Neural Processes Underlying the Intrusion of Unwanted Memories

Abstract

While memory retrieval is often voluntary, memories can also intrude into awareness against our will, disrupting ongoing cognitive processes and causing distress. Intrusive memories are a hallmark of a variety of psychiatric disorders, including post-traumatic stress disorder, anxiety, and depression. As such, understanding the attentional processes underlying the sudden intrusion of unwanted memories into our awareness is of great importance. This thesis investigates the attentional mechanisms involved in the intrusion of unwanted memories using functional magnetic resonance imaging (fMRI) and the Think/No-Think (TNT) task, a paradigm is a widely used to study the suppression of unwanted memories. The thesis is organized into six chapters, each addressing a different aspect of detecting and controlling intrusive memories in the TNT task. In the first chapter, an overview of the relevant literature is provided, highlighting the automatic nature of intrusive memories and their attention-capturing nature. The chapter also discusses how the brain responds when stimuli in the environment capture our attention and how ignoring distracting information can diminish capture responses. It also introduces the TNT task and highlight key findings. The second chapter focuses on activity that arises in the right dorsal intraparietal lobule when involuntary retrieval occurs. By conducting a spatial-cueing task in the same participants, I demonstrate co-localization of intrusion-related activity with areas engaged during reflexive reorienting of attention to invalidly cued items. Using multi-voxel pattern analysis (MVPA), I found a significant similarity in the activation patterns caused by mnemonic intrusions and visual reorienting. As such, an intruding memory may capture attention just like a goal-relevant visual stimulus does, signalling the demand for control processes to purge the intruded memory from awareness. The third chapter replicates the parietal intrusion effect in novel TNT data processed using the Human Connectome Project (HCP) minimal preprocessing pipelines. A further aim was to broaden the view of the attentional processes on trials both with and without intrusions by focusing on two key resting-state networks that consistently show up in the literature on attention: the frontoparietal control network (FPN) and the cingulo-opercular network (CON). The study also attempts to relate these networks to reactive control and proactive control processes, respectively. The results showed that intrusions almost uniquely activate the FPN, often observed in working memory and task-switching tasks. The fourth chapter looks at intrusions from a different perspective by quantifying traces of the specific memory that intruded with cross-task pattern analysis (MVPA). The study found evidence for item-specific memory reactivation during involuntary retrieval in the hippocampus, but also traces of control. Chapter 5 describes an accidental finding: a lingering effect of suppression on the processing of visual stimuli even days up to a week later. The study found that encountering visual stimuli that were previously suppressed memory targets in the TNT were processed less efficiently than stimuli that belonging to a baseline condition. The findings suggest that memory suppression can have a lasting effect on attentional processing. In the final chapter I highlight several gaps in our understanding of unwanted memories that still need to be addressed and argue that a comprehensive understanding of intrusive memories requires taking into account the dynamic interplay between attention, memory, and control processes.