Examining the sleep's role in emotional memory processing

Abstract

Sleep plays a vital role in affective-cognitive processes, including memory consolidation and emotional re-processing. This thesis aimed to investigate the impact of sleep on the early consolidation phase of emotional memory and traumatic memory processing. Across three laboratory studies, comparisons were made between healthy participants who had a normal night of sleep and those who experienced sleep deprivation, as well as individuals diagnosed with insomnia. Chapter 2 investigated the short- and long-term effects of sleep versus sleep deprivation on emotional memory using behavioral and electrophysiological measures. We found that compared to sleep deprivation, sleep preserved the content of emotional memories and their affective tones in an immediate test, with subsequent memory decay and amelioration of negative affective tones in the longer term, that is, a short-term memory preservation and long-term affect depotentiation effect. Moreover, uni-/multi-variate EEG analyses revealed different neurocognitive processes underlying the recognition of remote memory in sleep and sleep deprivation groups. Chapter 3 examined individuals with insomnia disorders and revealed impaired emotional processing among this group. Compared to healthy group, insomnia group showed preservation of the emotional memory and resistance to the over-time dissipation of emotional tones. Insomnia participants also maintained stable neural representations of emotion across tasks, indicating prolonged emotional processing. Furthermore, healthy participants showed the over-time memory decay and arousal reduction of negative memories, which were associated with the REM duration during the post-encoding night. In contrast, this pattern and the correlation were absent in the insomnia group. Chapter 4 investigated the impact of sleep versus sleep deprivation on the processing of lab-analogue traumatic memory using the trauma film paradigm. Following watching the trauma film, participants who slept showed enhanced explicit recognition, reduced involuntary intrusions, and self-reported lower hyperarousal during the subsequent week, compared to sleep-deprived participants. Moreover, we found that better self-reported sleep quality was associated with lower intrusion frequency specifically among those who had slept. Overall, these findings underscore the beneficial effects of healthy sleep on emotional and traumatic memory processing, including memory consolidation for both negative and neutral memories, negative memory decay, over-time emotion attenuation, and intrusion reduction. Moreover, the results also provided initial evidence suggesting the involvement of rapid-eye movement (REM) sleep in these beneficial processes, although further investigation is warranted to fully understand the underlying mechanisms. Future research shall explore the effects of chronic sleep disruptions on these processes using a longitudinal approach, taking into account the over-time dynamics of sleep and emotional memory.