Lower Sleep Duration Is Associated With Reduced Autobiographical Memory Specificity

J, Tandoc M, Antony J, Schapiro A. Memory reactivation during sleep does not act holistically on object memory

Memory reactivation during sleep is thought to facilitate memory consolidation. Most sleep reactivation research has examined how reactivation of specific facts, objects, and associations benefits their overall retention. However, our memories are not unitary, and not all features of a memory persist in tandem over time. Instead, our memories are transformed, with some features strengthened and others weakened. Does sleep reactivation drive memory transformation? We leveraged the Targeted Memory Reactivation technique in an object category learning paradigm to examine this question. Participants (20 female, 14 male) learned three categories of novel objects, where each object had unique, distinguishing features as well as features shared with other members of its category. We used a real-time EEG protocol to cue the reactivation of these objects during sleep at moments optimized to generate reactivation events. We found that reactivation improved memory for distinguishing features while worsening memory for shared features, suggesting a differentiation process. The results indicate that sleep reactivation does not act holistically on object memories, instead supporting a transformation process where some features are enhanced over others.

How do the sleep features that characterise depression impact memory?

Depression is associated with general sleep disturbance and abnormalities in sleep physiology. For example, compared with control subjects, depressed patients exhibit lower sleep efficiency, longer rapid eye movement (REM) sleep duration, and diminished slow-wave activity during non-REM sleep. A separate literature indicates that depression is also associated with many distinguishing memory characteristics, including emotional memory bias, overgeneral autobiographical memory, and impaired memory suppression. The sleep and memory features that hallmark depression may both contribute to the onset and maintenance of the disorder. Despite our rapidly growing understanding of the intimate relationship between sleep and memory, our comprehension of how sleep and memory interact in the aetiology of depression remains poor. In this narrative review, we consider how the sleep signatures of depression could contribute to the accompanying memory characteristics.

Factors that contribute to an inability to remember an important aspect of a traumatic event

Dissociative amnesia is controversial. We tested other factors that could contribute to an inability to remember an important aspect of a traumatic event: how traumatic the event was, organic amnesia, dissociative state, childhood amnesia, expression suppression, sleep disturbance, repeated experiences, and ordinary forgetting. Trauma survivors who reported an inability to remember an important aspect of a traumatic event rated the event as traumatic as trauma survivors who reported no such inability to remember. Moreover, all cases of an inability to remember an important aspect of the traumatic event could be explained by at least one factor other than dissociative amnesia. These findings are contrary to dissociative amnesia. Compared to participants who reported no inability to remember an important aspect of the traumatic event, participants who did report an inability to remember were more likely to (1) have felt disconnected from their body during the traumatic event, which may have altered memory encoding, (2) have experienced sleep problems in the year after the traumatic event, which may have reduced memory consolidation, and (3) have experienced the traumatic event repeatedly, which may have led to less detailed memories. These findings have implications for the inclusion of dissociative amnesia in the DSM.

Difficulties in retrieving specific details of autobiographical memories and imagining positive future events in individuals with acute but not remitted anorexia nervosa

INTRODUCTION

The factors that contribute to the maintenance of anorexia nervosa (AN) are not fully understood, although it is generally accepted that depression is a core feature and contributes to poor prognosis. Individuals with depression tend to have difficulties in producing specific details of autobiographical memories and future episodes. Our aim was to investigate autobiographical memory and episodic future thinking (EFT) in individuals with AN (n = 46), people recovered from AN (recAN; n = 40), and non-affected controls (n = 35).

METHOD

Using a remotely administered computerised version of the autobiographical memory test and episodic future thinking task, we measured six aspects of memory retrieval and EFT generation: specificity, detailedness, difficulty in remembering/imagining, positivity, vividness and realism. Memory and EFT cue valence was manipulated; cues were either positive, neutral, or disorder-related/negative. As the production of EFTs is theoretically linked to the ability to retrieve autobiographical memories, the relationship between autobiographical memory specificity and EFT specificity was explored. To investigate whether autobiographical memory and EFT performance were independent of performance on other forms of cognition, working memory, verbal fluency and cognitive flexibility were measured.

RESULTS

People with AN had difficulties retrieving specific details of autobiographical memories and rated autobiographical memories as less positive overall, and less vivid when primed by positive cues. People with a lifetime diagnosis (currently ill or recovered) reported greater difficulty in retrieving memories. The AN group generated less positive EFTs, particularly to positive and neutral cues. Comorbid depressive symptoms had some contribution to the observed findings. Lastly, in all groups autobiographical memory specificity predicted EFT specificity.

DISCUSSION

Problems with retrieving specific details of autobiographical memories and simulating positive EFTs may be a state feature of AN. Treatments targeted at alleviating depressive symptoms, as well those targeted towards facilitating memory retrieval or reconsolidation, and the construction of positive EFTs, may contribute to hope for recovery and strengthen the sense of self beyond the disorder.

Moderating effects of sleep difficulties on relations between posttraumatic stress disorder symptoms and positive memory count

OBJECTIVES

Posttraumatic stress disorder (PTSD) severity relates to positive memory retrieval difficulties. One variable potentially influencing this relation is sleep difficulties. We examined moderating effects of sleep difficulties (duration and quality) on relations between PTSD severity and count of specific positive memories covarying for age, gender, and depression.

METHODS

Participants were an Amazon Mechanical Turk-recruited trauma-exposed community sample of 205 respondents (M age  = 35.44; 61.40% women).

RESULTS

Moderated regression analyses indicated significant interaction effects between sleep quality (b = 0.03; p = 0.036) and PTSD severity on specific positive memory count. Among individuals reporting better sleep quality, there were negative associations between PTSD severity and specific positive memory count (b = -0.04, SE = 0.02, p = 0.010). Similar results were obtained for PTSD's intrusion and arousal clusters.

CONCLUSION

Results support targeting sleep quality and PTSD severity to improve positive memory retrieval in PTSD and memory interventions, and the importance of considering sleep when examining links between PTSD and positive memory retrieval.