Forming Memories and the Role of Sleep and Emotion

 Multiple studies have shown that sleep has a beneficial effect on memory and consolidation. Sleep can enhance the recall of declarative memories and has been seen to improve learning. Sleep is also linked to the circadian rhythm which is an internal sleep-wake cycle that is repeated over twenty-four hours. Poe et al. performed a study analyzing the development of the circadian rhythm in Drosophila melanogaster, the fruit fly, and how circadian rhythm development exhibits long-term memory. Sleep and memory have been investigated with neural processing and development before but the study by Carollo et al. investigated the possible contribution of emotion along with sleep and its impact on memory formation and retention. 

    Poe et al. demonstrated that the development of the circadian rhythm is what enabled complex cognitive processing which included the formation of long-term memories (Poe et al. 2022). Sleep rhythms and patterns appeared when analyzing the L3 stage of larvae, a further developed stage of larvae, and not the L2 stage. The L3 group showed deeper sleep at night compared to the L2 group. The L3 group also performed better on the long-term memory task. The duration and depth of sleep depend on the internal clock. Poe et al. demonstrated that disturbing the sleep cycle or producing stress showed a disturbance in long-term memory formation. Not only is the amount of sleep important but the quality of sleep in consideration of circadian rhythms is important as well for the retention of memories. 

Carollo et al. illustrated that emotions have a role in memory formation along with the period of wakefulness and sleep. The goal of this study was to investigate the effect of nocturnal sleep compared with daytime wakefulness and the subject of emotional reactivity and memory performance (Carollo et al. 2022). Two groups were compared for this study. Both groups slept after the learning task, the Sleep First group was asked to recall the information after sleeping, and the Wake first group was asked to recall the information before sleeping. Both were shown neutral and negative images to provoke emotion. This study demonstrated that negative images and information were remembered better over time than neutral information (Carollo et al. 2022) and that sleep did benefit the retention of memory. The Sleep First group performed better at memory recall than the Wake First group.

    Both of these studies demonstrate that sleep is a beneficial factor in setting long-term memories and the ability to recall information. The circadian rhythm is not only involved in the quality of sleep but also in establishing neural connections that improve cognitive processing and long-term memory retention. Emotion is also a factor at play in the retention of memories. Negative emotions attached to memory are better remembered than those that are not. The time at which one goes to sleep during memory recall is also an important factor. Overall, sleep improves cognitive processing, the formation of long-term memories, and recall. 

References:

Carollo, G., Degasperi, G., & Cellini, N. (2022). The role of sleep and wakefulness in the recognition of emotional pictures. Journal of Sleep Research, 31( 6), e13695. https://doi.org/10.1111/jsr.13695

Poe, A., Zhu. L., McClanahan, P., Szuperak, M., Anafi, R., Thum, A., Cavanaugh, D., Kayser, M.. (2022). Developmental emergence of sleep rhythms enables long-term memory capabilities in Drosophila

bioRxiv 2022.02.03.479025; doi: https://doi.org/10.1101/2022.02.03.479025