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Interacting brains coming in sync through their minds: An inter-brain neurofeedback study

We live in a social world where we interact with each other. Neurofeedback (NFB) is an indispensable element for such interaction. Single-person NFB studies using electroencephalography (EEG) or other neuroimaging recordings were extensively reported. However, hyperscanning studies using inter-brain synchrony (IBS) as an NFB feature are completely unknown. In this study, we present two different experimental designs where IBS was fed visually back either as two balls approaching each other (so-called “ball” design) or as two pendula reflecting oscillatory activity of two participants (so-called “pendulum” design). The NFB was provided at two EEG frequencies (2.5 and 5 Hz) and manipulated by enhanced (fake condition) and inverse feedback. We showed that the participants were able to increase IBS by using NFB, especially when it was fed back at the theta frequency. Apart from the intra- and inter-brain coupling, other oscillatory activities (e.g., power spectral density, peak amplitude and peak frequency) changed during the task compared to rest. Moreover, all the measures showed specific correlations to the subjective post-survey item scores, reflecting subjective feeling and appraisal. We conclude that hyperscanning with IBS as a feedback feature seems to be an important tool to examine neural mechanisms of social interaction and collective behavior.