Ever had that jerking sensation when you start to doze off打瞌睡?– so here's the science...每次睡着都会有震抖感觉？——看一下科学研究
You may have experienced sudden, jerky body movements as you drift into sleep. The sensation is common, and if paired with a dream, can feel like you’ve suddenly moved or fallen.当你正要入睡的时候，你可能经历过身体突然抽搐的感觉。如果这感觉和你的梦刚好一致，那么你就好像突然掉下来的感觉。
When it seems like it’s part of a dream, say falling through the air, this is called dream incorporation, and reveals our mind’s amazing capacity to improvise即兴创作, wrote Tom Stafford in his BBC Future Neurohacks column on the phenomenon in 2012.这种感觉叫梦境合并，显示了我们意识多么惊人的创作能力。
The experience is known as a ‘hypnic jerk’ 入梦抽动and it sheds light onto the conflict in our brains as we shut down for sleep.像在关灯睡觉时候突然来了一道光的冲突感觉。
What causes a hypnic jerk? 什么导致了入梦抽动？
In sleep our bodies are paralysed,麻痹 and we become oblivious不注意 to events in the outside world. But our muscle control isn’t flicked off like a switch.在睡觉时候，我们身体是麻木的，忽略了外部世界的所有事。但我们的肌肉控制却没有像开关那样关掉。
An area of the brain called the reticular activating system 网状激活系统controls our basic functions, like breathing, and tells us whether we feel alert. In contrast, the ventrolateral preoptic nucleus, 腹外侧核团located near the optic nerve视觉神经, dictates命令 tiredness. As we descend into sleep, the reticular activating system releases control of our body and the venterolateral preoptic nucleus takes over. The process is like a slow fade of a dimmer调光器 switch, but it isn’t always smooth.大脑的某个区域网状激活系统控制我们基本功能，像呼吸，感觉警惕。相反，在视觉神经附近的腹外侧核团，控制你的疲惫感，当你慢慢进入睡眠，网状激活系统会退出，由腹外侧核团来控制身体。这样的过程就像是慢慢调光暗的开关，但它并不总是那么灵敏。
We incorporate physical sensations into dreams 我们在梦里混入了生理感觉
Random bursts突发发作 of our remaining wakeful energy occasionally surface in the form of jerky movements, for reasons that aren’t fully clear. Unlike rapid eye movements, these have nothing to do with our dreaming brains, but are the last vestiges of our day.我们还保持着清醒的能力偶然性的抽搐行为发生的原因没有完全清楚，不像快速眼动，这对我们发梦的大脑没什么影响，但是我们一天当中最后的残余行为。
Is it dangerous?它有危险性吗？
A strange and very unpleasant phenomenon called ‘exploding head syndrome’突发性头鸣综合征 follows a similar pattern of behaviour – our wakeful and sleeping minds attempting to wrest扭曲 control from each other – and results in the sensation of seeing flashing lights and hearing loud bangs. In some extreme cases the phenomenon has led to severe insomnia失眠 and even claims of alien abduction.有一种奇怪又让人不愉快的突发性头鸣综合征会伴随类似的行为——我们清醒和沉睡的意识意图相互控制对方。——导致看见闪光和爆炸声。在某些极端例子，这种现象导致严重失眠和甚至声称被外星人绑架。
But in general, the feeling is nothing to worry about; it’s just a funny coincidence of falling asleep. “There is a pleasing symmetry对称 between the two kinds of movements we make when asleep,” Stafford writes. “Rapid eye movements are the traces of dreams that can be seen in the waking world. Hypnic jerks seem to be the traces of waking life that intrude on the dream world.”但一般来说，这些感觉并不用担心，只是熟睡间的搞笑的连锁反应。一种在睡与醒之间的愉悦的对称反应。快速眼动行为是梦关于清醒世界的踪迹，入梦抽动相当于清醒世界侵入梦中。
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