(Psychology)
Borderline Personality Disorder (BPD) is a severe disorder with general prevalence rates as low as 1-2%, yet accounts for as much as 10% of all outpatients and 20% of inpatients (American Psychiatric Association, 2013; Biskin, 2015). BPD is characterised by patterns of instability, specifically around affect, self-image, and interpersonal relationships, which typically manifest by early adulthood (American Psychiatric Association, 2013). Individuals with BPD tend to exhibit emotional dysregulation; experiencing depression, anxiety, and expressions of anger (Linehan, 1993). In addition, borderline individuals are at heightened risk of suicide. One meta-analysis which pooled eight studies of suicidal behaviour in connection to BPD found that 8% of borderline patients died by suicide (Pompili et al., 2005). Thus, there is an urgent need for research investigating the development of BPD, and relatedly, to examine whether the risk and resilience factors posited by theoretically based aetiological models are supported empirically.

On the latter point, research on the neurological mechanisms behind emotional lability in BPD suffers from notable design limitations. A critical review of studies using fMRI found that most research in this area suffers from limited statistical power (van Zutphen, Siep, Jacob, Goebel, & Arntz, 2015). For instance, a study by Guitart-Masip et al. (2009) found that BPD patients exhibited impaired ability to discriminate between faces depicting emotional expressions, and neutral faces in a sample of only 10 patients. Further, while Koenigsberg et al. (2009) found support for the long-standing assumption that increased activity in the amygdala was a defining feature of BPD, this was only support in a sample of 19 BPD patients.

Despite these limitations, extant aetiological models have suggested risk and resilience factors which may be supported by research from other areas. The nature of childhood environments is one factor which receives much attention. One such aetiological model, Marsha Linehan’s Biosocial Theory, posits Invalidating Childhood Environments (ICE) as the single risk factor all borderline individuals have in common. Invalidating environments, per this account, is explained by Linehan (1993) where the expression of internal states is met by inconsistent, inappropriate, and sometimes extreme responses such as punishment and dismissal. More simply, ICE refers to upbringings in which “parents do not recognise and acknowledge the affective states of the child” (Sturrock, Francis, & Carr, 2009, p. 41). Invalidation, in a wider sense, has been associated with a range of psychopathologies. A study with Australian adolescents found small to moderate correlations between parental invalidation and measures of shame, distress, and non-suicidal self-injurious behaviour (Mahtani, Melvin, & Hasking, 2017). Parental invalidation has also been shown to be a significant predictor of self-injurious behaviour among adolescents with BPD (Adrian et al., 2018). In addition, ICE has also been associated with the development of eating disorders but may be an indirect effect that is mediated by emotional regulation abilities (Haslam, Arcelus, Farrow, & Meyer, 2012; Mountford, Corstorphine, Tomlinson, & Waller, 2007). Thus, it is evident that early and consistent experiences of emotional invalidation play a role in inhibiting the normal development of faculties associated with emotional regulation.

Linehan explains that ICE represents a poor environmental fit for the emotional needs of a child with a predisposition toward emotional sensitivity (Linehan, 1993). Specifically, these environments fail to teach the child to label internal experiences, such as emotions, in a manner consistent with social norms. As these experiences are not able to be expressed, the child is not taught the skills necessary to manage them. This is consistent with another aetiological model of BPD, which illustrates the relationship between traumatic experiences with early attachment figures (“complex trauma”) and the development of mentalisation: the awareness of mental states (Luyten & Fonagy, 2019). The Biosocial model has been indirectly supported by studies associating BPD symptoms with abusive childhood environments. For instance, Kuo, Khoury, Metcalfe, Fitzpatrick, and Goodwill (2015) found that childhood emotional abuse was moderately associated with the severity of borderline symptoms in a sample of university students (r = .42, p < .01) with only weak or non-significant correlations with sexual and physical abuse. This was further supported by Hong, Ilardi, and Lishner (2011) who found that childhood sexual abuse alone was a poor predictor of borderline symptoms, but invalidation as well as invalidating reactions upon disclosure of childhood abuse contributed to the development of BPD. Further, the relationship between ICE and problems with distress tolerance may be mediated by difficulties expressing emotion (Krause, Mendelson, & Lynch, 2003). Regarding borderline symptomatology, ICE has been associated with the amount of time spent dwelling on negative experiences (“rumination”), as well as dichotomous thinking (“splitting”) (DeShong, Grant, & Mullins-Sweatt, 2019; Selby, Braithwaite, Joiner, & Fincham, 2008).

Direct support for the Biosocial model was found in Hope and Chapman (2019) who reported moderate correlations between recalled experiences of emotional invalidation during childhood, and BPD features. Together with the studies lending indirect support, these findings illustrate that childhood invalidation is a risk factor for emotional dysregulation, particularly to the degree exhibited by BPD individuals. However, it is important to recognise that much of the literature investigating ICE suffers from problems of comparison given the different measures that have been used. For instance, the Socialization of Emotion Scale has been used by some researchers, which measures both parental validation and invalidation (DeShong et al., 2019; Krause et al., 2003). By contrast, studies either use scales which measure implications of an invalidating environment such as the absence of parental warmth, and the presence of parental aggression or neglect, such the measures used by Hong et al. (2011). Finally, studies such as Selby et al. (2008) developed ad hoc measures for invalidation, resulting in single use scales. This disconnect between measurements has been attributed to the vague and broad outline given by Linehan in her original work, resulting in different conceptions on how the construct is to be measured (Musser, Zalewski, Stepp, & Lewis, 2018). Thus, ICE suffers from limitations of construct validity throughout the literature.

However, the Biosocial theory posits that environmental factors such as ICE inhibits the development of emotional regulation. This suggests that its normal development is either a conditioned or learned response. Little research to date has investigated invalidation on the development of psychopathology from a behaviourism perspective, but Linehan’s original account as well as the mechanisms of her intervention; Dialectical Behaviour Theory (DBT), assumes that validation fosters distress tolerance (Linehan, 1993). There are also findings which suggest that intergenerational transmission of emotional dysregulation can be partially accounted for by a cycle of parental invalidation (Buckholdt, Parra, & Jobe-Shields, 2014). Research on interoception may offer some insight into how emotional regulation abilities, such as mentalising, are environmentally procured. Interoception refers to the awareness and interpretation of internal signals originating from the body, via the nervous system (Khalsa et al., 2018). Interoception can be further reduced to 3 sub-faculties; interoceptive sensitivity as the accuracy of judgments made about an internal state, interoceptive sensibility as beliefs about one’s sensitivity, and interoceptive awareness as a form of metacognition encompassing awareness about both sensibility and sensitivity (Murphy, Brewer, Catmur, & Bird, 2017). In this way, interoception is an integral component of basic physiological functioning, as awareness of internal states is a necessary requirement for self-regulation. Specifically, interoceptive awareness is implicated in both top-down and bottom-up regulation processes.

As a result, we can expect the absence of interoceptive awareness to be a common feature in the development of many forms of psychopathology. For example, interoceptive deficits were found to have a large effect in both the development and perpetuation of eating disorders in a meta-analysis by Jenkinson, Taylor, and Laws (2018). The authors also found that alexithymia contributed to the effect size of interoceptive deficits. This is consistent with the theoretical proposal by Jenkinson et al. (2018) who suggest that alexithymia, characterised as a failure to correctly identify affective states, exhibits an inverse relationship with interoceptive sensitivity and that it is plausible to suggest that alexithymia reflects atypical interoceptive functioning. Given this, it is evident that there are conceptual similarities between interoception and mentalising, the latter being a goal among many BPD interventions. Interoceptive conditioning, the association of stimuli with internal states, has been suggested by Van Diest (2019) to be a special case of the classical conditioning paradigm. The author claims that while interoceptive conditioning contributes to physiological regulation, it largely occurs unconsciously.

Given this, we may expect that the development of emotional regulation involves a conditioned association of internal states with labels and expressions provided by the caregiver during early development. In addition, it would be expected that caregiver feedback received upon expressing an emotion by the child would be instrumental in learning to associate emotion with behaviour. While seldom discussed in the context of conditioning, much research has shown that caregivers are essential in the normal development of emotional regulation (see Cole and Hall, 2008 for a discussion). Regarding interoception, it has been shown that interoceptive awareness may develop early in life with the association of a caregiver’s facial expression with feelings of warmth, as frequently occurs in secure attachments (Quattrocki & Friston, 2014). By contrast, the invalidation of emotions results in a failure to learn how to label, express, and manage affective states, in line with Biosocial theory. Further, as interoception is conditioned, we can hypothesise that borderline individuals would exhibit significant deficits in interoceptive abilities. However, the relationship between BPD and interoception is under-studied, with one study finding no difference in task performance measuring interoceptive awareness between BPD patients and control participants (Hart, McGowan, Minati, & Critchley, 2013). However, this is one of the few studies to date which has investigated the matter, and it suffers from a small sample size (n = 24). By contrast, alexithymia has found to be present in individuals with BPD. For example, a study of 54 female outpatients with BPD found they exhibited greater ratings of alexithymia compared to a control group of university students and that this relationship was mediated by attachment style, specifically fearful attachment (Deborde et al., 2012).

However, the Biosocial model does not insist that invalidation is a one-way path to the development of borderline symptoms. It posits that the environment poses a lack of fit for emotionally sensitive children, where the development of BPD is the product of successive transactional exchanges between individual and environment. This indicates that biological or genetic factors mediate the relationship between ICE and BPD. When the Biosocial model was formulated, little was known at the time of the role of biological underpinnings of emotional sensitivity, however the literature is now saturated with investigations at the neurological, genetic, and developmental level. This has resulted in an expansion of the original model, which incorporates a biological predisposition towards both emotional sensitivity and poor impulse control (Crowell, Beauchaine, & Linehan, 2009). These predispositions shape subjective experiences, such as emotional sensitivity influencing evaluations and perceptions of interpersonal exchanges. For instance, Bennett et al. (2019) found a significant difference among borderline adolescents in their ratings of parental support than those by their caregivers compared to control groups, after controlling for the influence of BPD symptoms. This suggests that invalidating environments not only inhibit the development of emotional regulation, but the perception of the harsh environment itself may be amplified by factors influencing subjective experience.

This is consistent with previous findings from personality psychologists suggesting that predisposing temperaments in the development of BPD included high novelty seeking, and high harm avoidance (Joyce et al., 2003). Earlier accounts referred to borderline characteristics as indicative of an innate hyperbolic temperament, conceptualised as an extreme manifestation of ‘emotional hypochondriasis’ (Zanarini & Frankenburg, 1997). These theorists indirectly support the transactional account in the Biosocial model by suggesting that BPD symptoms result from the influence of a hyperbolic temperament on interpersonal exchanges, as well as on the appraisal of any negative emotions these exchanges may produce (Hopwood, Donnellan, & Zanarini, 2010). In this way, we can understand that an emotionally vulnerable child developing in an invalidating environment may experience negative affect consistently given their difficulty in expressing such emotions safely when they arise. Further, validation seeking, described as the need to share negative affective states with others, has been found to mediate the relationship between hyperbolic temperament and BPD (Hopwood, Thomas, & Zanarini, 2012). Lastly, the hyperbolic temperament has been found to be related to trait neuroticism (Hopwood & Zanarini, 2012). Among borderline individuals, trait neuroticism has been shown to negatively correlate with mindfulness abilities, such as acting with awareness (Elices et al., 2015). While the direction of this relationship has not been established, this suggests that a hyperbolic temperament either contributes towards, or is exacerbated by, interoceptive deficits.

Emotional sensitivity may also be characterised by heightened reactivity to emotional stimuli, as well as the subsequent avoidance behaviour such reactions may foster. A study of borderline features by Sturrock et al. (2009) found that avoidance of affect, as measured by distress tolerance, mediated the relationship between ICE and borderline symptoms. In addition to affect, avoidance of harm may be a risk factor for BPD symptoms. Although presenting a small sample size, Arens, Grabe, Spitzer, and Barnow (2011) found that, over a 5-year period, adolescents with increased levels of harm avoidance were more likely to be diagnosed with BPD in early adulthood. High harm avoidance was also shown to be associated with BPD in a group of borderline outpatients in the Netherlands (van Dijk, Lappenschaar, Kan, Verkes, & Buitelaar, 2012). However, Fossati et al. (2001) did not find a significant main effect of harm avoidance among borderline patients when controlling for the effect of attachment trauma. In addition, Kuo and Linehan (2009) did not find support for heightened emotional reactivity, measured by physiological changes, among borderline individuals, however they did find greater emotional intensity at baseline compared to control groups. Despite this, it has been suggested emotional reactivity, as a precursor to BPD, may be cue-specific where cue valence is influenced by experiences of trauma (Limberg, Barnow, Freyberger, & Hamm, 2011). Specifically, cues signalling rejection and abandonment resulted in increased physiological reactivity among borderline patients compared to control groups. As a result, studies measuring emotional sensitivity may benefit from measuring responses to stimuli known to foster avoidance behaviour among those with BPD.

While the absence of emotional vulnerability is an obvious protective factor against developing BPD, little is known about factors that buffer against the consequences of ICE among emotionally sensitive children. However, as emotional regulation and mentalising are learned or conditioned abilities, there are natural settings where victims of ICE can learn these skills prior to developing BPD. Studies of pairs of sisters, where only one developed BPD, found that having more delinquent friends and being less popular among peers increased the risk for BPD, and that having a supportive social network protected against its development (Laporte, Paris, Guttman, Russell, & Correa, 2012; Paris, Perlin, Laporte, Fitzpatrick, & DeStefano, 2014). This fits with findings that the relationship between ICE and psychopathology may be mediated by a cognitive schema which assumes that others will not be sympathetic towards one’s emotions (Westphal, Leahy, Pala, & Wupperman, 2016). This schema would be redundant in an individual with a social network of supportive peers. In addition, peer attachment was found to be a protective factor by Beck et al. (2017) who explained that peer attachment was associated with an increase in mentalising capacities. By this account, peer attachment provides an environment for an individual at risk of developing BPD to learn emotional regulation, via interoceptive conditioning. The motivation to establish and maintain social connections requires some degree of self-regulation, and the positive outcomes associated with this attachment may be conducive to this process. However, it is possible that the direction of this relationship ran contrary to that claimed by researchers. Specifically, that a latent mentalising skill fostered subsequent peer attachment. Thus, more research is required to test both the existence and source of a latent mentalising ability.

In sum, borderline personality disorder is a severe and debilitating disorder which is associated with a high suicide rate. A characteristic feature of BPD, emotional dysregulation, may reflect a poorness of fit between predisposing factors towards emotional sensitivity, and an invalidating childhood environment. Where children in environments of a good fit learn emotional regulation via interoceptive conditioning, sensitive children in invalidating environments are prevented from expressing affective states and thus fail to learn how to label and manage their emotions. Biological factors which influence subjective experience, such as perception and evaluation, moderate the relationship between invalidation and borderline symptoms. However, recent research gives rise to the possibility that adolescent peer attachment may be an opportunity conducive to developing interoceptive abilities involved in emotional regulation, such as mentalising.

At present, our understanding of invalidation in developing BPD is either theoretical or limited to correlational studies. Further work is required to establish mainstream consensus around both the definition and measurement of childhood invalidation. The plethora of scales and definitions in the literature prevents comparison between studies and limits the generalisability necessary to understand how invalidation hinders emotional regulation. While the literature on interoceptive faculties and conditioning may explain the mechanism behind normal development of emotional regulation, the breakdown of this process in an invalidating environment warrants empirical investigation, including at the neurological level. Further, the role of interoceptive abilities remains under-studied in BPD. At present, accounts of interoception are dependent either on research on alexithymia, or on parallel research on other topics such as eating disorders. In addition, little is known about the biological factors which produces known predisposing factors, such as hyperbolic temperament, and harm avoidance. Many studies in this area have limited statistical power, as sample sizes tend to involve a limited number of BPD patients in clinical settings, which limits the generalisability of any effects or relationships found. Lastly, and most importantly, much more work is required to isolate protective factors against developing BPD among emotionally sensitive adolescents who were raised in invalidating childhood environments. Adolescent peer attachment is a promising avenue for research, and work is required to establish whether this fosters the development of mentalising abilities, or if there is some additional biological or genetic mechanism which enhances either mentalising or interoceptive abilities.

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