Why We Sleep by Matthew Walker

  • How much I’d Recommend: 8/10
  • Date finished: 6/30/21
  • Why We Sleep, recommend borrowing from your local library

It’s a pretty enjoyable book, but you know that feeling when you have a bad cough and look up on WebMD and try to self diagnose and you feel like you have cancer? That’s kind of how I feel about reading this book. It feels like if you miss one night of sleep, hell, just a few hours of the sleep, you might as well just end right there because your brain will not recover completely ever again, you will have hyper tension, which leads to heart disease and cardiac arrest, you might get depression, schizophrenia, and just die from lack of sleep.

Other than that, it’s a pretty easy read. Here’s some notes from the book.

  • If sleep does not serve an absolutely vital function, then it is the biggest mistake the evolutionary process has ever made.
  • We sleep for a rich litany of functions, plural – an abundant constellation of nighttime benefits that service both our brains and our bodies.
  • Two main factors that determine when you want to sleep: 1 circadian rhythm (internal clock), 2 Melatonin (chemical sleep pressure)
  • Circadian rhythm is not precisely 24 hours but slightly longer.(24 hours and 15 minutes)
  • Sunlight methodically reset our inaccurate internal timepiece, even during an overcasting day.
  • It controls timed preference of eating and drinking, moods and emotions, amount of urine, core body temperature, metabolic rate, release of hormones.
  • Suprachiasmatic nucleus – samples light inside your eyes to reset the 24 hour cycle.
  • Morning larks and night owls are not “by choice”. Usually it’s genetically determined. 40% of people are early larks, 30% night owls, and another 30% lie somewhere in between with a slight leaning toward eveningness.
  • Melatonin: there is a significant sleep placebo effect – the most reliable effect in all of pharmacology. Over the counter melatonin is not regulated by FDA and can be 83% less than that claimed on the label, to 478% more than stated.
  • It feels harder to acclimate to a new time zone when traveling eastward than when flying westward. It’s easier for you to stay up a little longer (stretch your internal day) than to going to bed early (shorten your internal day). Ability to learn reduces and short term memory loss due to frequent time-zone travel
  • While you are awake, you produce adenosine. Caffeine can occupy the receptors of adenosine to make you feel that you are not sleepy. Caffeine peaks at 30 minutes after drinking, half-life is 5-7 hours.
  • Circadian rhythm and sleep-pressure do not sync up with each other. They are two separate systems that are ignorant of each other.
  • If you feel sleepy mid-morning, you are likely not getting enough sleep, or the quality of your sleep is insufficient.
  • Am I getting enough sleep?
    • After waking up in the morning, can you fall back asleep at 10 or 11 am? if so, you are not getting sufficient sleep quantity and/or quality
    • Can you function optimally without caffeine before noon? If no, then you are most likely self-medicating your state of chronic sleep deprivation.
  • What you experience during deep NREM sleep is one of the most epic displays of neural collaboration that we know of. Though an astonishing act of self-organization, many thousands of brain cells have all decided to unite and “sing” or fire, in time. It is a highly active, meticulously coordinated state of cerebral unity.
  • We do not dream in deep NREM sleep, nor do we keep explicit track of time. It is a near state of nocturnal cerebral meditation (different from brainwave activity of waking meditative states).
  • The brain paralyzes the body so the mind can dream safely.
  • Both NREM and REM sleep are equally important. When sleep deprived, the brain will attempt to get NREM sleep first, but in subsequent nights, the brain will get more REM sleeps. But none of this would ever “gain” back the sleep you lost.
  • Birds and aquatic mammals can sleep with one side of the brain at a time, leaving another side of the brain alert or conducting life-preserving tasks.
  • Humans sleep a little lighter in one side of their brain when they are in new environment to ensure safety.
  • REM sleep require both halves of the brain to be equally asleep.

How should we sleep: 1) mono phase – sleep once a day for 8 hours 2) biphase- sleep sleep the regular 8 hours but take a 20-40 min nap during mid afternoon.

  • Myth: Early 17 – 18 century Western Europe had a new way of sleeping: two long bouts of sleep separated by several hours of wakefulness. There is no anthropological reasons to do this, suggesting it is not the natural, evolutionarily programmed form of human sleep. It is rather a cultural phenomenon popularized with Western European migration. No biological rhythm of brain activity, neurochemical activity, or metabolically activity that would hint at a human desire to wake up for several hours in the middle of the night.

humans are special when it comes to sleep:

  • We have 20-25% REM sleep when primates usually have 9%
  • We sleep 8 hours when other primates sleep 10-15.
  • we sleep laying flat (exclusive terrestrial sleepers) while other primates prefer sleeping on branches or in nests
  • Extra REM sleep allows 1) our degree of sociocultural complexity and 2) our cognitive intelligence

What may at first blush have seemed like a modest asset awarded by REM sleep to a single individual is, I believe, one of the most valuable commodities ensuring the survival and dominance of our species as a collective.

  • Drinking while pregnant is not recommended because alcohol (even 2 glasses of wine) will disturb baby’s REM sleep which prevents baby’s brain development. Drinking while nursing is also not recommended for the same reason.
  • Teenagers’ sleep have more NREM to help them mature their frontal lobe and aid their transition into early adulthood. Young children’s circadian rhythm makes them sleep earlier at night (and more) and rise earlier than their parents while adolescents’ circadian rhythm makes them stay up at night, and rise later than the parents.
  • Adults lose their deep sleep (NREM) as they age. Their sleep become more fragmented (waking up at night) mostly due to medication and weakened bladder. Senior adults circadian timing regresses, leading to earlier and earlier bedtimes.
  • Sleeping (NREM) helps slowly upload all your information absorbed during the day into your memory, salvage those that appeared to have been lost soon after learning. Naps make your memory better.
  • Sleep (NREM) also help us forget – we have yet to harness this power to battle trauma, drug addiction, and substance abuse.
  • A pianist would practice a piece for many times and cannot play it perfectly, but after she goes to sleep, and next morning she wakes up, can simply play it perfectly. Sleep helps our motor skills so simply “learn offline.” Similarly, chromic lack of sleep increase sports injuries in adolescent athletes.

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