Does REM Sleep Retain Emotional Memories?

During sleep, our bodies can retain emotional memories. These memories are stored in our hippocampus and can be used later in life. But when we don't get enough sleep, these memories can become fragmented, and we can even develop nightmares.

REM sleep

Several studies have questioned whether REM sleep retains emotional memories. There is also a question about its role in declarative memory processes. In some instances, REM sleep may interfere with consolidating these types of memories.

Some studies suggest that REM sleep is critical in procedural memory consolidation. This is because certain types of visual learning depend on the timing of deep sleep. However, the effects of sleep on memory relevance have been found to rely on other factors as well.

For instance, a recent study found that sleep strengthens problem-solving skills. It also suggests that REM sleep plays an essential role in consolidating emotionally charged information.

Another study area has focused on the interaction between emotion and future relevance. For example, Kuriyama et al.,101 studied the impact of recalling/forgetting instructions on memory performance. Participants were asked to identify images from a series of clips. In some cases, they were instructed to quickly forget what they had seen, while in other cases, they were told to remember what they had seen.

The early half of the night

REM sleep has been associated with enhancements in emotional memory retention and recognition. However, the extent of this association needs to be clarified. The present study examined the effects of REM sleep on the consolidation of neutral and emotional memories. A split night design was employed to investigate this question. During the first night half of the experiment, participants encoded neutral images at various screen locations. They performed an emotionally laden source memory task. In the second half, participants watched a documentary film that exhibited a level of emotional familiarity. During the critical consolidation period, participants received high levels of SWS. The results suggested a functional dissociation between the processing of neutral and emotional source memories.

The study also measured several subjective parameters related to emotional reactivity. The most interesting of these was the number of images viewed after sleep compared to those viewed before. In general, sleep enhances the receptiveness of images presenting an emotional characterization. The best of these findings still need to be fully understood, but they confirm that consolidation processes are an essential part of the process.

Biasing the consolidation of different components from the same emotional scenes

Several studies have investigated sleep's effect on memory retrieval. They have examined different memory recall schemes, including delayed recall, REM, and a short-term retention period. Most studies used relatively small sample sizes, which limited their power. However, this study utilized a large online sample to facilitate a thorough exploration of potential moderators of the sleep-emotional memory trade-off. Consequently, the findings are generalizable across the population.

This study was designed to investigate whether sleep impacted memory for the emotional components of scenes. It was carried out in a randomized fashion in four groups of young adults. Participants viewed a series of 64 scenes in the morning and evening. They completed a surprise test to assess their memory for relational pairs. Interestingly, the most memorable memory of a positive scene was not associated with sleep. This was contrary to previous studies, which found a correlation between sleep and remembering a negative object.

Effects of sleep deprivation on traumatic memories

Whether sleep deprivation affects traumatic memories is an important question. A good night's sleep is widely believed to be the best way to heal from a stressful event. However, there are indications that this may not be the case. In this study, researchers tested the effect of total and inconsistent sleep deprivation on voluntary memory.

Participants were randomly assigned to a sleep group or a total sleep deprivation group. 

They were then exposed to a traumatic film and were also asked to provide their thoughts about the film. The people were then monitored in their home environment.

They were then assessed for their intrusion memories using VAS. They were also asked to complete a pen-and-paper intrusion diary. The recorded intrusions numbers were analyzed and fitted to a two-level generalized linear model.

Compared with the control group, the sleep-deprived group reported fewer intrusive memories on the first and second days. On the first day, the sleep-deprived group reported z = -2.44, whereas the sleep group reported z = 0.83 +- 1.01. On the second day, the sleep-deprived group reported a z = 2.24, whereas the sleep group reported z = -0.76.