Borderline personality disorder (BPD) is a severe mental illness with an estimated community prevalence of 2.7%. It is characterized by affective dysregulation, unstable identity and interpersonal relationships, and serious behaviors such as non-suicidal self-injury [1, 2]. The complexity and severity of BPD is characterized by high comorbidity with other psychiatric disorders, drug and/or alcohol abuse, and a high risk of suicide, which lead to an extensive use of healthcare resources, high costs of treatment, polymedication, as well as impaired psychosocial and occupational functioning [3–6].
One of the main features underlying cognitive, affective, and behavioral instability in BPD is a pervasive pattern of emotion dysregulation (ED) [7, 8]. ED involves the inability to regulate or change an emotional response or expression in a desired manner and involves a lack of (or maladaptive use of) emotion regulation strategies [9], which in turn facilitates the emergence of impulsive and risky behaviors (e.g., self-harm, substance use). These risk behaviors can be understood as a consequence of emotion regulation difficulties or as a strategy to regulate a distressing emotional state [10]. Therefore, prevention and treatment efforts are focused on addressing ED as a means of reducing distress, suffering, psychosocial impairment, and potentially life-threatening risk behaviors in individuals with a diagnosis of BPD [11].
Psychotherapy is the main recommended treatment for BPD [10, 12]. One of the empirically based therapies for the treatment of BPD is dialectical behavior therapy (DBT) [13]. DBT is a multifaceted intervention involving individual and group therapy. The group therapy addresses the skills training and comprises four different modules: mindfulness, emotion regulation, distress tolerance, and interpersonal effectiveness. Mindfulness is one of the main components of DBT, and mindfulness training are the first skills taught to support the other DBT skills [14, 15]. Interestingly, mindfulness skills training as a stand-alone intervention improves ED in BPD [16, 17], but the underlying mechanisms of change are not yet fully understood.
An understanding of the mechanisms (i.e., mediators) through which psychological interventions produce changes in desired outcomes (understanding how and why it works) is essential to optimize treatments [18]. In addition, identifying moderators (i.e., the effects on direction or magnitude of the relation between the intervention and outcome) may guide therapeutic strategies that effectively impact the mechanisms or processes of an intervention in order to obtain therapeutic improvements [19]. Thus, clinical research based on mechanisms of change (and moderators) may inform which processes (e.g., cognitive, behavioral) of an intervention contribute to the expected outcomes and in what ways. One way to study the mechanisms is to demonstrate that changes in the putative mechanism are related to changes in the expected outcome through a temporal precedence with repeated session-by-session measures [18, 20] and also disaggregating within- and between-person effects of the mechanisms [21]. This method allows for a more precise examination of the process of change within an individual.
Research has focused on uncovering the mechanisms of change by which DBT skills training improves ED in BPD [22]. Studies suggest that a greater use of behavioral skills (learned during DBT skills training) mediates changes in emotion dysregulation [9, 23]. More specifically, studies exploring the within-person effects found that greater skills use predicted improvements in ED [24, 25] and fewer risk behaviors associated with high ED [26] after undergoing DBT skills training. However, there is a scarcity of studies focused on studying the mechanisms of change of mindfulness skills training as a stand-alone intervention. For example, a recent study reported that the amount of mindfulness practice at a given week (a required dose of at least 3 days and 30 minutes) predicted improvements in ED at the following week in BPD outpatients [27].
As noted, previous findings suggest that the use of DBT skills (e.g., mindfulness) improves ED in people with BPD. Although prior theoretical and empirical accounts have proposed decentering (i.e., change in perspective on the self), emotion regulation (i.e., process emotional reactions with non-judgmental stance), body awareness and attention awareness as possible mechanisms or processes by which mindfulness practice may works [28, 29], the underlying mechanisms of change remains unclear. Decentering consists of adopting a change in perspective of one's own experience through the disidentification of the mental contents that are usually experienced as defining the self [30, 31]. This metacognitive capacity involves a process of meta-awareness by observing thoughts and emotions in a non-attached manner, which results in a reduced reactivity to thought content [32]. Interestingly, decentering has been proposed as a mediating mechanism both in mindfulness DBT skills training [17] and in emotion regulation interventions [33].
The emotion regulation process related to a nonjudgmental stance towards internal experience (i.e., when individuals stop criticizing themselves) is associated with a lower level of psychopathology [34]. However, individuals with BPD are characterized by a high tendency to judge their internal experience [14, 35]. Therefore, strategies that help increase the capacity for nonjudgment are particularly relevant to foster emotional acceptance in BPD [15]. Interestingly, this capacity (i.e., nonjudgment) is an active component of mindfulness DBT skills training. However, it has been shown to act as a mediating mechanism between DBT skills training and clinical outcomes in BPD [36, 37]. For instance, increased levels of nonjudgment over time predict fewer borderline symptoms in women with BPD features [38].
Body awareness involves paying attention to body information by identifying internal body sensations (e.g., tension) and the associated emotional state (feeling relaxed or stressed) as opposed to avoiding the bodily experience [39]. Bodily sensations are a common object of attention during mindfulness meditations [40] and would be cultivated through the ability to observe the inner experience [41]. Body awareness levels are significantly decreased in individuals with BPD compared to healthy controls, and this deficit is associated with ED [42]. Therefore, increasing body awareness is a relevant aspect in the treatment of psychological disorders, including BPD [15, 28]. Attention awareness is another putative mechanism underlying mindfulness practice and involves cultivating a present-moment awareness. For instance, mindfulness meditation involves focusing attention on an object (e.g., breathing), noticing distraction, and returning to the object of attention [43]. Promoting attention regulation in individuals with BPD is relevant to ameliorate ED and impulse control by teaching participants to observe what they are experiencing in the present moment, without attachment or avoidance of the content of the experience [15]. To our knowledge, no study has evaluated these proposed mechanisms at the same time in a mindfulness training for individuals with BPD. Knowing these specific mechanisms of change may be useful for clinicians to understand how mindfulness training works.
In summary, the main question guiding this study is how participants with BPD improve their level of ED through a mindfulness skills training. Therefore, this study explored the potential mechanisms of change within mindfulness training, focusing on decentering, nonjudgment, body awareness and attention awareness. Firstly, we evaluated whether these mechanisms and ED showed improvement over the course of mindfulness skills training. Secondly, we explored the temporal dynamics between mechanisms and ED throughout mindfulness skills training. Thirdly, based on previous findings [44], we explored decentering as a metacognitive ability that could moderate (i.e., increase the strength) the relationship between the other proposed mechanisms and ED. In summary, our hypotheses were: (1) Decentering, nonjudgment, body awareness and attention awareness would increase and ED would decrease during mindfulness skills training; (2) greater within- and between-person effects of mechanisms would predict improvements in ED in the following week; and this relationship would be bidirectional; and (3) the association between nonjudgment, body awareness, and attention awareness with ED would be greater among participants with higher decentering capacity.