EEG inter-brain synchrony in social interaction: A systematic review and meta-analysis of condition effects and outcome associations.

BACKGROUND: Electroencephalography (EEG) hyperscanning enables the examination of inter-individual neural coordination during social interaction. However, EEG inter-brain synchrony (IBS) studies vary in paradigms, metrics, frequency bands, regions, and statistical reporting. We examined whether conditions related to social interaction enhance EEG IBS and whether EEG IBS is associated with external outcomes. METHODS: We searched the Web of Science Core Collection, PubMed, IEEE Xplore, and APA PsycInfo and APA PsycArticles via EBSCOhost through May 14, 2026. Eligible studies used EEG hyperscanning or simultaneous scalp EEG recordings from at least two individuals and reported dyad- or group-level EEG IBS. Main analyses synthesized condition-related effects using Hedges' g; secondary analyses synthesized associations using Fisher's z. Random-effects models were used. RESULTS: Fifty-four unique studies were included. The core main analysis showed stronger EEG IBS under social-interaction-related conditions (k = 14, Hedges' g = 0.887, 95% CI [0.533, 1.241], p <.001). The core secondary analysis showed a positive association with external outcomes (k = 6, Fisher's z = 0.456, 95% CI [0.288, 0.621], p <.001; r = 0.426). Expanded models remained significant for condition effects (k = 36, g = 0.691) and outcome associations (k = 30, z = 0.474; r = 0.441). The restrictive secondary model also remained significant (k = 26, z = 0.418; r = 0.395). CONCLUSIONS: Social-interaction-related conditions were associated with stronger EEG IBS, and EEG IBS was positively associated with external outcomes. Interpretation should consider heterogeneity in task design, frequency band, shared stimulation, behavioral synchrony, outcome domain, and statistical modeling.