Efficacy and mechanisms of imagery rescripting and imaginal exposure for nightmares: study protocol for a randomized controlled trial

Background: Recurrent nightmares can effectively be treated with cognitive-behavioral techniques such as imagery rehearsal therapy, which involves imagery rescripting (IR) of nightmares, and imaginal exposure (IE) therapy. However, the underlying mechanisms of these treatments remain largely unknown. To investigate this, we identified a number of variables that might mediate the therapeutic effect of rescripting-based and/or exposure-based therapies. Also, to control for the possible confounding influence of (other) treatment components, we designed two stripped-down treatment protocols, which primarily consist of either (1) rescripting of, or (2) exposure to, the nightmare content. In a randomized controlled trial, we aim to investigate the therapeutic efficacy of these stripped-down IR and IE treatments, and explore their working mechanisms. Method: Three weekly sessions of either IR or IE will be compared to a waiting-list control group. Ninety participants suffering from nightmare disorder will be included and randomly allocated to one of the three groups. The primary clinical outcome measures are nightmare frequency and distress caused by nightmares. Secondary clinical outcome measures include sleep complaints, dysfunctional beliefs about nightmares, and posttraumatic stress symptom severity. Outcomes will be assessed weekly from week 1 (pre-assessment) to week 5 (post-assessment). Online follow-up assessments will take place at 3 and 6 months after post-assessment. In order to investigate temporal relationships between mediators and outcome, we will measure the proposed mediators of the treatment effect 1 day after each outcome assessment (but not after the follow-ups). Mediators include nightmare distress and valence, mastery of the nightmare content, predictability, controllability, and tolerability of emotions elicited by nightmares, as well as sleep quality. Discussion: The proposed trial allows us to investigate the efficacy of IR and IE as intervention techniques for the treatment of nightmares, and to explore mediators of their respective therapeutic effects. The results may advance our understanding of nightmare therapies by identifying possible mechanisms of psychological treatments for chronic nightmares. Moreover, the results of the proposed study might provide useful knowledge about the working mechanism of rescripting-based and exposure-based treatments in general.