Like an intricate dance between partners, the study of brain-to-brain synchrony offers a glimpse into the neural symphony of human interactions. Using various non-invasive neural recording technologies, scientists have delved into the shared rhythms of our minds. With this systematic review, the authors aim to guide future researchers on the paradigms, methodologies, and challenges in this exciting field. By evaluating numerous publications, it becomes clear that social psychology plays a dominant role in investigating brain-to-brain synchrony, closely followed by cognitive neuroscience applications. EEG studies utilize a coherence measure called phase-locking value (PLV) to gauge neural connectivity, while fNIRS studies rely on wavelet transform coherence (WTC). Control experiments are prevalent in most setups, but only a few employ algorithmic or stimulus-induced control to prevent false synchronization. This review serves as an invaluable resource, providing critical insights into the advancements and potential of brain-to-brain synchrony for future breakthroughs.

The study of brain-to-brain synchrony has a burgeoning application in the brain-computer interface (BCI) research, offering valuable insights into the neural underpinnings of interacting human brains using numerous neural recording technologies. The area allows exploring the commonality of brain dynamics by evaluating the neural synchronization among a group of people performing a specified task. The growing number of publications on brain-to-brain synchrony inspired the authors to conduct a systematic review using the PRISMA protocol so that future researchers can get a comprehensive understanding of the paradigms, methodologies, translational algorithms, and challenges in the area of brain-to-brain synchrony research. This review has gone through a systematic search with a specified search string and selected some articles based on pre-specified eligibility criteria. The findings from the review revealed that most of the articles have followed the social psychology paradigm, while 36% of the selected studies have an application in cognitive neuroscience. The most applied approach to determine neural connectivity is a coherence measure utilizing phase-locking value (PLV) in the EEG studies, followed by wavelet transform coherence (WTC) in all of the fNIRS studies. While most of the experiments have control experiments as a part of their setup, a small number implemented algorithmic control, and only one study had interventional or a stimulus-induced control experiment to limit spurious synchronization. Hence, to the best of the authors’ knowledge, this systematic review solely contributes to critically evaluating the scopes and technological advances of brain-to-brain synchrony to allow this discipline to produce more effective research outcomes in the remote future.

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