Sleep is the single most effective thing you can do to reset¹ the health of your brain and body. This is true for adults, teenagers and children alike.

睡觉是重置大脑和身体健康的最有效方法。对于成年人来说如此，对于青少年和儿童来说也是如此。

Yet, we do not start sleeping when we are born. We actually start sleeping many months before that. Often, through speech or song, expecting parents will thrill at their ability to elicit² small kicks and movements from their in-utero child.

但我们并不是出生的时候才开始睡觉。事实上，早在出生前几个月我们就开始睡觉了。通常，父母希望通过说话或音乐激发子宫内的宝宝踢一踢或动一动。

Though you should never tell them this, the baby is most likely fast asleep. Prior³ to birth, a human infant will spend almost all of its time in a sleep-like state, much of which resembles a stage called rapid eye movement sleep, or REM sleep. The sleeping fetus⁴ is therefore unaware⁵ of its parents' performative machinations.

虽然你永远都不该告诉他们，但子宫内的宝宝很有可能睡的很熟。出生之前，婴儿几乎所有时刻都处于睡眠状态，其中大部分过程与浅睡眠阶段相似。因此，正在睡眠状态中的宝宝根本就不知道父母的表演意图。

Any co-occurring arm flicks⁶ and leg bops that the mother feels from her baby are most likely to be the consequence⁷ of random⁸ bursts of brain activity that typify REM sleep. Adults do not-or at least should not-throw out similar nighttime kicks and movements, since they are held back by the body-paralyzing mechanism⁹ of REM sleep.

母亲感受到的宝宝的任何动作（胳膊动了或腿动了）都很有可能是浅睡眠阶段大脑活动随机爆发的结果。成年人不会--至少说不应该--在夜里有类似的踢动或动作，因为这些动作被浅睡眠时的身体瘫痪机制制止了。

But in utero, the immature¹⁰ fetus's brain has yet to construct the REM-sleep muscle-inhibiting system adults have in place. Other deep centres of the fetus brain have, however, already been glued in place, including those that generate sleep.

但在子宫内，婴儿大脑还未成熟，不能构筑成年人已有的浅睡眠阶段肌肉抑制体系。然而，婴儿大脑拥有的其它深层中心已经就位，包括触发睡眠的中心。

As a result of this mismatch, the fetus brain still generates formidable movement commands during REM sleep, except there is no paralysis¹¹ to hold them back. Without restraint, those activity signals are freely translated into frenetic body movements, felt by the mother as acrobatic kicks and featherweight punches.

由于这种搭配不当，婴儿的大脑仍会在浅睡眠阶段发布强大的运动指令，但是却没有瘫痪系统抑制这些动作。没有了限制，这些活动信号可以自由的转化为狂热的身体运动，而母亲则将其视作孩子杂技般的踢动和"绵绵拳"。

At this stage of in-utero development, most of the time is spent in sleep, split between REM sleep and deep sleep, also called non-REM sleep.

在子宫内发展的阶段，婴儿大多数时间都在睡觉，分为浅睡眠和深度睡眠。

It is only when the fetus enters the final trimester that the glimmers¹² of real wakefulness emerge. Far less than you would probably imagine, though-just two to three hours of each day are spent awake in the womb.

只有在最后三个月，清醒才会微露光芒。但比你想象的少多了--每天在子宫内只会醒2至3个小时。