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Journal of Child and Family Studies (2018) 27:2990–2998 https://doi.org/10.1007/s10826-018-1121-5

ORIGINAL PAPER

Linkage between Parent-Child Frontal Resting Electroencephalogram (EEG) Asymmetry: The Moderating Role of Emotional Parenting Hui Wang1 Xiaoqin Mai2 Zhuo Rachel Han1 Yannan Hu1 Xuemei Lei1 ●

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Published online: 6 June 2018 © Springer Science+Business Media, LLC, part of Springer Nature 2018

Abstract Frontal resting electroencephalogram (EEG) asymmetry is an important physiological indicator of emotion regulation, positive/negative emotion, and approach/withdrawal tendencies. The present study examined the relationship of parent-child frontal resting EEG asymmetry patterns and explored the potential moderating role of emotional parenting on such a relationship. We recorded the frontal resting EEG asymmetry of thirty-nine children (M age = 8.87 years) and their primary caregivers (M age = 39.41 years) and coded their emotional parenting behaviors (psychological control and psychological unavailability) based on behavioral observations. The results indicated that there was not a direct association between parentchild frontal resting EEG asymmetry but that the relationship was moderated by parental psychological control. Specifically, the resting frontal EEG asymmetry of the parents was negatively associated with the EEG asymmetry of their children only under higher levels of parental psychological control. However, psychological unavailability did not exhibit a moderating effect. Accordingly, our findings highlight the critical but differential role of emotional parenting behaviors with respect to the association between the frontal resting EEG asymmetry of parents and their children. Keywords Parent-child physiological similarity Frontal resting EEG asymmetry Emotional parenting Emotion regulation ●

Introduction Frontal resting electroencephalogram (EEG) asymmetry, the relative activation between the left and right frontal regions of the brain, has been regarded as an important physiological indicator of the emotional capacity of children (Diaz and Bell 2012; Kim and Bell 2006). Specifically, children with relative left frontal activation tend to display effective emotion regulation, positive emotion, and approach-related behaviors, whereas children with relative right frontal activation show poor emotion regulation,

* Zhuo Rachel Han [email protected] 1

Beijing Key Laboratory of Applied Experimental Psychology, National Demonstration Center for Experimental Psychology Education (Beijing Normal University), Faculty of Psychology, Beijing Normal University, Beijing, China

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Department of Psychology, Renmin University of China, Beijing, China

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negative emotion, and withdrawal-related behaviors (Coan and Allen 2004; Smith et al. 2016). A particularly rich literature has found that children’s atypical patterns of frontal EEG asymmetry at rest reflect their potential vulnerability to psychopathological symptoms (e.g., Forbes et al. 2006; Smith and Bell 2010). For example, Baving et al. (2002) examined baseline EEG asymmetry patterns for two age groups of anxious children. For the 8-year-old group, 3 min of resting EEG with eyes-open or eyes-closed were recorded. For the 11-yearold group, EEG data were obtained while watching a slightly positive film clip. The results demonstrated that in both age groups, girls with anxiety disorder exhibited greater right than left frontal activation. Additionally, Santesso et al. (2006) investigated the association between frontal EEG asymmetry and the externalizing problems among a group of ten-year-old children. Their study found that children with relatively greater right frontal activity at rest reported higher levels of externalizing problems. This evidence supports the importance of exploring factors that may relate to children’s frontal EEG asymmetry patterns at rest.

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Research has suggested that parents may influence their children’s emotional development biologically, i.e., inheriting parents’ physiological patterns, and socially, i.e., shaping through parenting behaviors (Graham et al. 2017; Morris et al. 2007). For instance, Graham et al. (2017) examined the association between the parent-child physiological index of emotion regulation, i.e., resting heart rate variability, and explored whether parenting behaviors moderated such a relationship. They found that parent’s resting heart rate variability was positively correlated with their child’s resting heart rate variability. Furthermore, this association was moderated by negative parenting, such that at lower levels of inconsistent discipline, parents’ resting heart rate variability was positively correlated with that of their children, whereas at higher levels of inconsistent discipline, there was no significant association between the parent-child resting heart rate variability. Similarly, research has documented the physiological similarity of the hypothalamic-pituitary-adrenal (HPA) axis functioning between parents and children and has determined that such a similarity is moderated by parenting behaviors, including parental reciprocity, monitoring and supervision behaviors (Papp et al. 2009; Pratt et al. 2017). As concluded from the existing literature, the majority of studies on the biological linkage between parent-child dyads have focused on the automatic nervous system (ANS) and the HPA axis, such that the autonomic arousal (i.e., hear rate variability; Giuliano et al. 2015; Graham et al. 2017), and the level of a stress hormone (i.e., cortisol; LeMoult et al. 2015; Pratt et al. 2017), frequently correlate between parents and their children. However, the similarities between the parent and child’s neural activity are less clear. A recent study by Lee et al. (2017), adopting the method of resting state functional magnetic resonance imaging (rsfMRI), reported a significant association between parentchild intrinsic resting-state network connectivity (RSN). The presence of a direct linkage with RSN between parentchild dyads potentially indicates that this brain activation similarity may occur during a wide range of resting brain processes, and hence, frontal resting EEG asymmetry may also exhibit this similarity. Although there is no direct empirical evidence, genetic heritability may underpin a portion of the linkage between parent-child frontal resting EEG asymmetry (Schmidt et al. 2009; Smit et al. 2007). For example, Gao et al. (2009) examined the heritability of frontal asymmetry in a group of 9- to 10-year-old twins. The results documented that the frontal asymmetry of children was modestly heritable, and a significant, albeit small, portion of the frontal asymmetry variability was due to genetic influences (11–28%). Consistently, Anokhin et al. (2006) found that 27% of the asymmetry variance at midfrontal locations (F3 and F4) was accounted for by genetic factors in a study of 246 young

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adult female twins. It may, therefore, be presumed that biological parent-child dyads may exhibit a similar pattern of frontal EEG asymmetry. The similar pattern of frontal resting EEG asymmetry between parent and child dyads, as an important aspect of physiological similarity, may be a developmental hallmark of parent-child relationships that permits parents to regulate their physiology to match with children’s states, supports parent-child dyads to sensitize one another’s physiological cues, and promotes the development of children’s physiological regulations of emotions through the physiological similarity with their parents (Feldman 2012, 2015). In addition to the physiological influence, parents may exert a social influence on their child’s emotional development (Feldman 2012; Pratt et al. 2017). Significant works have explored moderators of the association between parents and children’s physiological aspects of emotion regulation and have addressed the critical role of parenting on the linkage of mother-child diurnal cortisol secretion (Papp et al. 2009; Pratt et al. 2017) and resting heart rate variability (Graham et al. 2017). However, no study, to date, has tested the potentially moderating role of emotional parenting on the link between parent-child frontal resting EEG asymmetry, an important aspect of brain activation similarity, although previous studies provide insights into such a hypothesis. For example, by conducting a large longitudinal study, Hane and Fox (2006); Hane et al. (2010) found that infants of mothers with low-quality caregiving behaviors exhibited greater right frontal EEG asymmetry at 9 months than infants of mothers with high-quality caregiving behaviors and that they continued to show similar asymmetry patterns when they were two years old. Theoretically, parents with relative right frontal resting EEG asymmetry, which psychologically suggests higher levels of negative emotion, emotion dysregulation, and withdrawal behaviors, may have greater deleterious impact on their children under conditions of coercive and unavailable parenting, especially given that unsupportive parenting provides a less conducive environment for children to adaptively express and regulate emotion and appropriately exhibit behaviors (Gottman et al. 1997), all of which may, in turn, physiologically result in relative right frontal EEG asymmetry. Thus, this investigation examined the roles of two forms of emotional parenting behaviors on the association between parent-child frontal resting EEG asymmetry. The first form of emotional parenting behavior involves psychological control, which refers to the parents’ control of their children’s emotions through the use of psychological and emotional tactics, such as guilt induction, shaming, and love withdrawal (Barber 1996; Barber et al. 1994). The second form of emotional parenting involves psychological unavailability, which refers to a parent’s emotional

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detachment and unresponsiveness to the needs of the child (Egeland and Erickson 1987; Egeland et al. 1983). Given theoretical and empirical considerations, one may expect that parents’ relative right frontal resting EEG asymmetry may exacerbate the children’s relative right frontal asymmetry patterns in the context of parents’ high levels of psychological control and psychological unavailability. Collectively, given the theoretical proposition and the existing empirical evidence (Graham et al. 2017; Lee et al. 2017), it is likely that children’s frontal EEG asymmetry patterns as the physiological index of emotional tendencies, may be subject to the interactive influence of parents’ biological (i.e., parents’ frontal EEG asymmetry patterns), and social factors (i.e., emotional parenting). Therefore, the present study was designed to investigate the following questions: (1) Is parental EEG asymmetry at rest associated with the EEG asymmetry of their children? We hypothesized that the frontal EEG asymmetry scores of the parents would be positively correlated with those of the children. (2) Is the link between the resting frontal EEG asymmetry of parents and children moderated by emotion-related parenting behaviors? We hypothesized that under conditions of high levels of parental psychological control, the relationship of parent-child right EEG asymmetry patterns would be exacerbated, whereas under conditions of low levels of parental psychological control, the relationship of parentchild right EEG asymmetry patterns would be attenuated. Similarly, we also hypothesized that under conditions of high levels of psychological unavailability, the relationship of parent-child left EEG asymmetry patterns would be weakened, whereas under conditions of low levels of psychological unavailability, the relationship of parent-child left EEG asymmetry patterns would be strengthened.

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24 children (11 boys, M age = 9.55, SD = 1.92; 13 girls, M age = 8.73, SD = 1.51) and their parents (18 mothers, M age = 38.94, SD = 2.13; 6 fathers, M age = 40.67, SD = 2.58). The majority of families were middle class, and 82.9% of the families had an annual household income that exceeded the average income of the city (i.e., approximately 100,000 RMB, approximately 15,000 USD). All parents had completed high school, and the majority had completed a college education (70.7%) or higher (22%). All participating parents were currently married and all parent-child dyads were of Chinese Han ethnicity.

Procedures Each parent-child dyad visited our laboratory twice. During their first visit, parental consent and child assent were obtained from parents and their children upon arrival. The parent-child dyads were then asked to complete some questionnaires and interaction tasks. Emotional parenting behaviors were observed during a videotaped interaction task that required the dyad to collaboratively draw a picture of a house and a tree using an Etch-a-Sketch in 4 min. During the second visit, children and their parents completed resting EEG conditions. Participants sat quietly in a sound-attenuated cabinet, and electrodes were affixed to the scalp of the child and then the parent. The resting EEG was recorded for 8 min during which participants were instructed to sit still with their eyes either open or closed. The families received 180 RMB (approximately 27 USD) for the first visit and 500 RMB (approximately 75 USD) for the second visit. All procedures were approved by the university’s Institutional Review Board (IRB).

Measures

Method

EEG Acquisition and Data Reduction

Participants

Resting EEG was recorded using a Neuroscan Synamp2 Amplifier (Scan 4.3.1, Neurosoft Labs, Inc., Sterling, USA) from 64 cap-mounted Ag/AgCl electrodes arranged according to the 10–20 international placement system. The horizontal electrooculogram (EOG) was recorded with two electrodes placed at the outer canthi of the eyes, and the vertical EOG was recorded with electrodes placed above and below the left eye. All channels were referenced to the left mastoid online and then re-referenced to the Cz electrode offline. Electrode impedances were kept below 5 kΩ. The EEG signals were bandpass filtered at 0.05–100 Hz during data collection. The sampling rate was 500 Hz. Data reduction occurred offline using the Neuroscan4.3 software. Ocular artifacts were removed using a regression procedure implemented in the Neuroscan software (Semlitsch et al. 1986). Each participant’s data

Participants were recruited via flyers distributed at local communities and online. Interested families were invited to visit the university laboratory twice. Thirty-nine typically developing children (20 boys and 19 girls) and one of their primary caregivers (30 biological mothers and 9 biological fathers) participated in this study. Only families that participated in both visits and parent-child dyads that had acceptable EEG signals were entered into further analysis. Fifteen parent-child dyads were excluded due to a failure to complete the EEG task (one child) or excessive eye blinks and movement artifacts. Excluded and included dyads did not differ in age, gender, socioeconomic status (SES), EEG asymmetry scores or assessments of emotional parenting (ps > .05). The final sample of the current study consisted of

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were digitally filtered at 0.1 to 30 Hz. The acquired data were then submitted to a fast Fourier transform (FFT) using a Hanning window of 1-s width with 50% overlap. An artifact removal procedure rejected any data segments with channels that exceeded ± 100 μV because of eye-movement, blink or motor artifacts. Fourteen dyads were excluded (one member of the dyads: seven children, four parents; both members of the dyads: three parent-child dyads) because of excessive movement artifacts (averaged accepted epochs less than 20%). For the final data, 71.94% of children’s epochs were accepted, and 88.16% of parents’ epochs were accepted for subsequent analyses. Alpha power was defined as 8 to 13 Hz for parents and 7 to 12 Hz for children as this frequency band was believed to be equivalent to the alpha band in adults (Gatzke-Kopp et al. 2014; Lopez-Duran et al. 2012). Based on previous work (e.g., Allen et al. 2004; Kim and Bell 2006), frontal EEG asymmetry scores were calculated at the mid-frontal sites most often used, i.e., F3 and F4. Moreover, to normalize the distribution (Gasser et al. 1982), average alpha powers were natural log (ln) transformed. Finally, parent-child dyadic frontal asymmetry scores were computed as the differences between the lntransformed alpha power at the right and left sites (i.e., ln [F4]-ln[F3]). As the alpha band is an inverse measure of cortical activation (Allen and Kline 2004; Davidson 2004), higher values were indicative of relatively greater left frontal activity. Emotional Parenting Behaviors Emotional parenting behaviors, including psychological control and psychological unavailability, were assessed through behavioral observation during the above-described dyadic interaction task. A group of experienced researchers observed the video-recorded parent-child interactions and independently coded the parents’ display of the two emotional parenting behaviors. The inter-rater reliability of the coding scales is reported herein, as indexed by intraclass correlation coefficients among coders’ individual scores. Psychological Control This scale assesses the degree to which a parent attempts to control the child’s feelings, verbal expressions and ideas. Psychological control is coded on a 7-point Likert scale ranging from 1 (very low/no control) to 7 (very high control). At the higher end, a score of 7 indicates that the parent exhibits clear attempts to align the child with his/her own perspective through psychological means, such as guilt, shame, derision, manipulation, and coercion. By contrast, a score of 1 indicates that the parent recognizes and supports the ideas, opinions, and feelings of the child and does not actively deny the child’s perspective. Reliability for this scale was 0.93.

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Psychological Unavailability This scale assesses the degree to which a parent fails to respond to the emotional needs of the child. Psychological unavailability was coded on a 7-point Likert scale. Parents who scored 1 on this scale exhibited emotional availability and demonstrated appropriate responses to their child’s emotions and experiences, such as actively expressed curiosity and interest. By contrast, parents who scored 7 appeared to be unavailable to their children’s emotional needs and depressed or detached from interactions with their children. Reliability for this scale was 0.92.

Data Analyses First, the preliminary analyses evaluating the descriptive statistics, correlations among study variables, and possible group differences in study variables based on demographic characteristics were performed. Next, the moderation models, with parental psychological control and parental psychological unavailability as moderators, of the association between parent-child frontal resting EEG asymmetry were explored using the PROCESS SPSS macro (Hayes 2012) with a bootstrap resample of 5000. Moderating effects were valid when the interaction term between the predictor and the moderator variable was significant and the confidence interval did not include 0. We used 95% confidence intervals, and the conditional relationship between the independent and dependent variables was examined at low (−1 SD below the mean) and high (+1 SD above the mean) levels of the moderator variables (i.e., parental psychological control and parental psychological unavailability).

Results In preparation for the moderation analyses, we tested the relationships between and among parental resting EEG asymmetry, parental psychological control, parental psychological unavailability, and child frontal EEG asymmetry. Demographic characteristics, descriptive statistics and zeroorder correlations are presented in Table 1. Correlation analyses indicated that behavioral observation of parents’ display of psychological control was negatively correlated with child frontal resting EEG asymmetry (r = −.61, p < .01) but not significantly correlated with parental frontal resting EEG asymmetry. Furthermore, parental psychological unavailability observed during the task was not significantly correlated with any study variables. Moreover, parental and child resting EEG asymmetry scores were not significantly associated with each other. Additionally, the Pearson’s correlation test found no child age difference for any study variables, and the independent

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sample t-tests revealed no child gender differences with respect to any study variables. However, a significant parent gender difference was observed for psychological unavailability (t (22) = −2.66, p < .05) as fathers exhibited more psychological unavailability than mothers. Based on these results, parental gender was controlled in the moderation model of psychological unavailability in further analyses. The moderation analyses examined whether emotional parenting behaviors, i.e., psychological control and psychological unavailability, moderated the link between parental resting frontal EEG asymmetry and child resting frontal EEG asymmetry. Applying the PROCESS SPSS macro for moderation analyses, the conditional effect of parental frontal EEG asymmetry was estimated at two Table 1 Means, standard deviations, and bivariate correlation of study variables M

SD

1

2

3

4

1. Child age

9.10

1.72

2. Child gendera

.54

.51

−.24

3. Parent gendera

.75

.44

.12

−.15

4. Casymmetry

.02

.42

.30

.33

.20

5. Pasymmetry

−.13 .37

.33

.10

−.30 −.11

5

0.4 0.2

6. Parental PC 1.38

.77

−.26 −.21 −.10 −.61** −.03

7. Parental PU 2.88

.95

.16

.06

6

.50*

.19

.18

Child Asymmetry

Variables

values of the dichotomized levels of parental psychological control and psychological unavailability. The moderation analysis with observational psychological control as a moderator revealed that parental psychological control significantly moderated the relationship between parent-child frontal resting EEG asymmetry (see Table 2). Further probing of the conditional effect demonstrated that relatively greater left frontal activity of parents at rest was negatively associated with the left frontal EEG asymmetry scores among children who were subjected to high levels of psychological control (see Fig. 1). However, among children who were less likely to undergo psychological control imposed by their parents, parental frontal resting EEG asymmetry was not significantly associated with that of the children, and regardless of the patterns of parental frontal resting EEG asymmetry, child frontal resting EEG asymmetry scores were above zero (see Fig. 1). In other words, children who experienced higher levels of parental psychological control exhibited relatively less left frontal activation when the parental left resting EEG asymmetry score was high, whereas children who

.07

Note: C-asymmetry child frontal resting EEG asymmetry, Pasymmetry parental frontal resting EEG asymmetry, Parental PC parental psychological control, Parental PU parental psychological unavailability a

Gender was coded as 0 for males and 1 for females

*p < .05, **p < .01 Table 2 Results of moderation analyses on child resting frontal EEG asymmetry

Outcome variable

0 Low-PC

-0.2

High-PC -0.4 -0.6

*

-0.8 Low-P-Asymmetry

High-P-Asymmetry

Fig. 1 Parental psychological control moderates the relationship between parent-child frontal resting EEG asymmetry. Note: PC parental psychological control; ∗p < .05 R2

F

.49

6.40**

95% CI

b(SE)

t

P-asymmetry

1.11(.59)

.59

−.12, 2.34

Parental PC

−.47(.11)

−4.32***

−.69, −.24

C-asymmetry

P-asymmetry × parental PC

−1.13(.51)

−2.20*

−2.20, −.06

−1 SD (parental PC)

−.02(.19)

−.10

−.41, .37

+1SD (parental PC)

−1.31(.57)

−2.30*

C-asymmetry

−2.50, −.12 .15

.85

P-asymmetry

.04(.77)

.05

−1.57, 1.64

Parental PU

.16(.12)

1.29

−.10, .41

Parent gender

.33(.25)

1.35

−.18, .84

P-asymmetry × parental PU

−.04(.26)

−.16

−.59, .50

−1 SD (parental PU)

−.04(.34)

−.13

−.75, .66

+1SD (parental PU)

−.12(.37)

−.33

−.90, .65

Note: *p < .05, **p < .01, ***p < .001

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experienced lower levels of parental psychological control expressed relative left frontal activation regardless of the parental frontal EEG asymmetry. The moderation analysis with observational psychological unavailability as a moderator indicated that parental psychological unavailability was not a significant moderator for the association between parent-child frontal resting EEG asymmetry (see Table 2).

Discussion This study examined the direct correlation between the frontal EEG asymmetry of parents and their children and explored the potential role of emotional parenting on this relationship. Our results revealed that while there was no direct association between parent-child frontal resting EEG asymmetry, this relationship was moderated by emotional parenting behaviors. To be specific, under higher levels of parental psychological control, parental frontal resting EEG asymmetry was negatively correlated with that of their children. Nonetheless, the interaction between parental asymmetry patterns and parental psychological unavailability was not significantly associated with child frontal EEG asymmetry patterns. However, due to the crosssectional nature of the current study design, all findings should be interpreted with caution. The first goal of the present study was to investigate whether parents’ frontal EEG asymmetry patterns were directly associated with that of their children. Previous research with twins suggested that frontal resting EEG asymmetry was heritable and that the frontal resting EEG asymmetry scores of twin pairs were modestly but significantly correlated with each other (Anokhin et al. 2006; Gao et al. 2009; Smit et al. 2007), which potentially indicated a genetic and intergenerational transformation of frontal resting EEG asymmetry patterns. However, contrary to our hypothesis, the results revealed that the frontal resting asymmetry scores of parents were not significantly correlated with those of their children. Such surprising findings may suggest that the frontal EEG asymmetry of children is highly developmentally plastic and appears to be largely influenced by environmental factors (Anokhin et al. 2006; Davidson 2004; Gao et al. 2009). As the frontal cortex has not completely matured during childhood (Casey et al. 2000), the development of the frontal asymmetry patterns of children may be more sensitive to the influence of environment. Furthermore, the lack of similarity in parent-child frontal EEG asymmetry at rest was consistent with the view that the genetic transformation of asymmetry patterns may be weakened during childhood (Howarth et al. 2016; Müller et al. 2015). For example, although newborns and infants of

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depressed mothers may potentially mimic the frontal asymmetry profiles of their mothers, i.e., show greater right frontal EEG asymmetry activity at rest (Field et al. 2006; Lusby et al. 2014), such results were not found for children during their early and middle childhoods (Howarth et al. 2016; Müller et al. 2015). Given such findings, it may be that the linkage of parent-child frontal resting EEG asymmetry becomes less evident when children reach childhood or that it is only evident under certain contexts. Based on theoretical and empirical considerations, the magnitude of parent-child physiological associations may be moderated by social factors, and parenting may be of particular importance (Graham et al. 2017; Papp et al. 2009). Thus, the second goal of the present study was to further test the potential role of emotional parenting on the relationship between the frontal resting EEG asymmetry patterns of parents and their children. Although no study has directly examined the role of emotional parenting on the linkage between parent-child frontal resting EEG asymmetry as far as we know, some research notes that parents’ emotions and emotion regulation may correlate and interact with parenting and influence children’s emotional capacity (Crandall et al. 2015; Deater-Deckard et al. 2012; Martin et al. 2002). Whereas our results showed that parental frontal resting EEG asymmetry interacted with their emotional parenting behaviors (i.e., psychological control) to influence child frontal asymmetry patterns. However, we found no significant correlation between emotional parenting and parents’ frontal EEG asymmetry patterns at rest. This is a little surprising as many studies have found parents’ emotional abilities seem to associate with their emotion-related parenting behaviors (see Crandall et al. 2015 for a review). One explanation for these inconsistent findings may be that emotion and emotion regulation are multifaceted (Cole et al. 2004; Thompson 1994) with frontal EEG asymmetry patterns only reflecting one physiological aspect of parental emotion and emotion regulation, and therefore, they do not capture all elements of parents’ emotional abilities that are critical to parenting. Furthermore, it may be that the frontal EEG asymmetry at rest was investigated as a maker of dispositional affective and motivational styles (Gatzke-Kopp et al. 2014; Hagemann 2004), whereas emotional parenting, which was observed during parent-child interactions, was highly context-dependent (Killeen and Teti 2012). Then again, it may be that parents’ dispositional affective style is not always consistent with emotional parenting behaviors in response to interactions with their children. Accordingly, more comprehensive studies are highly encouraged to further explore the associations between parental psychosocial emotional regulation and emotional parenting behaviors. With respect to the roles of emotional parenting on the associations between the parent-child physiological aspects

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of emotional tendencies, our results demonstrated that the frontal EEG asymmetry patterns of parents might correlate with their psychological control over their children to influence child frontal EEG asymmetry. Specifically, under the condition of low levels of parental psychological control, the frontal resting EEG asymmetry patterns of the parents were not related to those of their children, and regardless of the parental frontal asymmetry, the children exhibited relative left frontal asymmetry patterns, i.e., asymmetry scores above zero. By contrast, under the condition of high levels of parental psychological control, the frontal resting EEG asymmetry patterns of the parents were significantly and negatively related to those of their children, in which the more left frontal lateralization of the psychologically controlling parents was related to the more right frontal lateralization of their children. These results documented a significant moderating role of parental psychological control on the direct link between parent-child frontal resting EEG asymmetry patterns. Regarding the findings that children tend to develop relative left frontal activation under low levels of parental psychological control, the present study suggests that low psychological control may buffer against the negative effects of parental relative right frontal EEG asymmetry on the frontal asymmetry activity patterns in children. It may be that parents with low levels of psychological control provide their children with more psychological autonomy, thus allowing them to create an independent identity and acquire a sense of self control (Nanda et al. 2012; Soenens and Vansteenkiste 2010). According to self-determination theory (Deci and Ryan 1985, 2000), individuals have inherent growth tendencies and innate psychological needs. Under low parental psychological control, which creates a low external pressure condition, children have more opportunities to freely adopt autonomous regulation behaviors, to exhibit more positive emotion, to embrace approach behaviors and to improve their capability to regulate negative emotion because emotions are perceived as personally meaningful, which then leads to the physiological manifestation of a relative left frontal EEG asymmetry activity in children. Interestingly, we found a significantly negative correlation between parents’ frontal resting EEG asymmetry and that of their children under high levels of parental psychological control. These results may suggest that parents with positive emotion and approach behaviors do not necessarily have children with similar emotional and behavioral tendencies. It may be that under conditions of high levels of psychological control, the positive emotion and approach behaviors of parents, combined with their psychologically controlling tactics, exacerbate the development of their children’s emotional propensity and effective coping strategies. Parents with relative left frontal asymmetry but who are psychologically controlling may not only express positive

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emotion, such as warmth and love toward their children, but also possess the inner motivation to align their children’s feelings and behaviors with their own, which may result in the parents adopting guilt induction or love withdrawal behaviors. For example, “I love you so much, but if you do not do or become what I expect, I will withdraw my love from you”. Based on self-determination theory (Deci and Ryan 1985, 2000), under conditions of higher external pressure from psychologically controlling parents, children must engage controlled regulation behaviors to avoid feelings of guilt and shame, while simultaneously preventing from these behaviors because they are contrary to their inner motivations. Such inner conflicts would undermine the child’s psychosocial adjustment and, instead, lead to the expression of more negative emotions and withdrawal behaviors (Barber et al. 2012; Ryan et al. 2006; Soenens and Vansteenkiste 2010), which may subsequently lead to the physiological expression of relative right frontal EEG asymmetry activity. However, with respect to the role of parental psychological unavailability, our results were contrary to our expectations in that they revealed that psychological unavailability did not moderate the association of parent-child frontal resting EEG asymmetry. These findings suggest that while both psychological control and psychological unavailability are important negative emotional parenting behaviors in families, the mechanisms by which they are related to the frontal resting EEG asymmetry patterns of parent-child dyads may differ as only psychological control moderated the association between parent-child frontal asymmetry patterns. As there was no evidence regarding the specific roles of these two different emotional parenting behaviors, our studies suggested the importance of continued exploration regarding the effects of different forms of emotional parenting on children’s emotional development and frontal resting EEG asymmetry patterns.

Limitations and Directions for Future Research Although the current study provided critical information regarding the direct relationship between the resting frontal EEG asymmetry patterns of parent-child dyads and the potential roles of emotional parenting, some limitations must be acknowledged. First, the cross-sectional design limited the interpretability of the direction of effects. It may be possible that child physiological components of emotion and emotion regulation, as evidenced by frontal asymmetry patterns, can also have an impact on parents’ emotions and on their parenting behaviors by serving as regulators of their parents’ affect (Eisenberg and Spinrad 2004). For instance, Forbes et al. (2008) found that mothers whose children exhibited relative right frontal EEG asymmetry experienced more negative emotion (i.e., depressive symptoms) one year later.

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Thus, further longitudinal designs are strongly encouraged to test the causal effects of parent and child frontal resting EEG asymmetry and parenting behaviors. Additionally, although we used bootstrapping analysis, as recommended by Preacher and Hayes (2004, 2008), to correct the potential bias and improve the confidence of inference, the sample size of the present study was relatively small. Thus, more studies with a larger sample size are recommended to replicate the current findings. Finally, the parent-child dyads in the current study were from a relatively high functioning community sample, limiting the generalizability of the current findings to other more clinical or at-risk populations. Despite these limitations, our study meaningfully expanded the current knowledge by demonstrating that, although there was no direct correlation between the frontal EEG asymmetry patterns of community parents and their children, this correlation was moderated by the degree of parental psychological control. Low levels of parental psychological control may serve as a protective factor to diminish the negative influences of a relative right frontal EEG asymmetry of parents on that of their children, whereas high levels of parental psychological control may act as a risk factor that exacerbates the positive effects of a relative left frontal resting EEG asymmetry of parents on that of the children. However, the degree of parental psychological unavailability does not moderate the relationship between parent-child frontal EEG asymmetry patterns. Accordingly, our results highlight the critical importance of parental psychological control in examining the link between parent-child frontal resting EEG asymmetry. Acknowledgements This project was funded by the National Natural Science Foundation of China (31500898), granted to the third author. Author Contributions: HW: designed and executed the study, analyzed the data, and wrote the paper. XM: collaborated with the design and writing of the study and assisted with data analyses. RH: designed the study, wrote the paper, and edited the final manuscript. YH: assisted with data analyses and paper writing. XL: assisted with data analysis and edited the final manuscript.

Compliance with Ethical Standards Conflict of Interest The authors declare that they have no conflict of interest. Ethics Approval The study procedures were approved by the Institutional Review Board (IRB) of Beijing Normal University. Informed Consent All participants provided written informed consent or minor assent.

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