Heart Rate Variability Synchronization relates to Trust Decisions during an Economic Investment Game

Trust enables cooperation, but it also exposes individuals to social risks. The physiological dynamics of trust in real-world interactions remain poorly understood. In this study, we investigated whether interpersonal physiological synchrony in dyads is a predictor of trust, an indicator of ongoing social interaction, and/or a result of interaction outcomes. One hundred participants (50 dyads) completed a modified investment game involving role reversal, during which their heart rate variability (HRV) was recorded. Using cross-wavelet power analysis, we quantified HRV synchrony across interaction phases (mere co-presence versus active exchange) and time-frequency bands. We observed that in the first round, higher investments by the trustor were associated with stronger synchrony at lower frequencies, while higher reciprocity by the trusted partner was associated with weaker synchrony. These simultaneous associations were not observed after role reversal. Synchrony prior to interaction during mere presence did not predict later reciprocity; only synchrony in the high-frequency band predicted higher initial investment. Conversely, reciprocity by the trusted partner predicted increased synchrony after interaction at lower frequencies, while initial investment did not. Overall, these results suggest that HRV synchrony during economic exchange is both phase- and frequency-specific, and is better characterized as a dynamic marker shaped by reciprocal interaction rather than as a stable baseline marker of trust.