“ Unlocking the Power of Sleep and Dreams ”

by Matthew Walker, PhD

Book Cover


Sleeping is a need second only to eating and drinking. 7 to 8h (more 8) of sleep are necessary every night (that is - sleep opportunity). Sleeping less, even 6h, is associated with issues on every aspects of life: medical, cognitive, emotional. Ideally a 30m to 1h nap in the early afternoon. Why we sleep is not certain, but sleep seems to bear several functions, both of the biologic (drain adenosine and such) and psychologic (what Walker calls: overnight therapy). Sleep hygiene requires a consistent sleep schedule, a cool and dark room, avoiding liquor and caffeine and slowing down before going to bed.


Half life of caffeine is up to 10h so it’s sometimes hard to trace back sleeplessness to coffee intake

Sleep is common to all animals including insects, so its evolutionary origin is ancient.

Primordial function is still uncertain, however it evolutionary cost (given the vulnerability during) tells it must be important

Humans require about 8h of sleep per night. The natural pattern in dicyclic: 8h at night, and 1/2 to 1h mid afternoon.

Sleep patterns in animals can be different. Certain birds can sleep half of their brains. Same for dolphins.

Stress or lack of food can reduce the capacity to sleep.

There are two systems triggering sleep: the circadian rythm, and the sleep pressure. Circadian rythm is regulated by the suprachiasmatic nucleus in the brain and is set onto an internal clock lasting a day, and triggers sleep through the release of melatonin. Sleep pressure is due to the accumulation of adenosin in the brain during wakefulness, which binds to receptors triggering drawsiness, and is expunged by sleep. Coffee binds to the same receptors as adenosin, which is how it acts. These two cycles explain why jetlag is a thing, and why in the end of morning after an all nighter, alertness is ok.

Sleep is decomposed into mrem, deep mrem and rem. Alternating with each other.

Effect on memory

Sleep deprivation in kids is correlated with cognitive disabilities

There is evidence that sleep transfers short term to long term memory, from hypothalamus to frontal cortex. Knowledge is reinforced after sleep. It also clears the short term memory and increases receptivity of new information and therefore learning

Sleep is also improving “muscle memory” and physical performance.

Sleep deprivation and drowsiness are dangerous for demanding tasks like driving. 10 days in a row with 7h of sleep is equivalent to an all nighter. When exhausted, the brain does micro sleep - short period of time with absence of reactivity.

There is a habituation to the effects of lack of sleep, meaning that people start to view as normal their degraded state after poor sleep and don’t realize their poor performance or change of character.

Effects of lack of sleep are exponential and not linear. “Power naps” can help reduce the effects of lack of sleep, the best use is prevention (before the fatigue accumulated too much) rather than remediation.

Sleep deprivation is also associated with coupling of amigdala and prefrontal cortex, which triggers mood swings between exacerbated positive and negative emotions.

Effect on body

Lack of sleep is associated with higher risk of heart disease

Lack of sleep is associated with poorer sugar assimilation, which leads to diabetes.

With lack of sleep Leptin (hormon of satiatyl) levels are lowered, and ghrelin (hormon of hunger) are increased.

Lack of sleep is associated with increased rates of cancer and issues with DNA transcription

Sleep is proven to have a link with immune response. Less than 7h of sleep increases chances of infection, and diminishes response to even vaccine. Sleeping also helps curing disease.


Dreams happen during REM sleep

Freudian theory of sleep has no scientific basis, and is scientifically disproven (interpretation by several psychoanalysts gives results with no correlation)

Dreams do not seem to be tied to current events of life or emotional states. They have an organic basis, but are not epiphenomenon to REM sleep (not a byproduct) but have a function.

Journaling life events and emotions has proven effect on mental health

Dreams act as an overnight therapy, helping to cope with emotions of the day

REM sleep and dreaming are associated with relational inference (deduction) between items. I.e finding relations between facts from day

Lucid dreamers are capable of controlling their dream, and are lucid throughout. Proven by experiences where scientist and dreamer agree on eye movement before sleeping (because muscles are paralyzed), then eye movement signal lucid dream, and taking MRI while dreaming to move left arm or right arm. Same for orgasm. This could be a next step of evolution if it brings an advantage

sleep disruptions

True insomnia is touching about 1/10 Americans. It is caused mainly by 1) emotional concern (worry) 2) emotional distress (anxiety).

little wonder that sleep becomes nearly impossible to initiate or maintain when the spinning cogs of our minds start churning, anxiously thinking about things we did today, things that we forgot to do, things that we must face in the coming days, and even those far in the future.

One culprit is an hypersensitive sympathetic nervous system (the body’s fight or flight system), which is not meant to be activated on long term, releasing chemicals like cortisol (stress) and adrenaline (heighten cardiac rate), thus preventing sleep. Chronic activation due to stress causes insomnia.

Since insomnia is then due to a 24x7 problem, fixing it with sleeping pills doesn’t really fix the problem.

Narcolepsy is a disorder where REM sleep mechanisms circuitry has issues. Result is the following symptoms:

  • sleep attacks: feeling an irresistible urge to sleep often through the day (similar to 3 days deprivation)
  • sleep paralysis: person is paralyzed when waking up and cannot move or talk
  • catapletsy: strong emotions trigger a total paralysis of the body (similar to paralysis of REM sleep). This might be one of the explanation for alien abductions

Total sleep deprivation is deadly. People with FFI can’t sleep anymore, and all die within 10 months. Rats die within 15 days without sleep (or just selective REM deprivation - 15days, MREM- 45 days), lose weight, cannot maintain their body temperature, and get a lot of skin infections and internal bleeding (immune system doesn’t work anymore). Cause of death is not certain but mostly seem to be septicemia from their gut bacteria

how much sleep

Recommended for adult is 7-9h of sleep opportunity. There had been a study on sleep of hunter gatherers, who slept 6.5h o average, however 1) was measured with wrist bands which aren’t precise, 2) 6.5h of sleep means more than that in sleep opportunity 3) their life expectancy is 59y, and leading cause of death is bacteria infection, while insufficient sleep is linked with lowered immune response 4) they don’t eat enough and so are pressed to sleep less in search for food

why crisis of less sleep

  1. Electric light (tricking our brains into thinking it’s still day, blocking melatonin secretions. Blue light (led) is the worst at that
  2. Regularized temperature: we need to decrease core temperature to go to sleep, and decreasing outside temperature also triggers melatonin production. Thermostat, especially when setting temperature too high, are not helping
  3. Caffeine
  4. Alcohol: is a sedative. Sleep while drunk is closer to light anesthesia, but prevents REM sleep, leading to less restorative sleep, memory assimilation issues, and when prolonged, delirium tremens
  5. Punching time cards: alarm clocks were created for shifts (fordism). They are triggering a fight or flight response, heighten cardiac rythm. Repeating with the snooze button is even worse. Rather, wake every day at the same time, and skip the snooze button

better sleep

Sleeping pills are also sedatives, their action does not trigger actual sleepbut sedation. In addition, their efficiency compared to placebo is marginal. There’s also evidence of increased rates of mortality for users (even occasional) of sleeping pills, by several factors. Unlikely there will be a reevaluation since Ambien generated 4B revenue in first 24 months of commercialization

  • add pdf @project(post)

Sleep problems are better fixed with help from sleeping medical expert. CBTI (Cognitive behavioral therapy) is the first line of defense against disorder. Some advices :

  • fix obvious issues: coffee, alcohol, screen, going to bed too late, cool room
  • establish regular sleep pattern, even on weekends
  • go to bed only when sleepy
  • never stay awake in bed for extended periods of time, rather get out and do something relaxing
  • remove clocks from room to prevent clock induced stress
  • avoid daytime napping
  • decelerate before bedtime
  • increase sleep pressure by staying awake longer (and skip caffeine)

Sleep hygiene:

  1. Go to bed and wake up every day at the same time
  2. Exercise, esp. for younger and mid life, although not as significant as sleep deprivation impacts exercise performance
  3. Food - don’t eat too much or not enough, and avoid carbs, esp sugar, and don’t drink too much
  4. Avoid caffeine and nicotine
  5. Avoid alcohol before bed
  6. Avoid medication that impair sleep (if possible)
  7. Dont take naps after 3pm
  8. Decelerate before bed
  9. Hot bath or shower before bed
  10. Dark room, no sound, no clock if insomnia
  11. Sunlight exposure, 1h in morning, low light at night
  12. Don’t lay awake in bed

societal issues

  • businesses are celebrating sending emails late then being at work early
  • torture
  • school starts earlier and earlier, making kids wake up earlier and earlier - which is bad both for kids long term health and ability to learn.
    • lots of societal pressure to keep it that way between school bus unions and parents wanting to start work earlier
    • Kids seem to sleep between 1 and 2h less than 100y ago. There’s a total overlap of ADHD and lack of sleep, drugs commonly given to solve ADHD are amphetamines. Estimate 50% of kids diagnosed with ADHD actually have a sleeping disorder. First line of response for a kid with ADHD should be more sleep.
    • cynically, amphetamines dealers are sent to prison but pharma can advertise ADHD medication on prime time


  • make sure companies integrate sleep hygiene in how they schedule and see employees
  • change healthcare accordingly
  • create systems (trackers and analytics) that help waking/going to bed at right times and predict issues

About Reading Notes

These are my takes on this book. See other reading notes. Most of the time I stop taking notes on books I don't enjoy, and these end up not being in the list. This is why average ratings tend to be high.