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

譯者: Ann Chen 審譯者: S Sung

In 1962, a cave explorer named Michel Siffre

1962 年，一位名叫米歇爾希佛 Michel Siffre 的洞穴探險家

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

開始進行一系列的實驗 他將自己隔離在地底下數月

without light or clocks.

沒有光線或時鐘

He attached himself to electrodes that monitored his vital signs

他在自己身上粘貼電極 以監測生命現象

and kept track of when he slept and ate.

並記錄他的睡眠和進食

When Siffre finally emerged,

最後，當希佛帝從洞穴出來時

the results of his pioneering experiments

他開創性研究的結果

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

顯示他的身體保持規律的 睡眠─清醒週期

Despite having no external cues,

即使沒有外在的信號

he fell asleep,

他入睡

woke up,

and ate at fixed intervals.

醒來

以及進食，都按固定作息

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

這被稱為「晝夜節律」 源自拉丁語的「大約一天」

Scientists later found these rhythms affect our hormone secretion,

後來，科學家發現這節律 影響我們荷爾蒙的分泌

how our bodies process food,

身體處理食物

and even the effects of drugs on our bodies.

甚至藥物對身體的功效

The field of sciences studying these changes is called chronobiology.

研究這些變化的科學 稱為「時間生物學」

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

能感知時間有助於我們做所有的事

從睡醒與入眠

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

到知道何時準確地 接住擲向我們的球

We owe all these abilities to an interconnected system of timekeepers

我們把這些能力歸功於 腦內計時器的互聯系統

in our brains.

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

它相等於能告訴我們 過了幾秒的碼錶

a clock counting the hours of the day,

量測每日鐘點的時鐘

and a calendar notifying us of the seasons.

以及告知季節的日曆

Each one is located in a different brain region.

每個各自位於大腦不同的區域

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

留在黑暗洞穴的希佛憑藉最原始的鐘

in the suprachiasmatic nucleus, or SCN of the hypothalamus.

它位於下視丘的視交叉上核，即 SCN

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

根據果蠅和老鼠的實驗 我們認為它的運作原理如下

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

名為 CLK 的蛋白質，也就是 CLOCK 一整天都積聚在視交叉上核

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

除了能活化讓我們 保持清醒的基因之外

they make another protein called PER.

它們還製造另一種 稱為 PER 的蛋白質

When enough PER accumulates,

當積聚足夠量的 PER

it deactivates the gene that makes CLK,

它會抑制製造 CLK 的基因

eventually making us fall asleep.

最後讓我們入睡

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

接著，CLOCK 的濃度降低 而後 PER 的濃度也下降

allowing CLK to rise,

讓 CLK 濃度再度上升

starting the cycle over.

重新開始新的週期

There are other proteins involved,

還有其他蛋白質參與此運作

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

但我們的日夜週期一部分是由於 白天 CLK 與夜間 PER 之間

between CLK by day and PER by night.

蹺蹺板作用原理

For more precision,

為求更精準

視交叉上核也依賴外在的信號

our SCNs also rely on external cues

like light,

如光線

food,

食物

noise,

and temperature.

噪音

以及溫度

We called these zeitgebers,

我們稱這些為 “zeitgebers”

German for "givers of time."

德語的「校時器」

Siffre lacked many of these cues underground,

希佛在地下，缺少這些信號

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

但在我們的正常生活中 它們會微調日常作息

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

例如，當自然的晨光映入眼簾

it helps wake us up.

會催促我們醒過來

Traveling through the optic nerve to the SCN,

此信號經由視神經傳到視交叉上核

it communicates what's happening in the outside world.

傳達了外界所發生的事情

The hypothalamus then halts the production of melatonin,

接著下視丘停止製造「褪黑激素」

a hormone that triggers sleep.

這是一種誘發睡眠的荷爾蒙

At the same time,

同時

it increases the production of vasopressin

它會增加整個腦部「抗利尿激素」 及「去甲腎上激素」的產生

and noradrenaline throughout the brain,

which help control our sleep cycles.

這兩者能協助控制睡眠週期

At about 10 am,

上午 10 點左右

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

體溫上升，提升了我們的精力與機敏

and later in the afternoon,

稍後在下午

it also improves our muscle activity and coordination.

我們的肌肉活動力與協調性也提高

Bright screens at night can confuse these signals,

夜間時，光亮的螢幕會干擾這些訊號

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

這就是為什麼 睡前看太多電視會難以入睡

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

但有時我們必須更精確知道時間

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

此時就需大腦的內在碼錶參與協調

One theory for how this works involves the fact

關於這種運作，一個理論曾提到

that communication between a given pair of neurons

某兩個神經元之間的傳遞訊號

always takes roughly the same amount of time.

總是花大約相同的時間

So neurons in our cortex and other brain areas

因此，大腦皮質及 其他區域的神經元

may communicate in scheduled, predictable loops

能依預定、可預知的迴路來進行傳遞

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

大腦皮質用它們來 精確判斷「經過了多久」

That creates our perception of time.

如此，建立了我們的時間感知

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

關於此點，希佛在洞穴裡 有額外有趣的發現

Every day, he challenged himself to count up to 120

每天，他都要求自己 以每秒一個數字的速度數到 120

at the rate of one digit per second.

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

一段時間後，原本只花 2 分鐘 變成需時 5 分鐘之久

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

孤獨、黑暗洞穴的生活 使希佛對時間的感知偏離軌道

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

儘管大腦盡最大努力 讓他維持在正軌上

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

這令我們深思

還有什麼會影響我們的時間感

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

假如時間不是客觀的 那又意謂著什麼？

Could each of us be experiencing it differently?

我們各自能以不同方式感知時間嗎？

Only time will tell.

只有時間能告訴我們了