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Optimizing collaborative behavior is crucial in educational activities, directly improving academic performance, social skills, and social-emotional learning for both teachers and students. In an effort to decipher the mechanisms underlying the effectiveness of collaborative learning, educators and neuroscientists have initiated the collection and analysis of learners' physiological parameters during such collaborative exercises. Considering both accuracy and portability, functional near-infrared spectroscopy (fNIRS) has emerged as a viable tool. The current study aims to understand its potential for studying neural mechanisms of collaboration. Sixty articles were reviewed from three databases to address three research questions: (1) What are the characteristics (i.e., number of publications per year and for different age groups of participants, sample size, and the usage of fNIRS devices) of fNIRS-based collaboration research? (2) What experimental designs are commonly employed in fNIRS-based collaboration research? (3) What is the relationship between neural activity and interactive behavioral performance? The results provide a comprehensive descriptive statistical analysis of the literature characteristics and offer a detailed summary of the research methods employed, including the experimental protocol, task, and duration. Importantly, these findings demonstrate compelling evidence of inter-brain synchrony (IBS), indicating synchronized cortical activities between interacting individuals, and it was observed in the prefrontal cortex or temporoparietal cortex during collaboration and interaction tasks, highlighting the crucial role of these brain regions in facilitating collaborative behavior. The finding of this review advanced our understanding of how fNIRS is ultilized in collaborative research and offer practical implications for designing educational interventions or programs aimd at enhancing collaborative behaviors and their associated benefits. [ABSTRACT FROM AUTHOR]

Mixed-reality (MR) environments, in which virtual objects are overlaid on the real environment and shared with peers by wearing a transparent optical head-mounted display, are considered to be well suited for collaborative work. However, no studies have been conducted to provide neuroscientific evidence of its effectiveness. In contrast, inter-brain synchronization has been repeatedly observed in cooperative tasks and can be used as an index of the quality of cooperation. In this study, we used electroencephalography (EEG) to simultaneously measure the brain activity of pairs of participants, a technique known as hyperscanning, during a cooperative motor task to investigate whether inter-brain synchronization would be also observed in a shared MR environment. The participants were presented with virtual building blocks to grasp and build up an object cooperatively with a partner or individually. We found that inter-brain synchronization in the cooperative condition was stronger than that in the individual condition (F(1, 15) = 4.70, p < 0.05). In addition, there was a significant correlation between task performance and inter-brain synchronization in the cooperative condition (rs = 0.523, p < 0.05). Therefore, the shared MR environment was sufficiently effective to evoke inter-brain synchronization, which reflects the quality of cooperation. This study offers a promising neuroscientific method to objectively measure the effectiveness of MR technology.

Mixed-reality (MR) environments, in which virtual objects are overlaid on the real environment and shared with peers by wearing a transparent optical head-mounted display, are considered to be well suited for collaborative work. However, no studies have been conducted to provide neuroscientific evidence of its effectiveness. In contrast, inter-brain synchronization has been repeatedly observed in cooperative tasks and can be used as an index of the quality of cooperation. In this study, we used electroencephalography (EEG) to simultaneously measure the brain activity of pairs of participants, a technique known as hyperscanning, during a cooperative motor task to investigate whether inter-brain synchronization would be also observed in a shared MR environment. The participants were presented with virtual building blocks to grasp and build up an object cooperatively with a partner or individually. We found that inter-brain synchronization in the cooperative condition was stronger than that in the individual condition (F(1, 15) = 4.70, p < 0.05). In addition, there was a significant correlation between task performance and inter-brain synchronization in the cooperative condition (rs = 0.523, p < 0.05). Therefore, the shared MR environment was sufficiently effective to evoke inter-brain synchronization, which reflects the quality of cooperation. This study offers a promising neuroscientific method to objectively measure the effectiveness of MR technology. [ABSTRACT FROM AUTHOR]

Humans may behave in different manners when making decisions with friends and strangers. Whether the interpersonal relationship and the characteristics of the individuals in the group affected the group decision-making under uncertainty in the real-time interaction remains unknown. Using the turn-based Balloon Analogue Risk Task (BART), the present study examined the group decision-making propensity under uncertainty with partners in different interpersonal relationships and interpersonal orientations. Corresponding inter-brain synchronization (IBS) patterns at the prefrontal cortex (PFC) were also uncovered with the fNIRS-based hyperscanning approach. Behavioral results identified that dyads in the friend group exhibited the uncertainty-averse propensity when comparing with the stranger group. The fNIRS results reported that feedback-related IBS at the left inferior frontal gyrus (l-IFG) and medial frontopolar cortex (mFPC) during different feedbacks was modulated by interpersonal relationships. The IBS at all channels in the PFC during the positive and negative feedbacks, respectively, predicted the decision-making propensity under uncertainty in the stranger and friend groups based on the support vector machine (SVM) algorithm. The moderating role of the social value orientation (SVO) was also verified in the mediation effect of the dyad closeness on the decision-making propensity under uncertainty via the IBS at the right lateral frontopolar cortex (r-FPC). These findings demonstrated disparate behavioral responses and inter-brain synchronization patterns underlying group decision-making under uncertainty with partners in different interpersonal relationships.

The use of hyperscanning technology has revealed the neural mechanisms underlying multi-person interaction in musical activities. However, there is currently a lack of integration among various research findings. This systematic review aims to provide a comprehensive understanding of the social dynamics and brain synchronization in music activities through the analysis of 32 studies. The findings illustrate a strong correlation between inter-brain synchronization (IBS) and various musical activities, with the frontal, central, parietal, and temporal lobes as the primary regions involved. The application of hyperscanning not only advances theoretical research but also holds practical significance in enhancing the effectiveness of music-based interventions in therapy and education. The review also utilizes Predictive Coding Models (PCM) to provide a new perspective for interpreting neural synchronization in music activities. To address the limitations of current research, future studies could integrate multimodal data, adopt novel technologies, use non-invasive techniques, and explore additional research directions. • The first systematic review of multi-person music activities using hyperscanning technology. • It provides a novel perspective for interpreting neural synchronization in music activities. • The neural synchronization and collaborative behavior in music activities are not simply positively correlated. [ABSTRACT FROM AUTHOR]

Group of people shows the shift towards extreme of decision-making as opposed to individuals. Previous studies have revealed two directions of group polarization, i.e., risky shift and cautious shift, but how group of brains drive these shifts remains unknown. In the current study, we arranged risk advantage and disadvantage situations to elicit group polarization of risky shift and cautious shift respectively, and examined the averaged inter-brain synchronization (ABS) among participant triads during group decision making versus individual decision making. The elicited group polarizations were accompanied by the enhanced ABS at bilateral prefrontal areas and left temporoparietal junction (TPJ). Specifically, the TPJ ABS was equivalent in risky shift and cautious shift, and based on machine learning analyses, could predict the extent of group polarization; for two shifts, it negatively correlated with negative emotion. However, the right prefrontal ABS was stronger in risky shift than in cautious shift, and the same area showed the larger brain deactivation in former shift, indicating weaker executive control. For the left prefrontal ABS, only the equivalent ABS was found for two shifts. In sum, group polarization of risky shift and cautious shift calls for inter-brain communication at the group level, and the former shift is with deactivation and more brain synchronization. Our study suggests emotional and cognitive adjustment in decision making of the group compared with individuals.

Punishment is a popular institution to enforce social norms in human society. However, how the punishment institution impacts the inter-brain neural signatures of two-person social interactions is still an open question. By performing electroencephalography recording of brain activity in two interacting parties as they simultaneously played both the revised repeated ultimatum game (rrUG) and the revised repeated dictator game (rrDG), this study focused on exploring how the introduction of external punishment influences inter-brain synchronization between the two parties. The data showed a significant negative effect of external punishment on inter-brain synchronization, with greater inter-brain synchronization observed in the rrDG than in the rrUG. We proposed a possible mechanism underlying this result. In the rrDG, the similar moral motivation of both proposers and responders results in inter-brain synchronization between them. However, in the rrUG, the introduction of external punishment crowds out the intrinsic moral motivation of the proposers, thereby undermining the inter-brain synchronization. Moreover, we found a significant positive correlation between the rejection rate from responders for disadvantageous inequal offer and inter-brain synchronization in the rrDG. These findings contribute to understanding the negative effect of punishment institution and shed light on the inter-brain mechanism underlying social interaction. [ABSTRACT FROM AUTHOR]

Inter-brain synchronization is primarily investigated during social interactions but had not been examined during coupled muscle action between two persons until now. It was previously shown that mechanical muscle oscillations can develop coherent behavior between two isometrically interacting persons. This case study investigated if inter-brain synchronization appears thereby, and if differences of inter- and intrapersonal muscle and brain coherence exist regarding two different types of isometric muscle action. Electroencephalography (EEG) and mechanomyography/mechanotendography (MMG/MTG) of right elbow extensors were recorded during six fatiguing trials of two coupled isometrically interacting participants (70% MVIC). One partner performed holding and one pushing isometric muscle action (HIMA/PIMA; tasks changed). The wavelet coherence of all signals (EEG, MMG/MTG, force, ACC) were analyzed intra- and interpersonally. The five longest coherence patches in 8–15 Hz and their weighted frequency were compared between real vs. random pairs and between HIMA vs. PIMA. Real vs. random pairs showed significantly higher coherence for intra-muscle, intra-brain, and inter-muscle-brain activity (p < 0.001 to 0.019). Inter-brain coherence was significantly higher for real vs. random pairs for EEG of right and central areas and for sub-regions of EEG left (p = 0.002 to 0.025). Interpersonal muscle-brain synchronization was significantly higher than intrapersonal one, whereby it was significantly higher for HIMA vs. PIMA. These preliminary findings indicate that inter-brain synchronization can arise during muscular interaction. It is hypothesized both partners merge into one oscillating neuromuscular system. The results reinforce the hypothesis that HIMA is characterized by more complex control strategies than PIMA. The pilot study suggests investigating the topic further to verify these results on a larger sample size. Findings could contribute to the basic understanding of motor control and is relevant for functional diagnostics such as the manual muscle test which is applied in several disciplines, e.g., neurology, physiotherapy. [ABSTRACT FROM AUTHOR]

• Experiment 1 examined the effects of regulatory focus (promotion, prevention, control) on group creativity's inter-brain neural synchronization (IBS). • Based on experiment 1, experiment 2 investigated the effect of regulatory fit (fit, misfit) on group creativity under the prevention focus. • The promotion focus is associated with more creative ideas and higher IBS in two ROI pairs (i.e., r-DLPFC_m-FPC; r-DLPFC_l-SMA). • The fitting strategic framework of prevention-focused groups is related to more creative ideas and higher IBS in four ROI pairs (i.e., l-DLPFC_l-FPC; r-FPC_r-FPC; l-FPC_r-FPC; l-FPC_ l-FPC). Despite numerous studies demonstrating connections between regulatory focus, regulatory fit, and group creativity, their impact on the inter-brain mechanism of creative communication is still unclear. Under the regulatory focus theory, Experiment 1 required dyads to complete creative tasks in three conditions (promotion focus, prevention focus, control) while monitoring hemodynamic inter-brain synchronization. In comparison to the other two conditions, dyads with a promotion focus showed higher levels of creative performance. This was also supported by increased inter-brain neural synchronization (IBS) in two ROI pairs (i.e., r-DLPFC_m-FPC; r-DLPFC_l-SMA), which signifies a positive shift towards prioritizing team members' opinions and improved alignment of body movements. Considering the lower creative performance of the prevention-focused dyad in Experiment 1, Experiment 2 referred to the regulatory fit theory and attempted to explore whether fit priming of prevention-focused dyads would facilitate their creative performance more than the misfit dyad. Both the fit and misfit dyads were induced with a prevention focus first. Results illustrated that prevention-focused dyads with fit priming accompanied by higher creative performance and enhanced inter-brain neural synchronization in four ROI pairs (i.e., l-DLPFC_l-FPC; r-FPC_r-FPC; l-FPC_r-FPC; l-FPC_ l-FPC), which potentially signifies a move towards more goal-oriented behavior to prevent team innovation from failing. Furthermore, there is a division that occurs when neural synchronization predicts diverse indicators of creativity across different regulatory focus/fit conditions. Therefore, promotion focus and regulatory fit of the prevention focus might be positive social cues to align and optimize inter-brain information transfer, thus facilitating group creativity. [ABSTRACT FROM AUTHOR]

[Display omitted] • Inter-brain synchronization is an important mechanism of interpersonal interaction. • Interacting brains are functioning as whole or superordinate system. • We present three-layered forward model of joint actions. • Neural network structures reveal a robust interplay between topology and function. It is now widely accepted that inter-brain synchronization is an important and inevitable mechanism of interpersonal action coordination and social interaction behavior. This review of the current literature focuses first on the forward model for interpersonal action coordination and functional system theory for biological systems, two broadly similar concepts for adaptive system behavior. Further, we review interacting-brain and/or hyper-brain dynamics studies, to show the interplay between intra- and inter-brain connectivity resulting in hyper-brain network structure and network topology dynamics, and consider the functioning of interacting brains as a superordinate system. The concept of a superordinate system, or superorganism, is then evaluated with respect to neuronal and physiological systems group dynamics, which show further accompanying mechanisms of interpersonal interaction. We note that fundamental problems need to be resolved to better understand the neural mechanisms of interpersonal action coordination. [ABSTRACT FROM AUTHOR]

Human cooperation behavior based on reciprocal altruism has been a hallmark of ancient and modern societies. Prior studies have indicated that inter-brain synchronization (IBS) between partners could exist during cooperation. However, how the sex composition of dyads influences the neural synchronization is still poorly understood. Here, we adopted functional near-infrared spectroscopy (fNIRS) based hyperscanning and a task of building blocks to investigate the sex composition effect on IBS in face-to-face cooperation in a natural situation, by evaluating brain-to-brain interactions of forty-five same-sex and mixed-sex dyads. Results showed significantly stronger inter-brain synchronization in Brodmann area 10 (BA10) in cooperation. In addition, variance analysis indicated that only male-male dyads showed increased inter-brain synchronization in left inferior frontal region (i.e., BA10) specific to cooperation. More importantly, the inter-brain synchronization in male-male dyads was significantly greater than that in male-female and female-female dyads. These findings provide support for the impact of sex composition on social cooperation in a naturalistic interactive setting and extend our knowledge on the neural basis of face-to-face cooperation. [ABSTRACT FROM AUTHOR]

Inter-brain synchronization is primarily investigated during social interactions but had not been examined during coupled muscle action between two persons until now. It was previously shown that mechanical muscle oscillations can develop coherent behavior between two isometrically interacting persons. This case study investigated if inter-brain synchronization appears thereby, and if differences of inter- and intrapersonal muscle and brain coherence exist regarding two different types of isometric muscle action. Electroencephalography (EEG) and mechanomyography/mechanotendography (MMG/MTG) of right elbow extensors were recorded during six fatiguing trials of two coupled isometrically interacting participants (70% MVIC). One partner performed holding and one pushing isometric muscle action (HIMA/PIMA; tasks changed). The wavelet coherence of all signals (EEG, MMG/MTG, force, ACC) were analyzed intra- and interpersonally. The five longest coherence patches in 8–15 Hz and their weighted frequency were compared between real vs. random pairs and between HIMA vs. PIMA. Real vs. random pairs showed significantly higher coherence for intra-muscle, intra-brain, and inter-muscle-brain activity (p < 0.001 to 0.019). Inter-brain coherence was significantly higher for real vs. random pairs for EEG of right and central areas and for sub-regions of EEG left (p = 0.002 to 0.025). Interpersonal muscle-brain synchronization was significantly higher than intrapersonal one, whereby it was significantly higher for HIMA vs. PIMA. These preliminary findings indicate that inter-brain synchronization can arise during muscular interaction. It is hypothesized both partners merge into one oscillating neuromuscular system. The results reinforce the hypothesis that HIMA is characterized by more complex control strategies than PIMA. The pilot study suggests investigating the topic further to verify these results on a larger sample size. Findings could contribute to the basic understanding of motor control and is relevant for functional diagnostics such as the manual muscle test which is applied in several disciplines, e.g., neurology, physiotherapy.

Social interactive learning denotes the ability to acquire new information from a conspecific—a prerequisite for cultural evolution and survival. As inspired by recent neurophysiological research, here we tested whether social interactive learning can be augmented by exogenously synchronizing oscillatory brain activity across an instructor and a learner engaged in a naturalistic song-learning task. We used a dual brain stimulation protocol entailing the trans-cranial delivery of synchronized electric currents in two individuals simultaneously. When we stimulated inferior frontal brain regions, with 6 Hz alternating currents being in-phase between the instructor and the learner, the dyad exhibited spontaneous and synchronized body movement. Remarkably, this stimulation also led to enhanced learning performance. These effects were both phase- and frequency-specific: 6 Hz anti-phase stimulation or 10 Hz in-phase stimulation, did not yield comparable results. Furthermore, a mediation analysis disclosed that interpersonal movement synchrony acted as a partial mediator of the effect of dual brain stimulation on learning performance, i.e. possibly facilitating the effect of dual brain stimulation on learning. Our results provide a causal demonstration that inter-brain synchronization is a sufficient condition to improve real-time information transfer between pairs of individuals. [ABSTRACT FROM AUTHOR]

Social interaction is a fundamental part of our daily lives; however, exactly how our brains use social cues to determine whether to cooperate without being exploited remains unclear. In this study, we used an electroencephalography (EEG) hyperscanning approach to investigate the effect of face-to-face contact on the brain mechanisms underlying the decision to cooperate or defect in an iterated version of the Prisoner's Dilemma Game. Participants played the game either in face-to-face or face-blocked conditions. The face-to-face interaction led players to cooperate more often, providing behavioral evidence for the use of these nonverbal cues in their social decision-making. In addition, the EEG hyperscanning identified temporal dynamics and inter-brain synchronization across the cortex, providing evidence for involvement of these regions in the processing of face-to-face cues to read each other's intent to cooperate. Most notably, the power of the alpha frequency band (8–13 Hz) in the right temporoparietal region immediately after seeing a round outcome significantly differed between face-to-face and face-blocked conditions and predicted whether an individual would adopt a ‘cooperation’ or ‘defection’ strategy. Moreover, inter-brain synchronies within this time and frequency range reflected the use of these strategies. This study provides evidence for how the cortex uses nonverbal social cues to determine other's intentions, and highlights the significance of power in the alpha band and inter-brain phase synchronizations in high-level socio-cognitive processing.

Third-party punishment occurs in interpersonal interactions to sustain social norms, and is strongly influenced by the characteristics of the interacting individuals. During social interactions, height is the striking physical appearance features first observed, height disadvantage may critically influence men's behavior and mental health. Herein, we explored the influence of height disadvantage on third-party punishment through time-frequency analysis and electroencephalography hyperscanning. Two participants were randomly designated as the recipient and third party after height comparison and instructed to complete third-party punishment task. Compared with when the third party's height is higher than the recipient's height, when the third party's height is lower, the punishment rate and transfer amount were significantly higher. Only for highly unfair offers, the theta power was significantly greater when the third party's height was lower. The inter-brain synchronization between the recipient and the third party was significantly stronger when the third party's height was lower. Compared with the fair and medium unfair offers, the inter-brain synchronization was strongest for highly unfair offers. Our findings indicate that the height disadvantage-induced anger and reputation concern promote third-party punishment and inter-brain synchronization. This study enriches research perspective and expands the application of the theory of Napoleon complex., (© The Author(s) 2024. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Understanding others as intentional agents is critical in social interactions. We perceive others' intentions through identification, a categorical judgment that others should work like oneself. The most primitive form of understanding others' intentions is joint attention (JA). During JA, an initiator selects a shared object through gaze (initiative joint attention, IJA), and the responder follows the direction of the initiator's gaze (reactive joint attention, RJA). Therefore, both participants share the intention of object selection. However, the neural underpinning of shared intention through JA remains unknown. In this study, we hypothesized that JA is represented by inter-individual neural synchronization of the intention-related activity. Additionally, JA requires eye contact that activates the limbic mirror system; therefore, we hypothesized that this system is involved in shared attention through JA. To test these hypotheses, participants underwent hyperscanning fMRI while performing JA tasks. We found that IJA-related activation of the right anterior insular cortex of participants was positively correlated with RJA-related activation of homologous regions in their partners. This area was activated by volitional selection of the target during IJA. Therefore, identification with others by JA is likely accomplished by the shared intentionality of target selection represented by inter-individual synchronization of the right anterior insular cortex. [ABSTRACT FROM AUTHOR]

Generally, successful cooperation can only be established when the interacting persons believe that they would not be betrayed; this belief can be updated by observing the other persons' actual choices. Thus, the process of belief updating plays an important role in conditional cooperation. Using the Prisoner's Dilemma Game (PDG) with event-related potential (ERP) hyperscanning, this study investigated the dynamics of belief updating in a dyad. During the task, participants were asked if they believed that their opponent would cooperate in the next trial, and their answers functioned as a self-reported index of reciprocal belief. The results suggested that this index shows strong associations with participants' behavioral choices (cooperate/betray). At the individual level, the amplitudes of the ERP components frontal P3a and parietal P3b elicited by the decision outcome were sensitive to belief updating. At the interpersonal level, the between-subject synchronization in P3b was higher than those in the other conditions when the paired participants confirmed each other's reciprocal beliefs. Since previous studies have linked the P3b with memory updating, we suggest that a cooperative relationship is built up when the memory systems (which support belief updating) of two interacting persons reach a high level of coordination. These findings may help explain how conditional cooperation develops between strangers. [ABSTRACT FROM AUTHOR]

• Threatening cooperation and competition have a positive effect on group creativity. • Increased inter-brain synchronization was observed during threatening cooperation in the temporo-parietal junction. • Decreased inter-brain synchronisation was observed during competition in the prefrontal cortex. • A machine learning approach could discriminate the experimental conditions. Previous research has revealed that threats lead to conflicting conclusions about the performance of group creativity. In this study, it was proposed that the interactive mode (cooperation and competition) would underly the divergent effects of threats on group creativity. The underlying neural mechanisms of the divergent effects were further explored. A total of 56 participants were paired into dyads, performing creative tasks cooperatively and competitively in threatening and non-threatening situations, without verbal communication. Brain signals were collected using functional near-infrared spectroscopy hyper-scanning techniques. The results showed that when participants cooperated with each other, threats (vs. without threats) enhanced group creativity, while no such enhancement was observed in competitive interactions. In the threatening situation, participants' group creativity in competitive interactions was as good as those in cooperative interactions. During the threatening cooperation situation, there were increased inter-brain synchronization in the right temporo-parietal junction and decreased brain activity at the prefrontal cortex and temporo-parietal junction. Regardless of the presence of threats, there were decreased inter-brain synchronization and decreased brain activity during competition in the prefrontal cortex. These results reveal a positive effect of threatening cooperation and competition on group creativity and provide further insight into the inter-brain mechanisms that enhance group creativity. [ABSTRACT FROM AUTHOR]

Abstract: Cheering for another person is a common experience. Cheering may facilitate the cheerer's subjective unity with the cheered‐for person, potentially involving synchronized activity between the two individuals’ brains. In the current study, we measured the sensorimotor cortical activity of a player and an observer simultaneously during a competitive game, using functional near‐infrared spectroscopy. The player performed the rock‐paper‐scissors game against an experimenter while the observer either cheered for that player (cheering group) or judged whether the player cheated or not (control group). In the cheering group, observers reported a significantly stronger sense of unity with the player, and exhibited greater sensorimotor activation when observing the player win, compared with the control group. The functional connectivity between the sensorimotor areas of the player and observer was significantly greater in the cheering group, exhibiting a significant correlation with the subjective sense of unity between the player and observer. These results suggest that cheering enhances the synchronization of the player's and the observer's internal states, establishing a sense of unity. [ABSTRACT FROM AUTHOR]

• Dyads in the friend group exhibited the uncertainty-averse propensity in BART. • IBS at l-IFG and mFPC during different feedbacks was modulated by the interpersonal relationship. • IBS at PFC in positive and negative feedback separately predicted decision-making propensity in stranger and friend groups. • Social value orientation moderated the mediation effect of dyad closeness on decision-making propensity via IBS at r-FPC. Humans may behave in different manners when making decisions with friends and strangers. Whether the interpersonal relationship and the characteristics of the individuals in the group affected the group decision-making under uncertainty in the real-time interaction remains unknown. Using the turn-based Balloon Analogue Risk Task (BART), the present study examined the group decision-making propensity under uncertainty with partners in different interpersonal relationships and interpersonal orientations. Corresponding inter-brain synchronization (IBS) patterns at the prefrontal cortex (PFC) were also uncovered with the fNIRS-based hyperscanning approach. Behavioral results identified that dyads in the friend group exhibited the uncertainty-averse propensity when comparing with the stranger group. The fNIRS results reported that feedback-related IBS at the left inferior frontal gyrus (l-IFG) and medial frontopolar cortex (mFPC) during different feedbacks was modulated by interpersonal relationships. The IBS at all channels in the PFC during the positive and negative feedbacks, respectively, predicted the decision-making propensity under uncertainty in the stranger and friend groups based on the support vector machine (SVM) algorithm. The moderating role of the social value orientation (SVO) was also verified in the mediation effect of the dyad closeness on the decision-making propensity under uncertainty via the IBS at the right lateral frontopolar cortex (r-FPC). These findings demonstrated disparate behavioral responses and inter-brain synchronization patterns underlying group decision-making under uncertainty with partners in different interpersonal relationships. [ABSTRACT FROM AUTHOR]

Concepts and techniques developed to investigate complex systems have found practical implications in the study of many complex physical, biological, and social phenomena. Social neuroscience is coherently moving to new investigation and analysis approaches to properly explore social dynamics and to qualify neural processes that mediate and define them. The present paper aims to sketch a global picture of the application of the concept of synchronization to study complex social systems and the neural signatures of interpersonal coupling during interaction dynamics. We then focus on an innovative experimental paradigm–hyperscanning–that allows researchers to sample, compare, and integrate information flows related to the bodily activities of two (or more) individuals involved in a shared naturalistic or experimentally-controlled task, thus giving the opportunity to explore inter-individual synchronization and inter-brain coupling. In particular, the potential of functional Near-Infrared Spectroscopy (fNIRS) as a primary investigation tool in the field is discussed. Finally, we introduce the most-used quantification and analysis methods for hyperscanning applications. [ABSTRACT FROM AUTHOR]

Social interaction is a fundamental part of our daily lives; however, exactly how our brains use social cues to determine whether to cooperate without being exploited remains unclear. In this study, we used an electroencephalography (EEG) hyperscanning approach to investigate the effect of face-to-face contact on the brain mechanisms underlying the decision to cooperate or defect in an iterated version of the Prisoner's Dilemma Game. Participants played the game either in face-to-face or face-blocked conditions. The face-to-face interaction led players to cooperate more often, providing behavioral evidence for the use of these nonverbal cues in their social decision-making. In addition, the EEG hyperscanning identified temporal dynamics and inter-brain synchronization across the cortex, providing evidence for involvement of these regions in the processing of face-to-face cues to read each other's intent to cooperate. Most notably, the power of the alpha frequency band (8–13 Hz) in the right temporoparietal region immediately after seeing a round outcome significantly differed between face-to-face and face-blocked conditions and predicted whether an individual would adopt a ‘cooperation’ or ‘defection’ strategy. Moreover, inter-brain synchronies within this time and frequency range reflected the use of these strategies. This study provides evidence for how the cortex uses nonverbal social cues to determine other's intentions, and highlights the significance of power in the alpha band and inter-brain phase synchronizations in high-level socio-cognitive processing. [ABSTRACT FROM AUTHOR]

• We investigated group polarization using three-person fNIRS hyperscanning. • The group polarization of risk shift and cautious shift was examined. • Two shifts were both with enhanced group-level brain synchronization. • Group polarization can be predicted by brain synchronization in left TPJ. • Risky shift recruited larger prefrontal brain synchronization and deactivation. Group of people shows the shift towards extreme of decision-making as opposed to individuals. Previous studies have revealed two directions of group polarization, i.e., risky shift and cautious shift, but how group of brains drive these shifts remains unknown. In the current study, we arranged risk advantage and disadvantage situations to elicit group polarization of risky shift and cautious shift respectively, and examined the averaged inter-brain synchronization (ABS) among participant triads during group decision making versus individual decision making. The elicited group polarizations were accompanied by the enhanced ABS at bilateral prefrontal areas and left temporoparietal junction (TPJ). Specifically, the TPJ ABS was equivalent in risky shift and cautious shift, and based on machine learning analyses, could predict the extent of group polarization; for two shifts, it negatively correlated with negative emotion. However, the right prefrontal ABS was stronger in risky shift than in cautious shift, and the same area showed the larger brain deactivation in former shift, indicating weaker executive control. For the left prefrontal ABS, only the equivalent ABS was found for two shifts. In sum, group polarization of risky shift and cautious shift calls for inter-brain communication at the group level, and the former shift is with deactivation and more brain synchronization. Our study suggests emotional and cognitive adjustment in decision making of the group compared with individuals. [ABSTRACT FROM AUTHOR]

Concepts and techniques developed to investigate complex systems have found practical implications in the study of many complex physical, biological, and social phenomena. Social neuroscience is coherently moving to new investigation and analysis approaches to properly explore social dynamics and to qualify neural processes that mediate and define them. The present paper aims to sketch a global picture of the application of the concept of synchronization to study complex social systems and the neural signatures of interpersonal coupling during interaction dynamics. We then focus on an innovative experimental paradigm—hyperscanning—that allows researchers to sample, compare, and integrate information flows related to the bodily activities of two (or more) individuals involved in a shared naturalistic or experimentally-controlled task, thus giving the opportunity to explore inter-individual synchronization and inter-brain coupling. In particular, the potential of functional Near-Infrared Spectroscopy (fNIRS) as a primary investigation tool in the field is discussed. Finally, we introduce the most-used quantification and analysis methods for hyperscanning applications.

People feel the sense of 'joint agency', which is the sense that 'we' did it, during a mutually cooperative action. Previous studies have reported that the inter-brain synchronization occurs during a mutually cooperative action, nevertheless the neural correlates of the sense of joint agency remains unclear. Here, we investigated whether the sense of joint agency reflects the inter-brain synchronization during a joint action. The pairs of participants engaged in constant rhythm tapping tasks with alternative (turn-taking) or sequential (non-turn-taking) coordination. Electroencephalograms (EEGs) of the participant pair during the tasks were simultaneously measured (hyperscanned), and the participants were subsequently asked to rate the sense of joint agency. The results showed that the participants felt strong sense of joint agency in the turn-taking cooperative actions, but not in the non-turn-taking actions. Moreover, EEG theta (4–7 Hz) oscillations were more synchronized between the frontal region in the leader, who tapped the first, and the right temporo-parietal region in the follower, who tapped following the leader, during the turn-taking cooperative actions than during the non-turn-taking cooperative actions. Furthermore, the degree of inter-brain synchronization was significantly correlated with the sense of joint agency, as well as the temporal accuracy of the tapping actions of the pair. These results indicate that the sense of joint agency strongly reflects the inter-brain synchronization, which depends on the quality of mutual cooperation during a joint action. • The neural correlates of the sense of joint agency is not fully investigated. • EEG hyperscanning of dyads during a cooperative finger tapping task was performed. • The dyad felt the strong sense of joint agency during the cooperative task. • The sense of joint agency strongly correlates with the inter-brain synchronization. [ABSTRACT FROM AUTHOR]

Flow is a highly motivated and affectively positive state in which a person is deeply engaged in an activity and feeling enjoyment from it. In collaborative activities, it would be optimal if all participants were in a state of flow. However, flow states fluctuate amongst individuals due to differences in the dynamics of motivation and cognition. To explore the possibility that inter-brain synchronization can provide a quantitative measure of the convergence and divergence of collective motivational dynamics, we conducted a pilot study to investigate the relationship between inter-brain synchronization and the interpersonal similarity of flow state dynamics during the collaborative learning process. In two English as a Foreign Language (EFL) classes, students were divided into groups of three-four and seated at desks facing each other while conducting a 60-min group work. In both classes, two groups with four members were randomly selected, and their medial prefrontal neural activities were measured simultaneously using wireless functional near-infrared spectroscopy (fNIRS) devices. Later the participants observed their own activities on recorded videos and retrospectively rated their subjective degree of flow state on a seven-point scale for each 2-min period. For the pairs of students whose neural activities were measured, the similarity of their flow experience dynamics was evaluated by the temporal correlation between their flow ratings. Prefrontal inter-brain synchronization of the same student pairs during group work was evaluated using wavelet transform coherence. Statistical analyses revealed that: (1) flow dynamics were significantly more similar for the student pairs within the same group compared to the pairs of students assigned across different groups; (2) prefrontal inter-brain synchronization in the relatively short time scale (9.3-13.9 s) was significantly higher for the within-group pairs than for the cross-group pairs; and (3) the prefrontal inter-brain synchronization at the same short time scale was significantly and positively correlated with the similarity of flow dynamics, even after controlling for the effects of within- vs. cross-group pair types from the two variables. These suggest that inter-brain synchronization can indeed provide a quantitative measure for converging and diverging collective motivational dynamics during collaborative learning, with higher inter-brain synchronization corresponding to a more convergent flow experience., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2021 Nozawa, Kondo, Yamamoto, Jeong, Ikeda, Sakaki, Miyake, Ishikawa and Kawashima.)