Inter-brain functional connectivity: Are we measuring the right thing?

Hyperscanning—the simultaneous recording of brain activity from multiple individuals—and the study of inter-brain synchronization is gaining popularity in social neuroscience. MEG/EEG hyperscanning studies often estimate inter-brain functional connectivity using phase-based metrics applied to oscillatory brain signals, assuming matching peak frequencies between the individuals studied. However, in reality peak frequencies typically differ between subjects and even between brain regions. Using simulated MEG/EEG signals, we systematically assessed how inter-individual frequency differences affect commonly used connectivity measures. Phase-based metrics were highly sensitive to frequency differences across individuals, whereas amplitude envelope correlation remained comparatively stable under these conditions. Our results underscore the need for connectivity metrics specifically tailored for inter-brain analyses. These findings are relevant to a range of disciplines that are increasingly integrating hyperscanning into their methodological toolkits.