Changing Unwanted Memories: A Consideration of Three Methods

Abstract

A substantial minority develops posttraumatic stress disorder (PTSD) in the months following a traumatic event. Central to disorder is an unwanted memory about the traumatic event. Though psychological treatment exists for PTSD, a significant number of patients may fail to improve or show relapse after successful psychological treatment. Therefore, in this thesis three different and novel interventions are examined that target unwanted memories. The first intervention to target unwanted, aversive memories is by deliberately recalling the “hotspot” of an aversive memory, while simultaneously making horizontal eye movements. The experiments in this thesis showed that performing different types of dual-task interventions (e.g., making eye movements, playing Tetris or counting) simultaneously with recall reduces self-reported ratings of vividness and/or emotionality. Additionally, more taxing dual-task interventions result in stronger reductions. Furthermore, our preliminary results showed that prolonged dual-task interventions might be able to reduce the number of intrusions, regardless of the modality of the dual-task intervention (visuospatial vs. verbal). Next to dual-task interventions, unwanted memories may also be targeted by behavioral new learning interventions during reconsolidation that disrupt or update unwanted memories. When consolidated unwanted memories are retrieved they may, under certain conditions, enter a phase in which these memories are temporarily sensitive to disruption or updating before that are re-stored in memory. However, in the experiments in this thesis we did not find that changes during reconsolidation were specific to conditions in which new learning followed reactivation. More specifically, we found that new learning, regardless of preceding reactivation, resulted in memory disruption and/or memory updating. The third intervention we examined is retrieval suppression or retrieval stopping. This ability allows individuals to limit the duration of unwelcome memories in mental awareness by cognitively preventing or interrupting the reflexive retrieval of these memories. In one experiment we showed that because of retrieval suppression people forget unwanted memories regardless of whether the memory is negative or neutral in valence. In a second experiment we show that the number of intrusive memories can be down-regulated, but that they experience more intrusions when they needed to suppress retrieval longer, and with progression of the total time suppressing. To conclude, this thesis shows that unwanted memories can be changed, and that different interventions can be employed to achieve this goal. The strongest evidence comes from memory change after dual-task interventions and retrieval suppression interventions. The results of dual-task interventions are especially promising and also support clear clinical implications (e.g., more taxing dual-task interventions have stronger effects). Regarding behavioral interventions during reconsolidation, our work is contradictory with a large body of evidence that does support memory change during reconsolidation, and this limits applying it in clinical settings currently. Clinical applicability of retrieval suppression interventions may be limited as well, because of questions about whether this is an effective intervention for everyone. Nevertheless, these interventions hold clear implications for future research, which may in the end eventually lead to new suggestions for improving treatment effectiveness.