Executive Functions and Externalizing Symptoms: Common and Unique Associations
In discussing the four papers in this special issue, we provide our perspective on the authors’ contributions and suggest directions for future research. First, we highlight the usefulness of the bi-factor model for investigating relations among specific aspects of executive functions (EFs) and externalizing symptoms. Next, we examine the role of EFs as a protective factor that can moderate the relation between risk factors – specifically, callous-unemotional behaviors – on externalizing symptoms. And finally, we address the contributions of innovative measurement approaches to understanding the relations between EFs and externalizing symptoms, using the state-space grid methodology as an example.
KeywordsExecutive functions Externalizing symptoms Working memory Bi-factor model Callous-unemotional State space grid
Executive functions (EFs) are an aspect of self-regulation that play a role in positive adaptation across a variety of different domains that include, but are certainly not limited to, mental health. There is already a staggering amount of scholarship documenting relations between EFs and externalizing symptoms in children. Nonetheless, the four papers included in this special section demonstrate that much is still unknown. In discussing these papers, we illustrate some of the important directions for future research. Notably, we address three main questions: (1) Does the strength of the relation between EFs and externalizing symptoms differ depending on the subdomain of either construct? (2) Does the relation between EFs and externalizing symptoms hold equally across all individuals, or is the relation between EFs and externalizing symptoms stronger or weaker depending on child characteristics? (3) What are some measurement approaches and research designs that have the potential to advance our understanding of the relation between EFs and externalizing symptoms?
Previous research has revealed robust relations between executive functions (EFs) and externalizing symptoms (e.g., Ogilvie et al. 2011). Yet EFs and externalizing symptoms are both multi-dimensional constructs, and the associations between specific EF skills and specific subtypes of externalizing symptoms remain unclear. Researchers have examined whether EF deficits differ between diagnostic groups such as ODD/CD, ADHD, and co-occurring ODD/CD + ADHD (Oosterlaan et al. 2005) or whether specific EFs (e.g., inhibitory control, working memory, and cognitive flexibility) are more strongly associated with externalizing symptoms than others (Schoemaker et al. 2013). But previous studies have largely ignored the overlap among different EF skills and among different types of externalizing symptoms.
The bi-factor model can advance our understanding of how different aspects of EFs are related to externalizing symptoms by separating these multi-dimensional constructs into common and unique variance components. Doing so enables us to test whether the unique variance components have predictive validity, net of their overlap with the common variance component. Huang-Pollock et al. (2017) and Lonigan et al. (2017) both used the bi-factor model to describe the structure of externalizing symptoms and examine whether EFs are related to externalizing symptoms “in general” (i.e., the common factor) and whether EFs are related to specific factors of externalizing symptoms beyond what is shared with the common factor.
Specifically, Huang-Pollock et al. (2017) used the bi-factor model to identify a common externalizing factor and three factors that were specific to inattention, hyperactivity, and ODD symptoms. They reported that working memory was associated with the common externalizing factor. Similarly, Lonigan et al. (2017) applied a bi-factor model and found three analogous specific factors (i.e., inattention, hyperactivity, and ODD symptoms). Like Huang-Pollock et al. (2017), Lonigan et al. (2017) documented a significant association between EFs and the common externalizing symptoms factor.
However, the two studies differed in their findings regarding the associations of EFs with specific factors of externalizing symptoms. Huang-Pollock et al. (2017) found that working memory was not associated with any of the specific externalizing subtypes, whereas Lonigan et al. (2017) found that their two broader measures of EFs were associated with symptoms specific to inattention. Divergence in these findings could be due to differences in the way that EFs were measured between these two studies. Huang-Pollock et al.’s (2017) investigation included multiple direct assessments of working memory, but did not include measures focused on other aspects of EFs such as inhibitory control or cognitive flexibility. Lonigan et al. (2017) used a composite of EFs that included a questionnaire measure of broad EF skills (the Behavior Rating Inventory of Executive Functions) and scores from the Head, Toes, Knees, and Shoulders task (Cameron Ponitz et al. 2008), which assesses a mix of inhibitory control, working memory, and cognitive flexibility.
To understand these differences in associations with specific subtypes of externalizing symptoms, researchers also need to consider the multidimensionality of EFs. Although investigators have used the bi-factor model to identify a common EF factor and specific factors for working memory and cognitive flexibility (Miyake and Friedman 2012), they have not yet tested how specific EF factors relate to the structure of externalizing symptoms. Previous work has linked broad measures of EFs to change in externalizing symptoms over time (Sulik et al. 2015), suggesting that targeting EFs may be an effective way to reduce externalizing symptoms. Furthermore, experimental studies have demonstrated that direct training can improve EFs such as working memory; however, this training has limited generalizability to other aspects of EFs (Melby-Lervåg and Hulme 2013). Because EF training has relatively narrow effects, a better understanding of the specific EF processes involved in different types of externalizing problems would provide more focused targets for intervention or treatment.
Waller et al. (2017) take a different approach to address the question of whether EF contributes to multiple aspects of externalizing symptoms. In contrast to other studies in this issue, they did not use formal diagnostic categories that are codified by the DSM, but rather focused on predicting various types of aggression that included reactive, proactive, and relational subtypes. The differentiation between subtypes of aggressive behavior is crucial for understanding whether or not they differ in their associations with emotion, motivation, and self-regulatory skills. For example, self-regulatory ability has been found to play a more important role for emotionally dysregulated children (Eisenberg et al. 1996). Indeed, Waller et al. (2017) found that good EFs were protective against the positive relation between callous-unemotional behaviors – which are characterized by an atypical absence of empathy and guilt – and change in externalizing symptoms. These findings are particularly helpful because they help inform ideas about how EFs contribute to symptomatology. For example, although children who exhibit callous-unemotional behaviors may be predisposed to aggression, those with strong EFs may be better able to plan ahead, consider possible negative consequences of their actions, and inhibit their aggressive behavior. Furthermore, no differences were found between the different subtypes of aggression, suggesting the joint contributions of callous-unemotional behaviors and EFs apply broadly. An important direction for future research will be to develop an understanding of the specific mechanisms (e.g., emotion regulation strategies, perspective taking, planning) that mediate the relations between EFs and externalizing symptoms.
Verbal ability helps support the development of EFs (Kuhn et al. 2014) and the two constructs are often highly co-linear in empirical studies. Thus, it is important to consider the degree to which EFs are distinctive from general measures of intelligence – and from verbal ability in particular – when predicting externalizing symptoms. Lonigan et al. (2017) addressed this issue by showing that teachers’ reports of EFs and children’s vocabulary were independently predictive of externalizing symptoms. Further, Lonigan et al. (2017) also raise the intriguing possibility that verbal ability and EFs may play a different role in symptom development for boys and girls. Because girls, relative to boys, tend to have better EFs, better verbal ability, and fewer externalizing symptoms, it is important to consider the role of socialization. Furthermore, girls and boys also differ in the ways that externalizing symptoms are typically expressed. For example, boys tend to exhibit more physical aggression, whereas relational aggression is more common among girls (Zimmer-Gembeck et al. 2005). We need more studies that explicitly address the role of gender, not only as a moderator of the relations among EF, verbal ability, and externalizing symptoms, but also as a source of differences in socialization practices that might explain the existence of these gender differences.
Complementing the three studies that focused exclusively on children’s characteristics, van Dijk et al. (2017) investigated the indirect role of dysregulated parent-child interactions as a contributor to externalizing symptoms, testing EFs as a mediator of this relation. Parenting is among the most salient aspects of children’s environments, but it is important to recognize that children and parents are both active partners who are mutually influential in constructing the quality of their relationship (Aksan et al. 2006). By examining dyadic emotional co-regulation during a parent child interaction as a predictor of children’s EFs and externalizing symptoms, van Dijk et al. (2017) capture aspects of the parent-child relationship that go beyond either participant’s sole contributions. This was facilitated by the use of the state space grid, which represents the combination of parent and child behavior at a point in time as a location on a two dimensional grid in which one axis represents the child’s behavior and one axis represents the parent’s behavior. This approach can be used to capture moment-to-moment changes in the dyadic state. There is evidence that the state-space grid methodology has predictive validity that goes beyond traditional measures of parenting. For example, positive dyadic co-regulation measured using a state-space grid has been found to uniquely predict teachers’ reports of children’s impulsivity and inattention, whereas a global composite of qualitative parenting ratings did not (Bardack et al. 2017).
In future work, the state-space grid methodology has the potential to be used in even more innovative ways. Modern theories of symptom development such as developmental psychopathology conceptualize interactions between an individual and his or her environment as a dynamic, bidirectional process. Yet there is a mismatch between this rich theoretical view and the reality of empirical studies, which tend to use static measures that separate environmental influences on symptom development from the child’s contribution to this process. The state-space grid methodology, which is grounded in Dynamical Systems Theory, can represent the functioning of the parent-child relationship as it unfolds over time (Hollenstein 2007). Rather than simply creating a single score that represents the state-space grid as a summary measure, future work should investigate how changes in the state-space grid over the course of parent-child interactions are related to symptom development; previous studies have ignored these temporal changes.
Longitudinal studies are crucial for understanding how children’s characteristics and environmental context contribute to the onset and maintenance of externalizing disorders, but one limitation of current work is that longitudinal studies predominantly use community samples. Because the distribution of externalizing symptoms is highly skewed in the general population, results from these studies are heavily influenced by small differences among the many individuals with few symptoms, differences that lack clinical significance. One important question is whether the longitudinal relations among EFs and externalizing symptoms that have been documented in community samples can be used to inform our understanding of how EFs contribute to externalizing disorders. To address this issue, we need studies that adequately sample the full range of symptoms to address this question, which will likely require screening and stratified sampling. Without using this type of study design, it remains unclear what – if anything – studies of low symptom individuals have to say about the prediction of clinical levels of symptomatology. Waller et al. (2017) address this concern by oversampling children with high parent-reported externalizing symptoms.
A second limitation of many current studies is that they often rely on questionnaire measures reported by a single informant. Although direct assessments of EF help address concerns about shared method bias when relating EF to externalizing symptoms (e.g., as implemented by Huang-Pollock et al. 2017, and van Dijk et al. 2017), it is important to recognize that externalizing symptoms can differ meaningfully across contexts such as home and school: Parents and teachers frequently differ in their views of a child’s symptom levels (Sulik et al. 2017). Even in studies that do adopt a multi-informant approach (Lonigan et al. 2017; Waller et al. 2017), the choice of informants should be theoretically informed and explicitly justified (De Los Reyes et al. 2013).
Ultimately, what are the clinical implications of understanding how EFs and externalizing symptoms are related? This special section was motivated by two conclusions from recent research. First, we are becoming increasingly confident that EFs play a role in the development and maintenance of externalizing symptoms. And second, EFs are clearly susceptible to improvement through environmental interventions, especially for at-risk children (Diamond and Lee 2011). As such, EFs represent a promising target for effective prevention and treatment. The studies in this special section bring us closer to realizing this goal by (1) providing information about the specificity of relations among subdomains of EFs and of externalizing symptoms (Huang-Pollock et al. 2017; Lonigan et al. 2017), (2) showing that EFs may be especially protective for children whose other characteristics (specifically, callous-unemotional behaviors) place them at risk for externalizing symptoms (Waller et al. 2017), and (3) demonstrating that EFs are a mediating mechanism that can explain the link between emotional qualities of parent-child interactions and the development of externalizing symptoms (van Dijk et al. 2017).
Compliance with Ethical Standards
Conflict of Interest
Michael J. Sulik has no potential conflict of interest.
Jelena Obradović has no potential conflict of interest.
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