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

The impact of trauma and how to intervene: a narrative review of psychotraumatology over the past 15 years

To mark 15 years of the European Journal of Psychotraumatology, editors reviewed the past 15-year years of research on trauma exposure and its consequences, as well as developments in (early) psychological, pharmacological and complementary interventions. In all sections of this paper, we provide perspectives on sex/gender aspects, life course trends, and cross-cultural/global and systemic societal contexts. Globally, the majority of people experience stressful events that may be characterized as traumatic. However, definitions of what is traumatic are not necessarily straightforward or universal. Traumatic events may have a wide range of transdiagnostic mental and physical health consequences, not limited to posttraumatic stress disorder (PTSD). Research on genetic, molecular, and neurobiological influences show promise for further understanding underlying risk and resilience for trauma-related consequences. Symptom presentation, prevalence, and course, in response to traumatic experiences, differ depending on individuals' age and developmental phase, sex/gender, sociocultural and environmental contexts, and systemic socio-political forces. Early interventions have the potential to prevent acute posttraumatic stress reactions from escalating to a PTSD diagnosis whether delivered in the golden hours or weeks after trauma. However, research on prevention is still scarce compared to treatment research where several evidence-based psychological, pharmacological and complementary/ integrative interventions exist, and novel forms of delivery have become available. Here, we focus on how best to address the range of negative health outcomes following trauma, how to serve individuals across the age spectrum, including the very young and old, and include considerations of sex/gender, ethnicity, and culture in diverse contexts, beyond Western, Educated, Industrialized, Rich, and Democratic (WEIRD) countries. We conclude with providing directions for future research aimed at improving the well-being of all people impacted by trauma around the world. The 15 years EJPT webinar provides a 90-minute summary of this paper and can be downloaded here [http://bit.ly/4jdtx6k].

Both slow wave and rapid eye movement sleep contribute to emotional memory consolidation

Sleep supports memory consolidation, but the specific roles of different sleep stages in this process remain unclear. While rapid eye movement sleep (REM) has traditionally been linked to the processing of emotionally charged material, recent evidence suggests that slow wave sleep (SWS) also plays a role in strengthening emotional memories. Here, we use targeted memory reactivation (TMR) during REM and SWS in a daytime nap to directly examine which sleep stage is primarily involved in consolidating emotional declarative memories. Contrary to our hypothesis, reactivating emotional stimuli during REM impairs memory. Meanwhile, TMR benefit in SWS is strongly correlated with the product of time spent in REM and SWS. The emotional valence of cued items modulates both delta/theta power and sleep spindles. Furthermore, emotional memories benefit more from TMR than neutral ones. Our findings suggest that SWS and REM have complementary roles in consolidating emotional memories, with REM potentially involved in forgetting them. These results also expand on recent evidence highlighting a connection between sleep spindles and emotional processing.

Recent Evidence of Non-Rapid Eye Movement Sleep Oscillation Abnormalities in Psychiatric Disorders

PURPOSE OF REVIEW

We review recent studies published from 2019 to 2024 examining slow waves and sleep spindles abnormalities across neurodevelopmental, mood, trauma-related, and psychotic disorders using polysomnography and Electroencephalogram (EEG).

RECENT FINDINGS

Individuals with attention-deficit/hyperactivity disorder (ADHD) showed higher slow-spindle activity, while findings on slow-wave activity were mixed. Individuals with autism spectrum disorder (ASD) showed inconsistent results with some evidence of lower spindle chirp and slow-wave amplitude. Individuals with depression displayed lower slow-wave and spindle parameters mostly in medicated patients. Individuals with post-traumatic stress disorder (PTSD) showed higher spindle frequency and activity, which were associated with their clinical symptoms. Psychotic disorders demonstrated the most consistent alterations, with lower spindle density, amplitude, and duration across illness stages that correlated with patients' symptom severity and cognitive deficits, whereas lower slow-wave measures were present in the early phases of the disorders. Sleep spindle and slow-wave abnormalities are present across psychiatric populations, with the most consistent alterations observed in psychotic disorders. Larger studies with standardized methodologies and longitudinal assessments are needed to establish the potential of these oscillations as neurophysiological biomarkers and/or treatment targets.

The importance of REM sleep fragmentation in the effects of stress on sleep: Perspectives from preclinical studies

Psychological stress poses a risk for sleep disturbances. Importantly, trauma-exposed individuals who develop posttraumatic stress disorder (PTSD) frequently report insomnia and recurrent nightmares. Clinical studies have provided insight into the mechanisms of these sleep disturbances. We review polysomnographic findings in PTSD and identify analogous measures that have been made in animal models of PTSD. There is a rich empirical and theoretical literature on rapid eye movement sleep (REMS) substrates of insomnia and nightmares, with an emphasis on REMS fragmentation. For future investigations of stress-induced sleep changes, we recommend a focus on tonic, phasic and other microarchitectural REMS measures. Power spectral density analysis of the sleep EEG should also be utilized. Animal models with high construct validity can provide insight into gender and time following stressor exposure as moderating variables. Ultimately, preclinical studies with translational potential will lead to improved treatment for stress-related sleep disturbances.

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.

Emotional memories are enhanced when reactivated in slow wave sleep, but impaired when reactivated in REM

Sleep supports memory consolidation. However, it is not completely clear how different sleep stages contribute to this process. While rapid eye movement sleep (REM) has traditionally been implicated in the processing of emotionally charged material, recent studies indicate a role for slow wave sleep (SWS) in strengthening emotional memories. Here, to directly examine which sleep stage is primarily involved in emotional memory consolidation, we used targeted memory reactivation (TMR) in REM and SWS during a daytime nap. Contrary to our hypothesis, reactivation of emotional stimuli during REM led to impaired memory. Consistent with this, REM% was correlated with worse recall in the group that took a nap without TMR. Meanwhile, cueing benefit in SWS was strongly correlated with the product of times spent in REM and SWS (SWS-REM product), and reactivation significantly enhanced memory in those with high SWS-REM product. Surprisingly, SWS-REM product was associated with better memory for reactivated items and poorer memory for non-reactivated items, suggesting that sleep both preserved and eliminated emotional memories, depending on whether they were reactivated. Notably, the emotional valence of cued items modulated both sleep spindles and delta/theta power. Finally, we found that emotional memories benefited from TMR more than did neutral ones. Our results suggest that emotional memories decay during REM, unless they are reactivated during prior SWS. Furthermore, we show that active forgetting complements memory consolidation, and both take place across SWS and REM. In addition, our findings expand upon recent evidence indicating a link between sleep spindles and emotional processing.