Cool and hot executive functions at 5 years old as predictors of physical and relational aggression between 5 and 6 years old

Abstract

To study the role of executive function (EF) in the early development of aggression, the role of cool and hot EF skills at 5 years old, in the development of physical and relational aggression between 5 and 6 years old, was explored. Typically developing children (N = 80) completed tasks assessing their cool (inhibition, working memory, planning) and hot EF (affective decision making, delay of gratification) skills at 5 years old. Longitudinal data were collected from teachers that rated children’s aggression when they were 5, 5.5, and 6 years old. Inhibition at 5 years old predicted changes in physical and relational aggression between 5 and 6 years old. Early cool EF, but not hot EF, may therefore be associated with aggression and inhibitory control specifically with changes in aggression during early childhood.

Keywords

Aggression executive function early childhood

Introduction

Models of social behavior, derived from social neuroscience literature, have suggested that executive function (EF) is fundamental to children’s social development (Beauchamp & Anderson, 2010; Yeates et al., 2007). ‘EF’ refers to the higher-order, cognitive skills required for goal-directed behavior (Goldstein, Naglieri, Princoptta, & Otero, 2014). These higher-order cognitive functions are mediated by the pre-frontal cortex and provide control and direction to lower-order brain functions (Stuss & Levine, 2002). In the literature, a conceptual distinction is commonly made between ‘cool’ and ‘hot’ executive functions (Zelazo & Müller, 2002). Cool EF is associated with the dorsolateral pre-frontal cortex and includes cognitive processes such as inhibition, working memory, and planning, which are involved in abstract, emotionally neutral problems. Hot executive functions are mediated by the ventromedial and orbito-frontal cortices, which support affective processes (e.g., ability to delay gratification, affective decision making) and are tapped by emotion-laden problems (Zelazo & Müller, 2002). The view posed by social neuroscience models and held by many researchers is that children with poor EF abilities may be less able to inhibit maladaptive behaviors and adapt to novel social situations, and as a result these children may mismanage social interactions leading to peer-directed aggression (Anderson, 2008; Astington, 2003). Therefore, a persisting question over the last decade has been whether subtle cognitive problems in early EF precede aggression, and contribute to its onset and development.

There is a substantial body of evidence that poor cool EF, particularly inhibition, is related to increased aggression during childhood (Masten et al., 2012; Poland, Monks, & Tsermentseli, 2016; Utendale, Hubert, Saint-Pierre, & Hastings, 2011). However, this research often fails to consider the varied nature of aggression. Aggression is argued to comprise distinct subtypes (Dodge, 1991; Dodge & Coie, 1987; Grotpeter & Crick, 1996). Aggression can be physical (e.g., hitting), verbal (e.g., name calling), or relational (e.g., social exclusion; Crick, Casas, & Ku, 1999; Ostrov & Crick, 2007), and these forms of aggression can be used to achieve reactive or proactive functions (Dodge & Coie, 1987). However, the utility of this distinction between functions has been called into question as aggression may serve both a reactive and proactive function (Bushman & Anderson, 2001). In contrast, distinct forms of physical and relational aggression have been widely supported in the literature, and these forms of aggression have been associated with varying underlying cognitive factors, such as deception (Ostrov, 2006; Ostrov & Godleski, 2010).

EF is not a unitary construct, and hence different aspects of EF might relate to different types of aggression. In line with this, emerging evidence has indicated that poor EF is associated with physical, but not relational, aggression in children between 6 and 17 years of age (Dane & Marini, 2014; Terranova, Morris, & Boxer, 2008). However, a study of 9–12 year olds also reported that poor EF was related to both physical and relational aggression (McQuade, Murray-Close, Shoulberg, & Hoza, 2013), but only one cool EF skill—working memory—was considered. Although it has been hypothesized that social problem-solving is likely to occur in motivationally and emotionally significant environments and consequently may require hot EF (Zelazo & Müller, 2002), research into the role of hot EF in aggression has not been adequately investigated. The few studies that have been carried out have found mixed results, with some finding a negative relation between hot delay of gratification and aggression in 2–5-year-old children (Di Norcia, Pecora, Bombi, Baumgartner, & Laghi, 2015; Garner & Waajid, 2012; Kim, Nordling, Yoon, Boldt, & Kochanska, 2014), and other research failing to find a relationship beyond that of cool EF in children 3–6 years of age (Willoughby, Kupersmidt, Voegler-Lee, & Bryant, 2011). However, these studies did not consider subtypes of aggression. One study did look at the role of hot EF across forms of aggression, but failed to find a relation (Poland et al., 2016). Further investigation of the relations between EF domains and subtypes of aggression is therefore crucial, as it may provide a greater insight into the varied nature of aggression.

Understanding of the development of subtypes of aggression is further limited by the fact that the majority of previous research looking at the relation between EF and aggression in typically developing children (e.g., Garner & Waajid, 2012; Hughes, White, Sharpen, & Dunn, 2000; Willoughby et al., 2011) has been carried out at one time point and longitudinal associations were not assessed. The only prospective longitudinal study, to date, followed children from 3 to 6 years of age and revealed that children’s cool and hot inhibition significantly predicted children’s concurrent, but not later aggression (Olson, Lopez-Duran, Lunkenheimer, Chang, & Sameroff, 2011). However, this study did not take into account the other EF sub-domains or forms of aggression. Forms of aggression have been found to follow varying trajectories. Children’s use of physical aggression tends to decline with age and rates of relational aggression typically increase across early to middle childhood (Björkqvist, Ősterman, & Kaukiainen, 1992; Gray, Carter, Briggs-Gowan, Jones, & Wagmiller, 2014; Monks, Smith, & Swettenham, 2003). Exploring specific cognitive predictors of the development of forms of aggression may therefore increase understanding of the underlying mechanisms for these varied pathways.

If EF contributes to aggression, then from a developmental perspective identifying whether EF is an underlying mechanism for change in aggression across childhood is not just beneficial for understanding the development of aggression but also for intervening. Criminology literature has suggested that “impulsivity” (a concept related to poor inhibition) in childhood is associated with later aggressive criminal behavior in adolescence and adulthood (Farrington, 2005; Murray, Irving, Farrington, Colman, & Bloxsom, 2010), suggesting that cognitive development in childhood may have lasting developmental effects. Early childhood is an important period in the development of EF. It is in this period EF abilities undergo rapid advances, consistent with the ongoing development of the prefrontal cortex (P. J. Anderson, 2008; V. Anderson, P. J. Anderson, Jacobs, & Spencer-Smith, 2008). Thus, early childhood represents a sensitive period in the evaluation of individual differences in EF and their contribution to social development. EFs are thought to be necessary for adequate social development and as a result, disruptions in early EF development may influence the emergence and expression of social behaviors across childhood (Beauchamp & Anderson, 2010). Deficits in children’s EF have been found to disrupt children’s social skills development, reducing their repertoire of socially appropriate behaviors for use in interactions with their peers (Eisenberg et al., 1995) and affecting their standing with them (Tseng & Gau, 2013). Poor EF abilities in early childhood may therefore disrupt children’s social development and have a lasting influence on social behavior, such as aggression, across childhood.

Examining gender differences in the development of social behaviors, such as aggression, is also important in order to identify patterns of development specific to each gender (Ostrov & Godleski, 2010). According to the results of a meta-analysis, physical aggression is more common in boys whereas relational aggression is more typical of girls (Card, Stucky, Sawalani, & Little, 2008). However, gender differences in relational aggression may be more prominent during adolescence (Archer, 2004). This may be reflective of differences in the organization of girls’ and boys’ peer groups. Girls tend to form smaller, more exclusive peer groups than boys (Lagerspetz, Bjorkqvist, & Peltonen, 1988). The development of aggressive behavior may consequently vary for boys and girls. Added to this, girls have also been found to exhibit greater EF skills (Gur et al., 2012). The role of cognitive abilities in aggression may therefore vary across genders, especially in early childhood when EF is rapidly developing.

Given that early childhood is a period of rapid growth in EF and that existing findings suggest that EF may play a role in the development of different types of aggression, the current study examined the role of early cool and hot EF skills at 5 years old in the development of physical and relational aggression between 5 and 6 years old, in order to identify whether early EF represents an underlying mechanism for change in aggression. Children’s EF at 5 years old was measured because this is at the end of the rapid period of EF development in early childhood (P. J. Anderson, 2008; V. Anderson et al., 2008). This study therefore aimed to build upon current research that has found an association between EF and aggression concurrently (Masten et al., 2012; Poland et al., 2016), and research that has found early cognitive abilities influence pathways of aggressive behavior (Farrington, 2005; Murray et al., 2010) by examining whether early cool and hot EF skills differentially influence the developmental trajectories of subtypes of aggression across early childhood. Early childhood is a period where children are old enough to have a high probability of demonstrating individual differences in EF and aggression, but still young enough that any detected differences could not be attributed to prolonged aggression. The age span adopted in this study therefore enables a short-term longitudinal evaluation of the predictive value of any cognitive risks identified to be explored. Further, children at this age are able to participate in the relatively lengthy and difficult assessment batteries required to evaluate a range of EF abilities. It was tentatively hypothesized that poorer cool EF, especially inhibition, would be associated with increasing physical aggression during early childhood due to the link between impulsive behavior and aggression in young children (Dane & Marini, 2014; Poland et al., 2016). Further, it was tentatively hypothesized that poorer hot EF would predict relational aggression due to the more affective nature of relational aggression.

Methods

Participants

Eighty children (40 boys and 40 girls) from two mainstream primary schools in the United Kingdom were recruited to participate in the current study from a larger sample of 106 children between 3 and 6 years of age. The subsample was selected based on child age (5 years old) and having an aggression measure at all three time points. The schools from which children were recruited were comparable on the percentage of pupils receiving free school meals: 26.6% and 24.7%. At initial recruitment, children were 5 years old (M = 58.8 months, SD = 6.66 months). At initial recruitment children were selected from four nursery classes and two reception classes. Exclusionary criteria included a mental health diagnosis (e.g., attention deficit hyperactivity disorder, autism spectrum disorder, conduct disorders) or a learning disability. The children were assessed at three time points during the course of 12 months: initial recruitment, 6 months later, and 12 months after the initial time point. At the second time point, 73 children were followed up (9% attrition); and at the third time point, 72 children were followed up (1% attrition). Attrition was due to children no longer attending the school. At the second time point, children had a mean age of 64.65 months (SD = 7.20 months); and at the third time point, children’s mean age was 71.36 months (SD = 7.17 months). The Class Teachers (N = 16) and Teaching Assistants (N = 23) of the children involved in the study were also recruited to participate. All children were evaluated by one teacher and at least one teaching assistant. The maximum number of teaching assistants providing a score for one child was 3.

Measures

EF. Three cool EF skills were assessed at the first time point: inhibition, working memory, and planning. Children completed a computerized Fish and Shark Go/No-Go task to measure their inhibitory control (Simpson & Riggs, 2006). Children were required to catch the fish by pressing a button on the response pad (Go trials), but to avoid catching the sharks by withholding pressing the button (No-Go trials). Feedback was provided for correct and incorrect responses. Each child first completed six practice trials (three Go and three No-Go trials) and then 40 test trials (30 Go and 10 No-Go trials). The proportion of correct No-Go trials was measured.

To assess children’s working memory, the Digit Span forward and backwards subtests (Wisconsin Intelligence Scale for Children III; Wechsler, 1991) were used. The forward subtest involves recalling a series of number sequences (increasing from two to nine digits) in the same order as spoken. The backward subtest involves recalling a series of number sequences (increasing from two to eight digits) in reverse order. Although the Digit Span was initially designed for use with children between six and 16 years of age, it has been successfully used with children five years old and below (Alloway, Gathercole, Kirkwood, & Elliott, 2008; Bull, Espy, & Wiebe, 2008). Children were awarded 1 point for each correct trial. Scores from the forward and backward subtest were summed and potential scores ranged from 0 to 30.

Children’s planning skills were measured using the Tower of London test (Shallice, 1982). Children first completed two 2-move practice problems, before completing 12 test problems ranging from two to five moves (Shallice, 1982). Each trial lasted a maximum of 2 min and up to two attempts at each problem was allowed (Hughes, Dunn, & White, 1998; Monks, Smith, & Swettenham, 2005). The task ceased after the child completed the problem set or failed two consecutive problems. Children were awarded 2 points if they completed the problem on the first trial, 1 point if they took two attempts, and 0 points if they failed to complete the problem in two trials. Potential scores ranged from 0 to 24.

Two hot EF skills were assessed at the first time point: affective decision making and delay of gratification. A modified version of the Children’s Gambling Task developed by Kerr and Zelazo (2004) was used to measure children’s affective decision making (Poland et al., 2016). Children were instructed to select cards from one of two decks. When turned the cards revealed happy faces, corresponding to the number of beads won, and sad faces, representing the number of beads lost. There was an advantageous deck which resulted in a net win of five beads per 10 cards and a disadvantageous deck which resulted in a net loss of 5 beads per 10 cards. There were six demonstration trials and 50 test trials. At the end of the task, children could trade their beads for stickers. Affective decision making was assessed on whether predominately advantageous or disadvantageous decisions were made across the last three trial blocks (Poland et al., 2016).

To assess children’s ability to delay gratification, the Gift Delay task was used (Kochanska, Murray, Jacques, Koenig, & Vandegeest, 1996). Each child was instructed not to peek while the researcher pretended to wrap them a gift. The researcher wrapped the gift in a standardized manner: rifling through a plastic bag, cutting wrapping paper with scissors, folding the paper and tearing off the tape for 60 s. Children scored 2 points if they did not turn around, 1 point if they peeked over their shoulder, and 0 points if they turned around completely. At each time point, the range of gifts was altered in order to maintain task novelty.

Verbal ability. At Time 1, the short version of the British Picture Vocabulary Scale (BPVS; Dunn, Whetton, & Pintilie, 1982) was used to assess children’s receptive vocabulary. The BPVS requires the child to select the picture (from four options) that best matches a word. Standardized scores according to age were used.

Aggression. Teacher reports of children’s aggression were gathered at each of the time points. Class teachers and teaching assistants completed the 12-item Preschool Proactive and Reactive Aggression Scale (PPRA) for each child in their class participating in the study (Ostrov & Crick, 2007). The PPRA has four subscales, with three items for each: proactive physical aggression (e.g., this child often threatens others physically to get what s/he wants); reactive physical aggression (e.g., if other children make this child mad, s/he will often physically hurt them); proactive relational aggression (e.g., to get what this child wants, s/he often tells others that s/he won’t be their friend anymore); and reactive relational aggression (e.g., if other children hurt this child, s/he often keeps them from being in their group of friends). Teaching staff rated how true each statement was of the child on a 5-point Likert scale, ranging from 1 (never or almost never true) to 5 (always or almost always true). Teacher and teaching assistant ratings for each subscale were averaged.

Teacher and teaching assistant scores were averaged to provide an overview of children’s aggression inside and outside the classroom; children had different informants and a varying number of informants. Teacher and teaching assistant ratings were significantly and positively correlated between these informants, indicating adequate agreement (correlations based on sample of 106 children: proactive physical aggression, r = 0.51, p = <0.001; reactive physical aggression, r = 0.67, p = <0.001; proactive relational aggression, r = 0.42, p = <0.001; reactive relational aggression, r = 0.39, p = <0.001). The PPRA has been found to have good internal consistency (proactive physical aggression, α = 0.88; reactive physical aggression, α = 0.92; proactive relational aggression, α = 0.88; reactive relational aggression, α = 0.82; Ostrov & Crick, 2007). However, in the current study, functions of aggression were positively and significantly correlated (proactive and reactive physical aggression, r = 0.90, p = <0.001; proactive and reactive relational aggression, r = 0.95, p = <0.001), indicating that in the present sample the measure was not able to adequately distinguish between functions of aggression. The scales were therefore collapsed into physical and relational forms of aggression in the present study.

Procedure

The current study received ethical approval from the University’s Research Ethics Committee. Informed consent was obtained from teaching staff and primary caregivers of children participating in the research. This was a longitudinal study that began in April 2014 and finished in July 2015. There were three time points, approximately 6 months apart. At the first time point, when children were aged 5 years old, cool and hot EF skills were assessed. Children completed the tasks individually with the researcher in a quiet room at their school. The tasks were spread over three sessions that each lasted between 20 and 45 min. Children completed the tasks in a fixed order at each time point. Session 1: BPVS and Children’s Gambling Task; Session 2: Tower of London, Digit Span, and Go/No-Go; Session 3: gift wrap. At each time point, teacher reports of children’s aggressive behavior were obtained.

Results

Descriptive statistics for EF and aggression are reported in Table 1 and correlations between variables are reported in Table 2. Two 2-level hierarchical linear mixed model analyses were undertaken to test for the effect of EF at 5 years of age on physical and relational aggression and on changes in physical and relational aggression between 5 and 6 years of age. The models contained either physical or relational aggression as the dependent variable and selected cool and hot EF variables (see below), with age, gender, and verbal ability as explanatory variables. The models allowed repeated measures for each child to be correlated by fitting random intercepts that varied at the level of each individual. Residual plots were used to check normality assumptions and the final generalized linear mixed models were fitted by maximum likelihood. Time was entered as a continuous predictor and interactions between time and EF skills were included to test for the effect of EF skills on changes in aggression over time. Hierarchical modeling was implemented with SPSS Mixed Models, Version 24.

Table 1.

Mean and SD for executive function and aggression variables.

	Time 1		Time 2		Time 3
	M	SD	M	SD	M	SD
Physical aggression	3.56	1.64	3.53	1.73	3.19	1.75
Relational aggression	4.40	1.52	3.61	1.55	3.48	1.88
Inhibition	0.82	0.22	—	—	—	—
Working memory	6.45	2.78	—	—	—	—
Planning	4.56	4.35	—	—	—	—
Decision making	−0.03	0.44	—	—	—	—
Delay of gratification	1.43	0.80	—	—	—	—
Verbal ability	96.64	16.95	—	—	—	—

Note. N = 80. Range of physical aggression scores: Time 1 = 2.0–8.67; Time 2 = 2.0–9.17; Time 3 = 2.0–9.83. Range of relational aggression scores: Time 1 = 2.0–8.08; Time 2 = 2.0–9.33; Time 3 = 0–8.50. Range of measures of EF scores: Inhibition = 0.11–1.0; Planning = 0–18; Working memory = 0–13; Decision making = −1.0–1.0; Delay of gratification = 0–2.

M: mean; SD: standard deviation; EF: executive function.

Table 2.

Correlations between executive function skills and physical and relational aggression.

	1	2	3	4	5	6	7	8	9	10	11	12
1. Gender	—	0.22*	0.05	0.10	0.05	0.25*	−0.30**	−0.25*	−0.32**	0.13	−0.14	−0.06
2. Inhibition		—	0.33**	0.14	0.11	0.43***	−0.46***	−0.06	−0.10	−0.22*	0.14	0.12
3. Working memory			—	0.26**	−0.04	0.106	−0.18	0.07	0.02	−0.07	0.14	0.24*
4. Planning				—	0.12	0.23*	−0.28**	-0.24*	−0.25*	−0.32**	-0.15	−0.12
5. Decision making					—	−0.04	0.10	0.04	−0.03	−0.01	0.08	0.07
6. Delay of gratification						—	−0.33**	−0.10	−0.19	−0.19	0.06	0.07
7. T1 Physical aggression							—	0.33**	0.36**	0.62***	0.25*	0.22*
8. T2 Physical aggression								—	0.81***	0.15	0.79***	0.67***
9. T3 Physical aggression									—	0.16	0.74***	0.73***
10. T1 Relational aggression										—	0.21*	0.27**
11. T2 Relational aggression											—	0.75***
12. T3 Relational aggression												—

Note. N = 80.

* p < 0.05, **p < 0.01, ***p < 0.001.

To test whether EF skills at 5 years of age predicted changes in physical or relational aggression between 5 and 6 years of age, we included all EF skills that correlated with either physical or relational aggression at 5 years of age in hierarchical linear mixed models. For physical aggression these were inhibition, planning, and delay gratification. For relational aggression these were inhibition, planning, and working memory. Gender and verbal ability were also included as covariates. The results of the hierarchical linear mixed models are reported in Table 3.

Table 3.

Estimated effects of executive function skills and covariates on changes in physical and relational aggression.

	Physical aggression				Relational aggression
	B (SE)	95% CIs	t (df)	p	B (SE)	95% CIs	t (df)	p
Time	−1.49 (0.39)	−2.26, −0.72	−3.82 (155)	<0.001	−1.77 (0.41)	−2.59, −0.96	−4.30 (151)	<0.001
Gender	0.79 (0.29)	0.22, 1.36	2.77 (79)	0.007	0.02 (0.28)	−0.53, 0.57	0.08 (78)	0.937
Age	0.04 (0.02)	−0.01, 0.08	1.71 (78)	0.092	0.04 (0.02)	−0.01, 0.09	1.66 (77)	0.101
Verbal ability	−0.00 (0.00)	−0.02, 0.02	−.13 (82)	0.894	0.00 (0.01)	−0.01, 0.02	0.57 (80)	0.567
Planning	−0.09 (0.05)	−0.20, 0.02	−1.62 (223)	0.107	−0.12 (0.06)	−0.24, −0.01	−2.13 (233)	0.034
Delay	−0.10 (0.33)	−0.74, 0.55	−0.31 (224)	0.754	—	—	—	—
Memory	—	—	—	—	−0.07 (0.08)	−0.26, 0.12	−0.72 (233)	0.469
Inhibition	−3.65 (1.22)	−6.06, −1.23	−2.98 (223)	0.003	−2.01 (1.21)	−4.39, 0.38	−1.65 (233)	0.099
Time*Planning	0.00 (0.02)	−0.04, 0.05	0.07 (154)	0.944	0.01 (0.03)	−0.04, 0.06	0.445 (151)	0.657
Time*Delay	−0.06 (0.14)	−0.33, 0.20	−0.48 (151)	0.632	—	—	—	—
Time*Memory	—	—	—	—	0.07 (0.04)	−0.01, 0.15	1.78 (151)	0.077
Time*Inhibition	1.64 (0.51)	0.62, 2.65	3.18 (157)	0.002	0.99 (0.49)	0.01, 1.96	2.00 (151)	0.047

Note. B: unstandardized beta; SE: standard error; CI: confidence interval; t (df): t-distribution, degrees of freedom; p: p-value.

N = 78.

*interaction term.

Physical aggression. Time was associated with physical aggression, indicating reductions in physical aggression between 5 and 6 years of age (B = −1.45, 95% CI: −2.26, −0.72; t (df) = −3.82 (155); p < 0.001). Gender was associated with physical aggression, with boys being more physically aggressive than girls (B = 0.79, 95% CI: 0.22, 1.36; t (df) = 2.77 (79); p = 0.007); however, age and verbal ability were not significantly associated with physical aggression. Neither planning nor delay gratification were significant predictors of physical aggression, and did not moderate the effect of time on the development of physical aggression. Inhibitory control significantly predicted lower physical aggression (B = −3.65, 95% CI: −6.06, −1.23; t (df) = −2.98 (223); p = 0.003) and the interaction between time and inhibitory control was significant (B = 1.64, 95% CI: 0.62, 2.65; t (df) = 3.18 (157); p = 0.002).

To explore the interaction between inhibition and physical aggression, this relation over time was plotted (see Figure 1). Children at least 1 SD below the mean for inhibition were categorized as being low in inhibition, and children at least 1 SD above the mean were categorized as being high in inhibition. The remaining children were classed as average in inhibition. The figure indicates that the lower a child’s inhibition, the greater their physical aggression between 5 and 6 years old. However, the effect of inhibition on physical aggression appears to reduce between 5 and 6 years of age.

Figure 1.

Mean physical aggression across time points for children categorized as low (n = 15), average (n = 33) and high (n = 32) in Inhibition.

Relational aggression. Time was associated with relational aggression, indicating reductions in relational aggression between 5 and 6 years of age (B = −1.77, 95% CI: −2.59, −0.96; t (df) = −4.30 (151); p < 0.001). Neither gender, age, verbal ability, working memory, nor inhibitory control were significantly associated with relational aggression. Planning did predict lower relational aggression (B = −0.12, 95% CI: −0.24, −0.01; t (df) = −2.13 (233); p = 0.03) but did not predict changes in relational aggression over time. The interaction between time and inhibitory control was significant (B = 0.99, 95% CI: 0.01, 1.96; t (df) = 2.00 (151); p = 0.047). To explore this interaction, the relationship between inhibition and relational aggression was plotted over time (see Figure 2). The figure indicates that similar to physical aggression, inhibition appears to have a greater effect on relational aggression at 5 years old than at 6 years old. At 5 years old, children with low inhibition demonstrated higher relational aggression than children with high inhibition, but at 6 years old, low and high inhibition groups had similar levels of relational aggression.

Figure 2.

Mean relational aggression across time points for children categorized as low (n = 15), average (n = 33), and high (n = 32) in inhibition.

Discussion

This study examined the role of cool and hot EF skills in changes in physical and relational aggression between 5 and 6 years old in order to increase understanding of individual differences in the development of aggression. The present research revealed three main findings:

Poorer cool inhibition at 5 years old predicted higher physical and relational aggression between 5 and 6 years old.

Planning at 5 years old was negatively associated with relational aggression.

Gender was associated with physical aggression, with boys being higher in physical aggression compared to girls.

The current study therefore indicated that early cool inhibition may influence the development of subtypes of aggression between 5 and 6 years old. Hot EF skills, in contrast, were not associated with the development of physical or relational aggression between 5 and 6 years old.

In accordance with the findings of prior research (Alink et al., 2006; Nærde, Ogden, Janson, & Zachrisson, 2014), physical aggression showed age-related declines between 5 and 6 years old. This decline in physical aggression may reflect the fact that during this age period most children learn to control their behavior and regulate their anger, develop a theory of mind, and become empathic (e.g., Hoffman, 2000; Sroufe, 1996; Wellman, 1990). As a result, children learn to respond in a socially acceptable way instead of acting aggressively. In addition, the exponential growth in children’s language skills that takes place in early childhood may contribute to the decline in prevalence of physical aggression (Tsao, Liu, & Kuhl, 2004). Relational aggression also showed age-related declines between 5 and 6 years old, which may similarly reflect children’s developing behavioral and emotional control (Hoffman, 2000; Housman, 2017). However, with children’s developing understanding of the mind and language skills, they may move from using direct relational aggression (as assessed in this study) to more indirect, covert relational aggression (Björkqvist et al., 1992).

Boys demonstrated higher physical aggression than girls. This is line with the extensive literature that has found that boys rely on physical aggression more than girls (Card et al., 2008; Crick & Grotpeter, 1995; Hay et al., 2011; Lussier, Corrado, & Tzoumakis, 2012; Yuan et al., 2014). The present study, however, failed to find gender differences in relational aggression. However, a study of children 9–15 years of age found that gender differences in relational aggression are not apparent until around 10–11 years of age, with girls being rated as higher in relational aggression (Smith, Rose, & Schwartz-Mette, 2009). Thus, gender difference in physical aggression may be apparent earlier on than in relational aggression.

In line with prior studies (Poland et al., 2016; Utendale et al., 2011), cool inhibition at 5 years old predicted physical aggression. Children with poor inhibition may be less able to regulate their impulsive behavior, frustration and anger (V. Anderson et al., 2008), and as a result may be unable to withhold using a physically aggressive act. Added to this, poor cool planning at 5 years old was associated with higher relational aggression, expanding prior research that has suggested planning is associated with social behavior more broadly (Jacobson,Williford, & Pianta, 2011). When confronted with situations that provoke relational aggression, children with poor planning skills may be less able to generate non-aggressive strategies in their interactions with peers. Relational aggression in early childhood is typically much more direct in nature (Monks et al., 2003). This may be due to the fact that indirect aggression is a more cognitively sophisticated form of aggression (Björkqvist et al., 1992). Children with particularly low planning ability may consequently rely on direct relational aggression to a greater extent; therefore, this may be more noticeable to teachers.

This research extends prior studies that have highlighted the central role of inhibition (Poland et al., 2016; Utendale et al., 2011). The current results suggest that inhibition at 5 years old predicts changes in physical and relational aggression between 5 and 6 years of age. Children with low inhibition continued to show higher levels of physical aggression than children with high inhibition between 5 and 6 years old, although this effect attenuated with time. This supports the view that early impulsive behavior may influence the development of physically aggressive behavior (Farrington, 2005). EF undergoes rapid development during early childhood (V. Anderson et al., 2008; Wellman, Cross, & Watson, 2001), with inhibition being one of the first EF abilities that children reach proficiency in childhood (Smidts, Jacobs, & Anderson, 2004; Tillman, Brocki, Sørensen, & Lundervold, 2015). This early development in inhibition may set the foundation for children’s emerging aggressive behavior. Poor inhibition may lead to limited or poor quality peer interactions that serve to disrupt children’s social skills development, reducing their repertoire of socially appropriate behaviors for use in interactions with their peers (Eisenberg et al., 1995). Indeed, children who were highly aggressive demonstrated externalizing personality patterns across childhood and adulthood; that is, they reported more conflictual relationships with their mother and partners, underachieved academically and occupationally, and engaged in higher delinquency (Asendorpf, Denissen, & van Aken, 2008). Poor inhibition may therefore have a continued effect on social development through its impact on children’s social interactions. Poor inhibition in early childhood may consequently represent a risk factor for poor social development, and may be a prime target for early intervention.

Inhibition was also associated with changes in relation aggression. Children with low inhibition showed higher relational aggression than children with high inhibition at 5 years old, but showed a much steeper decline in relational aggression between 5 and 5.5 years old. By 6 years old, there appeared to be little difference in relational aggression levels across low, average, and high inhibition groups. In typically developing children, EF may be more strongly related to relational aggression during the transition to school. With the transition to school (which occurs around 4 years of age in the UK), children begin to interact with their peers, and their verbal skills increase as well as their social understanding (Hughes, 2011), which may allow children to understand how to use aggression to manipulate relationships. Children who therefore have the necessary social understanding to use proactive aggression and lack the planning abilities to generate alternative strategies, or the impulse control to withhold aggression, may consequently engage in higher proactive aggression. In early childhood, relational aggression is likely to be more direct and unsophisticated (e.g., telling a peer you won’t play with them) (Crick et al., 1999) and may consequently be associated with negative consequences, such as punishment by teachers or peer rejection (McNeily-Choque, Hart, Robinson, Nelson, & Olsen, 1996). This may result in children who lack the inhibition to withhold aggression to switch to the more indirectly aggressive behaviors as they gain the cognitive and verbal abilities to do so (Björkqvist et al., 1992). This hypothesis, however, needs to be further investigated.

The finding that inhibition predicts the development of aggression is in agreement with research conducted with adult samples. Research with adults has suggested that individuals with low inhibition are unable to inhibit aggression due to their failure to use inhibition feedback cues to regulate their behavior (Hoaken, Shaughnessy, & Pihl, 2003). Consequently, it may be that individuals with poor inhibition, who demonstrate poor social information processing, and an inability to cope with overwhelming response options, fail to access more socially appropriate response options and instead make default aggressive responses. From a neuropsychological theoretical perspective, the inhibitory control model suggests that violence and aggression in frontally impaired patients results from their inability to inhibit their aggressive impulses (Barratt, 1994; Séguin, 2009). In support of the inhibitory control model, there is evidence that individuals who engage in antisocial, aggressive, and criminal behavior demonstrate impaired inhibition (Farrington, 2005). Further, more recently there has been a move in research focus to identifying the factors underlying the joint development of neuropsychological function (such as impulsivity) and aggression (Séguin, 2009). This work has suggested that the link between physical aggression and hyperactivity problems and neuropsychological function can be identified early in childhood (Séguin & Zelazo, 2005). The present study indicates this may also be the case for relational aggression. Added to this, maternal prenatal smoking predicts both increased physical aggression and hyperactivity in young children (Huijbregts, Séguin, Zoccolillo, Boivin, & Tremblay, 2007). Poor inhibition and aggressive behavior may therefore go hand in hand, and this relationship may be evidenced early on in a child’s life.

In contrast to prior studies that have indicated hot EF is related to disruptive and aggressive behavior (Garner & Waajid, 2012; Kim et al., 2014), hot EF skills at 5 years old did not predict changes in physical or relational aggression between 5 and 6 years old. The lack of a significant relation between hot EF and aggression may reflect the fact that the present study focused on early childhood, whereas previous research has focused on middle childhood to adolescence. EF skills follow varying trajectories of development, with inhibition being one of the first EF abilities that children reach proficiency in childhood (Smidts et al., 2004; Tillman et al., 2015). Due to its early development, inhibition may therefore influence aggression during early childhood. Hot EF has been posited to follow a more protracted developmental course than cool EF, with more marked changes occurring around 14–15 years old (Prencipe et al., 2011). During early childhood, children show limited advancement in hot EF abilities (O’Toole, Monks, & Tsermentseli, 2017) and as a result, hot skills have not been formed yet and therefore may not be related to aggression. Indeed, Willoughby et al. (2011) also failed to find an association between hot EF and aggression in young children. Hot EF may therefore play a more central role in aggression in later childhood and adolescence.

Limitations

This study made novel contributions to current understanding of the development of the different forms of aggression across early childhood. The findings of this study, however, should be considered in light of the following limitations. EF was assessed at 5 years old only. EF undergoes rapid development during early childhood (V. Anderson et al., 2008) and therefore understanding the links between the developmental advances in EF skills and changes in aggression would further add to current understanding of the development of aggression. The relatively small sample size may have reduced the power of the models, and as a result relations between some EF abilities and aggression may not have been detected. This research provides a first exploratory look at the role of early EF in the development of forms of aggression, and findings therefore need to be corroborated with larger samples. Further, the fact that EF was assessed at Time 1 only, and the sample size was relatively small, meant that indirect and bidirectional relations between EF and aggressive subtypes could not be examined. Future studies that explore the relation between developmental trajectories of EF and aggression would therefore be beneficial. Lastly, the study included forms, but not functions, of aggression. The underlying cognitive factors of physical and relational aggression may vary depending on their function (Poland et al., 2016). However, as found in the present study, differentiating between functions of aggression is challenging. Research directed toward developing methods of distinguishing between functions of aggression in young children, combined with exploring the development of functions and forms of aggression, is needed.

Conclusions and Directions for Future Research

This study suggests that early cool inhibition plays a central role in the development of both physical and relational aggression between 5 and 6 years old, indicating children’s early inhibition may have a lasting influence on their social development. Targeting inhibition in interventions, especially during early childhood, at a time when there is particular growth in EF may be beneficial in reducing later aggressive behavior. The present study included a relatively short follow-up period of one year. Future research examining the influence of early inhibition on aggression across a broader age range will therefore increase understanding of its underlying role in changes in aggression. The present study revealed that hot EF was not associated with the development of physical or relational aggression. There is much debate around whether distinct cool and hot EF domains are evident (O’Toole et al., 2017) and few assessments of hot EF skills are currently available. An important aim for research going forward is therefore to elucidate models of cool and hot EF and develop more developmentally appropriate measures of hot EF to assess its links to behavior. Studying the developmental trends of hot and cool EF, and their longitudinal associations to other cognitive abilities, such as theory of mind, may aid in gaining a greater understanding of the link between cognition and behavior in typical and atypical development.

Footnotes

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

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