Matthew Walker - Why we sleep

Adenosine:

A chemical in the brain that keeps rising when awake. When you are awake for a long period, you will want to sleep because adenosine has reached its peak. When you sleep, it will decrease, but if you wake up before it has dropped to its lowest point, adenosine will continue to accumulate in the brain.

在腦內的化學物質 醒著的時候會持續上升，清醒很長一段時間就會想睡覺，因為腺苷已到峰值 睡覺的時候會下降，但還沒降到最低就醒來，腺苷會繼續在腦袋累積

Melatonin: Secreted by the pineal gland.

After dusk, it will increase significantly in the blood, telling the body "it's dark".

For healthy people, taking melatonin is not a powerful sleeping pill.

- 黃昏後會大量增加到血液中，告訴身體「天黑摟」

- 對健康的人，服用褪黑激素不是強力的住眠劑

Coffee:

Caffeine will take over the receptor in the brain that should receive adenosine, which is why you don't feel sleepy after drinking coffee.

The half-life of caffeine is 5-7 hours. So if you drink coffee in the afternoon, by the time you want to sleep, half of the caffeine is still in your brain.

Decaffeinated coffee still contains 15-30% of caffeine content.

- 咖啡因會搶奪腦中該接受腺苷的受體，也是因此喝咖啡才不會想睡覺

- 咖啡因的半衰期是5-7小時 所以下午喝咖啡，到要睡覺的時候，還有一半的咖啡因在腦袋裡。

- 低咖啡因的咖啡還是有15-30%的咖啡因含量

Sleep structure:

Rapid Eye Movement (REM) phase – When you sleep, your body muscles are soft, and only your eyeballs can move, hence the name. This phase can reorganize what you have learned, generate and strengthen neural connections, and deepen memory. It's like your brain is awake, but your body is sleeping.

Non-Rapid Eye Movement (NREM) phase – The eyeballs will not move, and this phase eliminates unimportant neural connections.

- 快速動眼期(REM) – 睡著時身體肌肉癱軟，只有眼球可以動作，因此得名 此階段重新可以組織學過的東西，產生及加強神經連結，加深記憶 像腦袋醒著，身體卻在睡覺

- 非快速動眼期(NREM) – 眼球不會動作，此階段淘汰不重要資訊的神經連結

Two-segment sleep:

Napping helps memory. Sleep after learning can help memory.

Power Nap is helpful, but it cannot replace long hours of sleep at night.

- 午睡幫助記憶，學習之後的睡眠可以幫助記憶

- Power Nap 有幫助，但無法取代夜晚長時間的睡眠

Exercise:

The less you sleep, the higher the chance of injury from exercise.

Exercise performance will also be affected (Usian Bolt takes a nap before the competition, including the Olympics).

睡得越少，運動傷害的機率越來越高

運動表現也會影響 (Usian Bolt 在賽前會小睡，包括奧運)

Fatigue driving:

The risk is no less than drunk driving. 危險程度不比酒駕低

Staying up late to read:

The learning efficiency between adequate sleep and insufficient sleep varies by up to 40%, which is a huge difference between 100 points and 60 points.

After sleep deprivation, the formed memory is not easily consolidated, because without the neural connections of the REM phase, the memory circuit cannot be strengthened.

If you don't sleep the night you learn, the memory is almost impossible to retain.

- 睡眠充足與睡眠不足，學習效率相差到40%，也就是100分和60分的巨大差異

- 在睡眠剝奪之後，形成的記憶不容易鞏固，因為沒有快速動眼期的神經連結，記憶迴路無法強化

- 學習當晚沒睡覺，記憶幾乎是留不住

Alzheimer's disease:

There are malignant beta-amyloid proteins in the brain, which cause loss of deep sleep (deep NREM).

The memory area (hippocampal circuit) is not affected by the protein, but the memory consolidation area (frontal lobe) is severely affected, and the memory cannot be preserved.

There is a glymphatic system in the brain – which cleans up metabolites (including toxic amyloid proteins). Loss of sleep means the glymphatic system does not operate, and toxic metabolites accumulate in the brain.

- 腦中有惡性的beta類澱粉蛋白，會喪失深層睡眠(深層NREM)

- 記憶區(海馬迴)不受蛋白影響，但鞏固記憶區(額葉)受嚴重影響，記憶無法保存

- 腦內有膠淋巴系統 – 清除代謝物(包括有毒的澱粉蛋白) 失去睡眠，就沒有膠淋巴系統運作，有毒的代謝物在腦內累積

Obesity:

Hormones controlling appetite – Leptin, Ghrelin.

When sleep is insufficient, the chemical signal of Leptin fails, but the effect of Ghrelin is amplified, unconsciously eating too much.

Short sleep and obesity are proportional.

Adequate sleep results in better skin.

- 控制食慾的激素 – 瘦素(Leptin)、飢餓肽(Ghrelin)

- 睡眠不足時，瘦素的化學訊號失效，但飢餓肽的影響被放大，不自覺的吃太多

- 睡眠短缺和肥胖成正比

- 睡飽皮膚更好

Sleep temperature:

It's easier to fall asleep when the body temperature is lower. Modern society's heaters, blankets, quilts, pajamas, on the contrary, make it harder to fall asleep.

體溫較低的時候比較容易睡著 現代社會的暖氣、毛毯、棉被、睡衣，反而讓人不太容易入睡

Mobile phones, computers, blue light screens:

Artificial light at night makes humans think it's still daytime, reduces the production of melatonin

夜晚的人造光，讓人類以為仍然在白天，褪黑激素的產生也減少，睡覺的時間也往後移

睡前一小時盡量看印刷紙就好，手機平板都不要碰