted to the
alpha oscillations and the central area and associated with mothers' perception
of their relationship with their children. The results suggested an
observer-actor neural alignment within the actor's oscillations, which was
modulated by the actor-toward-observer emotional bonding. Our findings
contribute to the understanding of how inter-brain synchrony is established and
dynamically changed during mother-child reciprocal interaction.

Neurons and Cognition