Can you be awake and asleep at the same time? - Masako Tamaki

譯者: Yi-Ping Cho (Marssi) 審譯者: Regina Chu

Many animals need sleep.

很多動物都需要睡眠。

Even brainless jellyfish enter sleep-like states where they pulse less

即使是無腦的水母也有似睡狀態： 牠們收縮的次數會變少，

and respond more slowly to food and movement.

對食物和周圍動靜的反應也會變慢。

But all of the threats and demands animals face

但這些動物必須面對的威脅和需求

don’t just go away when it’s time to doze.

不會因為正值睡眠時間就自動消失。

That’s why a range of birds and mammals experience some degree

這也就是為什麼某些鳥類和哺乳動物 會有某種程度

of asymmetrical sleep where parts of their brain are asleep

兩側大腦睡眠不對稱的狀態， 也就是一部分大腦進入睡眠，

and other areas are more active.

而另一部分還在運轉。

This is even true for humans.

就連人類也會這樣。

So how does it work?

這是怎麼一回事？

All vertebrate brains consist of two hemispheres: the right and left.

所有脊椎動物的大腦都包含 兩個半球：右腦和左腦。

Brain activity is usually similar across both during sleep.

睡眠中左右腦的活動相似，

But during asymmetrical sleep,

但是在睡眠不對稱的期間，

one brain hemisphere can be in deep sleep while the other is in lighter sleep.

一邊的腦半球可能在沉睡， 而另一邊則在淺眠狀態。

And in an extreme version called “unihemispheric sleep,”

在稱為「單側腦半球睡眠」的極端情況中，

one hemisphere may appear completely awake while the other is in deep sleep.

一邊的腦半球可能完全清醒， 而另一邊則還在沉睡。

Take bottlenose dolphins.

以瓶鼻海豚為例：

Their breathing is consciously controlled,

牠們有意識地控制呼吸，

and they must surface for air every few minutes or they’ll drown.

而且每隔幾分鐘就得浮出水面換氣， 否則就會溺斃。

When they have a newborn calf, they must actually swim nonstop for weeks

牠們剛有新生兒的時候 得要連續幾週不斷游來游去，

in order to keep it safe.

才能讓寶寶存活下來。

So dolphins sleep unihemispherically, with just one hemisphere at a time.

海豚採用單側腦半球睡眠， 一次只讓一邊的腦睡覺。

This allows them to continue swimming and breathing while snoozing.

這樣一來牠們就可以在打盹時 一邊游泳一邊呼吸。

Other marine mammals also need asymmetrical sleep.

其他海洋哺乳類也需要 兩腦不對稱的睡眠。

Fur seals might spend weeks on end migrating at sea.

海狗可能會連續數週在海洋中遷徙，

They slip into unihemispheric sleep while floating horizontally,

牠們水平漂浮的時候 陷入單側腦半球睡眠，

holding their nostrils above the surface, closing their upward-facing eye,

將鼻孔保持在水平面之上， 闔起朝上的眼睛，

and keeping their downward-facing eye open.

睜著向下的眼睛。

This may help them stay alert to threats from the depths.

此舉可以幫助牠們 保持對海底威脅的警戒。

Similar pressures keep birds partially awake.

類似的壓力則讓鳥類呈現半醒狀態。

Mallard ducks sleep in groups, but some must inevitably be on the peripheries.

綠頭鴨會結伴成群一起睡， 但免不了有些會在外圍。

Those ducks spend more time in unihemispheric sleep,

那些鴨子較常有單側腦半球睡眠，

with their outward-facing eyes open

會睜著向外的眼睛，

and their corresponding brain hemispheres more active.

同側的腦半球會較靈敏。

Other birds have been shown to catch z’s in midair migration.

還有些鳥會在半空中遷徙時打盹。

While undertaking non-stop transoceanic flights of up to 10 days,

在長達十天跨洋飛行中，

frigatebirds either sleep with one or both hemispheres at a time.

軍艦鳥會讓一邊的腦 或是兩邊腦同時入睡。

They do so in seconds-long bursts, usually while riding air currents.

牠們會短暫入睡幾秒， 通常是在乘著氣流飛行之際。

But the frigatebirds still sleep less than 8% of what they would on land,

但飛著睡的量 依然比平常在陸地上時還少 8%，

suggesting a great tolerance for sleep deprivation.

這也代表了牠們很能忍受睡眠剝奪。

It’s currently unclear whether asymmetrical sleep

目前還不確定的是： 兩腦不對稱的睡眠

packs the same benefits as sleep in both hemispheres

和雙側腦半球睡眠是否有同樣的好處，

and how this varies across species.

是否也因物種而有所不同？

In one experiment, fur seals relied on asymmetrical sleep

實驗中，海狗靠兩腦不對稱的睡眠

while being constantly stimulated.

持續讓身體運作。

But in recovery, they showed a strong preference

但牠們在康復期間會偏好

for sleep across both hemispheres,

讓兩側的腦半球都進入睡眠，

suggesting that it was more restorative for them.

也就是說這樣能讓牠們修復功能更強。

Dolphins, on the other hand,

海豚反而

have been observed to maintain high levels of alertness for at least five days.

會保持至少五天高度警戒。

By switching which hemisphere is awake,

牠們透過轉換清醒的半腦，

they get several hours of deep sleep in each hemisphere

讓每一側的腦 都有幾小時的深度睡眠

throughout a 24-hour period.

分布在 24 小時之間，

This may be why unihemispheric sleep alone meets their needs.

也許是因為單側腦半球睡眠 就能滿足牠們的需求。

So, what about humans?

那人類呢？

Have you ever woken up groggy after your first night in a new place?

你是否曾在外宿第一晚時 半夜頭腦昏沉地醒來？

Part of your brain might’ve spent the night only somewhat asleep.

你的腦可能有部分沒有完全入睡。

For decades, scientists have recognized that participants sleep poorly

數十年來，科學家發現受試者

their first night in the lab.

在實驗室第一晚都睡不好，

It’s actually customary to toss out that night’s data.

根據慣例，當晚的數據通常會被扔掉。

In 2016, scientists discovered that this “first night effect”

科學家在 2016 年發現 「第一夜效應」這種

is a very subtle version of asymmetrical sleep in humans.

非常不易察覺的 人類兩腦不對稱睡眠。

They saw that, during the first night,

他們發現第一晚

participants experience deeper sleep in their right hemisphere

受試者的右腦有較深層的睡眠，

and lighter sleep in their left.

左腦則較淺眠。

When exposed to infrequent sounds,

偶爾有聲響時，

that lighter sleeping left hemisphere showed greater bumps in activity.

那個淺眠的左腦在活動中 呈現較大的波動。

Participants also woke up and responded to infrequent sounds faster

受試者第一晚醒來 並對那些聲響做出反應的時間

during the first night than when experiencing deep sleep

也會比接下來幾晚深層睡眠時

in both hemispheres during nights following.

更加快速。

This suggests that, like other animals,

也就是說，就像其他動物，

humans use asymmetrical sleep for vigilance,

人類用兩腦不對稱睡眠來提高警戒，

specifically in unfamiliar environments.

尤其是身在不熟悉的環境。

So, while your hotel room is obviously not trying to eat you

所以雖然你的旅館客房 顯然不是要吃掉你，

and you’re not going to die if you don’t continue moving,

你也不會因為不動而喪命，

your brain is still keeping you alert.

但你的大腦仍然處在警戒之中，

Just in case.

以防萬一。