Children and parents are wired to connect as it provides the foundation for developing children to adapt to an increasingly complex environment (Ainsworth et al., 2015). For a long time, human developmental studies have demonstrated that parent-child dyads often show similarities at the behavioral, psychological, and physiological levels (Kochanska and Aksan, 1995; Harrist and Waugh, 2002; DePasquale, 2020; Rogers et al., 2022) and such dyadic similarities play a major role in children's adjustment across development (Boyum and Parke, 1995; Feldman, 2007; Feng et al., 2007). Despite extensive studies highlighting the importance of parent-child dyadic similarity in fostering children's learning and psychological wellbeing, little is known about parent-child similarity at the neural level until recently. In the past few years, a growing number of studies begin to investigate parent-child neural similarity using a variety of neuroimaging approaches, such as functional magnetic resonance imaging (fMRI), functional near-infrared spectroscopy (fNIRS), and electroencephalography (EEG) (e.g., Lee et al., 2017a,b, 2018; Reindl et al., 2018; Nguyen et al., 2021b; Haresign et al., 2022). Therefore, our review aims to summarize recent advances in empirical research on parent-child neural similarity. First, we explain why parent-child neural similarity serves as an important lens to understand human development within the family context and provides unique information beyond prior methods (e.g., survey, observation, and interview). Second, we showcase how parent-child neural similarity is assessed and quantified using different neuroimaging approaches in recent research. Third, we synthesize empirical evidence regarding the contextual and individual factors that may contribute to variability in parent-child neural similarity and delineate how such neural similarity is related to different aspects of child adjustment. Finally, we point out important directions for future research. Taken together, this integrative review systematically demonstrates cutting-edge research that explores neural similarity in parent-child dyads, and provides researchers with a clear roadmap to further this endeavor in order to gain a better understanding of socialization process and brain development.

Examining neural similarity in parent-child dyads can provide novel theoretical and empirical insights in multiple ways. First, it can offer direct evidence on how parents and children's brains are wired together from a dyadic perspective. Although previous neuroimaging studies have shed light on the role of parents in children's brain development (e.g., Belsky and De Haan, 2011; Whittle et al., 2014), the scope of these studies has largely been limited because much of these works just scan children's brain while evaluating parental profiles via traditional measures such as self-report or observation. For example, prior research has examined how parent-child relationships, parental depression, and even the mere presence of parents, modulate adolescents' brain development and psychological adjustment (Qu et al., 2015, 2016a; Telzer et al., 2015). The paucity of understanding in dyadic similarity at the neural level is partly due to the lack of studies that take parents' brain into consideration to explain children's neurobiological development beyond a single-brain perspective. Similarly, a growing body of literature on parental brain typically just assesses parents' neural responses to multiple types of stimuli related to children (e.g., infant cry, baby movies; Feldman, 2015; Kringelbach et al., 2016; Lee et al., 2019; Stark et al., 2019). For example, research found that mothers showed enhanced activity in specific brain regions (e.g., inferior frontal regions, striatum) when hearing their own infants' cries across cultures (Bornstein et al., 2017). However, without employing brain scans for both parents and their children, it remains unknown about the shared neural processes in parent-child dyads.

Second, the brain-level measures of parent-child similarity can provide insights into the mechanisms of within-family interpersonal concordance. Scholars have long been interested in understanding interpersonal similarity in parent-child dyads, including physiological (e.g., heart rate; Feldman et al., 2011), hormonal (e.g., cortisol levels; Papp et al., 2009), and emotional similarity (e.g., shared affect; Feldman et al., 1999). However, there are still open questions about why such coordinated behavior and psychophysiology occur and what might predict such concordance. Recent neuroimaging studies indicate that parent-child neural similarity is related to their behavioral similarity. For example, parent-child dyads with similar default-mode network connectivity showed greater similarity in daily sleep behavior routines (Lee et al., 2017a). Therefore, examining the similarity of neural configruation profiles between children and parents help understand the underlying mechanisms of dyadic similarity in affect, behavior, and psychophysiology.

Third, parent-child neural similarity can serve as a unique lens and provide a novel perspective to understand the well-established theories on human development. For example, examining parent-child neural similarity may enable more in-depth investigation of the attachment theory. Specifically, parent-child neural similarity can increase the understanding of the mechanisms regarding how attachment to primary caregivers may get under the skin (Pietromonaco et al., 2013; Pietromonaco and Powers, 2015) and have long-lasting effects on individuals' psychological, emotional, and social development from a neurobiological perspective (Lee et al., 2018). It allows researchers to examine many central propositions of the attachment theory such as the consistency hypothesis. Decades of research demonstrates the continuity of attachment over time and across relationships (e.g., from parent-child relationship to romantic relationship and friendship; Rubin et al., 2004; Selcuk et al., 2010; Feldman et al., 2013; Ulmer-Yaniv et al., 2022). The advances in quantifying neural similarity may offer novel empirical evidence for testing such theoretical hypotheses (e.g., how parent-child neural similarity may predict whom children become friends with later in life). Similarly, understanding parent-child neural similarity can provide insights into the theories regarding parental socialization and children's internalization. Given that parents and children may not be able to articulate their psychological processes, assessment of dyadic neural similarity can provide a powerful tool to sensitively capture parents and children's autonomic responses to interactions. Understanding this invisible process can shed light on theories on parental socialization and parent-child interactions. For example, scholars argue that elucidating dyadic neural synchrony during parent-child interactions can help distinguish competing theories regarding the interactive directionality in parent-child dyads (e.g., a uni-directional process in which children implicitly model their parents vs. bidirectional influences between children and parents) (Ratliff et al., 2021).

It is worth to note that there are different methods to examine parent-child neural similarity and they can be broadly divided into two approaches based on which features of interpersonal process they focus on. The first approach, with relatively long tradition in dyadic studies, is to focus on the moment-to-moment inter-personal synchronization of neural signals when both parents and children are engaged in interactive activities (e.g., conversation) or exposed to the same stimuli at the same time (e.g., listen to the same music) (e.g., Reindl et al., 2018; Nguyen et al., 2020; Turk et al., 2022). This approach is interested in the contexts in which parents and children show in-synched temporal changes of neural activity, namely real-time neural synchronization, to capture their reciprocal processes with assumptions that such dyadic synchrony occurs instantaneously and may reflect their harmonized psychological and behavioral status at the given moments. Given that this approach directly compares the temporal characteristics of neural signals in parent-child dyads online, it is necessary to adopt neuroimaging techniques with higher temporal resolution such as electroencephalography (EEG), functional near-infrared spectroscopy (fNIRS), and magnetic electroencephalography (MEG), and thus the analyses are more often focused to quantify temporal coherence of inter-brain signal fluctuation (i.e., temporal synchrony). For instance, the phase synchronization level of EEG signal oscillations at a certain frequency band (e.g., gamma band, 30–80 Hz; Figure 1A) is calculated directly between electrodes attached to the brain of each individual (Babiloni and Astolfi, 2014; Hari et al., 2015; Hasson and Frith, 2016). However, the limitations of spatial resolution in the neural synchrony approach prevent the identification of the specific brain regions or networks mainly responsible for synchronization, and hinder the investigation of whole-brain activity, especially the limbic system.

The measure of parent-child neural similarity has recently been extended to fMRI approach. Different from the first approach, the implications of fMRI approach focus on neural pattern similarity through either intrinsic connectivity pattern (Lee et al., 2017a,b) or response pattern to a certain event (Lee et al., 2018) between parents and children. Even though fMRI has limitation in capturing the real-time interactive process, the approach using fMRI is possible to quantify the extent to which parent-child dyads' neural profiles remain in-tuned over time as well as how similarly they respond to the environments. The connectivity-based pattern similarity has been examined more through the resting-state fMRI data (Figure 1B), as it reflects neural foundation of individuals' psychological status, namely intrinsic neural systems (Cole et al., 2014). That is, this approach measures the similarity of the intrinsic brain system with the assumption that the interactive process over time tunes the functional configurations of the brains, resulting in similar neural profiles between parents and children. For example, recent work assessed the similarity of functional connectivity patterns across intrinsic networks to evaluate the extent to which the brain's functional architectures are similarly formed between parents and children (Lee et al., 2017b).

Another way of using the pattern similarity is to examine how similarly parents and children respond to a specific event (i.e., representational pattern similarity; Kriegeskorte et al., 2008; Diedrichsen and Kriegeskorte, 2017). This approach focuses more on the similarity of the neural response pattern to task-specific events between parents and children, rather than on the connectivity configuration similarity (Figure 1C). In fact, this approach can be implemented using various neuroimaging modalities such as EEG, fNIRS, and MEG, as the response pattern can be measured across electrodes, after stimulus onsets. However, fMRI can offer greater benefits as it allows for the examination of specific regions of interest (ROIs) considered as a core region for the task-specific process. For example, a recent study by Lee et al. (2018) aimed to evaluate the neural representational similarity between parents and children when they are exposed to stressful stimuli. The researchers first identified the brain regions particularly involved in stress processing (e.g., insula), and they calculated the neural response pattern similarity during stress-inducing task between parents and children within the ROI.

Notably, recent studies attempt to measure parent-child neural synchrony using fMRI (Ratliff et al., 2021), especially with hyper-scanning protocols (using two fMRI machines simultaneously). Although temporal resolution in fMRI is relatively less precision than EEG/fNIRS/MEG methods, it provides important information of low frequency trends in neural processing, and thus fMRI-based neural synchrony studies increase in last couple of years. However, given the simultaneous scanning of parent-child dyads during reciprocal interactions, this approach requires two fMRI scanners on site.

It is also important to note that similar to dyadic concordance at behavioral or physiological levels, there is significant variability in dyadic concordance at the neural level (e.g., Lee et al., 2018). Therefore, scholars have begun to identify the antecedents that may modulate the level of parent-child neural similarity. Below we summarize familial and individual factors that receive relatively more attention in prior research.

Researchers not only quantify parent-child neural similarity across various contexts, but also examine the implications of such similarity for children's performance and adjustment. Decade of research demonstrates that parent-child dyadic similarities at the behavioral and psychological levels are associated with children's positive outcomes (Boyum and Parke, 1995; Feldman, 2007; Feng et al., 2007). Moreover, evidence from social neuroscience suggests that greater inter-brain synchrony in teams predicts better collective performance (e.g., Gumilar et al., 2021; Reinero et al., 2021). In line with this research, extant studies have examined how neural similarity in parent-child dyads is related to short-term outcomes during parent-child interactions. For example, increased parent-child neural synchrony in the dorsolateral prefrontal and frontopolar cortex during prior cooperation was predictive of their better cooperative performance in subsequent trials (Reindl et al., 2018), but not vice versa, suggesting the potential causal link between neural synchrony and performance. Furthermore, mother-child neural synchrony predicted the dyad's problem-solving success beyond their behavioral reciprocity (Nguyen et al., 2020), highlighting the unique role of neural synchrony in predicting task performance.

More importantly, a series of research examine how parent-child neural similarity is associated with children's adjustment. For example, children who had higher level of dyadic neural similarity with their parents showed better psychological adjustment such as higher emotional competence (Lee et al., 2017b), more optimal sleep quality (Lee et al., 2017a), lower level of stress (Lee et al., 2018), and more rapid decreases in internalizing behaviors (Quiñones-Camacho et al., 2022). Similarly, recent evidence suggests that parent-child neural synchrony in emotion-related brain regions during conflict discussion was associated with fewer adolescent-reported depressive symptoms (Ratliff et al., 2021). Together, these studies provide initial and promising evidence that parent-child neural similarity has predictive validity for children's performance and wellbeing.

Extant research has provided exciting advances in understanding parent-child neural similarity, which also points to the directions for future research.

With rapid development in the research on parent-child neural similarity, this promising line of research requires scholars to systematically integrate empirical evidence and clarify theoretical contributions. To address this issue, our review synthesizes recent advances in the study of parent-child neural similarity, delineates different types of measurements, and points out important directions for future research. The advances in this vibrant field not only provide novel insights into how parents and children's brains are wired together from a dyadic perspective, but also identify important antecedents and consequences of parent-child neural similarity. Ultimately, this endeavor will provide researchers with a unique lens to understand parental socialization process, parent-child interactions, and brain development.

YQ, ZZ, and T-HL wrote the first draft of the manuscript. All authors contributed to manuscript revision, read, and approved the submitted version.