The long-held myth that “intentionality must reside within individual minds” has only been challenged in recent decades by converging evidence from comparative psychology, ethology, evolutionary psychology, and social neuroscience. This paradigm shift has inspired a novel research approach in social cognition that transcends individual neurobiological constraints, focusing instead on inter-brain interactions between individuals and collectives. The collective dimension of mental activities gives rise to the synchronized minds thesis, which posits that individual minds shape synchronized collective outcomes through conceivable and implementable social interactions.

Recent advancements in hyperscanning techniques have enabled the precise measurement and analysis of dynamic inter-brain synchronization, drawing significant attention to neural oscillations in individual cognition and social interaction. Notably, neural oscillations extend beyond individual brains to bridge biological and environmental boundaries, serving as critical mediators of interpersonal social interaction. Their role in guiding cognition and conscious experience manifests through phase locking—— the adjustment of persistent neural rhythms to external stimuli. This phase-locking mechanism proves essential for achieving genuine inter-brain synchronization, in which individuals adapt their endogenous neural rhythms to match others’ oscillatory frequencies. Comparative studies across species systematically validate the evolutionary universality of inter-brain synchronization in biological systems, while cognitive science perspectives elucidate its theoretical plausibility, collectively enriching our understanding of this phenomenon.

Based on this foundation, Shteynberg et al. put forward the viewpoint of the Theory of collective mind (TCM), which posits the capacity to attribute a unified mental state to groups sharing common experiences, including the individuals themselves. Diverging from traditional Theory of Mind’s focus on individual mental state inference, the TCM emphasizes representing group members’ mental states from a collective perspective. This capacity facilitates experiential synchronization among individuals, enabling unified yet pluralistic perspectives toward external stimuli and group mental states. Within the TCM framework, “we-representations” are categorized as representations of collective reality and collective psychology. This distinction offers novel insights into the cognitive foundations of group behavior and clarifies synchronization’s role in collective mind formation. Through the lens of TCM, group members’ minds evolve along synchronization trajectories from initial “we-intentions” to deeper “feelings of socially entitative”, partially reconstructing the fusion process from individual to collective mentality.

While conducting a comprehensive review of the phenomenon of inter-brain synchronization and its extended theoretical framework, the Theory of Collective Mind, we have actively incorporated the cutting-edge methodology of Collective Neuroscience. This integrative approach aims to provide interdisciplinary insights for understanding the new manifestation of collective intentionality embodied in TCM. This innovative paradigm employs advanced neuroimaging to investigate social animals’ brain states during collective activities, revealing the neural encoding mechanisms of collective perception. Emphasizing cross-disciplinary collaboration among biologists, psychologists, neuroscientists, engineers, and computer scientists, it utilizes predictive coding and active inference frameworks to derive testable hypotheses about synchronized minds from generative computational models. This integrative approach promises to deepen our understanding of synchronization and coordination mechanisms in social interactions.

Despite substantial progress in synchronization research, the explanatory gap between innate behaviors and learned normative actions persists. However, exploring synchronized minds helps re-examine Zahavi’s paradox of reconciling collective intentionality with individual self-consciousness——the “We in Me or Me in We” dilemma. We propose interpreting inter-brain synchronization as proto-collective intentionality, which advances a radical collective neuroscience perspective. According to this perspective, individual “I” emerges as an inference from the primordial collective “We”. Thus, the synchronized minds thesis carries potentially revolutionary implications for understanding the fundamental nature of human and animal cognition.