Do executive functions predict change in forms of aggression in middle childhood
This study investigated concurrent and 2 year longitudinal relations between three executive functions (inhibition, working memory, and shifting) and forms of aggression in children. The Instrument of Proactive and Reactive Aggression (IRPA) was considered for applicability for measuring forms of aggression in middle childhood. The mean age of the sample (n 844) was 6.7 years at first assessment and 8.8 years at the final assessment. Neuropsychological test scores of executive functions and teacher report of aggression were obtained at both time points. The IRPA was examined through exploratory (EFA) and confirmatory factor analysis (CFA) growth of forms of aggression were regressed on executive functions. Unlike in the original study (Polman, de Castro, Thomaes, van Aken, 2009) CFA was not able to distinguish physical, verbal and covert forms, but a significant 2 factor solution consisting of physical and covert aggression was identified through revision of the instrument. Regression analysis revealed modest significant concurrent associations between the executive component working memory with physical aggression at first assessment, and with physical and covert aggression at the second assessment. Executive functions, however, did not predict change in any form of aggression. EXECUTIVE FUNCTIONS AND CHILDHOOD AGGRESSION 3 Do executive functions predict change in forms of aggression in middle childhood? Childhood onset aggression is associated with numerous adverse outcomes, including substance dependence, psychopathic traits, financial and work problems, mental health problems, and drug related and violent crime (Huesmann, Eron, Lefkowitz, Walder, 1984; Moffitt, Caspi, Harrington, Milne, 2002) Early interventions are recommended to prevent this maladaptation (Moffitt et al. 2002) Therefore, to inform the improvement of such interventions, it is important to strive to understand what causes early emerging aggression. However, as repeatedly shown, different forms of aggression, such as physical or covert aggression, may have different impact on maladjustment. Physical aggression is for example associated with externalizing problems, while covert aggression is associated with internalizing problems (Card, Stucky, Sawalani, Little, 2008; Murray Close Ostrov, 2009) Hence, as suggested by Card et al. (2008) and Murray Close and Ostrov (2009) different forms of aggression may have different precursors, i.e. direct physical aggression may have an etiology that differs from indirect and verbal aggression. Intervention efforts towards direct physical aggression may therefore profit from targeting other factors than interventions directed towards indirect verbal aggression. As it turns out, there is a lacuna of research addressing the possibility that the predictors of different forms of aggression may be different a gap of knowledge that will be addressed in the current research. Aggression is complex human behavior, and there is agreement that many factors probably interact in an intricate fashion. These factors can be environmental (Kimonis et al. 2006; Tremblay et al. 2004) psychological (Giancola, Mezzich, Tarter, 1998; Kimonis et al. 2006) and biological (Raine, 2002) including genetic (Craig Halton, 2009; Johansson et al. 2012) Forms of aggression Historically research on aggression has focused mainly on direct physical forms, whereas indirect aggression was introduced later as the manner in which girls expressed aggressive urges (Bjorkqvist, 1994) Indeed girls seem to be less physically aggressive than boys, while boys and girls both display similar amounts of relational aggression (Card et al. 2008) The use of verbal and covert forms are suggested to replace physical forms when social and verbal skills improve, and girls are suggested to precede boys in these skills and will therefore use these alternative forms earlier than boys (Bjorkqvist, 1994) The distinct gender distribution supports the validity of discrete aggressive forms. Forms of aggression also show stability over time (Murray Close Ostrov, 2009; Vaillancourt, Brendgen, Boivin, Tremblay, 2003) which further support their discreteness. EXECUTIVE FUNCTIONS AND CHILDHOOD AGGRESSION 4 Forms of aggression are usually divided into two factors. Although their names vary, they mainly refer to the same construct; a direct, physical form which also include overt verbal attacks, and an indirect covert and relational form (Card et al. 2008) Alternatively, aggression can also be divided into a physical, verbal and covert form (Bjorkqvist, 1994; Polman et al. 2009) Contradictive to dividing aggression into forms is the substantial intercorrelation between the forms. Average correlation is high .76) but there is considerable heterogeneity among effect sizes (Card et al. 2008) However, moderately high to high correlations do not disprove the usefulness of different forms of aggression, e.g. different components of intelligences are highly correlated, still it is meaningful to discern verbal intelligence from e.g. perceptual reasoning (WISC IV; Wechsler, 2003) In a similar fashion the division between forms of aggression is nevertheless argued to be relevant because of the statistical separateness of factors, the stability of the forms, and because the distinct forms are associated with unique properties and patterns of behavior (Card et al. 2008) As illustrated by the finding that children who exhibit different forms of aggression differ in regard to social dominance and gender (Murray Close Ostrov, 2009) In a similar vein, a meta analysis by Card et al. (2008) revealed a different pattern of maladjustment associated with the different forms of aggression. Specifically, direct aggression was related to externalizing problems, poor peer relations, and low prosocial behavior, whereas indirect aggression was related to internalizing problems and higher prosocial behavior. Thus, existing evidence concerning the outcome of direct versus indirect aggression supports the validity of the distinction. A substantial limitation is that most of the research on aggressive forms has been conducted with concurrent data, which means that we know little about causality (Card et al. 2008) Nevertheless it is plausible that the different forms of aggression have different antecedents (Ostrov, Murray Close, Godleski, Hart, 2013) Executive functions and aggression Executive functions (EFs) refer to a group of top down mental processes, which enable people to reach goals and solve problems, when automatic processes are insufficient. The different EFs combined constitute a regulation system (Diamond, 2013; Zhou, Chen, Main, 2012) There is general agreement that there are three core EFs: inhibition, working memory and set shifting; and that they show stability across time (e.g. Lehto, Juujarvi, Kooistra, Pulkkinen, 2003; Miyake et al. 2000) These EFs are also the ones considered here. Numerous authors have hypothesized that deficits in EFs are important correlates or risk factors for aggression. Different EFs may be differentially important for controlling EXECUTIVE FUNCTIONS AND CHILDHOOD AGGRESSION 5 aggressive impulses and for directing attention towards relevant stimuli that helps activate constructive feelings and behavior, and away from stimuli that activate uncomfortable aggressive impulses (Liew, 2012; Olson, Sameroff, Kerr, Lopez, Wellman, 2005) Furthermore, it has been suggested that aggression peak in adolescence because EFs and prefrontal brain development at this age are lagging behind environmental demands, and make the adolescent incapable of regulating powerful emotions, such as aggression (Raine, 2002) It has also been hypothesized that individual differences in aggression during the life course might partly be explained by variance in executive functioning, which interact with differences in environmental demands and social support (Raine, 2002) Unfortunately, there is little research considering longitudinal relationships between aggression and EFs in middle childhood. (Riggs, Blair, Greenberg, 2004; Seguin, Pihl, Harden, Tremblay, Boulerice, 1995) Several researchers have discovered concurrent associations between laboratory measures of EFs and aggression (e.g. Raaijmakers et al. 2008; Sprague, Verona, Kalkhoff, Kilmer, 2011) nevertheless, the results have varied, and there have also been examples of studies where no such associations were reported (Riccio, Hewitt, Blake, 2011) There are no meta analytic reviews considering the literature on aggression and EFs. However, reviews have been conducted on the relation between EFs and antisocial behavior (Morgan Lilienfeld, 2000; Ogilvie, Stewart, Chan, Shum, 2011) and aggression is often present in such antisocial behavior (American Psychiatric Association, 2013) In these reviews moderate effect sizes (i.e. d .44 to d= .62) were identified. This might indicate a connection between EFs and more grave types of aggression. The use of indirect aggression involves some level of theory of mind, which is the ability to consider other people's mental states. Theory of mind is associated with executive functioning (Hughes, 1998) It can therefore be assumed that indirect aggression demands a higher level of EF than physical aggression. Direct aggression is often triggered by an external cause, for instance being hit or insulted. This is not neccesarily the case with indirect aggression (Card et al. 2008) Thus, withholding direct aggressive urges when provoked may demand greater impulse regulation skills than when indirect aggression is at play (Baumeister Heatherton, 1996) Indeed, physical aggression is more related to emotional dysregulation and ADHD symptoms than indirect aggression (Card et al. 2008) which again are related to EFs (Barkley, 1997; Liew, 2012) Therefore it is reasonable to hypothesize that limited executiv