Hyper-tACS-induced interbrain synchronization in the frontal cortex improves romantic relationships

Interpersonal relationships are among the most essential yet fragile aspects of human life, and recent advances in dual-brain stimulation provide a unique opportunity to causally probe and modulate their neural underpinnings. While prior work has linked interpersonal brain synchronization (IBS) to relationship quality, its causal contribution to long-term relational outcomes remains unclear. Here, we present the first application of dual-brain transcranial alternating current stimulation (hyper-tACS) to social bonding, specifically targeting romantic partners, with a focus on the temporal dissociation between neural and behavioral effects. Across six consecutive days of intervention, active hyper-tACS induced clear increases in prefrontal IBS immediately after stimulation, yet these neural gains did not translate into concurrent improvements in subjective relationship satisfaction. Mediation analyses further showed that individual differences in IBS increases mediated the effect of baseline IBS on relationship improvement, suggesting that behavioral benefits rely on neural alignment consolidating over time. At a one-year follow-up, the active group exhibited a substantially lower breakup rate relative to sham controls. These findings provide causal evidence for a delayed effect of dual-brain stimulation, in which neural changes precede and gradually consolidate into durable relational benefits. Together, this work provides the first causal evidence that dual-brain stimulation can be extended from motor coordination to the social domain, advancing mechanistic accounts of intimacy and highlighting hyper-tACS as a translational tool for strengthening long-term relationship stability.