The Development of Internalizing Behaviors in Early Adolescence: Introduction to the Special Issue

This special issue highlights a number of important processes that help explain the emergence and continuation of internalizing psychopathology (i.e., problem behaviors characterized by inner distress) during early adolescence. The five articles making up the special issue are introduced, each of which represents exciting new work regarding how, why, and for whom internalizing problems develop and are maintained. The introduction to the special issue further elaborates on transdiagnostic and person-oriented approaches, internalizing interpretations and functional effects of internalizing as relatively underused methodological and theoretical perspectives that might help move the field forward and further our understanding regarding the development of internalizing psychopathology early on in life.

Internalizing psychopathology is an empirically derived dimension used to describe problem behaviors characterized by inner distress during childhood and adolescence (Achenbach & McConaughy, 1997). Classified by a range of related phenomena, including clinical and subclinical levels of depression, anxiety, social anxiety, and various phobias (Epkins & Heckler, 2011;Hankin et al., 2016;Krueger & Markon, 2006a, 2006bWaszczuk, Zavos, Gregory, & Eley, 2016), internalizing is considered part of a two-category hierarchical factor model also typified by externalizing problems (Achenbach & McConaughy, 1997). Internalizing could also be further subdivided based on fear (including panic, social anxiety, and agoraphobia) versus distress (including depression, trait anxiety, and worry; Kushner et al., 2013). Because of their early emergence and links to later-life psychopathology, internalizing problems are in much focus across various subdisciplines of psychology. A number of theoretical frameworks attempting to explain developmental changes in terms of internalizing problems exist, including the diathesisstress models, models highlighting cumulative/simultaneous events, accentuation of symptoms via transitions, and variability in sensitivity (Graber & Sontag, 2009). One review of the literature eloquently summed up common empirical considerations with two significant questions: "Why adolescence?" and "why more girls?" (Graber & Sontag, 2009). Yet, despite advances in understanding internalizing symptoms as well as disorders, these questions are just as relevant as they were more than 10 years ago when the aforementioned review was published.
This special issue aimed to address a number of gaps in the current literature on internalizing psychopathology, focusing on factors contributing to its development. One of the aims was attempting to explain why internalizing occurs for some, but not all individuals (i.e., precursors), as well as what factors contribute to its maintenance. Another aim was to focus on different types of internalizing problems and to understand more about their co-occurrence over time. Knowing more about what processes help explain the links between internalizing problems and psychosocial functioning was another key aim for the special issue-as was examination of gender differences regarding contributing factors as well as consequences of internalizing for girls and boys. In sum, the special issue aimed to increase the understanding about how, why, and for whom internalizing problems develop and are maintained.

New Insights From This Special Issue
The findings from this special issue represent new steps in furthering the knowledge about the emergence and maintenance of internalizing psychopathology. Klinck, Vannucci, and Ohannessian (2020) examined school connectedness as a particular factor contributing to internalizing problems by evaluating the transactional effects between the two in a sample of U.S. early adolescents. Adolescents with low risk for an anxiety disorder improved in depressive symptoms when they had higher baseline levels of school connectedness, but there were no links between the latter for high-risk adolescents. In addition, the authors did not find a bidirectional relationship between school connectedness and anxiety. Consequently, feeling connected at school during early adolescence might help provide protection against depressive symptoms-advice that could readily be implemented by school personnel and other concerned adults. Nevertheless, the authors note that understanding how to help adolescents in the high-risk zone for internalizing remains a challenge. Simpson, Vannucci, Lincoln, and Ohannessian (2020) investigated the impact of internalizing symptoms on early adolescent family functioning and the moderating effects of stress in a sample of U.S. adolescents. The results indicate that depressive symptoms were related to lower family conflict for low-stress boys, whereas depressive symptoms predicted less communication with mothers for low-stress girls. There was also evidence of higher family cohesion and lower adolescent-father communication as predicted by anxiety, but only for low-stress girls. These findings point to the importance of considering stress in conjunction with internalizing problems when studying family functioning in early adolescence.
Van Zalk, Tillfors, and Mörtberg (2020) examined the heterogeneity and long-term consequences of subclinical social anxiety-impulsivity in a longitudinal sample of Swedish adolescents. Four latent classes of adolescents were identified across three timepoints, namely, those low on social anxiety and impulsivity, those with high social anxiety and high impulsivity, those with high social anxiety and low impulsivity, and those with low social anxiety but high impulsivity. In turn, the highly anxious-impulsive girls and boys had the highest levels of Time 4 internalizing problems, whereas the class with highly impulsive adolescents fared the worst regarding both internalizing and externalizing problems. The authors point to the importance of understanding the heterogeneity of behavioral patterns within the counterintuitive trait combination which is social anxiety-impulsivity to help prevent potentially negative consequences in the long run.
Ohannessian and Vannucci (2020) looked at the links between self-competence and depressive symptoms over time in a large U.S. longitudinal sample. The study showed initial higher levels of depressive symptoms and self-competence among girls compared to boys. Nevertheless, higher depressive symptoms were more strongly predictive of lower self-competence than vice versa, regardless of gender. This study is a replication and extension of previous work looking at links between depressive symptoms and self-competence. Importantly, as the authors point out, the results indicate that depressive symptoms need to be dealt with first to increase self-competence among early adolescents.
Finally, Diaconu-Gherasim, and Mairean (2020) looked at longitudinal links between depressive symptoms and achievement goals, and whether rejection by mothers and fathers had an impact on these links in a Romanian sample of early adolescents. The results showed a positive link between depressive symptoms and performance-avoidance goals, but a negative link to both mastery and performance-approach goals. There were also differences between the effects of rejection by parents, as father's rejection was positively related to performance-avoidance and negatively related to mastery, whereas no such links were found for mothers. Nevertheless, mothers' rejection moderated the links between depressive symptoms and performance-avoidance over time, as those with high levels of depressive symptoms reported more performance-avoidance goals when identifying high levels of maternal rejection. This study furthers the literature by showing unique links between depressive symptoms, performance-avoidance goals, and maternal rejection.

Underused Conceptual Frameworks for the Study of Internalizing Development
Early adolescence is characterized by major neurobiological (Tillfors & Van Zalk, 2015) and social (Steinberg & Morris, 2001) changes, among others, and the emergence and variation in these changes are likely to produce an impact on future development. Although what constitutes "healthy" or "positive" development is far from clear-cut (though some good suggestions exist; see, for example, Lerner, Almerigi, Theokas, & Lerner, 2016), avoiding an increase in internalizing problems is likely a desirable outcome important for future psychosocial functioning. Prevention is expectedly the most favorable mode of avoiding a negative development in the first place, although this is easier said than done considering that internalizing problems such as symptoms of depression, generalized anxiety, and social anxiety are often present early on in childhood (Kagan & Snidman, 1999;Patton et al., 2014) and commonly co-occur during adolescence (e.g., Epkins & Heckler, 2011;Waszczuk et al., 2016). Innovative theoretical and methodological frameworks that help increase the likelihood of early detection of internalizing problems are therefore necessary. The frameworks mentioned in this special issue commentary remain underused in the developmental literature at large but might prove useful in understanding how internalizing psychopathology develops across the life span.

Adopting a Transdiagnostic Perspective
One approach of particular usefulness concerns transdiagnostic factors, or elements similar across disorders that contribute to their development and maintenance (Harvey, Watkins, Mansell, & Shafran, 2004). Although this approach is increasingly used in the clinical literature, it should be adopted for wider use in the study of internalizing development as well. For instance, unhelpful emotion regulation strategies, including intrusive or ruminative thoughts, repetitive thinking, trait suppression, and less cognitive reappraisal, are commonly reported by individuals with different types of internalizing problems, including social anxiety (Blalock, Kashdan, & Farmer, 2016;Farmer & Kashdan, 2012) and depression (Gross, 1998). In addition, sleeprelated problems are also likely underlying transdiagnostic factors shared by several types of internalizing problems (Harvey et al., 2004). This is unsurprising, considering similarities in their biological underpinnings, including related brain structures such as the amygdala or neurotransmitters such as serotonin (Harvey et al., 2004). Thus, understanding more about shared risk factors across internalizing problems would help increase the knowledge about their common co-occurrence and continuation.

Taking a Person-Oriented Approach
Although not new under the sun, the person-oriented approach is widely underused in the study of internalizing problems (Van Zalk & Smith, 2019). Instead, the majority of studies on development of internalizing psychopathology rely on variable-centered approaches. In a person-oriented approach, the holistic-interactionist view of human development is emphasized by identifying various patterns or profiles of data to study interindividual differences (Bergman & Magnusson, 1997;Bergman, Magnusson, & El-Khouri, 2003). Individuals likely show different patterns of mental, biological, and/or behavioral factors operating at all levels of individual functioning (Bergman & Magnusson, 1997;Bergman et al., 2003), and understanding them requires heterogeneous profiling of individuals. The typical information provided via the variable-centered approach is variable-oriented rather than individualoriented (Bergman & Magnusson, 1997;Bergman et al., 2003). Although the person-oriented approach also relies on the use of variables, however, they are considered components of a particular pattern under analysis. This is further related to the larger issue of categorization of psychopathology. The vast majority of studies in the developmental literature rely on threshold (i.e., subclinical) symptoms rather than clinical (i.e., diagnoses) of internalizing, and this is often done by categorizing continuous variables.
Especially in the instance of internalizing psychopathology, however, categorizing continuous variables is not only problematic (Rucker, McShane, & Preacher, 2015) but also lacks in providing information beyond extreme or clinical levels of symptomatology based on often arbitrary cut-offs (Harvey et al., 2004). For instance, one approach to distinguish between shyness and social anxiety disorder is related to anxiety severity as well as associated impairment and distress (Dalrymple & Zimmerman, 2013). Nevertheless, especially during adolescence, it is difficult to gauge when typical "moodiness" ends, and psychopathology begins. With the advent of sophisticated analyses allowing for the study of individual patterns across time such as latent transition analysis (Collins & Lanza, 2010), however, the person-oriented approach could be beneficial in discerning more about the development of internalizing patterns instead.

Internalizing Interpretations
One reason for the apparent comorbidity or co-occurrence of internalizing problems could be due to individuals' interpretation of them. For instance, anxiety and depression appear to represent constructed emotional categories rather than core affect (Barrett, 2017). That is, they are people's interpretations of how they feel. The assumption here is not that the various internalizing problems are identical, but rather that they represent the brain's way of categorizing sensations into similar emotions-and they could equally well be interpreted as anxiety, depression, pain or stress (Barrett, 2017). When asking participants about various symptoms of anxiety or depression, the questions themselves become subsequent templates for participants' own descriptions of current feelings (Barrett, 2017). This leaves open the question whether one of the reasons internalizing problems commonly co-occur is because of the way we ask questions about them, and whether they need to be measured in alternative ways (such as via observation or using complex machine learning algorithms). This is an area requiring further attention in the literature.

Functional Effects of Internalizing
One initial aim of the special issue that did not receive any attention via paper submissions was examining whether internalizing problems can serve a potential protective function under certain circumstances. In my view, this is a largely unadopted perspective in the study of internalizing problems, as examining some of their less negative functions might help explain their continuation and apparent longevity for some individuals. For instance, social anxiety appears to moderate the links between chatting and developing compulsive internet use (Van Zalk, 2016), as well as the links between advanced maturity and early adolescent risk behavior for boys (Van Zalk, Kerr, & Tilton-Weaver, 2011). Consequently, parents who worry about their shy, socially anxious children might have a lot less to worry about compared with parents of more outgoing children-even though adults often attempt to bring socially anxious children out of their shells. And although one would not necessarily prescribe social anxiety as a "cure" for any of the aforementioned outcomes, understanding more about some of the dampening/moderating effects of internalizing problems on important outcomes could help against overproblematizing of early psychopathology.

Conclusion
The study of internalizing psychopathology is a good example of the complexity of studying human experience. The more complex the subject matter is, the less likely researchers are able to generate simple, parsimonious, specific, and precise theories or provide more than cautious recommendations of the studied phenomena (Sanbonmatsu & Johnston, 2019). This is certainly the case for the study of the behaviors and experiences falling under the internalizing dimension, which represents a useful descriptive tool, but often lacks in parsimoniousness and specificity in terms of prediction-especially across the life span. This is not strange, considering the features of the phenomena under study, including comorbidity or co-occurrence of a number of internalizing problems as well as overlapping transdiagnostic symptoms that might precede or follow them. The findings from this special issue provide a glimpse into this complexity and further the understanding of how internalizing develops, and what factors might contribute to it.

Declaration of Conflicting Interests
Dr. Nejra Van Zalk is the Guest Editor for this Special Issue.

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