Introduction
Behavioral inhibition is a temperamental trait characterized by a relatively consistent pattern of behavioral and emotional responses to unfamiliar people and novel stimuli and situations. That is, inhibited children typically respond with restraint, caution, and withdrawal to novel objects and situations, and they are usually timid, fearful, and shy with unfamiliar people (Kagan et al.
1988; Kagan
1994). Behavioral inhibition shows moderate to good levels of continuity during childhood and is to a certain extent also associated with aspects of adult personality (for a review of the research on lifetime continuity in behavioral inhibition, see Fox et al.
2005). During the past 20 years, a number of studies have shown that there is an increased prevalence of anxiety disorders among behaviorally inhibited children (see for reviews Hirshfeld-Becker et al.
2004,
2008a). Noteworthy in this regard is the 3-year longitudinal study by Biederman et al. (
1993) who found that children initially identified as behaviorally inhibited were subsequently more likely to develop anxiety disorders as compared to control children (i.e., children who at study onset were not classified as behaviorally inhibited). It should be noted that in particular children with stable behavioral inhibition ran an increased risk for developing pathological anxiety (see also Hirshfeld-Becker et al.
1992).
While there is clear evidence indicating that behavioral inhibition is an important risk factor for the development of pathological anxiety in youths, it should also be noted that not every child with an inhibited temperament develops an anxiety disorder (see for instance Biederman et al.
1990), and so the question arises under what conditions behaviorally inhibited children develop anxiety disorders. Further, not every anxious child has a behaviorally inhibited temperament (Turner et al.
1996). As with other types of psychopathology, it is generally assumed that anxiety disorders are the result of multiple variables and influences (Muris
2007; Vasey and Dadds
2001). Therefore, when studying the role of behavioral inhibition in childhood anxiety disorders, one should also consider other vulnerability factors so that it becomes possible to study the unique and interactive effects of this temperamental trait. In the literature, a number of other factors have been identified that may play a role in the formation of anxiety problems, which may operate in conjunction or interaction with behavioral inhibition. These include an insecure parent–child attachment, negative parenting styles, parental anxiety, and adverse life events (see also Rapee et al.
2009), and will be discussed in the following paragraphs.
In their longitudinal study, Warren et al. (
1997) found a specific link between insecure (in particular, ambivalent) attachment measured in infancy and anxiety disorders that were assessed some 16 years later. A couple of studies have examined insecure attachment in interaction with behavioral inhibition (e.g., Calkins and Fox
1992; Mannasis et al.
1995; Muris and Meesters
2002; Shamir-Essakow et al.
2005). Altogether, the results of these studies have shown that children who combine a behaviorally inhibited temperament with an insecure attachment status display the highest levels of anxiety disorders symptoms, which of course indicates that these two vulnerability factors have a cumulative effect on the development of anxiety pathology in youths.
Two parenting dimensions that have been consistently associated with the development of anxiety in children and adolescents are
overprotection and
anxious rearing (e.g., Wood et al.
2003).
Overprotection can best be described as parental behaviors aimed at guiding children during their daily activities. These parental behaviors often have the effect of directing the child and reducing the development of autonomy (Rapee
1997).
Anxious rearing pertains to the explicit encouragement of anxious cognitions and avoidance behaviors in children (e.g., Barrett et al.
1996; Grüner et al.
1999). Several studies have yielded evidence for the proposed relationship between overprotective and anxious rearing behaviors and anxiety disorder symptoms, some of them relying on
direct observation of parent–child interactions (Hudson and Rapee
2001; Whaley et al.
1999) and others making use of
questionnaires that intend to measure children’s perceptions of parental rearing behaviors (Grüner et al.
1999; Muris et al.
2000,
2003). Overprotective and anxious parenting have been found to play a unique role in the development of childhood anxiety symptoms when examined together with behavioral inhibition (Van Brakel et al.
2006), and there are also studies indicating that parenting interacts with an inhibited temperament (Rubin et al.
1997,
1999).
Clear associations exist between adverse life events and psychiatric disorders in children and adolescents and these also include anxiety disorders (Tiet et al.
2001). It seems plausible to assume that behaviorally inhibited children are particularly prone to develop anxiety problems when confronted with negative life events. Brozina and Abela (
2006) tested this idea and examined the relationship between behavioral inhibition and anxiety symptoms within a diathesis-stress framework. The results of this study indicated that only behaviorally inhibited children who experienced high levels of stressful events (e.g., fighting parents, being teased at school, being punished) displayed an increase of anxiety symptoms during a 6-weeks period. In contrast, behaviorally inhibited children who did not experience such events exhibited a decrease in anxiety symptoms.
Research has shown that children of parents with anxiety disorders run a greater risk for developing anxiety disorders themselves (Biederman et al.
1991). Furthermore, Rosenbaum et al. (
1988) reported that a substantial proportion of the children of parents with clinically significant anxiety disorders were behaviorally inhibited. Finally and most importantly, there is also evidence to demonstrate that children with a behaviorally inhibited temperament who also have parents suffering from an anxiety disorder are most vulnerable to develop anxiety disorders (e.g., Rosenbaum et al.
1992).
Many studies suggest that behavioral inhibition is associated with a wide range of anxiety-related symptoms and disorders (Biederman et al.
1993; Broeren and Muris
2010; Gest
1997; Muris et al.
1999,
2001,
2003,
2009; Reznick et al.
1992; Shamir-Essakow et al.
2005), but there are also several studies that indicate that behavioral inhibition is a more specific risk factor and is only involved in the pathogenesis of social anxiety. For example, Townsley-Stemberger et al. (
1995) noted that social phobic patients reported significantly higher levels of shyness (which seems to be a clear marker of behavioral inhibition) in childhood than did control participants. In line with these findings, Mick and Telch (
1998) asked students with high symptom levels of social anxiety or generalized anxiety to retrospectively report their level of behavioral inhibition during childhood. These researchers found that behavioral inhibition in childhood was strongly associated with symptoms of social anxiety in adulthood, but not with symptoms of generalized anxiety. Hayward et al. (
1998) showed that adolescents (
N = 2242) who retrospectively reported that they had been behaviorally inhibited in childhood were four to five times more likely to suffer from a social phobia than adolescents who reported that they had not been behaviorally inhibited in childhood. Recently, Gladstone et al. (
2005) have also demonstrated that a behaviorally inhibited temperament in childhood may be a specific vulnerability factor to social anxiety rather than to anxiety in general.
Adolescents’ self-reports of behavioral inhibition are not only positively correlated with anxiety, but also with depression symptoms (Muris et al.
1999,
2001,
2003). One explanation for this association is that behavioral inhibition acts as a common vulnerability factor to both anxiety and depression. Another explanation could be that the association between behavioral inhibition and depression is a statistical artifact of the strong associations between anxiety and both behavioral inhibition and depression (Brozina and Abela
2006). Gladstone and Parker (
2006) obtained evidence to suggest that the presence of a behaviorally inhibited temperament may pose a developmental risk for lifetime depression. However, it is important to note that the relationship between behavioral inhibition and depression was dependent on the presence of social anxiety. That is, only behaviorally inhibited children who had developed social anxiety were prone to develop a depression (see also Muris et al.
2003). Nevertheless, other studies can be found in the literature indicating that behavioral inhibition is clearly associated with depression (Hirshfeld-Becker et al.
2003; Gullone et al.
2006; Jaffee et al.
2002; Shatz
2005). Taken together, although it has been proposed that behavioral inhibition is associated with the development of a wide range of anxiety-related symptoms and disorders, there is also evidence indicating that this temperamental trait acts as a more specific risk factor for social anxiety (see also Chronis-Tuscano et al.
2009; Essex et al.
2010; Hirshfeld-Becker et al.
2007). In addition, more research is required to examine whether behavioral inhibition is specifically linked to anxiety symptomatology or whether this temperamental trait also plays a role in the etiology of depression or even other psychological disorders in youths.
So far, research has demonstrated that behavioral inhibition, and other vulnerability factors like insecure attachment, negative parenting styles, adverse life events, and parental anxiety contribute to the development of anxiety disorders in youths. Only a few studies can be found that have investigated whether combinations of these factors yield an increased risk for anxiety problems (e.g., Calkins and Fox
1992; Van Brakel et al.
2006; Brozina and Abela
2006), but no study can be found that examined the additive and interactive effects of behavioral inhibition and a wide range of other vulnerability factors in the development of pathological anxiety in youths (Hirshfeld-Becker et al.
2008b). With this issue in mind, the present longitudinal research project was set-up. A group of 261 5- to 8-year-old children, 124 who displayed high levels of behavioral inhibition and 137 control children, were followed during a 3-year period. Each year, an assessment took place to measure children’s level of behavioral inhibition, anxiety disorder symptoms, other psychopathological symptoms, and a number of other vulnerability factors such as insecure attachment, negative parenting, adverse life events, and parental anxiety. In this way, it became possible to study (1) the unique and interactive effect of behavioral inhibition on the development of anxiety symptoms, and (2) whether behavioral inhibition plays a role in the development of anxiety problems in general, social anxiety, or a broad range of psychopathological symptoms (e.g., depression).
It was hypothesized that behavioral inhibition would be predictive of anxiety symptoms, especially social anxiety symptoms, over the 3-year period. Consistent with a diathesis-stress framework (see Brozina and Abela
2006), it was expected that behaviorally inhibited children who experienced high levels of stress as a result of adverse life events would be particularly prone to display an increase of anxious symptoms. Further, insecure attachment, an anxious and overprotective parenting style, and parental anxiety were all expected to play a unique role in the development of children’s anxious symptoms, and it was explored to what extent these vulnerability factors interacted with behavioral inhibition.
Discussion
The present study examined the additive and interactive effects of behavioral inhibition and other risk factors on the development of childhood anxiety symptoms using a longitudinal research design. Moreover, it was investigated whether behavioral inhibition plays a role in the development of social anxiety, anxiety problems in general, or a broad range of psychopathological symptoms. The main results of the study can be summarized as follows. Consistent with the hypothesis that behavioral inhibition is a rather specific vulnerability factor, the results indicated that high levels of this temperamental factor were particularly associated with an increase of social anxiety symptoms over time. The longitudinal associations between behavioral inhibition and other anxiety problems were clearly less strong, whereas prospective connections with other psychopathological symptoms were not found. Thus, the current findings seem to justify the conclusion that behavioral inhibition primarily acts as a specific risk factor for the development of social anxiety symptoms (see Hirshfeld-Becker et al.
2008a).
Second, the current study demonstrated that besides behavioral inhibition, a number of other risk factors made significant additional contributions in the model explaining anxiety symptoms across the three-year period. For example, anxious rearing on occasion I significantly predicted symptoms of other anxiety disorders on occasion II (see for comparable results Grüner et al.
1999; Muris et al.
2000,
2003), whereas trait anxiety of both parents as measured on occasion II made independent contributions to anxiety symptoms on occasion III. The latter finding is in line with a study of Biederman et al. (
1991) who showed that children of high anxious parents run a greater risk for developing anxiety disorders themselves.
Further, some evidence emerged showing that risk factors interacted with each other, thereby creating an increased vulnerability for developing anxiety. That is, behavioral inhibition and attachment on occasion II had an interactive effect on other anxiety disorders on occasion III. That is, children who were defined as high on behavioral inhibition and insecurely attached displayed the highest levels of anxiety symptoms over time, whereas children who were classified as low on inhibition and securely attached on occasion II exhibited the lowest anxiety levels. This result adds to earlier studies showing that children who combine a behaviorally inhibited temperament with an insecure attachment status tend to display the highest levels of anxiety disorders symptoms (e.g., Calkins and Fox
1992; Mannasis et al.
1995; Muris and Meesters
2002; Shamir-Essakow et al.
2005), which shows that individual risk factors may influence each other, thereby yielding an even greater risk for the development of anxiety pathology in youths.
Moreover, the final model showed that not only anxiety symptoms were predicted by various risk factors, behavioral inhibition itself was also influenced by some of the vulnerability factors. That is, overprotection on occasion I had a small but unique effect on behavioral inhibition on occasion II. Further, behavioral inhibition and trait anxiety of the father on occasion I had an interactive effect on behavioral inhibition on occasion II, indicating that high behaviorally inhibited children
with an anxious father displayed an increase of behavioral inhibition levels on occasion II. These findings are in keeping with the notion that overprotective/anxious parents may hinder their behaviorally inhibited children from developing effective coping strategies and acquiring adequate social skills (Rapee
1997), which is likely to result in avoidance of ‘anxious’ situations. As a consequence, these children remain inhibited or even become more inhibited (Rubin et al.
1997,
1999; Van Brakel et al.
2006; for a review see Rubin et al.
2009). Note that the current data suggest that fathers might play a specific role in this respect: if he shows high levels of anxiety, the inhibited child is particularly prone to continue or even intensify his/her temperamental vulnerability (Bögels and Phares
2007).
Finally, the current study tested the idea (consistent with a diathesis-stress framework) that behaviorally inhibited children who experienced high levels of stress as a result of adverse life events would be particularly prone to display an increase of anxious symptoms. This hypothesis could not be confirmed. The results showed that ‘life events’ did not interact with behavioral inhibition in the prediction of symptom levels, but rather acted as an independent factor influencing the development of depression and other anxiety disorders. In contrast, Brozina and Abela (
2006) found that stress (as a result of adverse life events) moderated the relationship between behavioral inhibition and anxiety symptoms. That is, children with high behavioral inhibition showed increases in anxious symptoms when they experienced high levels of stress. A possible explanation for these contrasting findings could be, first of all, the length of the follow-up period (i.e., 6 weeks in the Brozina and Abela study versus 1 year in the current study). It might be possible that a period of 1 year is too long to retrospectively assess stress levels in a valid way. Second, it may well be that the children in the present study were too young to really experience the negative impact of these adverse life events. Third and finally, the measures that were used in both studies differed. That is, whereas the current investigation relied on an index listing serious but rather infrequent life events (e.g., death of a parent, financial problems, divorce of parents), Brozina and Abela employed a scale measuring daily hassles, which simply may have been more sensitive to assess children’s levels of experienced stress.
Altogether, the recent findings confirm the validity of etiological models which assume that the pathogenesis of anxiety can best be conceptualized as a dynamic interplay of various predisposing factors. Vasey and Dadds (
2001) and Muris (
2007) have described such multifactorial frameworks for the development of childhood anxiety disorders. Of particular importance in these models are the reciprocal connections between the different risk and protective factors within a developmental context.
Several limitations of the current study should be considered when interpreting the current results. First, we did not assess diagnoses of anxiety disorders and other mental disorders (e.g., depression). Nevertheless, it should be mentioned that the SCARED which was employed as the primary outcome measure, provides a good indication of various DSM-defined anxiety disorders in non-clinical and clinically referred children and adolescents (Muris et al.
2004). Second, despite the fact that the BIS has been thoroughly investigated in previous studies (e.g., Van Brakel et al.
2004; Shatz
2005) and turned out to be a valid and reliable measure, it predominantly measures
social aspects of behavioral inhibition. Although the choice for the BIS can be defended by pointing at past research indicating that the non-social aspects of behavioral inhibition are more susceptible to developmental changes than the social aspects of behavioral inhibition (Hirshfeld-Becker et al.
2004; Van Brakel et al.
2004; Van Brakel and Muris
2006), the study would have gained in strength if we had included a measure that also covers the non-social aspects of the inhibited temperament (such as the Behavioral Inhibition Questionnaire; Bishop et al.
2003; Broeren and Muris
2010), especially since there are some indications that non-social behavioral inhibition may be a more reliable predictor of ‘other anxiety disorder symptoms’ (e.g., Van Brakel et al.
2004). Third, most of the data on behavioral inhibition, attachment, parental rearing and psychopathological symptoms were obtained from one and the same informant (i.e., parents). As such, it is possible that the observed associations might have been elevated due to shared method variance. Preferably, researchers should rely on multiple informants when investigating such relationships. Note, however, that the children in the current study were too young to reliably fill out these complex questionnaires. Fourth, despite the longitudinal set-up of the study, children were only followed for 3 years. Thus, it remains unclear how behavioral inhibition assessed at a young age relates to social phobia, various types of anxiety disorders, and depression over longer time periods. In this context, Brozina and Abela (
2006) have pointed out that it is possible that the association between behavioral inhibition and depressive symptoms is not evident until adolescence when depressive disorders become more prevalent. In other words, it might be possible that our sample of children was too young to detect the development of certain types of problems. Fifth, according to current temperament researchers (see Muris and Ollendick
2005), vulnerability to psychopathology is not only characterized by reactive temperament features such as behavioral inhibition but also by lack of regulative traits such as effortful control. That is, high levels of behavioral inhibition make children prone to develop psychological disorders, but it may well be the case that the negative impact of this temperament variable can be buffered by effortful control. The present study mainly focused on reactive temperament (behavioral inhibition) but it may well be that ‘effortful control’ accounts for some of the variation in the development of anxiety symptoms within our group of behavioral inhibited children. Sixth and finally, another issue which needs attention is the possible tautological nature of the link between (social) behavioral inhibition and social anxiety. Note, however, that the current data demonstrate that even when controlling for social anxiety on previous assessment occasions, behavioral inhibition still remained a significant predictor of subsequent social anxiety symptoms.
Despite these limitations, the current data provide support for the notion that various predisposing factors have additive and, to some extent, interactive effects on the pathogenesis of anxiety in children. Further, the present findings suggest that behavioral inhibition should be primarily viewed as a specific risk factor for the development of social anxiety in children rather than a general vulnerability factor for a broad range of anxiety problems, although there might be clear methodological issues (i.e., age of the children, use of the BIS for measuring behavioral inhibition) that may have biased our results. Future research might address the role of reactive and regulative factors when examining the predictive value of temperament on the development of anxiety and other psychopathological symptoms in children (e.g., Calkins and Fox
1992; Muris and Ollendick
2005). In addition, more prospective studies are needed in which children are followed for longer periods of time, preferably from birth to adulthood. In this way, individual developmental trajectories could be elucidated, and clinical, cognitive, and developmental information might be further integrated in a comprehensive model on the development of childhood anxiety disorders.