Department of Health Sciences, University of L’Aquila, L’Aquila, Italy.
Curr Top Med Chem. 2011;11(19):2423-37. doi: 10.2174/156802611797470268.
In the present paper, we reviewed a large body of evidence, mainly from quantitative EEG studies of our laboratory, supporting the notion that sleep is a local and use-dependent process. Quantitative analyses of sleep EEG recorded from multiple cortical derivations clearly indicate that every sleep phenomenon, from sleep onset to the awakening, is strictly local in nature. Sleep onset first occurs in frontal areas, and a frontal predominance of low-frequency power persists in the first part of the night, when the homeostatic processes mainly occur, and then it vanishes. Upon awakening, we showed an asynchronous EEG activation of different cortical areas, the more anterior ones being the first to wake up. During extended periods of wakefulness, the increase of sleepiness-related low-EEG frequencies is again evident over the frontal derivations. Similarly, experimental manipulations of sleep length by total sleep deprivation, partial sleep curtailment or even selective slow-wave sleep deprivation lead to a slow-wave activity rebound localized especially on the anterior derivations. Thus, frontal areas are crucially involved in sleep homeostasis. According to the local use-dependent theory, this would derive from a higher sleep need of the frontal cortex, which in turn is due to its higher levels of activity during wakefulness. The fact that different brain regions can simultaneously exhibit different sleep intensities indicates that sleep is not a spatially global and uniform state, as hypothesized in the theory. We have also reviewed recent evidence of localized effects of learning and plasticity on EEG sleep measures. These studies provide crucial support to a key concept in the theory, the one claiming that local sleep characteristics should be use-dependent. Finally, we have reported data corroborating the notion that sleep is not necessarily present simultaneously in the entire brain. Our stereo-EEG recordings clearly indicate that sleep and wakefulness can co-exist in different areas, suggesting that vigilance states are not necessarily temporally discrete states. We conclude that understanding local variations in sleep propensity and depth, especially as a result of brain plasticity, may provide in the near future insightful hints into the fundamental functions of sleep.
在本文中，我们回顾了大量证据，主要来自我们实验室的定量脑电图研究，支持睡眠是局部和使用依赖的过程的观点。从多个皮质衍生部位记录的睡眠脑电图的定量分析清楚地表明，从睡眠开始到觉醒，每个睡眠现象都是严格局部的。睡眠开始首先发生在前额区域，并且在主要发生稳态过程的夜间前半部分，低频功率的额优势持续存在，然后消失。在觉醒时，我们显示出不同皮质区域的异步 EEG 激活，前部区域首先醒来。在长时间的清醒期间，在前额衍生部位再次出现与困倦相关的低频 EEG 频率增加。同样，通过总睡眠剥夺、部分睡眠剥夺甚至选择性慢波睡眠剥夺来实验性地改变睡眠长度，导致局部在前额衍生部位出现慢波活动反弹。因此，额叶区域在睡眠稳态中起着至关重要的作用。根据局部使用依赖理论，这源于额叶皮层更高的睡眠需求，而这反过来又归因于其在清醒时的更高活动水平。不同的大脑区域可以同时表现出不同的睡眠强度，这一事实表明睡眠不是如理论中假设的那样是一种空间全局和统一的状态。我们还回顾了关于学习和可塑性对 EEG 睡眠测量局部影响的最新证据。这些研究为理论中的一个关键概念提供了至关重要的支持，即局部睡眠特征应该是使用依赖的。最后，我们报告了数据证实了睡眠不一定同时存在于整个大脑中的观点。我们的立体 EEG 记录清楚地表明，睡眠和觉醒可以同时存在于不同的区域，这表明警觉状态不一定是时间离散的状态。我们得出的结论是，理解睡眠倾向和深度的局部变化，特别是由于大脑可塑性，可能在不久的将来为睡眠的基本功能提供有见地的提示。
