As soon as a person opens their eyes for the very first time, they are experiencing the first memories they will ever have in their life. There is a focus on new sights, sounds, smells, embraces that are categorized in such a way that this first experience with memory is unique to their life. However, these memories are quickly compartmentalized, and not to be seen again. As a person grows up, they can develop longer lasting memories that are from a combination of experiences and sensory information that they were unable to recall at a younger age. Memory in a human can be formed in multiple ways and has varying factors both internal and external. But one of the most important causes of memory retention is encoding done in the stages of sleep. The ability to sleep is in part of the body's natural Circadian rhythm, which gives natural cues to help the body sleep when necessary, and if these two things relate to memory. This was a focus on Dr. Cavanaugh's results of study on sleep consolidation and Circadian rhythm.
Dr. Cavanaugh et al., had worked on a study with Drosophila that showed how disruption of sleep could cause confusion and inability to sleep. However, the study had also shown there being no effect on short term memory, only the potentiation of long-term memories. The Drosophila study showed the interruptions caused by stimulation activated regions that would cause the inability to retain information learned by the flies previously. This was seen in another study that stimulated mice. This study was also studied to show the effects of optogenetic procedures put into place.
This research article "Shining a Light on the Mechanisms of Sleep for Memory Consolidation" by Frazer et al, shows that sleep is one of the most important functions that help with memory formation. This is not a new discovery, as multiple studies have proven how important sleep is for the ability to function normally. Previously, it was speculated that stress was a leading cause of memory loss. While stress has factors of memory loss and deformation on the brain regions such as the hippocampus, it is being seen more and more that sleep deprivation is a leading cause. The most important factor of that is the role of interrupted sleep versus uninterrupted sleep. Sleep has a role in ensuring memory is encoded to the long-term potentiation that helps memories become more solidified in the subconscious. In this study, there was heavy emphasis on sleep cycles being the main feature of why memories are created. Multiple interruptions of sleep cycles were found to not retain as much information. This study utilizes optogenetic technology to excite the brain at certain times of sleep period. The location they had focused on seeing changes was the CA1 location of the hippocampus. The brain was unable to fully commit to REM sleep as an effect of this because of the consistent excitements from the light firing on the nerves. What does it mean to have sleep interrupted? It is the lack of continuation of a full sleep cycle. Instead of reaching the deeper sleep, the brain when interrupted is put through the same cycle of sleep for multiple hours. This is because the activation of optimal nerves cause more activation in the hippocampus than necessary, making it so the sleep is not restful or deep enough to retain information.
Both of these studies had concluded that short term memory was not deeply affected by interruptions of sleep. However, they both severely impacted long term potentiation and caused disorder due to the consistent stimuli. This could lead to further studies on what stimuli causes the greatest reaction as a pull out of deep sleep cycle, and which ones will cause little to no interruptions.
References:
Poe, A. R., Zhu, L., McClanahan, P. D., Szuperak, M., Anafi, R. C., Thum, A. S., Cavanaugh, D. J., & Kayser, M. S. (2022). Developmental emergence of sleep rhythms enables long-term memory capabilities in Drosophila. https://doi.org/10.1101/2022.02.03.479025
Frazer, M. A., Cabrera, Y., Guthrie, R. S., & Poe, G. R. (2021). Shining a Light on the Mechanisms of Sleep for Memory Consolidation. Current Sleep Medicine Reports. https://doi.org/10.1007/s40675-021-00204-3
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