Dyadic fNIRS Hyperscanning: Experimental Paradigms and What They Reveal About Interbrain Synchrony

Functional near-infrared spectroscopy (fNIRS) hyperscanning enables the simultaneous measurement of the brain activities of various individuals performing shared or interactive tasks and estimating their interbrain synchrony (IBS). IBS is believed to reflect different mechanisms, including social bonding or mutual prediction, and to be modulated by various factors, such as familiarity or the experimental paradigm. In this systematic review, we assessed fNIRS hyperscanning studies conducted until January 2026, focusing on the experimental protocols and their relation to reported IBS findings. Specifically, we aimed to understand task dependence of IBS results and how they differ between different kinds of dyad compositions. Additionally, we investigated other parameters, including IBS metrics and the association between IBS and psychological, behavioral, and physiological measures. We reviewed a total of 206 studies, revealing a predominance of joint action task paradigms. Our findings suggest that IBS is modulated by the characteristics of dyad composition. IBS is usually higher in dyads with closer bonds, and varies with gender, although a universal pattern could not be identified. Furthermore, the study protocols employed also seem to have an influence on IBS, as participants who engage in face-to-face interactions frequently show higher IBS than those who do not. We also observed that IBS is often associated with behavioral and psychological outcomes, while the association with physiological outcomes is scarcely studied. Future research should consistently include details about dyad familiarity and sex pairings, expand to underrepresented dyads, and investigate IBS across diverse paradigms and contexts in association with other metrics.