Many prior studies have investigated the relationship between motivational systems and attachment, childhood trauma, and temperament. All of these behaviors influence different domains of mental health and general wellbeing [1,2]. Insecure attachment, childhood trauma, low reward sensitivity, and behavioral inhibition have all been suggested to be important risk factors affecting the onset, duration, and prognosis of depression [3-9]. However, few studies have clinically examined the interrelationships between attachment, childhood trauma, and temperament. Therefore, this study examines the interrelationships among adult attachment styles, sensitivities of behavioral inhibition system/behavioral activation system (BIS/BAS), and childhood trauma.

Attachment theory postulates that individuals seek the company of others in stressful situations. However, there are individual differences with regard to whom the distressed person approaches or avoids in their attachment figure [10-12]. Reinforcement sensitivity theory (RST) involves temperament and may deepen our understanding of these individual differences [13]. The RST suggested that people differ in sensitivity and responsiveness of two fundamental motivational systems that are thought to determine behavioral response in threatening situations, the BIS/BAS [14]. The BIS is a neural system that deals with threat-related information and triggers anxiety, arousal, and inhibition of the ongoing behavior. In contrast, the BAS is a neural system that process reward-related information and triggers positive feelings and approach behavior.

Dysregulation of these motivational systems may be related to difficulties with socio-emotional processing [15]. In Ochsner’s model, one of the main constructs of socio-emotional processing is the identification of social stimuli that lead to aversive or appetitive results [16]. One study suggested that the quality of attachment relationships is related to increased vigilance to rejection and avoidance of social reinforcement [17]. Attachment theory is also thought of as a theory of motivation. It postulates that accounts of behaviors are based on approach-avoidance motivation dynamics. Bowlby described avoiding threats or approaching the attachment figure as a “twin process of survival.” Variations in this behavioral pattern characterize individual differences in attachment behavior [10]. Therefore, an integrative study could further the understanding of the underlying motivational mechanisms of attachment styles. Several prior studies have suggested that both attachment anxiety and avoidance are associated with heightened responses to threatening stimuli, linking them to defensive motivations [18]. Some empirical studies have supported the theory that attachment avoidance is negatively correlated with BAS sensitivity, and that attachment anxiety is positively associated with BIS sensitivity [11,19]. However, most studies were performed in mentally healthy people. There are very few studies performed in clinical settings.

In addition to motivational system, childhood trauma, and especially that perpetrated by the primary caregiver, can be also critical to a child’s attachment [20]. Children who are exposed to maltreatment have been found to be more likely to have an insecure-disorganized type of attachment. Several empirical studies have previously suggested that childhood emotional trauma is associated with insecure attachment [21,22]. Furthermore, in context of temperament-environment interaction, it would be possible that childhood emotional trauma may give an interaction effect on the relationship between motivation system and adult attachment style.

Based on theoretical background and previous studies, we examined the relationships between adult attachment style, childhood trauma, and BIS/BAS sensitivity in patients with depressive disorders and developed three hypotheses. First, the BAS sensitivity would be negatively correlated with attachment avoidance and positively correlated with attachment anxiety. In addition, the BIS sensitivity would be positively correlated with both dimensions of attachment insecurity. Based on this theory, individuals with a high BAS sensitivity would be likely to engage in approach rather than avoidance behavior in their relationships. In contrast, the BIS sensitivity is involved with emotional distress when potentially harmful events occur [14]. Considering the vulnerability of increasing anxiety, arousal, and emotional instability in relationships, both dimensions of attachment insecurity would be positively correlated with BIS sensitivity. Our second hypothesis was that, among various types of childhood trauma, emotional trauma would be significantly associated with both attachment styles, as a caregiver’s emotional sensitivity and response are important for shaping attachment style and security. Thirdly, we hypothesized that there would be a significant interaction effect of BIS/BAS sensitivity and childhood trauma on attachment style. Individuals with high BIS/BAS sensitivity would suffer from more insecure attachment when exposed to severe childhood emotional trauma.

Prior evidence suggests that individual differences in attachment patterns are important factors that affect widespread mental health problems, including depression. However, there was previously no information regarding which factors affect an individual’s attachment pattern. Several factors, including temperament (such as BIS/BAS sensitivity) and early life traumatic experience, have been previously investigated with mixed results [18,19]. Based on this background, our study investigated the interrelationships among BIS/BAS sensitivity, childhood trauma, and adult attachment styles.

We found that attachment avoidance was only negatively correlated with BAS sensitivity. In contrast, attachment anxiety was positively correlated with both BIS and BAS sensitivity. The negative association between BAS sensitivity and attachment avoidance was consistent with the findings of several previous findings [18,19]. Attachment avoidance was associated with the reduction of positive emotional experiences, devaluation of intimate relationships [28], and lower satisfaction withrelationships [11]. These findings suggest that low sensitivity to rewards extends to the evaluation of one’s attachment figure as less rewarding. This evaluation may be linked to the avoidant attachment’s discomfort with intimacy.

In partial support of the hypothesis and previous findings, attachment anxiety was positively correlated with both BIS and BAS sensitivity. Previous studies suggested that BIS sensitivity is more strongly associated with attachment anxiety than it is to attachment avoidance. This finding is also is consistent with our results [29,30]. Furthermore, previous studies found that attachment anxiety was related to more sensitive threat perception in relationships and greater ambivalence. In contrast, attachment avoidance was associated with low sensitivity to reward perception and decreased level of ambivalence [29]. However, the previous findings regarding attachment and BAS sensitivity were inconsistent. In one study, attachment anxiety appeared to be weakly negatively associated with BAS sensitivity [18]. Consistently, other studies have suggested that BAS sensitivity and attachment anxiety arepositivelycorrelated [19]. Individuals with high levels of attachment anxiety are inclined to attempt to resolve relational problems, using both approach and distancing strategies [31,32]. Such tendencies of an anxious attached person might be associated with a high sensitivity of both BIS/BAS. In contrast, the literature consistently and specifically suggests that people with avoidant attachment seek interpersonal distance in stressful or threatening situations. Such characteristics of avoidant attachment might be specifically associated with low sensitivity of the BAS.

Emotional neglect was the only type of childhood trauma that was significantly associated with both dimensions of insecure attachment styles. Emotional neglect occurs when a caregiver overlooks the signs that a child needs comfort or attention. It includes a range of behaviors including withholding love, constant belittling, denying needs for interacting, failing to express positive feelings to a child, and refusing to provide necessary psychological care [33]. Some theorists have suggested that childhood emotional neglect can have particular psychological meanings, such as rejection and abandonment by the parent as a key attachment figure. In contrast, abusive trauma does not have these psychological meanings [34]. Such negative interactions with parents can leave a child feeling uncertain about the availability of a protective figure in times of trouble [10]. The internal working model based on early neglect experience may be linked to insecure attachment. Several empirical studies have suggested that childhood emotional trauma is a vulnerable factor for insecure attachment. However, there are mixed results regarding whether specific types of childhood trauma have different effects on attachment anxiety and attachment avoidance. Several community studies have suggested that childhood emotional neglect is related to anxiety and depressive symptoms, mediated by attachment anxiety [33,35,36]. Other studies have reported that emotional abuse was associated with schizotypy and partially mediated by both dimensions of insecure attachment [37]. Considering that childhood emotional neglect was a more important factor in adulthood depression than were other types of childhood trauma [38,39], the participants’ characteristics (potentially with clinically significant depressive symptoms) may have influenced our results. Further studies are needed to investigate how specific types of childhood trauma are related to attachment style in individuals with clinically significant mental illness.

Our findings suggest that individuals with high BAS sensitivity are more susceptible to anxious attachment styles under childhood emotional neglect. Inferring the reinforcement sensitivity theory, individuals with high BAS sensitivity tend to have reward-guided approach behavior [13]. Under a severely emotionally neglected environment in which there are little opportunities to receive positive rewards, individuals may suffer from severe distress. This distressful foundation can cause such individuals to lose confidence that they will have a protective figure during stressful times. This thinking ultimately creates attachment anxiety. To the best of our knowledge, no prior studies have examined the interaction effect between BIS/BAS sensitivity and childhood traumatic experience on adult attachment styles. A larger, longitudinal study is needed to confirm the interrelationship among BIS/BAS sensitivity, childhood trauma, and adult attachment style.