Mechanisms of Memory Triage during Sleep

乍一看，睡眠似乎是进化的一个不适应阶段。睡眠延长了一段“不活动”的时间，减少了动物用于觅食、狩猎和寻找/吸引配偶的时间。此外，睡眠实际上比保持清醒更危险，因为保护我们免受捕食的感官输入被抑制了。那么，我们能得到什么回报呢？简短的回答是，我们不知道。很明显，进化使睡眠成为一种生物需求。你的大脑不会让你自愿避免超过几个晚上的睡眠，而非自愿的睡眠剥夺会导致慢性压力、疲劳、迷失方向、健康状况不佳甚至死亡。然而，尽管经过了几十年的研究，我们仍然不能完全理解为什么我们有这种生理上的睡眠需求。睡眠可能有多种作用，得益于长时间的“离线”状态，减少了感官输入。一个主要的假设功能是系统级的记忆巩固，这是一个存储在海马体中的新记忆被稳定并转移到大脑新皮层区域进行长期存储的过程。记忆巩固的一个关键方面是记忆分类现象，通过这种现象，与无关的经验相比，突出或重复的经验更有可能得到巩固。大脑是如何完成这种对重要记忆的选择性强化的尚不清楚，这也是我们研究计划的重点。在经历中发生的连续的神经活动模式已经被观察到在睡眠中自发地重新激活。这种被重新激活的记忆痕迹，被称为重放，被认为是大脑巩固记忆的方式，将驻留在海马体中的记忆转移到大脑的其他区域。我们将研究回放是如何被一个经历的显著性调节的，并假设更重要的经历会在睡眠中回放得更多。此外，我们预测皮质反馈在调节基于显著性的重放中起关键作用。为了验证这一点，我们将使海马体的皮质输入失活，并检查海马体是否不再偏向于回放更突出的经历。大约70%的英国人睡眠时间少于医学界建议的每晚7-9小时。此外，社交媒体使用的增加与睡眠质量下降以及焦虑和抑郁的增加有关。随着我们生活中“垃圾信息”数量的增加，我们睡眠时间的减少，我们的记忆分类系统面临着越来越大的压力，需要有效地优先巩固重要信息，并且越来越需要了解这是如何发生的。这些问题在老年人身上更加严重，因为睡眠质量和持续时间都随着年龄的增长而下降。我们的研究将直接检查记忆分类的潜在机制，并为如何进一步优化这一过程提供新的思路。

At first glance, sleep appears to be a maladaptive step of evolution. Sleep imposes a prolonged period of "inactivity", reducing the time an animal can spend on foraging, hunting, and finding/attracting mates. Furthermore, sleep is substantially more dangerous than staying awake, as the very sensory inputs protecting us from predation are suppressed. So, what then do we get in return? The short answer is that we do not know. It is clear that evolution has made sleep a biological requirement. Your brain will not let you voluntarily avoid sleeping more than a few nights, and involuntary sleep deprivation leads to chronic stress, fatigue, disorientation, poor health and even death. However, in spite of decades of research, we still do not fully understand why we have this biological need to sleep.Sleep likely serves a multitude of roles benefiting from a prolonged "offline" state with reduced sensory inputs. One major hypothesized function is systems-level memory consolidation, a process by which new memories stored in the hippocampus are stabilized and transferred to neocortical brain regions for long-term storage. One key aspect of memory consolidation is the phenomenon of memory triage, by which salient or repeated experiences are more likely to be consolidated compared to irrelevant experiences. How the brain accomplishes this selective strengthening of important memories is unknown, and the focus of our research proposal.Sequential patterns of neural activity occurring during an experience have been observed to spontaneously reactivate during sleep. This reactivated memory trace, referred to as replay, is postulated to be how the brain consolidates a memory, with the transfer of a memory residing in the hippocampus to other brain regions. We will examine how replay is modulated by an experience's salience, and hypothesize that more important experiences will replay more during sleep. Furthermore, we predict that cortical feedback plays a key role in modulating replay based on salience. To test this, we will inactivate cortical inputs to the hippocampus and examine whether the hippocampus no longer biases replay towards more salient experiences.Approximately 70% of Brits sleep less than the 7-9 hours per night recommend by the medical community. Furthermore, increased social media use is correlated with poorer sleep quality, along with an increased occurrence of anxiety and depression. As the amount of "junk information" in our lives increases, and the amount we sleep decreases, there is a growing pressure on our memory triage system to effectively prioritize the consolidation of salient information, and an increased need to understand how this occurs. These issues are exasperated further in older individuals, as both sleep quality and duration decline with age. Our research will directly examine the underlying mechanisms of memory triage, and provide new ideas on how this process could be further optimised.