Borderline personality disorder (BPD) is a commonly occurring, severe, and costly condition that interferes greatly with quality of life. Considerable comorbidity with other disorders and existing multicomponent treatments with largely untested putative mechanisms of action represent obstacles for effective dissemination of BPD treatment; in light of this gap, the purpose of the present study is to isolate the effects of individual treatment components on putative mechanisms implicated in both BPD. This study will answer important theoretical questions about the mechanism of treatment change, and might lead to more efficacious, cost-effective, and easily disseminable treatment strategies for BPD, a severe and understudied disorder.

Borderline personality disorder (BPD) is a commonly occurring, severe, and costly condition for which treatment efforts have been hindered by several factors. First, extant treatments for BPD are long-term, intensive and consist of multiple components, largely focused on resolving the life-threatening dysregulation that characterizes this disorder. It is important to note, however, that most individuals diagnosed with BPD never attempt suicide or require inpatient hospitalization. Multi-component interventions may not be the most efficient approach for patients with less severe levels of BPD and also make it difficult to draw conclusions regarding which treatment strategies are influencing mechanisms maintaining symptoms. Additionally, extant BPD treatments do no explicitly address high rates of comorbidity with anxiety and depressive disorders; high levels of co-occurrence amongst these disorders underscores the utility of identifying transdiagnostic treatment components relevant to maintaining mechanisms across diagnostic boundaries. The proposed Mentored Patient-Oriented Research Career Development Award (K23) is a four-year plan in support of the applicant's long-term career goal to become a clinical scientist proficient in developing parsimonious, easily disseminated treatments for BPD and other emotional disorders. This project will be completed in two phases. The goal of Phase I, in line with an experimental therapeutics approach, is to investigate the effect of acting inconsistent with emotion-driven behavioral urges on emotional intensity in a sample of individuals diagnosed with BPD in the context of a single-case experiment (alternating treatment design). Phase II will also utilize single-case experimental design (in this case a multiple baseline study) to explore the effects of brief intervention focused solely on acting inconsistent to emotional action tendencies on emotional intensity, tolerance of emotions, and BPD symptoms in a sample diagnosed with BPD. Boston University's Center for Anxiety and Related Disorders, where all research and the bulk of the training activities will take place, is a world-renown clinical research institution with a successful history of treatment development research. Overall, the broader aim of these research and training goals is to address the need for improved treatments for BPD. This study will answer important theoretical questions about the mechanism of treatment change, and might lead to more efficacious, cost-effective, and easily disseminable treatment strategies for BPD, a severe and understudied disorder.

Inclusion Criteria:

1. Diagnostic and Statistical Manual (5th Edition; DSM-5) diagnosis of borderline personality disorder;
2. willing to maintain a stable dose on prescribed psychotropic medication throughout the study duration. This avoids problems with reluctance to discontinue or difficulty with discontinuing, and also the confounding of outcomes from initiation of medication during treatment; this procedure is a longstanding practice at the Center for Anxiety and Related Disorders (CARD) at Boston University for treatment outcome research. Additionally, participants must be
3. fluent in English.

Exclusion Criteria:

In order to maximize generalizability, exclusion criteria are based solely on the well-being of the participant and will consist primarily of conditions that would require prioritization for immediate treatment (e.g., severe suicidality or substance dependence). These include:

1. Current DSM-5 diagnoses of bipolar disorder, schizophrenia, schizoaffective disorder, or organic mental disorder;
2. Clear and current suicidal risk (intent);
3. Current or recent (within 3 months) history of drug dependence;
4. Willingness to refrain from additional psychosocial treatment across the course of the study; and
5. has access to own smartphone.

16 weeks