By
Matthew Walker
3: Being well rested is part of the environment that makes it easier to eat well.
4: Human beings are the only species who deprive themselves of sleep for reasons that don’t benefit them.
Circadian rhythm regulates the timing of many bodily functions including when we feel alert and sleepy and when we desire to eat and drink.
16: Organisms evolved a circadian rhythm to synchronize themselves with the rotation of the earth.
17: The average circadian rhythm is 24 hours and 15 minutes; any cue (such as light and darkness) that resets our rhythm to 24 hours (required maintenance) is called a zeitgeber.
This could explain why my routines tend to drift later when I’m not consistent with my zeitgebers. In theory, with no resetting at all, I would drift 15 minutes forward each cycle forever.
18: Circadian rhythm dictates wakefulness and sleep, not the other way around.
Your body will want to be awake or asleep on the rhythm’s schedule regardless of whether you are actually awake or asleep.
26: Adenosine builds up in your brain as soon as you awake. Its accumulation produces the desire to sleep and peaks for most individuals after 12-16 hours of being awake. This chemical tells you to sleep.
Caffeine blocks adenosine receptors giving the brain the illusion of less time having passed since the last sleep.
It’s interesting to me that the thing that makes you sleep isn’t a lack of something like energy but rather an abundance of something telling you to sleep.
33: Circadian rhythm continues on like a metronome without regard to when we are asleep or awake. Adenosine levels DO depend on sleep to change.
50: Waking brain waves are frenzied and lack pattern; they are the sum of many parts of the brain simultaneously processing the information they are responsible for. Deep, slow NREM waves are steady and discernible as one wave emanating from the front to the back of your brain. Just as FM radio waves have high fidelity but low range and AM radio waves have low fidelity but high range, Deep sleep waves transmit information further across your brain, allowing distant parts of the brain to share information with each other. This has implications for how we learn or consume information generally. I used to consume a ton of articles, videos, podcasts, etc. It was all just noise. I’ve moved to a slower form of learning that allows connections to be made from distant parts of my knowledge graph.
53: During REM sleep, dreams occur and your voluntary muscles lose all tone. This allows you to dream safely without physically acting out the motor signals that occur during dreams.
56: Sleep is so ancient and so universal that one theory suggests that sleep was the original state of life from which wakefulness emerged.
62: Following sleep deprivation, human brains favor NREM during the first night of sleep recovery, but in subsequent nights favor REM.
68: Midnight refers to the middle of the night...the middle of our sleep phase. Sleep before the Industrial Age began around 9pm—2-3 hours after sunset—and ended at or around dawn.
71: Humans are an outlier in sleep, differentiating themselves from all other primates in needing shorter amounts of sleep with higher proportions of REM.
74: One function of REM sleep is to collide newly formed memories with the long term history of our lives, forging new creative connections between unrelated ideas. We can actually solve problems or originate new ideas in our sleep.
111: Sleeping before learning empties short term memories into long term storage, leaving more room for new learning.
125: The brain can supplement practice, improving motor skills during sleep.
139: The brain begins to fail after 16 hours of being awake, and humans need more than 7 hours of sleep each night.
164: Sleep isn’t just the third pillar of health, it is the foundation upon which diet and exercise stand. Lack of sleep decreases the impact of good diet and exercise and exacerbates the consequences of bad diet and exercise.
199: Science sees dreams as 100% localized to and products of our brains, with no external input, whereas ancient beliefs placed emphasis on revelation from the gods or external sources (Aristotle being an exception).
204: Dreams are not a replay of the events of our day (1-2%), but have a higher overlap with emotional themes of our day (35-55%).
206: Dreams are not simply a byproduct of REM sleep, but have their own necessary function.
210: It seems that REM sleep separates the accurate memory of traumatic events from the traumatic emotions associated with them, thus allowing us to learn from our past experiences without reliving the emotional distress. This is in part because stress hormones are completely shut off during REM sleep.
220: Story of Mendeleev. He puzzled for years over the elements, looking for patterns and organization. One night he dreamt the solution, awoke, and wrote it down.
226: Our wakeful, logical brain associates thoughts logically, while our REM brain seeks the most obscure connections possible between unrelated ideas.
270: Artificial light delays the release of melatonin in the brain.
272: Alcohol is a sedative and produces sedation not sleep. It also reduces REM sleep and causes people to wake up many times in the night even if they don’t remember it.
279: Cool ambient temperature (65 degrees), washing face and hands, or having a hot bath all help lower the core body temperature and reduce time to sleep.
294: The best action you can take to improve sleep quality is to go to bed and arise at the same time every day no matter what even though it requires an alarm clock.
294: Good sleep and exercise can form a virtuous cycle where one enhances the other.
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