为什么在车上打盹，总能在到站前醒来？

你有没有过这样的经历，在车上不小心睡着了，醒来刚好是自己要下的那一站？明明脑子已经入睡，却总能及时醒来，这是怎么回事呢？大脑是怎么知道该下车了的呢？

‍对于这一神奇的现象，有着几种不同的解释。

Perhaps you’ve seen them, those mysterious people who can fall asleep on the bus or the train and then, somehow, rouse themselves exactly at their stop. Perhaps you’re one of them. It’s as if the subway napper’s brain can sense exactly where and when it is in time and space, rousing the sleeper so she can exit at the right time.

生物钟的作用

生物钟（biological clock）是生物在长期的演化过程中被环境选择出来的一种预见和预警机制，它可以预见一个规律事件的发生。生物钟影响着人体内的基因表达、新陈代谢和蛋白质水平等。我们感到饥饿、感到精力充沛或者精疲力尽，就是受到这些指标波动的影响。

Our body clock generates a 24-hour rhythm that affects things such as gene expression, metabolism, and protein levels. And the ebb and flow of these influences when we feel hungry, when we feel energetic and when we feel tired.

反映到日常生活层面，生物钟在下车前能够叫醒我们，和我们平时到点就要吃饭、睡觉是同样的道理。当我们每天定时定点乘坐固定的地铁路线，并且在固定的站点下车时，生物钟会标记这个时间，即使我们在地铁上入睡，身体也可以感知到需要下车的时间点，并在此之前自然苏醒，做好下车准备。

Humans have a pretty good knack for counting the passing hours, even while asleep. Your body is able to learn a routine as long as it’s a routine. Thus, the commuter’s body could be used to waking up at a certain time every ride.

潜意识的告知

潜意识（subconscious mind）是指那些并未达到显意识层面的心理活动。

潜意识是我们所察觉不到的，比如蝉鸣声、潮汐声等背景噪音，往往在我们无意识的状态下被接收到。

同样的道理，我们在坐地铁和公交时，在睡觉状态下潜意识会暗示我们应该在哪一站下车，因而大脑会将其作为一件需要注意的事情，并且在到站之前将你唤醒。

The subconscious is our unaware part, like background noises such as cicadas or tides, received in an unconscious state. Similarly, when we are riding the subway or bus, while asleep, the subconscious mind subtly guides us as to which stop we should disembark. The brain considers it important and wakes us up before reaching the destination.

鸡尾酒会效应

心理学中有一个概念叫做“鸡尾酒会效应（Cocktail Party Effect）”，指人的听觉具有选择性，在一个充斥各种声音的房间里，人们可以选择性地屏蔽其他噪声而跟随自己想要听到的声音。

The definition of the cocktail party effect in psychology is when we tune into one voice from many conversations going on in a noisy room.

当你处在一个陌生且吵闹的环境中时，突然听见熟人的声音或是有人提到你的名字，尽管周围很嘈杂，你也能马上注意到。这是因为我们的大脑中存在一个“网状激活系统（Reticular Activating System）”，当我们听到自己的名字时，网状激活系统就会启动，提醒我们注意那个声音。

At a party, you’ll hear lots of sounds, see lots of lights. That’s a lot of information, but when you hear your name, your RAS will kick in and immediately direct your attention to whoever just said your name in conversation.

同样地，当我们在车上睡着时，我们的听觉注意力会集中在要下车的站名上，所以当我们听到广播中播报自己所要前往的站点时，大脑能够马上捕捉到，我们就能立刻清醒过来了。

You’re still hearing the announcements of the stops, even while you sleep. Thus it’s possible that you’re able to wake up for your particular stop due to an oral cue.

以上这些身体机制能够像守护精灵一样，在你入睡时替你注意车站信息，避免坐过站的尴尬问题。

不过，当我们的身体太过疲惫，入睡太深，或者乘坐陌生路线的地铁时，这些机制可能会失效，所以出行时还是要提前做好规划，同时注意休息，不要让身体太累啦。

编辑：陈月华

实习生：刘子涵

来源：National Geographic 广西疾控 European Commission YS Life Psy Blog The Drum