Cell子刊：听说过“首夜效应”吗？

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（图片摘自www.sciencealert.com）

不知道大家有没有这样的经历，一旦处于陌生的环境，比如新房子或者旅馆的时候，将会难以入睡，这被称之为"首夜效应 （first night effect）"。虽然首夜效应早已被科学家们熟知，这也是研究睡眠的专家们会考虑的一项因素：即在对志愿者的睡眠记录进行分析时通常会把第一夜的睡眠记录删除。

但是造成"首夜效应"的因素究竟是什么呢？根据最新的研究，我们在陌生的环境中难以入睡其实是一种防御机制。当我们的身体试图进入休息状态时，大脑的一个半球会比平时更加的清醒，这是睡眠时产生的一种平衡机制，用于提防潜在的危险。


"在我们不清楚哪间房子安全的情况下，这一防御机制便会启动，用于检测任何可疑的事件"，睡眠领域的科学家，来自布朗大学的Masako Tamaki说道，其相关研究成果发表在Cell子刊《current biology》上。


为了找到导致失眠情况产生的原因，研究者们对35名志愿者的睡眠情况进行了相关研究。科学家们记录了志愿者们在实验室环境下两个晚上的睡眠情况，以及利用脑电图与核磁共振成像法监测了志愿者大脑的活动情况。

结果显示，第一夜中即将进入睡眠状态的志愿者们大脑左半球活跃程度明显高于右半球，而且在深度睡眠的情况下这一现象更为显著。这一现象使得他们更加容易被惊醒。


当研究员们在这些睡着的志愿者右耳边播放鸣音（即能够刺激左半球）时，他们惊醒的概率更高，反应时间也更短。


当然，大家可能会认为这也许是这些志愿者们没有做好充分的思想准备，就被叫去参加这么折磨人的试验，才会出现如此的结局。


事实上，处于其它睡眠状态（即不处于深度睡眠状态）的志愿者并没有表现出相似的现象，而且上述表现出左脑兴奋的现象的志愿者在第二晚的实验室睡眠检测中也不再出现上述现象。这说明这种效应仅仅出现在第一夜。


研究者们称目前仍有许多未知的事情需要继续研究，但至少此时，我们对陌生环境下会失眠的现象背后的原因应当有所了解了。

来源：生物谷

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Night Watch in One Brain Hemisphere during Sleep Associated with the First-Night Effect in Humans

Masako Tamaki, Ji Won Bang2, Takeo Watanabe, Yuka Sasaki

Highlights
•Interhemispheric asymmetry in sleep depth occurs for the first night in a new place
•This interhemispheric asymmetry occurs in the default-mode network
•The less-asleep hemisphere shows increased vigilance in response to deviant stimuli
•One brain hemisphere may work as a night watch during sleep in a novel environment

Summary
We often experience troubled sleep in a novel environment [ 1 ]. This is called the first-night effect (FNE) in human sleep research and has been regarded as a typical sleep disturbance [ 2–4 ]. Here, we show that the FNE is a manifestation of one hemisphere being more vigilant than the other as a night watch to monitor unfamiliar surroundings during sleep [ 5, 6 ]. Using advanced neuroimaging techniques [ 7, 8 ] as well as polysomnography, we found that the temporary sleep disturbance in the first sleep experimental session involves regional interhemispheric asymmetry of sleep depth [ 9 ]. The interhemispheric asymmetry of sleep depth associated with the FNE was found in the default-mode network (DMN) involved with spontaneous internal thoughts during wakeful rest [ 10, 11 ]. The degree of asymmetry was significantly correlated with the sleep-onset latency, which reflects the degree of difficulty of falling asleep and is a critical measure for the FNE. Furthermore, the hemisphere with reduced sleep depth showed enhanced evoked brain response to deviant external stimuli. Deviant external stimuli detected by the less-sleeping hemisphere caused more arousals and faster behavioral responses than those detected by the other hemisphere. None of these asymmetries were evident during subsequent sleep sessions. These lines of evidence are in accord with the hypothesis that troubled sleep in an unfamiliar environment is an act for survival over an unfamiliar and potentially dangerous environment by keeping one hemisphere partially more vigilant than the other hemisphere as a night watch, which wakes the sleeper up when unfamiliar external signals are detected.

http://www.cell.com/current-biology/abstract/S0960-9822(16)30174-9