Why we sleep: unlocking the power of sleep and dreams

by Matthew Walker

Posted on
health sleep science

There is controversy around some of the claims made in this book, so I don’t take any single point of evidence extremely seriously. But the person who critiqued the book also has some weird ideas about sleep,For instance, he believes that we evolved in a sleep-deprived environment so sleep deprivation must be healthier for us. so in the end I think I probably side with the sleep scientist for most issues except when he seems extreme. Isn’t epistemology fun?

REM sleep is associated with building synapses, while NREM sleep is associated with pruning.

  • Babies and young children need lots of REM sleep.
    • Alcohol disrupts REM sleep for babies in womb and breastfeeding infants (not to mention the adults).
    • Disregular REM sleep in early childhood is associated with autism. We aren’t sure about causality.
  • A teen’s circadian rhythm is shifted back 2 hours compared to an adult, and they need more sleep than adults. Let’s give them that.
  • Caffeine should be avoided by kids and teens because it’s so disruptive to the development that occurs during sleep. Even for adults, caffeine in the blood can take 12 hours to decay to normal, which means a coffee taken after lunch will have deleterious effects.
  • Old people don’t need less sleep, they just get less because their body has a harder time generating sleep. Lack of sleep is correlated with memory problems and dementia onset in the elderly.

Stage 2 NREM sleep has sleep spindles, which are little flashes of activity between specific regions of the brain, most common in the last two hours of the 8 hour sleep cycle. They’re used to move factual information from short-term to long-term storage, and motor memory into subconscious motor regions. They are even selective in what gets retained vs. forgotten, based on what we “want” to remember.

The prefrontal cortex (reasoning area) has a regulatory effect on the amygdala (emotions, fight-or-flight) when well slept, but not when sleep deprived. This results in poor emotional reasoning, e.g. high reactivity, unhealthy pleasure-seeking, increased depression. Sleep disturbance is at least correlated with and possibly causal of mental illness, depression, and suicide.

Recommendations for getting a good night’s sleep:

  • cold room
  • screens not in bedroom
  • reduce caffeine and alcohol
  • regular bed and wake
  • only go when sleepy
  • don’t lie in bed long
  • avoid daytime napping
  • learn to mentally decelerate before bed
  • remove clocks from bedroom
  • for difficult cases: restrict sleep time to 6 hours per night, building up sleep pressure, then ramp up once they have confidence they can generate sleep quickly

Later school start times drastically reduce car accidents, and result in higher SAT scores. Kids who sleep less are probably getting prescribed amphetamines for ADHD, which make it even harder to sleep.