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While substantial research supports the role of parent–child interactions on the emergence of psychiatric symptoms, few studies have explored biological mechanisms for this association. The current study explored behavioral and neural parent–child synchronization during frustration and play as predictors of internalizing and externalizing behaviors across a span of 1.5 years. Parent–child dyads first came to the laboratory when the child was 4–5 years old and completed the Disruptive Behavior Diagnostic Observation Schedule: Biological Synchrony (DB-DOS: BioSync) task while functional near-infrared spectroscopy (fNIRS) data were recorded. Parents reported on their child's internalizing and externalizing behaviors using the Child Behavior Checklist (CBCL) four times over 1.5 years. Latent growth curve (LGC) modeling was conducted to assess neural and behavioral synchrony as predictors of internalizing and externalizing trajectories. Consistent with previous investigations in this age range, on average, internalizing and externalizing behaviors decreased over the four time points. Parent–child neural synchrony during a period of play predicted rate of change in internalizing but not externalizing behaviors such that higher parent–child neural synchrony was associated with a more rapid decrease in internalizing behaviors. Our results suggest that a parent–child dyad's ability to coordinate neural activation during positive interactions might serve as a protective mechanism in the context of internalizing behaviors.

Parent–child synchrony, or the coordination of biological and behavioral processes between parent and child, is thought to promote healthy relationships and support youth adjustment. Although extensive work has been conducted on parent–child synchrony during infancy and early childhood, less is known about synchrony in middle childhood and adolescence and the contextual factors that impact synchrony, particularly physiological synchrony. This is a systematic and qualitative review of 37 studies of behavioral and physiological synchrony in parent–child interactions after early childhood (parents with youth ages 5–18). Behavioral and physiological synchrony were typically identified in youth and their parents beyond early childhood and related to positive outcomes; however, research on father-child synchrony is rarer with mixed findings. Multiple factors are associated with synchrony, including parent and youth psychological symptoms and disorders, parenting factors, such as over-controlling parenting, and parent characteristics, such as interparental aggression and conflict. Few studies have examined behavioral and physiological synchrony simultaneously and longitudinally, limiting our ability to understand the relationship between types of synchrony and later adjustment. Available studies suggest that the context, such as presence of psychopathology or exposure to trauma, influences whether synchrony is associated with positive or negative outcomes. This review highlights the need for additional research to understand the relationship between types of synchrony and the long-term effects and contextual factors that impact youth outcomes.

A key emergent property of group social dynamic is synchrony – the coordination of actions, emotions, or physiological processes between group members. Despite this fact and the inherent nested structure of groups, little research has assessed physiological synchronization between group members from a multi-level perspective, thus limiting a full understanding of the dynamics between members. To address this gap of knowledge we re-analyzed a large dataset (N=261) comprising physiological and psychological data that were collected in two laboratory studies that involved two different social group tasks. In both studies, following the group task, members reported their experience of group cohesion via questionnaires. We utilized a nonlinear analysis method-multidimensional recurrence quantification analysis that allowed us to represent physiological synchronization in cardiological interbeat intervals between group members at the individual-level and at the group-level. We found that across studies and their conditions, the change in physiological synchrony from baseline to group interaction predicted a psychological sense of group cohesion. This result was evident both at the individual and the group levels and was not modified by the context of the interaction. The individual- and group-level effects were highly correlated. These results indicate that the relationship between synchrony and cohesion is a multilayered construct. We re-affirm the role of physiological synchrony for cohesion in groups. Future studies are needed to crystallize our understanding of the differences and similarities between synchrony at the individual-level and synchrony at the group level to illuminate under which conditions one of these levels has primacy, or how they interact.

It is well known that EEG signals of Alzheimer's disease (AD) patients are generally less synchronous than in age-matched control subjects. However, this effect is not always easily detectable. This is especially the case for patients in the pre-symptomatic phase, commonly referred to as mild cognitive impairment (MCI), during which neuronal degeneration is occurring prior to the clinical symptoms appearance. In this paper, various synchrony measures are studied in the context of AD diagnosis, including the correlation coefficient, mean-square and phase coherence, Granger causality, phase synchrony indices, information-theoretic divergence measures, state space based measures, and the recently proposed stochastic event synchrony measures. Experiments with EEG data show that many of those measures are strongly correlated (or anti-correlated) with the correlation coefficient, and hence, provide little complementary information about EEG synchrony. Measures that are only weakly correlated with the correlation coefficient include the phase synchrony indices, Granger causality measures, and stochastic event synchrony measures. In addition, those three families of synchrony measures are mutually uncorrelated, and therefore, they each seem to capture a specific kind of interdependence. For the data set at hand, only two synchrony measures are able to convincingly distinguish MCI patients from age-matched control patients, i.e., Granger causality (in particular, full-frequency directed transfer function) and stochastic event synchrony. Those two measures are used as features to distinguish MCI patients from age-matched control subjects, yielding a leave-one-out classification rate of 83%. The classification performance may be further improved by adding complementary features from EEG; this approach may eventually lead to a reliable EEG-based diagnostic tool for MCI and AD.

Interpersonal synchrony refers to the temporal coordination between two individuals, signaling the coupling of their behaviors. Optimal movement synchrony in dyads is linked to more affiliative behavior, cooperation, and trust. However, there is limited research on how the sensory environment impacts interpersonal synchrony. One significant environmental factor influencing human behavior and social interactions is ambient odors. This study aimed to examine the effect of ambient odor on interpersonal synchrony, particularly in-phase movement synchrony. Motion energy analysis and windowed cross-correlations were used to measure synchrony levels between participants during video-recorded interactions. Twenty-five same-sex friend dyads performed three interaction tasks designed to create fun, cooperative, or competitive atmospheres. These tasks were conducted with a pleasant, stimulating peppermint odor or in a control condition without odor. Consistent with previous studies, higher synchrony levels were observed in fun atmospheres compared to competitive and cooperative ones. No significant effects of odor stimulation were found. Overall, the results confirm that social context significantly influences movement synchrony and affiliation, while ambient odor might not affect interpersonal synchrony, at least when the odor is irrelevant to the task.

Brain-to-brain synchrony has been proposed as an important mechanism underlying social interaction. While first findings indicate that it may be modulated in children with autism spectrum disorder (ASD), no study to date has investigated the influence of different interaction partners and task characteristics. Using functional near-infrared spectroscopy hyperscanning, we assessed brain-to-brain synchrony in 41 male typically developing (TD) children (8–18 years; control sample), as well as 18 children with ASD and age-matched TD children (matched sample), while performing cooperative and competitive tasks with their parents and an adult stranger. Dyads were instructed either to respond jointly in response to a target (cooperation) or to respond faster than the other player (competition). Wavelet coherence was calculated for oxy- and deoxyhemoglobin brain signals. In the control sample, a widespread enhanced coherence was observed for parent–child competition, and a more localized coherence for parent–child cooperation in the frontopolar cortex. While behaviorally, children with ASD showed a lower motor synchrony than children in the TD group, no significant group differences were observed on the neural level. In order to identify biomarkers for typical and atypical social interactions in the long run, more research is needed to investigate the neurobiological underpinnings of reduced synchrony in ASD.

Synchrony is broadly important to population and community dynamics due to its ubiquity and implications for extinction dynamics, system stability, and species diversity. Investigations of synchrony in community ecology have tended to focus on covariance in the abundances of multiple species in a single location. Yet, the importance of regional environmental variation and spatial processes in community dynamics suggests that community properties, such as species richness, could fluctuate synchronously across patches in a metacommunity, in an analog of population spatial synchrony. Here, we test the prevalence of this phenomenon and the conditions under which it may occur using theoretical simulations and empirical data from 20 marine and terrestrial metacommunities. Additionally, given the importance of biodiversity for stability of ecosystem function, we posit that spatial synchrony in species richness is strongly related to stability. Our findings show that metacommunities often exhibit spatial synchrony in species richness. We also found that richness synchrony can be driven by environmental stochasticity and dispersal, two mechanisms of population spatial synchrony. Richness synchrony also depended on community structure, including species evenness and beta diversity. Strikingly, ecosystem stability was more strongly related to richness synchrony than to species richness itself, likely because richness synchrony integrates information about community processes and environmental forcing. Our study highlights a new approach for studying spatiotemporal community dynamics and emphasizes the spatial dimensions of community dynamics and stability.

Interspecific population synchrony, or co‐fluctuations in the population dynamics and demographic parameters of different species, is an important ecological phenomenon with major implications for the stability of communities and ecosystems. It is also central in the context of biodiversity loss, as interspecific synchrony can influence how ecological communities are affected by anthropogenic stressors. Studies of interspecific synchrony are therefore important for understanding fundamental mechanisms underlying the biodiversity changes occurring worldwide. Interspecific synchrony has received increased interest in recent years, and studies have focused on synchrony in abundances, growth rates and vital rates at species, community and metacommunity levels. However, there is little cohesiveness in the literature, as studies focused on different levels of biological organization are largely separate from each other. Still, synchrony at these levels of biological organization is likely interconnected in nature. Understanding these connections would greatly benefit our understanding of interspecific synchrony and its implications for populations and communities. Here, we provide an overview of the current status and future perspectives of interspecific synchrony research, highlighting major knowledge gaps. We show how interspecific synchrony at different levels of biological organization is conceptually linked and present an accessible overview of the terminology and methods used to study it. By providing a common understanding of the meaning and applicability of terms and an overview of commonly used methods, this overview will serve as a point of departure for integrating research on interspecific synchrony. Such integration is important to fully understand the impacts of environmental change on species and ecological communities.

Interpersonal neural synchrony provides a neural index of how individuals align cognitively and socially during interaction. While previous work has shown that personality traits shape interpersonal behavior, and that trait similarity can enhance dyadic coordination, little is known about whether such similarity predicts neural synchrony. The present study used an electroencephalography (EEG) hyper-scanning methodology to investigate the relationship between the degree of similarity in Big 5 scores of interacting participants in dyads and their interbrain synchrony during naturalistic dialogue. A total of 23 female dyads completed the Big 5 questionnaire and performed a goal-oriented social task while each wearing lightweight EEG headsets. Similarity for each Big 5 personality scale was created by calculating the absolute difference between the two participants within each dyad. Interpersonal neural synchrony was measured using Dynamic Time Warping (DTW), which quantified the similarity between separate temporal signals, based on a time-frequency decomposition of EEG. Results showed that similarity of Conscientiousness scores within dyads significantly predicted interpersonal neural synchrony within dyads (with openness showing marginal prediction). No relationship was evident for any other Big 5 trait. These findings demonstrate that personality similarity, particularly in conscientiousness, contributes to interpersonal neural synchrony, highlighting a trait-based pathway through which social alignment emerges during naturalistic interaction.

Laughter is a widespread social behavior that has been associated with increases in social connection. However, the mechanisms behind this link are not yet well understood. We hypothesized that laughter supports positive social outcomes by enhancing neural synchrony during social interactions. Neural synchrony is a process of mutual alignment of brain areas, which has been shown to positively affect social interactions. In a 2 × 2 design, participant pairs watched either funny or neutral videos (Laughter Manipulation: yes/no), either together or separately (Social Context: yes/no). Afterwards, they engaged in a 10-minute free interaction. Laughter behavior was annotated during both phases. Neural synchrony was measured using fNIRS hyperscanning for both phases and quantified across frontal and temporal regions using Wavelet Transform Coherence. As social outcomes, we measured Liking, Prosociality, and Bonding after the free conversation. We tested our hypotheses with Bayesian models that assessed the effects of Laughter and Social context on social outcomes, with synchrony modeled as a mediator. Parameter estimates for the effects of Laughter and Social Context on interpersonal neural synchrony were close to zero, with Bayes Factors indicating evidence for the null hypothesis. Similarly, the effects of Laughter and Social Context on Liking, Prosociality, and Bonding showed no effects. However, model comparisons provided evidence for annotated Laughter Behavior as a predictor of Liking, Prosociality, and Bonding. Mediation analyses revealed no overall effect, but some findings stood out. We observed a negative association between right IFG and right TPJ synchrony during the manipulation phase and later Liking, and a positive association between right and left IFG synchrony and subsequent Prosociality. Additionally, synchrony during the free interaction phase between the left IFG and right TPJ predicted Liking and synchrony between the left and right TPJ predicted Bonding. In total, our findings show no direct link between Laughter and neural synchrony. However, Laughter Behavior was associated with social outcomes. Additionally, neural synchrony was also linked to social outcomes, with distinct positive and negative associations depending on the brain regions involved. These results highlight the complexity of the relationship between laughter, neural synchrony, and social connection, suggesting the need for further research.