How does your body know what time it is? - Marco A. Sotomayor

翻译人员: Yulin Li 校对人员: Xu Junqing

In 1962, a cave explorer named Michel Siffre

1962年， Michel Siffre, 一名岩洞探险者，

started a series of experiments where he isolated himself underground for months

把自己封闭在地下数月 并开始了一系列的试验，

without light or clocks.

那里没有光也没有表。

He attached himself to electrodes that monitored his vital signs

他通过连接的电极片 来监测自己的生命体征，

and kept track of when he slept and ate.

并记录下何时吃饭，睡觉。

When Siffre finally emerged,

当Siffre最终出关时

the results of his pioneering experiments

这一系列实验结果表明

revealed that his body had kept to a regular sleeping-waking cycle.

他的身体保持了 规律的作息周期。

Despite having no external cues,

尽管没有外界的线索，

he fell asleep,

他入睡,

woke up,

and ate at fixed intervals.

起床，

和吃饭都在特定的时间段。

This became known as a circadian rhythm from the Latin for "about a day."

这就是昼夜节律， 源于拉丁文，意思是‘一日’。

Scientists later found these rhythms affect our hormone secretion,

科学家后来发现 这个节律会影响激素分泌，

how our bodies process food,

对食物的消化，

and even the effects of drugs on our bodies.

甚至是药物对身体的药效。

The field of sciences studying these changes is called chronobiology.

研究这一领域的学科 叫做时间生物学。

Being able to sense time helps us do everything from waking and sleeping

我们做任何事都离不开 对时间的感知能力。

to knowing precisely when to catch a ball that's hurtling towards us.

比如起床和入睡以及判断， 何时接住呼啸而来的球。

We owe all these abilities to an interconnected system of timekeepers

这些能力都归于 我们脑中互联的计时系统。

in our brains.

It contains the equivalent of a stopwatch telling us how many seconds elapsed,

它集合了记秒的秒表,

a clock counting the hours of the day,

报时的时钟，

and a calendar notifying us of the seasons.

播报季节的日历于一身。

Each one is located in a different brain region.

每个计时器都处在大脑不同的区域。

Siffre, stuck in his dark cave, relied on the most primitive clock

困在黑暗的洞穴里， Siffre依靠最原始的计时器

in the suprachiasmatic nucleus, or SCN of the hypothalamus.

它们位于下丘脑的 视交叉上核(SCN)中。

Here's the basics of how we think it works based on fruitfly and mouse studies.

基于果蝇和老鼠实验， 我们认为其原理是这样的

Proteins known as CLK, or clock, accumulate in the SCN throughout the day.

被称为CLK的蛋白，也读作「表」， 在一天中都在SCN中积累

In addition to activating genes that tell us to stay awake,

在激活那些让我们保持清醒的基因的同时，

they make another protein called PER.

产生另一种被称为PER的蛋白质。

When enough PER accumulates,

当PER积累到足够的量，

it deactivates the gene that makes CLK,

它会给制造CLK蛋白的基因一个负反馈，

eventually making us fall asleep.

最终使我们进入梦乡。

Then, clock falls low, so PER concentrations also drop again,

之后，「表」的浓度降低，PER的浓度也随之降低，

allowing CLK to rise,

使得CLK的浓度回升，

starting the cycle over.

开始了新一个轮回。

There are other proteins involved,

这一过程不乏其他蛋白质的参与，

but our day and night cycle may be driven in part by this seesaw effect

但我们的昼夜循环

between CLK by day and PER by night.

受到这样一个在白天的CLK和夜晚的PER之间 跷跷板效应的驱使。

For more precision,

为了变得更精确，

our SCNs also rely on external cues

我们的SCN也会依赖外界的线索，

like light,

比如光，

food,

食物，

noise,

and temperature.

噪音，

还有温度。

We called these zeitgebers,

我们把这些称作「zeitgebers」，

German for "givers of time."

德语中的意思是“时间之源”

Siffre lacked many of these cues underground,

Siffre在地下时缺乏这些线索

but in normal life, they fine tune our daily behavior.

但在日常生活中，他们对我们的行为进行微调。

For instance, as natural morning light filters into our eyes,

比如说，一束晨光射到我们眼睛里

it helps wake us up.

唤醒了我们，

Traveling through the optic nerve to the SCN,

穿过视神经传到了SCN

it communicates what's happening in the outside world.

传达着外界正在发生的事情，

The hypothalamus then halts the production of melatonin,

下丘脑于是不再产生褪黑素。

a hormone that triggers sleep.

（褪黑素：一种触发睡眠的荷尔蒙）

At the same time,

同时，

it increases the production of vasopressin

在大脑中，

and noradrenaline throughout the brain,

下丘脑增加对抗利尿激素和去甲肾上腺素的分泌，

which help control our sleep cycles.

如此帮助我们管控睡眠周期。

At about 10 am,

早上10点左右，

the body's rising temperature drives up our energy and alertness,

逐渐升高的体温 促使我们的能量和警觉性提升；

and later in the afternoon,

傍晚，

it also improves our muscle activity and coordination.

我们的肌肉活力和协调性也得到提升。

Bright screens at night can confuse these signals,

夜间的亮光会扰乱这些生物信号，

which is why binging on TV before bed makes it harder to sleep.

这就是为什么 在睡前长时间看电视会导致失眠。

But sometimes we need to be even more precise when telling the time,

然而有些时候我们需要更准确的知道时间

which is where the brain's internal stopwatch chimes in.

这就是脑内秒表发挥作用的时候

One theory for how this works involves the fact

关于它的工作原理，一种臆测认为

that communication between a given pair of neurons

任意一对神经元间的信号传递

always takes roughly the same amount of time.

大致总是一个特定的时长。

So neurons in our cortex and other brain areas

所以我们大脑皮层和其他区域的神经元，

may communicate in scheduled, predictable loops

在一个设定的，可预测的环路传递信息。

that the cortex uses to judge with precision how much time has passed.

大脑皮层就从这一机制来精确判断过去了多少时间，

That creates our perception of time.

我们的时间概念由此产生。

In his cave, Siffre made a fascinating additional discovery about this.

在洞里时，Siffre还有另一个有趣的发现：

Every day, he challenged himself to count up to 120

每天，他都会挑战自己

at the rate of one digit per second.

以每秒一个数字的速度数到120。

Over time, instead of taking two minutes, it began taking him as long as five.

随着时间的推移，从开始的用时2分钟， 到后来用时可以长达5分钟

Life in the lonely, dark cave had warped Siffre's own perception of time

在孤寂，黑暗的洞穴中的生活， 使得Siffre的时间概念也扭曲了。

despite his brain's best efforts to keep him on track.

尽管他的大脑很努力的使他保持正轨

This makes us wonder what else influences our sense of time.

这就使得我们怀疑 还有什么会影响到我们对时间的感知。

And if time isn't objective, what does that mean?

如果时间不是客观的， 这又意味着什么？

Could each of us be experiencing it differently?

可不可能我们每个人 对时间的感受都不同？

Only time will tell.

只有时间会给出答案。