ACTing on Repetitive Negative Thinking (RNT) A cross-cultural investigation on the efficacy of a brief ACT intervention for RNT

Acceptance and Commitment Therapy (ACT) is a contextual behavioural therapeutic approach rooted in Functional Contextualism (FC) and Relational Frame Theory as its theoretical foundation (RFT). FC emphasizes understanding behaviour in context with the goal of predict-and-influence, while RFT provides a behavioural model for language and cognition, explaining symbolic behaviour and indirect learning. This comprehension bases the therapeutic ACT approach, which aims to promote Psychological Flexibility (PF) as a healthy psychological state, contrasting with Psychological Inflexibility, which describes psychopathology. PF includes present-moment awareness, cognitive defusion, acceptance of internal experiences, self-as-context, valued and values-oriented actions, while in PI we have inflexible attention (towards the future or past), cognitive fusion (CF), experiential avoidance (EA), self-as-content, lack of clarity of values and values-oriented behaviours. Despite the extensive research supporting ACT’s efficacy, it still lacks cross-cultural investigations that test its transcultural effectiveness. Repetitive Negative Thinking (RNT) is a transdiagnostic cognitive process strongly associated with psychological distress and mental health disorders, such as anxiety and depression. It functions as an avoidance strategy that targets regulating emotions by avoiding unpleasant thoughts. Previous research on brief ACT interventions for RNT in Colombia yielded promising results, yet gaps remain regarding its cross-cultural applicability. Moreover, although several ACT-RNT studies have been conducted, to date, none have evaluated the mechanism responsible for clinical change. Thus, this PhD program has two primary goals. (1) to explore the cross-cultural application of the ACT-RNT framework in Brazil; (2) evaluate the processes responsible for clinical change. Three interconnected studies were conducted. Study 1 investigated the relationship between RNT, CF, EA, valued living, psychological inflexibility (PI) and psychological distress (PD) on a Brazilian sample with n=187 participants. Correlational and a regression analysis identified CF as the primary mediator in the relation between RNT and PI. Furthermore, Study 1 validated brief measures which were used on the following study. Study 2 adapted an existing 2-session ACT intervention for RNT to the online setting for the Brazilian population, innovative methodologies for data collection and analysis, investigating mediational variables responsible for change in emotional symptoms on a Single Case Experimental Design (SCED). Seven adults with moderate to severe levels of and high psychological distress completed the intervention. Results demonstrated that the protocol benefited most participants and demonstrated that RNT and RNT-related EA mediated significantly clinical improvements. Study 3 further explored the effectiveness of the protocol by addressing methodological limitations. Therapists with different levels of experience delivered sessions to seven participants (adults with high RNT and PD). Results replicated and extended the ones from Study 2, reinforcing the efficacy of ACT for RNT in Brazilian populations. This thesis contributes to the literature by demonstrating the transcultural applicability of ACT, advancing understanding of processes of change and validating brief, scalable ACT interventions. The innovative statistical mediational model developed for SCD studies offers a robust mechanism for analysing therapeutic mechanisms of change. These findings emphasize the importance of culturally sensitive, process-based approaches in mental health research and highlights the potential of brief ACT interventions to address transdiagnostic issues, such as RNT in a variety of settings. These results provide a foundation for future research that aim to expand ACT-RNT framework’s reach ad refine interventions targeting PD in different cultural contexts.