Sleep spindle dynamics suggest over-consolidation in post-traumatic stress disorder

Devastating and persisting traumatic memories are a central symptom of post-traumatic stress disorder (PTSD). Sleep problems are highly co-occurrent with PTSD and intertwined with its etiology. Notably, sleep hosts memory consolidation processes, supported by sleep spindles (11-16 Hz). Here we assess the hypothesis that intrusive memory symptoms in PTSD may arise from excessive memory consolidation, reflected in exaggerated spindling. We use a newly developed spindle detection method, entailing minimal assumptions regarding spindle phenotype, to assess spindle activity in PTSD patients and traumatized controls (n=2x14, matched on gender). Our results show increased spindle activity in PTSD, which positively correlates with daytime intrusive memory symptoms. Together, these findings provide a putative mechanism through which profound sleep disturbance in PTSD may contribute to memory problems. Due to its uniform and unbiased approach, the new, minimal assumption spindle detection method seems a promising tool to detect aberrant spindling in psychiatric disorders.

Selectively Interfering With Intrusive but Not Voluntary Memories of a Trauma Film: Accounting for the Role of Associative Memory

Intrusive memories of a traumatic event can be reduced by a subsequent interference procedure, seemingly sparing voluntary memory for that event. This selective-interference effect has potential therapeutic benefits (e.g., for emotional disorders) and legal importance (e.g., for witness testimony). However, the measurements of intrusive memory and voluntary memory typically differ in the role of associations between a cue and the emotional memory “hotspots.” To test this, we asked participants to watch a traumatic film followed by either an interference procedure (reminder plus Tetris) or control procedure (reminder only). Measurement of intrusions (using a laboratory task) and voluntary memory (recognition for film stills) were crossed with the presence or absence of associative cues. The reminder-plus-Tetris group exhibited fewer intrusions despite comparable recognition memory, replicating the results of prior studies. Note that this selective interference did not appear to depend on associative cues. This involuntary versus voluntary memory dissociation for emotional material further supports separate-trace memory theories and has applied advantages.

Do Cognitive Tasks Reduce Intrusive-Memory Frequency After Exposure to Analogue Trauma? An Experimental Replication

Cognitive task interventions that interfere with visuospatial working memory during the memory consolidation window hold promise for reducing intrusive memories in trauma-exposed people. Our study provides an independent replication study to test and verify findings that have primarily originated from a single research group. We hypothesized that participants engaging in a visuospatial task (cognitive task intervention including Tetris or D-Corsi) following a trauma-film paradigm (TFP) would report fewer intrusive memories over the course of a week compared with control participants. Participants ( N = 110) were randomly assigned to an experimental condition after viewing the TFP. Generalized linear mixed models indicated that the cognitive task including Tetris was associated with fewer intrusions for the TFP compared with both the D-Corsi-intervention and control conditions. Our findings are congruent with existing literature indicating that cognitive tasks, such as an intervention including Tetris, may promote effective memory consolidation after exposure to a potentially traumatic event.

Wakeful rest compared to vigilance reduces intrusive but not deliberate memory for traumatic videos

Intrusive memories are prominent features of post-traumatic stress disorder, but the mechanisms supporting their development, and their relationship to deliberate memories, are subject to competing theories. Are they strengthened examples of a unitary memory system, or fragmented representations lacking aspects of healthy memories? Given the importance of post-encoding processing in memory consolidation, we investigated the effects of a brief wakeful rest compared to a vigilance task immediately after the encoding of traumatic material on subsequent intrusive and deliberate memory. Across two experiments, participants watched emotionally negative film clips immediately followed by a brief wakeful rest or a simple vigilance (0-back) task. Brief wakeful rest had distinct effects on memory compared to the 0-back task, reducing intrusive memory frequency but not changing deliberate memory performance. These differential effects suggest that intrusive memory and deliberate memory reflect dissociable systems, arguing against unitary accounts. Our findings highlight the importance of post-encoding processing in the consolidation of traumatic material and the development of intrusive memories and provide a new perspective for interpreting mechanisms of therapeutic intervention.