Methods to induce dissociation and their effects on intrusions and memory: a randomized controlled trauma-film study

<b>Background:</b> Peritraumatic dissociation is thought to contribute to posttraumatic symptoms like intrusions and memory disturbances. However, trauma-analogue studies that examined effects of experimental dissociation-induction on intrusions and memory were inconclusive. To better understand this, a necessary first step is to more systematically compare various induction methods.<b>Objective:</b> We evaluate different dissociation-induction-methods regarding their effectiveness, the intensity and quality of induced dissociation, and their effects on intrusions and memory in a pre-registered randomised-controlled online experiment.<b>Method:</b> Healthy participants (<i>N</i> = 213) were randomised to one of six dissociation-induction-methods: audio-photic stimulation, hypnotic-suggestion, or spiral-staring, each for one-minute or three-minute duration. Participants also completed two further conditions: a non-dissociation-inducing picture task (control condition) and the comparison dissociation-induction-method dot-staring (benchmark condition). Each condition was followed by an aversive ('trauma') film. Peri-film dissociation intensity (measured using an adapted version of the Peritraumatic Dissociative Experiences Questionnaire) and quality, as well as film-specific intrusion-load and memory performance, were assessed. Dissociation-induction-methods were deemed successful if they elicited dissociation levels higher than the control condition and at least as high as the benchmark condition. Only successful dissociation-induction-methods were examined further.<b>Results:</b> Three minutes of hypnotic-suggestion and one minute of spiral-staring successfully induced dissociation during the film, while other methods did not meet the effectiveness threshold. Hypnotic-suggestion led to a greater increase in dissociation intensity than spiral-staring, dissociation induced by spiral-staring was perceived as more uncontrollable and unpleasant. Results did not support an adverse effect of dissociation-induction or dissociation intensity on intrusion-load, but they did support an adverse effect on self-reported and objectively assessed memory performance.<b>Conclusions:</b> Results indicate that hypnotic-suggestion and spiral-staring constitute effective, easy-to-implement, and in principle, neuroimaging-compatible dissociation-induction-methods that allow studying dissociation in the laboratory. The present data did not support the notion that dissociation fosters intrusion formation but provides causal support for effects of dissociation on trauma memory.