A walk through the stages of sleep | Sleeping with Science, a TED series

Sleep is perhaps the single most effective thing

翻訳: Yoko Emori 校正: Moe Shoji

睡眠は私たちが毎日出来ることで おそらく一番効果的なことだと思います

that we can do each and every day

to reset the health of our brain and our body.

脳や身体の健康を回復させるのです

And by understanding a little bit more about what sleep is,

睡眠が何かを もう少し理解することで

perhaps we can get the chance to improve both the quantity and the quality

もしかすると 睡眠の量や質も 改善する機会があるかもしれません

of our sleep.

[Sleeping with Science]

［睡眠の科学］

(Music)

（静かな音楽）

So, exactly what is sleep?

では 睡眠とはいったい何なんでしょう？

Well, sleep, at least in human beings,

睡眠は 少なくとも人間の睡眠は

is subdivided into two main types.

２つの主なタイプに分かれます

On the one hand, we have non-rapid eye movement sleep,

１つは 眼球運動を伴わない睡眠

or non-REM sleep for short.

略して ノンレム睡眠です

But on the other hand,

もう１つは

we have rapid eye movement sleep, or REM sleep.

急速眼球運動を伴う睡眠 レム睡眠です

And non-REM sleep has been further subdivided

ノンレム睡眠は 更に４つに分かれており

into four separate stages,

unimaginatively called stages one through four,

面白くもない名前ですが ステージ１からステージ４と呼ばれています

increasing in their depth of sleep.

数字が大きいほど 眠りが深くなります

And as we go into those light stages of non-REM sleep,

ノンレム睡眠の浅い段階に入ると

your heart rate starts to decrease,

心拍数が減少し始め

your body temperature starts to drop

体温が低下し始めます

and your electrical brain wave activity starts to slow down.

また 脳電位波の動きが減速し始めます

But as we move into deeper non-rapid eye movement sleep,

ノンレム睡眠のより深い段階に入り

stages three and four,

ステージ３や４になると

now all of a sudden the brain erupts

突然 脳は活性化し

with these huge, big, powerful brain waves.

巨大な 力強い脳波を出します

The body is actually recharged in terms of its immune system.

身体は 免疫機能の再充電をするのです

We also get this beautiful overhaul of our cardiovascular system.

同時に 心臓血管をきれいに全面修復します

And, in fact, upstairs in the brain,

そして 上にある脳では

deep non-REM sleep will help consolidate memories

深いノンレム睡眠により記憶が統合され

and fixate them into the neural architecture of the brain.

脳の神経系に定着します

So that's non-REM sleep.

以上がノンレム睡眠でした

But let's come on to REM sleep,

では もう１つの眠りの種類である レム睡眠の話に移りましょう

which is the other main type of sleep.

And it's during REM sleep when we principally have the most vivid,

主に このレム睡眠中に

非常に鮮明な 幻覚を起こすような夢を見ます

the most hallucinogenic types of dreams.

The brain wave activity actually starts to speed up again.

再び 脳波の活動が 速くなります

It's during REM sleep that we receive almost a form of emotional first aid.

このレム睡眠中に 言わば 感情の応急処置を受けます

And it's also during REM sleep where we get a boost for creativity,

また このレム睡眠中に 創造性が強化されます

that it stitches information together

情報が縫い合わされて

so that we wake up with solutions

目が覚めた時に

to previously difficult problems that we were facing.

それまで直面していた困難な問題の 解決策が分かっているのです

Coming back to these two types of sleep,

２つの睡眠の種類に話を戻すと

it turns out that non-REM and REM will play out

ノンレム睡眠とレム睡眠は

in a battle for brain domination throughout the night,

一晩中 どちらが脳を支配するのか バトルを繰り広げています

and that cerebral war is going to be won and lost

この脳内のバトルは 90分毎に 勝者と敗者が入れ替わります

every 90 minutes,

and then it's going to be replayed every 90 minutes.

そして 90分毎に 繰り返されるのです

And what this produces is a standard cycling architecture of human sleep,

その結果 人間の睡眠の 標準的な周期を形成します

a standard 90-minute cycle.

標準的な90分の周期です

But what's different, however,

ただ 違いがあり

is that the ratio of non-REM to REM within those 90-minute cycles

この90分周期の間の ノンレムとレムの比率は

changes as we move across the night,

夜の間に変わっていきます

such that in the first half the night,

夜の前半においては

the majority of those 90-minute cycles

90分周期の大半が

are comprised of lots of deep non-REM sleep,

深いノンレム睡眠で構成されており

particularly stages three and four of non-REM sleep.

特に ノンレム睡眠の ステージ３と４が多いのです

But as we push through to the second half of the night,

夜の後半に入って行きますと

now that seesaw balance actually shifts over,

シーソーのようなバランスが変わり

and instead, most of those 90-minute cycles

90分周期のほとんどが

are comprised of a lot more rapid eye movement sleep, or dream sleep,

レム睡眠 つまり睡眠中に夢を見る状態と

as well as stage-two non-REM sleep,

ステージ２のノンレム睡眠 つまり 浅いノンレム睡眠とで構成されます

that lighter form of non-REM sleep.

And it turns out that there are implications

そして 分かったのは

睡眠の構成について理解することには 意味があるということです

for understanding how sleep is structured in this way.

Let's take someone who typically goes to bed at 10pm,

夜10時に寝て 朝６時に起きる人を 例に取ってみましょう

and they wake up at 6am,

so they have an eight-hour sleep window.

睡眠時間は８時間です

But this morning, they have to wake up early

でも 早朝からミーティングなので 今朝は 早起きしないといけません

for an early morning meeting,

or they want to get a jump start on the day

それか ジムに行って元気をつけてから 一日を過ごしたいかもしれません

to get to the gym.

And as a consequence, they have to wake up at 4am in the morning,

その結果 いつもは６時に起きるのに 朝４時に起きないといけないのです

rather than 6am in the morning.

How much sleep have they actually lost?

実際にどれだけ睡眠が 減ったのでしょうか？

Two hours out of an eight-hour night of sleep

８時間の睡眠時間のうちの ２時間ですので

means that they've lost 25 percent of their sleep.

睡眠の25％が減ったということですね

Well, yes and no.

そうとも言えますが 違うとも言えます

They have lost 25 percent of all of their sleep,

睡眠全体の25％が取れなかったのですが

but because REM sleep comes mostly in the second half of the night

レム睡眠は一晩の主に後半

and particularly in those last few hours,

特に最後の数時間に起こります

they may have lost perhaps 50, 60, maybe even 70 percent

つまり レム睡眠全体の50%か60% いや 70％も失ったかもしれません

of all of their REM sleep.

So there are real consequences to understanding what sleep is

ですので 睡眠と その構成を理解すると 実際に役に立つのです

and how sleep is structured.

And we'll learn all about the benefits of these different stages of sleep

このような睡眠の各ステージが どういう役割を果たしており

and the detriments that happen when we don't get enough of them

各ステージの睡眠を十分に取らないと どういう害があるのかは

in subsequent episodes.

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