Sleep differentially impacts involuntary intrusions and voluntary recognitions of lab-analogue traumatic memories

Despite the critical role of sleep in memory and emotion processing, large remains unknown regarding how sleep influences trauma-related symptoms arising from maladaptive memory/emotional processes, such as those among patients with post-traumatic stress disorder. Employing a trauma film paradigm, we investigated how post-trauma sleep versus sleep deprivation influenced involuntary intrusions and voluntary recognition of traumatic memories. Sixty participants were randomly assigned to sleep or total sleep deprivation group following experimental trauma induction. Participants were assessed with: (a) lab-based and 7-day diary-based involuntary intrusions; (b) voluntary recognitions of traumatic memories 12-hr and 7-day post-trauma induction; and (c) post-traumatic stress disorder-like symptoms measured by the Impact of Event Scale-Revised. We found that compared with sleep deprivation, slept participants experienced fewer traumatic intrusions across 7 days, reported lower emotional hyperarousal, and showed more accurate recognition of trauma-related stimuli. Moreover, higher subjective sleep quality was associated with fewer intrusions only in the sleep group, while a reversed pattern emerged in the sleep deprivation group. These results provide novel evidence supporting the therapeutic benefits of sleep in protecting mental well-being from trauma exposure. To the extent that sleep modulates trauma-related symptoms, sleep can be conceived as the potential target for early interventions among trauma victims.

The effect of cathodal transcranial direct current stimulation during rapid eye-movement sleep on neutral and emotional memory

Sleep-dependent memory consolidation has been extensively studied. Neutral declarative memories and serial reaction time task (SRTT) performance can benefit from slow-wave activity, characterized by less than 1 Hz frequency cortical slow oscillations (SO). Emotional memories can benefit from theta activity, characterized by 4-8 Hz frequency cortical oscillations. Applying transcranial direct current stimulation (tDCS) during sleep entrains specific frequencies to alter sleep architecture. When applying cathodal tDCS (CtDCS), neural inhibition or excitation may depend on the waveform at the applied frequency. A double dissociation was predicted, with CtDCS at SO frequency improving neutral declarative memory and SRTT performance, and theta frequency CtDCS inhibiting negative emotional memory. Participants completed three CtDCS conditions (Theta: 5 Hz, SO: 0.75 Hz and control: sham) and completed an SRTT and word recognition task pre- and post-sleep, comprising emotional and neutral words to assess memory. In line with predictions, CtDCS improved neutral declarative memory when applied at SO frequency. When applied at theta frequency, no negative emotional word memory impairment was found but a positive association was found between post-stimulation theta power and emotional word recognition. SRTT performance was also not altered by either CtDCS frequency. Future studies should investigate overnight theta CtDCS and examine the effects of CtDCS during and after stimulation.

Sleep Consolidates Motor Learning of Complex Movement Sequences in Mice

Introduction

Sleep-dependent consolidation of motor learning has been extensively studied in humans, but it remains unclear why some, but not all, learned skills benefit from sleep.

Aims and Methods

Here, we compared 2 different motor tasks, both requiring the mice to run on an accelerating device. In the rotarod task, mice learn to maintain balance while running on a small rod, while in the complex wheel task, mice run on an accelerating wheel with an irregular rung pattern.

Results

In the rotarod task, performance improved to the same extent after sleep or after sleep deprivation (SD). Overall, using 7 different experimental protocols (41 sleep deprived mice, 26 sleeping controls), we found large interindividual differences in the learning and consolidation of the rotarod task, but sleep before/after training did not account for this variability. By contrast, using the complex wheel, we found that sleep after training, relative to SD, led to better performance from the beginning of the retest session, and longer sleep was correlated with greater subsequent performance. As in humans, the effects of sleep showed large interindividual variability and varied between fast and slow learners, with sleep favoring the preservation of learned skills in fast learners and leading to a net offline gain in the performance in slow learners. Using Fos expression as a proxy for neuronal activation, we also found that complex wheel training engaged motor cortex and hippocampus more than the rotarod training.

Conclusions

Sleep specifically consolidates a motor skill that requires complex movement sequences and strongly engages both motor cortex and hippocampus.

The impact of obstructive sleep apnea on motor skill acquisition and consolidation

STUDY OBJECTIVE

Recent investigations suggest that motor skill learning is impaired in patients with obstructive sleep apnea (OSA) syndrome; however, it is not fully understood at what stages of learning this impairment occurs. The current study aimed to compare motor learning and memory across both daytime acquisition and overnight consolidation.

METHODS

Twelve OSA patients and twelve control participants, matched for age and education, were recruited and completed the Karolinska Sleepiness Scale and the sequential finger-tapping task (SFTT), a motor skill learning task, both before and after polysomnographic recorded sleep.

RESULTS

During the evening acquisition phase both groups showed significant and equitable improvement in the number of correctly typed sequences across trials. On retesting the following morning, the control patients showed significantly greater improvement overnight (15.35%) compared to OSA patients (1.78%). The post sleep improvement in controls, but lacking in OSA patients, was typical of a sleep dependent enhancement effect. The magnitude of improvement overnight for either group was not significantly correlated with any of the recorded sleep variables.

CONCLUSIONS

These results suggest daytime/practice related acquisition of motor skill is largely intact in OSA patients; however, marked impairment in the consolidation phase is evident following a sleep period. This particular pattern of dysfunction may remain unnoticed following single-day learning/memory assessments.