Dissociation and later intrusive memories

This study examines the relationship between peri-traumatic dissociation (dissociation at the time of a trauma) and later intrusive memories in two non-clinical groups. Peri-traumatic dissociation is a known predictor of later pathological reactions (Van der Kolk and Van der Hart 1989), and poorer outcome (Shalev, Peri, Canetti and Schrieber, 1996) in clients with Post-traumatic stress disorder (PTSD). One of the reasons for this could be that peri-traumatic dissociation has been shown to increase later intrusive memories of stressful events (Brewin and Saunders 2001; Holmes, 2000). In order to study this, an analogue trauma was created using stressful films of the aftermath of road traffic accidents. Non-clinical participants were then exposed to the films under controlled laboratory conditions. Participants completed before and after measures of state and trait dissociation and rated how they felt during the films before recording their intrusive memories of the films in a diary over the following week. Two experimental studies were conducted using different participants. The first study attempted to decrease dissociation using a grounding technique (manipulating plasticine). The second attempted to increase dissociation using a hypnotic induction. The manipulation of dissociation in the laboratory is extremely difficult. Both studies conducted were within-subjects designs, and all participants received the dissociation manipulation whilst viewing a stressful film and a control no-task condition in which they viewed a stressful film only. Previous studies have given participants guidelines on how to dissociate (Murray, 1997) and practice in the technique (Holmes, 2000) but they were unsuccessful in increasing state dissociation. Holmes and Brewin (2001) suggested a more powerful technique should be used such as a pharmacological agent or hypnosis. Contrary to predictions, participants did not experience significantly more intrusions from the film in which they received hypnotic suggestions to dissociate than from the control condition film. However, they did report an increased level of dissociation, indicating that hypnosis is a useful technique for increasing self-reported dissociation. As predicted, fewer intrusive memories were reported from the film in which participants performed a grounding task than from the control film, however, participants did not report decreased levels of dissociation. The theoretical implications of these studies are discussed, including the way in which dissociation should be measured, and the support found for Brewin, Dalgliesh, and Joseph's, (1996) Dual Representation Theory of post-traumatic stress disorder. Suggestions for incorporating these findings into clinical settings are made, and future research topics are highlighted