Why We Sleep: The New Science of Sleep and Dreams

By Matthew Walker

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  • Your biological circadian rhythm coordinates a drop in core body temperature as you near typical bedtime, reaching its nadir, or low point, about two hours after sleep onset.

    Page: 19
  • Melatonin helps regulate the timing of when sleep occurs by systemically signaling darkness throughout the organism. But melatonin has little influence on the generation of sleep itself: a mistaken assumption that many people hold.

    Page: 23
  • Caffeine is removed from your system by an enzyme within your liver, which gradually degrades it over time. Based in large part on genetics, some people have a more efficient version of the enzyme that degrades caffeine, allowing the liver to rapidly clear it from the bloodstream.

    Page: 29
  • A key function of deep NREM sleep, which predominates early in the night, is to do the work of weeding out and removing unnecessary neural connections. In contrast, the dreaming stage of REM sleep, which prevails later in the night, plays a role in strengthening those connections.

    Page: 45
  • The very simplest forms of unicellular organisms that survive for periods exceeding twenty-four hours, such as bacteria, have active and passive phases that correspond to the light-dark cycle of our planet. It is a pattern that we now believe to be the precursor of our own circadian rhythm, and with it, wake and sleep.

    Page: 57
  • Whatever the functions of REM-sleep dreaming—and there appear to be many—they require participation of both sides of the brain at the same time, and to an equal degree.

    Page: 66
  • Elderly individuals fail to connect their deterioration in health with their deterioration in sleep, despite causal links between the two having been known to scientists for many decades.

    Page: 96
  • The more deep NREM sleep they get, the more information an individual remembers the next day.

    Page: 114
  • A final benefit of sleep for memory is arguably the most remarkable of all: creativity. Sleep provides a nighttime theater in which your brain tests out and builds connections between vast stores of information.

    Page: 132
  • If you wake up at seven a.m. and remain awake throughout the day, then go out socializing with friends until late that evening, yet drink no alcohol whatsoever, by the time you are driving home at two a.m. you are as cognitively impaired in your ability to attend to the road and what is around you as a legally drunk driver.

    Page: 138
  • The recycle rate of a human being is around sixteen hours. After sixteen hours of being awake, the brain begins to fail.

    Page: 140
  • With a full night of plentiful sleep, we have a balanced mix between our emotional gas pedal (amygdala) and brake (prefrontal cortex). Without sleep, however, the strong coupling between these two brain regions is lost. We cannot rein in our atavistic impulses—too much emotional gas pedal (amygdala) and not enough regulatory brake (prefrontal cortex). Without the rational control given to us each night by sleep, we’re not on a neurological—and hence emotional—even keel.

    Page: 147
  • There is no major psychiatric condition in which sleep is normal. This is true of depression, anxiety, post-traumatic stress disorder (PTSD), schizophrenia, and bipolar disorder (once known as manic depression).

    Page: 149
  • Those few memories you are able to learn while sleep-deprived are forgotten far more quickly in the hours and days thereafter. Memories formed without sleep are weaker memories, evaporating rapidly.

    Page: 154
  • High-calorie foods became significantly more desirable in the eyes of the participants when sleep-deprived.

    Page: 176
  • Short sleep (of the type that many adults in first-world countries commonly and routinely report) will increase hunger and appetite, compromise impulse control within the brain, increase food consumption (especially of high-calorie foods), decrease feelings of food satisfaction after eating, and prevent effective weight loss when dieting.

    Page: 178
  • Dreams are not, therefore, a wholesale replay of our waking lives. We do not simply rewind the video of the day’s recorded experience and relive it at night, projected on the big screen of our cortex. If there is such a thing as “day residue,” there are but a few drops of the stuff in our otherwise arid dreams.

    Page: 204
  • Like viewing an image through frosted glass, or looking at an out-of-focus picture, a dream-starved brain cannot accurately decode facial expressions, which become distorted.

    Page: 215
  • During the dreaming sleep state, your brain will cogitate vast swaths of acquired knowledge,I and then extract overarching rules and commonalities—“the gist.” We awake with a revised “Mind Wide Web” that is capable of divining solutions to previously impenetrable problems. In this way, REM-sleep dreaming is informational alchemy.

    Page: 219
  • It is sleep that builds connections between distantly related informational elements that are not obvious in the light of the waking day.

    Page: 227
  • The content of one’s dreams, more than simply dreaming per se, or even sleeping, determines problem-solving success.

    Page: 230
  • I suspect that you cannot recall any truly significant action in your life that wasn’t governed by two very simple rules: staying away from something that would feel bad, or trying to accomplish something that would feel good. This law of approach and avoidance dictates most of human and animal behavior from a very early age.

    Page: 246
  • Alcohol is one of the most powerful suppressors of REM sleep that we know of.

    Page: 272
  • To successfully initiate sleep your core temperature needs to decrease by 2 to 3 degrees Fahrenheit, or about 1 degree Celsius. For this reason, you will always find it easier to fall asleep in a room that is too cold than too hot, since a room that is too cold is at least dragging your brain and body in the correct (downward) temperature direction for sleep.

    Page: 275
  • Give participants the ability to choose between work tasks of varying effort, from easy (e.g., listening to voice mails) to difficult (e.g., helping design a complex project that requires thoughtful problem solving and creative planning), and you find that those individuals who obtained less sleep in the preceding days are the same people who consistently select less challenging problems. They opt for the easy way out, generating fewer creative solutions in the process.

    Page: 299
  • When it comes to the quantified self, it’s the old adage of “seeing is believing” that ensures longer-term adherence to healthy habits.

    Page: 329
  • Sleep appears to be a natural analgesic, and without it, pain is perceived more acutely by the brain, and, most importantly, felt more powerfully by the individual.

    Page: 336
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