Dr. Matthew Walker’s “Why We Sleep”: Book Review, Notes + Analysis

Poor Ash’s Almanack > Book Reviews > STEM > sleep

Overall Rating: ★★★★★★★ (7/7) (life-changing)

Per-Hour Learning Potential / Utility: ★★★★★★★ (7/7)

Readability: ★★★★★★★ (7/7)

Challenge Level: 2/5 (Easy) | ~340 pages ex-notes (368 official)

Blurb/Description: Scientists have discovered an amazing medical intervention, described as “Mother Nature’s best effort yet at contra-death.”  It’s proven to prevent cancer, Alzheimer’s, car crashes, and the common cold.  It enhances learning and memory.  It improves your mood and willpower.

It regulates your emotions and helps you make better decisions, it causes you to shed fat and gain muscle mass, and – ahem – it makes your you-know-what bigger and makes you objectively more attractive to prospective significant others.  It’s free, 100% natural – organic, even – and has no known side effects no matter how much of it you take.

It’s called sleep.  So why are the vast majority of teenagers, and 70% of adults in industrialized nations, not getting enough?  Sleep is the foundation of health and good decision-making, explored thoroughly and fascinatingly in Walker’s Why We Sleep.”  

This is probably one of the most important books you’ll read in your lifetime, and every household in America should have a copy.  I bought all ACM clients copies to celebrate the launch of Poor Ash’s Almanack.  I usually don’t tell y’all to do this, but don’t bother reading the review, and just go buy a copy and read the book ASAP.  (Don’t skip any sleep to do so, though.)

Sleep is not an optional lifestyle luxury. Sleep is a non-negotiable biological necessity. It is Mother Nature's best attempt yet at contra-death. - Dr. Matthew Walker Click To Tweet

Summary: Take heed, hard-charging macho-man executives who plan to sleep when they’re dead: men who don’t sleep enough have smaller testicles and 30% lower sperm count.

Do I have your attention with that salient soundbite?  That’s, unfortunately, the least bad piece of news regarding sleep deprivation that sleep researcher Dr. Matthew Walker has to deliver.  The consequences of foregoing sleep only get worse from small balls and weak swimmers, as he explains in the intro to his memorable Talk at Google (he should’ve started his book the same way).  

Sleep is more important than diet or exercise for maintaining both physical and mental health in the short and long-term, and is critical both before and after learning to ensure lessons are retained in memory – yet many people who focus on diet and exercise completely neglect sleep.  

Whenever you need an alarm clock to wake up, you’re not getting enough sleep – full stop.  Research demonstrates that if you’re chronically sleep-deprived – like much of the working population – sleep is far more important than diet or exercise for your health, so you’re doing yourself a disservice if you’re getting up early (or staying up late) to hit the gym.  In other words, if you’ve ever felt like you’re dying during a 5 am bootcamp – you’re right.  You are dying.  The bootcamp – more specifically, the time of day it’s held at – is, quite literally, killing you.

Much like buzzed drinkers who still think they’re good to drive, sleep deprivation renders us incapable of even accurately evaluating our own level of sleep deprivation: so even if you think you’re doing okay on six or seven hours of sleep, chances is you’re not, and a sleep lab could measure objective impairments.

Sleep deprivation is so pervasive that it’s officially been recognized as an epidemic by the CDC and WHO.  It’s a leading contributor to all mortality causes among adults. Moreover, research demonstrates that brutally early school start times are impairing learning, causing mental health disorders ranging from depression to schizophrenia, and directly killing many adolescents via suicides, increased propensity for drug/alcohol use, and car accidents (not to mention long-term immune impacts).  For the sake of their long-term health, adolescents engaging in any pre-school activity should quit and sleep as long as they can.

Thankfully, via inversion, simply getting enough sleep is the single most effective, easiest, and costless intervention to improve immune function, prevent cancer, enhance learning, promote positive mental attitude, and arm the logical/rational neocortex with the resources it needs to override the emotional/primitive amygdala.

Walker’s engaging, science-backed “ Why We Sleep is probably one of the most important books you’ll read in your entire lifetime.  Sleep is a structural problem solving solution to functionally every cognitive bias, stressagency, and a number of other mental models.

Highlights: Walker is pretty funny; he has a touch of the Shawn Achor humor.  He also does a phenomenal job of translating fairly technical concepts into easily-understandable language and analogies; any reasonably intelligent twelve-year-old could read this book just fine.

Lowlights: While Walker does briefly address chronotypes, discuss the blatant and irrational societal discrimination against late chronotypes, and advocate that schools start later and corporations allow flexible work hours with a core overlap period, he doesn’t go very deep into the process of entrainment and the origin of chronotypes; sleep deprivation tends to be a proportionately worse problem the later your chronotype is, given the status quo bias irrationally favoring early mornings.  Fortunately, Till Roenneberg’s phenomenal “ Internal Time ( IntTm review + notes) covers chronotypes in quite some depth.  

Additionally, while reading, I felt like the order of the book was a bit odd… for example, I thought the bit about chronotypes should have come after the discussion of the physiological impacts of sleep, when it would have been more impactful.  Nonetheless, this is a very modest and irrelevant nitpick.

Mental Model / ART Thinking Points: sleepinversiontrait adaptivityculture / status quo bias,overconfidencescientific thinkingmemorycorrelation vs. causationempathyfeedback,confirmation biashabitutilityschema bottleneckfeedbackn-order impactssalience, a/b tests,base ratesnonlinearitybase ratesagencystructural problem solving

You should buy a copy of Why We Sleep if: you have a pulse.

Reading Tips: Follow up with Till Roenneberg’s Internal Time (IntTm review + notes) to get more out of it.  Also consider watching his Talk at Google, either before or after reading – on a separate day, separated by plenty of sleep – to enhance learning.

This five-minute video is useful for sending to friends who won’t read the book or the one-hour interview.

Pairs Well With:

Internal Time” by Till Roenneberg (IntTm review + notes).  As discussed, Walker doesn’t go that deep into chronotypes and entrainment – Roenneberg does, in this indispensable book.

Deep Survival” by Laurence Gonzales (DpSv review + notes).  “Rambo types are the first to die” is one of the key takeaways from Gonzales’s wonderful book on  cognition / intuition / habit / stress.  Gonzales also stresses the importance of rest and the very real nature of fatigue.

The Genius of Birds” by Jennifer Ackerman (Bird review + notes).  Ackerman touches on how important sleep is for the development of birds – for example, birds that don’t sleep well never learn their songs properly.

Misbehaving” by Richard Thaler (M review + notes).  Once you’re well-rested, you’ll want to learn all the other ways your brain is impaired – this and Tavris/Aronson’s “ Mistakes were Made (but not by me) ( MwM review + notes) are great places to start.

Reread Value: 5/5 (Extreme)

More Detailed Notes + Analysis (SPOILERS BELOW):

Please remember: these notes were created primarily for my own personal reference and are not intended to be an abstract or summary of the book; in other words, they don’t substitute for reading the book, and most of their content will not make sense without the broader context of the book.  These simply represent some of the points that I found interesting / thought-provoking / related to other material that I’ve learned from.

I share them for a few reasons: first, and primarily for those who’ve read the book, hopefully these will serve as some thought-provoking marginalia as well as a “refresher course” on some of the concepts if it’s been a while since you’ve read the book.  Second, in more limited circumstances, if you haven’t read the book but have seen it referenced in one of the mental models or other pages in Poor Ash’s Almanack, you may find the notes to be a useful “information bridge” (albeit a very temporary/rickety one) until you’re able to read the book yourself.

Page 3: How to tell you’re not getting enough sleep, by inversion: is the answer to any of the following yes?

  • Do you regularly use an alarm clock to wake up?
  • Do you feel tired when you wake up?
  • Is your first action in the morning to drink some coffee?
  • Is your total amount of sleep (not time in bed) lower than seven and a half hours?

If the answer to any of those is yes, you’re highly likely to be sleep deprived.

Page 4: Walker here notes:

“Human beings are in fact the only species that will deliberately deprive themselves of sleep without legitimate gain.”

One of the consistent themes throughout the book is that we can only partially catch up on sleep: once the opportunity is gone, it’s gone.  

I don’t recall if Walker goes into it in depth in the book – I don’t think he does – but in his Talk at Google, he analyzes why we have a “credit system” for energy (fat storage) but not a “credit system” for sleep.  

One potential answer, per Walker, is the above quote: never in our evolutionary history did we intentionally and routinely deprive ourselves of sleep, so there was no need for such a system.   Trait adaptivity.

Also, Walker notes that the WHO has declared sleep loss an epidemic in industrialized nations.  It seems the CDC has as well.

Page 5: Walker on sleep-related crashes:

“It is disquieting to learn that vehicular accidents caused by drowsy driving exceed those caused by alcohol and drugs combined.”

He later notes that these are not “accidents” because they were preventable (by sleep.)

Page 6: Discussing the evolutionary origin of sleep, Walker notes that given our vulnerability and lack of productivity during sleep, it’s unimaginable (in theory, without any research) that it doesn’t serve a critical purpose.  He cites a sleep researcher, Dr. Allan Rechtschaffen, as stating:

“If sleep does not serve an absolutely vital function, then it is the biggest mistake the evolutionary process has ever made.”

Trait adaptivity.

Page 8: I’m going to have to restrain myself from basically block-quoting this entire book (I am always mindful of fair use.)  Walker notes that while diet and exercise are important,

“The physical and mental impairments caused by one night of bad sleep dwarf those caused by an equivalent absence of food or exercise […] sleep is the most effective thing we can do to reset our brain and body health each day – Mother Nature’s best effort yet at contra-death.”

Page 9: Interestingly, like chronobiologist Till Roenneberg (author of “ Internal Time – IntTm review + notes), Walker ended up in sleep accidentally.  Unlike Roenneberg, who started in physics, Walker started in medicine.

Page 12: Like Thaler, Walker doesn’t mind if you don’t finish this book… like a good masseuse, he’d take it as a compliment if you snoozed off in the middle of it.

Pages 14 – 15: Walker here briefly overviews how circadian rhythms and chronotypes work.  He starts with the Jean-Jacques d’Ortous de Mairan experiment in 1729 on a mimosa plant; this experiment was more or less forgotten for 200 years.  Till Roenneberg does a better job with the chronobiology angle in Internal Time (IntTm review + notes).

Also ahahaha the footnote.

Pages 17, 18: Walker notes that our internal rhythm isn’t actually 24 hours; we require an external cue – “zeitgeber” – to synchronize to a 24 hour cycle.  The clock is located in the suprachiasmatic nucleus, which is a tiny little thing (20,000 neurons vs. 100 billion in the brain). He doesn’t really explain in depth how early and late chronotypes come to be, as Roenneberg does.

Pages 20 – 22: Even though Walker doesn’t go into detail on chronotypes, he does a good job with the conclusions:

“When a night owl is forced to wake up too early, their prefrontal cortex remains in a disabled, ‘offline’ state.  Like a cold engine after an early-morning start, it takes a long time before it warms up to operating temperature […]

Sadly, society treats night owls rather unfairly on two counts.  First is the label of being lazy […] night owls are not owls by choice.  They are bound to a delayed schedule by unavoidable DNA hardwiring. It is not their conscious fault, but rather their genetic fate.

Second is the engrained, un-level playing field of society’s work scheduling, which is strongly biased toward early start times that punish owls and favor larks.  Although the situation is improving, standard employment schedules force owls into an unnatural sleep-wake rhythm […]

Most unfortunately, owls are more chronically sleep-deprived [than larks]. […] greater ill health caused by a lack of sleep therefore befalls owls, including higher rates of depression, anxiety, diabetes, cancer, heart attack, and stroke.”

As a night owl, I appreciate that.  🙂  I talk about my own experiences with this elsewhere – ex. in the notes on “ Internal Time ( IntTm review + notes) and “ Rest ( Rest review + notes) and more narratively in the sleep model- so I won’t duplicate that here.  But let’s just say that sleep is my secret weapon and I’ve definitely observed the majority of Walker’s discussed points – improved immune function, better emotional control, improved athletic performance, better learning andmemory, you name it.

Walker addresses lighting in the industrial era and how it messes with our circadian rhythm, but again, Roenneberg does a better job with the longitudinal culture / status quo bias angle here, exploring how this stupid notion came to be.

Like Roenneberg, Walker provides a trait-adaptivity angle for the variation in chronotypes: it’s usefulfor us to not all be asleep at the same time!

Page 23: Walker makes a curious argument here that I don’t wholly buy.  Basically, he argues (here and in the Google Talk) that melatonin isn’t effective for healthy adults as a sleep aid.

I think he should’ve specified a bit.  I think that’s true if you don’t have a chronotype issue.  On the other hand, he later notes that one cause of not being able to fall asleep is a delayed melatonin rhythm thanks to blue light.  I’ve personally found that melatonin (in addition to avoiding blue light late at night) does help me fall asleep earlier and stay asleep longer.  

Walker seems to argue it’s a placebo effect, but I think some of the research Roenneberg cites with regard to Smith-Magenis syndrome contradicts this.  See pages 219 – 220 of Internal Time ( IntTm review + notes).

Pages 25 – 26: Walker here discusses why flying west is easier than flying east: it’s easier to synchronize to a longer-than-24-hour-day than a shorter one.

He also cites research suggesting memory impairment and brain shrinking of pilots and airplane cabin crews who fly transcontinental a lot, as well as higher rates of cancer, type 2 diabetes, etc.

Similar stuff is seen with regards to shift workers, as both Walker and Roenneberg cover in some depth.

Pages 27 – 29: Walker is more thorough on sleep than Roenneberg (obviously).  I love Walker’s discussion of adenosine and caffeine: Roenneberg talks about sleep pressure but doesn’t go as deep here (if I recall).

Summarily, the reason caffeine makes us alert – and then tired when it wears off – is that it blocks adenosine binding to receptors that signal sleepiness.  The adenosine still builds up, though; it just has nowhere to bind to until the caffeine goes away.

Walker seems pretty hardcore anti-caffeine, and although I love my coffee (currently at 1 – 1.5 10 oz cups a day, down from 2, which was down from 3), I have to say his argument is pretty compelling.  Not only is the half-life 5 – 7 hours – such that a 3 pm cup of coffee is still half in your system at midnight – but he also notes (not here) that systemic caffeine can actually reduce the quality of sleep, even if you are asleep.  The same goes for sedative sleep aids.

Page 30: He shows that famous NASA chart about spiders building webs on various drugs.  After reading about Tusko in Geoffrey West’s “ Scale ( SCALE review + notes), I’m not going to take this at face value…

Pages 38 – 40: The coma bit is funny… Walker notes some of the interesting physiological elements of sleep, including the odd fact that we lose conscious awareness of time but can still often subconsciously wake up at the right time before flights and stuff.  We’ve all observed this.

Page 41: In The Genius of Birds” (Bird review + notes), Jennifer Ackerman discusses how when birds sleep, the areas of their brain that saw heavier use during the day correspondingly see heavier activity during sleep.  Walker notes the same thing in humans and rats. (He goes into the mechanism later.)

Intriguingly, he posits one potential reason for dream time distortion: slower neuron firing.

Pages 42 – 43: Here, he starts to introduce NREM and REM stages.  I think he also blows up a popular hypothesis throughout the book – I used to think that only deep sleep and REM were important, but he presents research suggesting that even stage 1 / stage 2 sleep has uses (although deep sleep and REM seem to be the most important).

Also, the thalamus is what filters out information / stimulus when we sleep, apparently.

Pages 44 – 46: Walker does a good job of not being overconfident and retaining scientific thinking: he notes that our odd, helter-skelter cycle between NREM and REM (with later in the night having proportionately more REM), might be because it’s a cycle of removing and adding, like a sculpture.

As a quick analogy, Walker cites NREM as removing unnecessary information from memory, while REM enhances and interconnects what’s left.  We’ll get to that, and the glymphatic system, later.

He notes that a danger in cutting sleep short, given this cycle, is that all is not equal: by waking up early, we’re predominantly sacrificing REM sleep:

“[If you forego the last two hours of your sleep], you will lose 60 to 90 percent of all your REM sleep, even though you are losing 25% of your total sleep time.”

Pages 49 – 53: The discussion of sleep spindles is fascinating.  Deep sleep waves originate in the middle of the frontal lobe, two inches above the bridge of our nose.  They emanate from front to back.

In deep NREM, the cortex relaxes into its “default mode” (not clear if this is related to the “default mode network” I’ve read about elsewhere.)

Walker uses AM/FM radio to compare/contrast REM and NREM: NREM is like AM; long-distance transfer.

He also notes that REM sleep cannot be distinguished from wakefulness with brain electricity; in some cases it’s more intense.

The thalamus is open during REM – but not to the outside word.  Walker categorizes NREM as reflection / storage/strengthening (like a file transfer protocol) and REM as integration / interconnection.  He notes the correlation between REM and creativity/ intuition later.

Page 54: Here, Walker briefly discusses muscle atonia during REM, which generally prevents us from acting out our dreams.  (My mental image is dogs “running” in their sleep…)

Pages 56 – 57: Walker notes that:

“Without exception, every animal species studied to date sleeps, or engages in something remarkably like it.”

Also, ahahahahahaha, in my “science can be fun and surprisingly approachable” file: how do scientists figure out how deeply worms are asleep?  It’s not via some fancy-schmancy electrode apparatus. Nope, it’s:

“Defined by their degree of insensitivity to prods from experimenters.”

The idea of being paid to poke sleeping worms to see if they wake up and getting to call it science is honestly pretty hilarious.  Can I have that job?  Not, forever, but like for an hour.  Just imagine the conversations with friends and family:

“What did you today, honey?”

“Oh, the usual.  Poked some worms.  What about you?”

Page 58: Walker notes that there’s not a good correlation between sleep time and any other characteristic… it varies from four hours in elephants to nineteen hours in bats and, surprisingly, 16 hours in squirrels.  Never would’ve guessed that.  Squirrels don’t seem particularly sleepy.  I guess all that nearly-being-hit-by-a-car is stressful.

Pages 60 – 61: Walker notes that while all animals experience NREM, it seems to be only birds and mammals that experience REM.  Interestingly, seals have lots of REM on land, but not a lot in the ocean. It obviously works different in the ocean because you can’t, like, stop swimming and drown.  Trait adaptivity.

Pages 63 – 64: On sleep rebounding after deprivation: initially we try to catch up on NREM; in subsequent nights, the focus shifts to REM.  However, and this is critical from a public-health standpoint: we can never fully “catch up” on sleep.  Some, yes, but not all of it: when the opportunity’s gone, it’s gone.

Pages 64 – 66: Interesting explanation here of sleeping on half of the brain in cetaceans:

“The neural engineering and tricky architecture required to accomplish this staggering trick of oppositional ‘lights-on, lights-off’ brain activity is rare.  Surely Mother Nature could have found a way to avoid sleep entirely under the extreme pressure of nonstop, 24/7 aquatic movement […]

Apparently not.  Sleep is of such vital necessity that no matter what the evolutionary demands of an organism […] Mother Nature had no choice.  […] Sleep is non-negotiable.”

Interestingly, a version of this occurs in humans: we sleep better in safe environments because in new environments, one half of our brain sleeps less lightly and is more open to outside threats.

Page 67: The examples here about whale calves and migrating birds are fascinating: apparently, during that period, and that period only, they can deal with extreme sleep deprivation… but not in other circumstances.  

Pages 69 – 71: Walker argues that the nighttime biphasic sleep (sleep, wake, sleep) that is purported to be “original” is not, in fact, original.  

On the contrary, he argues biphasic sleep via a long sleep at night and a nap in the afternoon is biologically wired.

He cites some scary research on napping in Greece; apparently siestas are cardioprotective.  Maybe I should start taking naps?

Pages 74 – 75: Walker posits (though it’s not proven / perhaps not provable) that REM sleep was one of the accelerators of human cognition / intelligence.  He notes (as he’ll go into in more depth later) that REM sleep is critical for both social/emotional processing and creativity. He notes:

“The coolheaded ability to regulate our emotions each day […] depends on getting sufficient REM sleep night after night.”

Recall from earlier that alarm clocks tend to disproportionately deprive us of REM sleep.  So, if you want to make optimal decisions and not undergo amygdala hijacks of the sort explored in Deep Survival (DpSv review + notes) and elsewhere… get your sleep.

Pages 78 – 80: Apparently most unborn baby kicks are during REM sleep.  Walker here overviews how fetuses have a tremendous amount of REM sleep, which is “vital for promoting brain maturation.”  Experiments on rats suggest that depriving infant rats of REM sleep “ground to a halt” development of critical portions of their brain; this has been replicated in other mammalian species.

Pages 82 – 84: Walker is here careful to separate correlation vs. causation, but he does note that alcohol consumed by pregnant mothers powerfully disrupts the fetus’s REM sleep, which may be a contributing mechanism to slower brain development.  Additionally, infants’ breathing rate slowed down from 381 per hour to 4 per hour.

Lesson: don’t drink during pregnancy, ever.  Additionally, alcohol is absorbed via breastmilk, so breastfeeding mothers shouldn’t imbibe either.  

Page 86: Walker recommends the audiobook version of Go The Fuck To Sleep, narrated by Samuel L. Jackson.  Even if you don’t buy the audiobook, the sample on Amazon is worth listening to and laughing at.

Pages 90 – 91: Walker notes here that deep NREM sleep in childhood precedes cognitive and developmental milestones and may drie brain maturation.

The corollary to this is that in teenagers, lack of deep sleep can slow prefrontal cortex development, thereby impairing decisionmaking…

Pages 92 – 94: Walker notes that sleep deprivation among teenagers is also a predictor of mental illnessses.

He goes into the evolving chronotype across lifespan here; again, Roenneberg goes into more depth in Internal Time ( IntTm review + notes).  Nonetheless, Walker notes about teenagers – and this could be equivalently interpreted for adult owls in a good example of framing to remove the schema bottleneck:

“Asking your teenage[r] to go to bed and fall asleep at ten p.m. is the circadian equivalent of asking you, their parent, to go to sleep at seven or eight p.m..  No matter how loud you enunciate the order, no matter how much that teenager truly wishes to obey your instruction, and no matter what amount of willed effort is applied […] the circadian rhythm of a teenager will not be miraculously coaxed into a change.

Furthermore, asking that same teenager to wake up at seven the next morning and function with intellect, grace, and good mood is the equivalent of asking you, their parent, to do the same at four or five a.m.

[…] teenagers’ sleep patterns [… are] non-volitional, non-negotiable, and strongly biological.  We parents would be wise to accept this fact […] and praise it, lest we wish our own children to suffer developmental brain abnormalities or force a raised risk of mental illness upon them.”

I think it would take a profound lack of empathy – or a lot of confirmation bias – to actually look at the cold, hard science here and justify the trauma that many teenagers go through every morning on schooldays.

Pages 96 – 97: Walker notes that the quality and quantity of deep NREM sleep declines over life; sleep fragmentation increases.  It’s not clear which way the causality works – or whether it works both ways, i.e. feedback – but he does note that:

“Far more of our age-related physical and mental health ailments are related to sleep impairment than either we, or many doctors, truly realize or treat seriously.”

Page 101: Here’s the feedback bit: a lot of age-related degeneration of the brain occurs in the regions that generate deep sleep.  This can cause up to a 70% loss in deep sleep.

Page 107: Walker presents a version of my blurb above… sleep is free, it has no side effects, and it’s pretty much a miracle panacea for everything, according to “more than 17,000 well-scrutinized scientific reports to date.”

Pages 108 – 111: I found this section, on memory and learning, particularly fascinating.  Walker makes the analogy of our hippocampus (short-term memory storage) being a bit like a USB stick.  Sleep before learning moves old stuff out to an external hard drive, creating room for the new; sleep after learning makes sure that stuff gets stored instead of lost.

Walker is careful to note – as anyone who has studied memory understands – that the human brain is NOT like a hard drive.  But the file transfer visualization is useful, in this case. Walker cites a lot of research here on the link between sleep and learning.

On memory, you may be wondering about the adaptivity of forgetting stuff – i.e., why wouldn’t we just remember it all?  For an answer to that, see Daniel Schacter’s The Seven Sins of Memory (7SOM review + notes) for a functional perspective.  Schacter notes toward the end of the book howuseful it is to be able to forget things:

A system that renders information less accessible over time is therefore highly functional, because when information has not been used for longer and longer periods of time, it becomes less and less likely that it will be needed in the future.  

On balance, the system would be better of setting aside such information… [our memory… makes a bet that when we haven’t used information recently, we probably won’t need it in the future.  

We win the bet more often than we lose it, but we are acutely aware of the losses… and never aware of the wins.”  

While the idea of a photographic memory is often romanticized in film or fiction, Schacter notes when recounting an anecdote about a famous Russian mnemonist –

“he was unable to function at an abstract level because he was inundated with unimportant details of his experiences.”  

Schacter also references how the same neurological mechanisms that enable autistic children and adults to have amazing memories can prevent them from effectively generalizing.

Schacter points out, as well, that the rate of decay in memory is pretty rapid at first, then slower over time.  Walker doesn’t go into the longer-term remodeling, which might be an interesting angle to investigate.

Anyway.  Other good books on memory: Tavris/Aronson’s “ Mistakes were Made (but not by me) is one of the best in a practical context – MwM review + notes.

Don Norman’s The Design of Everyday Things (DOET review + notes) is also good / illustrative with regard to illustrating what sort of information we find important and remember.  His discussion of money (both coins and bills) is particularly memorable.

Pages 113, 115: Walker notes that deep NREM sleep solidifies memory not only in humans, but in all animals.

Pages 117 – 119: Walker overviews some intriguing research on sleep stimulation with a big “do not try this at home” warning.

Pages 121 – 122: Walker points out that sleep selectively strengthens memory of things we want to remember.

Pages 125 – 126: Here, Walker examines the effect of sleep on non-fact-based learning, i.e. riding a bike or typing a sequence on a keyboard.  He notes that sleep leads to a 20% jump in performance speed and a 35% improvement in accuracy, also leading to better flow / smoothness.  He focuses more on physical things, but the mental angle is more interesting.

Clearly sleep is an underlying mechanism in habit / conditioning; see the aforementioned Deep Survival by Laurence Gonzales (DpSv review + notes) and The Power of Habit by Charles Duhigg (PoH review + notes) for more of the science on how powerful conditioning is.

Duhigg notes, among other interesting bits, that up to 40% of our daily decisions are in fact habitual, and this pops up well beyond the context of physical actions: it applies to mental processes too.

One of my favorite bits from Philip Tetlock’s “ Superforecasting” (SF review + notes) is his hypothesis on the mental process of superforecasters transitioning from  cognition to  intuition:

“My sense is that some superforecasters are so well practiced in System 2 corrections – such as stepping back to take the outside view – that these techniques have become habitual.  In effect, they are now part of their System 1. 

[…] No matter how physically or cognitively demanding a task may be – cooking, sailing, surgery, operatic singing, flying fighter jets – deliberative practice can make it second nature.

Ever watch a child struggling to sound out words and grasp the meaning of a sentence?  That was you once.  Fortunately, reading this sentence isn’t nearly so demanding for you now.”  

Walker’s discussion here would suggest these sort of cognitive improvements, whether in the context of cognitive biases,  cognitive behavioral therapy, or otherwise, might be difficult to accomplish without proper sleep.

Page 127: this whole book is a refutation to Alex Soojung-Kim Pang’s asinine recommendation about early mornings in the otherwise-useful “Rest” (Rest review + notes), but here Walker specifically highlights that losing the last two hours of sleep to get a jump start on the day” is very no bueno, because the sleep spindles in “the last two hours of the late morning” were the ones linked with memory boost.

Page 129: Sleep boosts athletic performance and reduces injury risk, and nobody who is paying attention should be surprised…

Page 130: Walker notes the irony – and marginal utility – of how sports teams spend tons of money on resources on everything for athletes… and little for sleep.  The same goes for businesses, by the way.

Page 131: Walker on sleep:

“There is much that sleep can do that we in medicine currently cannot.  […] we should make use of the powerful health tool that sleep represents in making our patients well.”

Page 134: The stats on drowsy driving: one death per hour.  As Walker noted earlier, it’s more than drugs and alcohol combined.

Pages 136 – 137!: These are some of the most important pages in the book.  Citing research, Walker notes that cumulative, low-level chronic sleep deprivation adds up, such that after 10 days of sleeping six hours per night, you’re as impaired as if you’d just pulled an all-nighter.  

And Walker uses the bar-drunk analogy here: participants in these studies:

“consistently underestimated their degree of performance disability.  It was a miserable predictor of how bad their performance actually, objectively was. […]

With chronic sleep restriction […] that low-level exhaustion becomes their accepted norm, or baseline.  Individuals fail to recognize how their perennial state of sleep deficiency has come to compromise their mental aptitude and physical vitality, including the slow accumulation of ill health.”

Schema bottleneck and feedback effects and n-order impacts, anyone?  Being sleep-deprived makes you unable to realize you’re sleep deprived, like being drunk makes you unable to realize you’re not safe to drive.

Pages 138 – 140: Being even modestly sleep-deprived (awake for 19 hours – i.e. 7 AM to 2 AM) is similar to being legally drunk while driving.

Also, importantly:

“Humans need more than seven hours of sleep each night to maintain cognitive performance.  After ten days of just seven hours of sleep, the brain is as dysfunctional as it would be after going without sleep for twenty-four hours.  

Three full nights of recovery sleep (i.e., more nights than a weekend) are insufficient to restore performance back to normal levels after a week of short sleeping.  Finally, the human mind cannot accurately sense how sleep-deprived it is when sleep-deprived.”

Page 141: Here’s where Walker argues that drowsy driving collisions aren’t accidents, because they have a cause.

On salience: governments spend 100x on drunk driving as drowsy driving.

Pages 144 – 145: Discussing the frequent misinterpretation of power naps and so on, Walker notes that there’s no replacement for proper sleep – not  willpower, not caffeine, not brief naps, not nothing.

He also notes that while there are genetically some people who can sleep six hours a night without impairment, the chances of you being one of them is less likely than the chances of you being struck by lightning. So, the base rate is that you need eight hours of sleep.  Seven to nine is the technical range, but given margin of safety and the clear deleterious effects of sleep deprivation – and the fact that sleep is, as Walker called it, nature’s “best attempt at contra-death” –  why the hell would anyone shoot for seven to seven and a half?

Pages 146 – 147: Sleep deprivation:

“showed well over a 60 percent amplification in emotional reactivity […] without sleep […] the strong coupling between [the prefrontal cortex and amygdala] 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.”

Again, anyone who’s read broadly on cognitive biases, emotion, etc – “ Deep Survival by Gonzales ( DpSv review + notes) is a good starting point here – knows how critical it is for us to be able to use our prefrontal cortex to override the amygdala.  

Gonzales compares the amygdala to his overzealous chocolate Lab, who barks at anything that comes to the door.

Gonzales notes that information hits the amygdala, which screens for danger, before it hits the neocortex.  He quips that “Like Lucy, the amygdala isn’t very bright,” but it is powerful and responds in an emergency.

Gonzales, in fact, notes – among other things – that the Rambo types who go hard and try to tough it out are the first to die, and that rest is hugely important in survival situations.  Sweating is bad.  Resting and hydrating and taking it slow are good.

Which is why it’s crazy that people in positions of decision-making responsibility routinely and intentionally short-circuit their own sleep, and – even more crazily – encourage or force others to do the same.

Pages 148 – 150: Insufficient sleep doesn’t just make us irritable; it increases emotional sensitivity in both directions.  The negatives are obviously bad (low empathy, anger, etc) but so are the positives – increased sensation-seeking.  Walker notes that insufficient sleep can make us hypersensitive to drugs and other risky behavior.

He goes on to discuss some evidence suggesting that sleep disruption may be a contributing factor to mental illness.

Page 151: Hey, cognitive behavioral therapy sighting!  Obligatory shoutout to Dr. Judith Beck’s phenomenal Cognitive Behavior Therapy (CBT review + notes), which, while technically a textbook, is a phenomenal psychology book.

Here, Walker mentions CBT-I – cognitive behavioral therapy for insomnia – which you can read about here.

Walker here explains why the “sleep deprivation for depression” approach is not as effective as the media has portrayed it to be.

Pages 153 – 155: How big is the deficit in memory after pulling an all-nighter?  Apparently 40%. Studies in rats have found that it’s ‘nearly impossible” to imprint lasting memories in sleep-deprived animals.

Walker here references Memento.

Page 157: Walker pounds in the fact that we can’t “catch up” on sleep, either from a health or memory perspective:

“if you don’t sleep the very first night after learning, you lose the chance to consolidate those memories, even if you get lots of ‘catch-up’ sleep thereafter.”

Pages 160 – 161: The section about Alzheimer’s and the glymphatic system is fascinating.  It’s also mentioned on pages 141 – 142 of Soojung-Kim Pang’s “Rest” (Rest review + notes).

Glial cells shrink by up to 60% in NREM sleep, letting cerebrospinal fluid clean out waste.  This is relatively new research – i.e. this decade – and I’ve encountered it before elsewhere.  Here is a link to Nedergaard’s site… 

Nedergaard’s words:

“The brain only has limited energy at its disposal and it appears that it must choice between two different functional states – awake and aware or asleep and cleaning up,” said Nedergaard. “You can think of it like having a house party. You can either entertain the guests or clean up the house, but you can’t really do both at the same time.”

That page’s embedded video explanation by Nedergaard (three minutes) is great too, including (at around 1:20) graphical/visual explanation of the process.

A lack of deep sleep is thus implicated in the amyloid plaque buildup in Alzehimer’s.

Page 164: Walker used to view sleep, diet, and exercise as the pillars of health.  Now, he views sleep as:

“the foundation on which the other two health bastions sit.”

Page 165: Controlling for factors such as smoking and exercise, sleep still has a huge impact on coronary heart disease – one study finds up to a 45% increased risk.

Pages 166 – 167: Back to the Gonzales / Deep Survival (DpSv review + notes) crossover: Gonzales does the best job of any book I’ve read on elucidating the risks of stress, the biochemical marker of which is the hormone “cortisol.”

Walker here notes how sleep loss causes higher blood pressure – even if it’s merely an hour or two of lost sleep.  And, in case you were wondering:

“physical fitness proves no match for a short night of sleep; it affords no resistance.”

The intermediary is the sympathetic nervous system, which releases cortisol.  Walker notes, of course, that stress is adaptive in small doses – fight or flight – but it’s not supposed to be in “perpetual overdrive,” which is where it gets thanks to lack of sleep.

Walker doesn’t go into this, but if you’ve read around, you also know that stress causes narrowed selective perception, which in turn causes worse decisions… so you see less information and you’re less able to process it.  Fun!  As Gonzales puts it on pages 38 – 39 of “ Deep Survival (DpSv review + notes),

“Most people are incapable of performing any but the simplest tasks under stress […] stress (or any strong emotion) erodes the ability to perceive.  Cortisol and other hormones released under stress interfere with the working of the prefrontal cortex… where… decisions are made […]

you see less, hear less, miss more cues from the environment, and make mistakes […] stress causes most people to focus narrowly on the thing they consider the most important, and it may be the wrong thing.”

In other words, sleep is the  structural problem solving solution to  stress.  Of course, there are feedback mechanisms here too: Duhigg’s book ( PoH review + notes) overviews the well-known phenomenon of alcoholics relapsing under stress:

“They picked up a bottle because that’s how they automatically dealt with anxiety.

And that alcohol disrupts REM sleep, which in turn reduces emotional control, which leads to more amygdala hijacks and more stress… stress is thus an autocatalytic process.

(Thankfully, as both Duhigg and Shawn Achor explore – the latter in both “ Before Happiness” and “ The Happiness Advantage” – there are structural problem solving solutions to stress that can break the cycle.)  THA review + notes | BH review + notes

Pages 168 – 169: Here’s a fun natural a/b test: Walker notes that in spring, when people lose an hour of sleep thanks to daylight savings time, there’s a huge spike in heart attacks, traffic collisions, etc… the reverse is true in fall.  Various sources I reviewed suggest that the heart attack impact is in the ~20 – 25% range, while accidents are in the ~10% range.

Considering nonlinearity, it is of course difficult to extrapolate linearly from that small sample sizeto what would happen if the world, on average, got an hour more sleep per night.  What is clear, however, is that the number of lives saved would be non-trivial.

Page 171: Sleep deprivation causes your glucose absorption to worsen, your insulin function to worsen, and your blood sugar to rise to pre-diabetic levels.  

Walker doesn’t tie it together, but it does bear noting that there’s a double-whammy here: Walker elsewhere notes our tendency to eat more junk food when we’re sleep deprived… and we’re less able to process it efficiently.

Pages 173 – 175, 177, 178: sleep deprivation leads to increased calorie consumption, and (as mentioned), a tilt toward junk foods.  The stress (cortisol) response also reduces absorption of nutrients in your intestines (via a bacteria intermediary), and lack of sleep also leads to more lean muscle loss vs. fat loss (when you’re on a calorie restrictive diet.)

Additionally, sleep deprivation does a double whammy on appetite by reducing leptin (the fullness / “satiety” hormone) and increasing ghrelin (the “hunger” hormone.)

Andddddd here’s the money bit about testosterone, ball size, and sperm count.  😛

Pages 181 – 183: you know how Shawn Achor has trouble getting the review board to approve his experiments wherein students play charades?  Well, Walker discusses a study where people were intentionally given rhinovirus up the nose. Although the sample size here is small (150 individuals), the result is replicable; Walker notes there’s a “clear, linear relationship with infection rate.”

Additionally, Walker notes that immune response to the flu shot can decline by 50% or more in sleep-deprived individuals… and, like memory, this is a one-time, all-or-nothing opportunity: even if they caught up on sleep later, antibody count didn’t move.

This is intriguing on several levels.  One is: you probably shouldn’t send your kids for a sleepover the night before they have an appointment with their pediatrician.  Dr. Paul Offit discusses in Deadly Choices (VAX review + notes) how occasionally, vaccines don’t confer full protection.

Clearly this is a  multicausal phenomenon, but it’s astonishing how much impact sleep has, and if the data Walker is citing is even directionally reasonable, parents should ensure kids get good sleep before and after their immunizations…

Pages 184 – 185: More gruesome data: a single night of of four hours of sleep can reduce our count of killer T cells by 70%.

Again, recall the earlier data suggesting that it doesn’t matter if you have one really bad night of sleep, or chronic modest sleep deprivation.  You can’t really linearly extrapolate, but…

Walker notes some studies with total sample size exceeding 100,000 found a 40% increased risk of cancer among those sleeping six hours or less (vs. seen hours or more.)  Additionally, sleep deprivation speeds up metastasis.

The book here mentions some vivid images of rat tumors that he uses in public talks.  Walker’s Talk at Google includes a brief snippet of these, and they are definitely worth seeing to drive the point home. I’ve time-synced the video for you here.  Starting at 29 minutes, Walker explains the experiment, then the pictures are at about 30 minutes and 50 seconds.

Page 188: Walker discusses gene transcription… see the footnote, too:

“inappropriately timed sleep, such as that imposed by jet lag or shift work, can have equally large effects on the expression of human genes as inadequate sleep.”  

There is no reason the same mechanism shouldn’t apply to “social jetlag” – i.e., that created by the mismatch between chronotype and societally-dictated work or school hours.  

This is a good time for a Till Roenneberg quote. (It’s always a good time for a Till Roennberg quote!) Discussing the lateness in chronotype across most modern populations, Roenneberg notes  “work times are too early for 60 percent of the population.”  Roenneberg goes on, later in “ Internal Time ( IntTm review + notes), to state:

“In view of the lateness of most people in our modern societies, one could argue that a majority of the workforce is scheduled in a permanent early shift when they work from nine to five.”

Roenneberg cites much of the same (directional) research as Walker on the topic of the health consequences of shift work, etc.  In fact, he goes deeper into this with some vivid examples.

“Chronotypes matter” is my answer to the Peter Thiel “secret” question – What is something you think is true, but almost nobody else agrees with you on?

Pages 201 – 202: IMistakes were Made (but not by me) – MwM review + notes – psychologists Carol Tavris and Elliot Aronson make the point that Freud’s theories are unfalsifiable, and make the correlation between that and human cognitive biases.  Here, Walker makes a similar point.

As for whether or not psychoanalysis holds any merit, Dr. Judith Beck – author of the previously-referenced Cognitive Behavior Therapy (CBT review + notes) – has an amusing take.  She agrees with Tavris/Aronson and Walker, coming at it from an amusing angle: her father Aaron, the pioneer of CBT as a field, set out to prove psychoanalysis worked and then found out that, um, oops, it doesn’t.  😛

Here, Walker notes that psychoanalytic dream analysis is mostly bullshit because of the fortune-teller fallacy – speaking in vague generalities (you’re scared of something!  You’re having trouble letting go of someone!) that apply to everyone.

Page 206: Neat discussion of “epiphenomena” here – Walker explains an “epiphenomenon” as something that happens as an n-order impact of some other intended behavior; for example, we designed lightbulbs to create light, but they create heat too, so heat’s an “epiphenomenon.”

His question: are dreams epiphenomena, or do they have a purpose?  He argues for the latter.

Pages 210 – 211: Walker here cites researcher Rosalind Cartwright, who has written books too (I ordered this one.)  Walker clearly admires Cartwright a lot; he notes that her work found that dreaming about the emotional themes and sentiments of the waking trauma” allowed patients to move past those events and generate emotional closure.

Page 213: Interesting example of n-order impacts: a blood pressure drug called prazosin, it turns out, also suppresses noradrenaline in the brain, which can help PTSD patients avoid recurring nightmares.  Kind of like the Viagra origin story…

Pages 216 – 217: Walker here goes deeper into the impact of REM sleep deprivation: a flattening of the interpretation of emotional signals; Walker notes “by removing REM sleep, we had, quite literally, removed participants’ levelheaded ability to read the world around them.”  Cross-reference earlier discussion of REM being late in sleep, so alarm clocks are lowering your emotional intelligence…

Page 219: Walker notes that REM sleep is responsible for integrating information with existing knowledge and creating far-flung connections.  

Page 221: Examples of REM-driven insight occur in both science and music.  It’s often said “ intuition comes to the prepared mind.” REM is the mechanism for this.  (or at least, one of them.)

Page 224: Interesting discussion here about improved creativity when people are awoken from REM sleep… wonder if there was any of this contaminating the research cited by Soojung-Kim Pang in Rest, which he (inappropriately and inanely) used to justify advising everyone, universally, to get up earlier.  (When science demonstrates that most of the population is already getting up too early.)

Page 228: One example of REM-driven abstraction is infants’ learning of new languages.

Pages 258 – 259: Rats die almost as quickly from total sleep deprivation as from total food deprivation.  The cause of death was septicemia, from an immune system so ravaged that normally non-harmful gut bacteria wreaked havoc on the body.  

Also, amazing footnote on a women’s magazine getting excited about total sleep deprivation as a weight-loss mechanism.  Yes, if you want to die in horrible pain, give it a try… 😛

Pages 260 – 263: Walker here dispels some common myths.  He refutes a study that has been interpreted by some of the media as “we only need 7 hours of sleep a night” – nope.  Those tribespeople were not in good health.

Walker also notes that there’s no  dose-dependency with sleep, within reason.  In his Talk at Google, he does acknowledge that he thinks there would be some point at which more sleep might not be better… but it seems like that would be well into the double digits, and certainly not anywhere close to where most people are today.  Seven is better than six, eight is better than seven, and nine or more is better than eight.

He notes that there’s a correlation vs. causation problem in mortality data associated with people who sleep a lot: many of the people who are sleeping a lot are seriously or terminally ill, and obviously we sleep more when we’re ill for a variety of reasons.  That doesn’t mean that the sleep is the cause of the negative health outcomes; in fact, it’s the other way around.

Anecdotally, for example, one of my friends’ family members who is struggling with advanced multiple sclerosis (MS) is currently “sleeping about 12 hours a day.”  Assuming she is representative of those with her specific condition, certainly a study that included subjects like her would find a correlation between length of sleep and higher mortality, but it’s very difficult to tell a plausible story in which the sleep is the cause of her health issues – rather, it’s the other way around.

Walker notes that:

“No biological mechanisms that show sleep to be in any way harmful have been discovered.”

Pages 267 – 270: Walker tackles the industrial-era light bit here; I’m not sure how he’s reconciling the “lower melatonin due to iPads and lights” with “melatonin isn’t an effective sleep aid.”  I’d like to ask him that…

Pages 272 – 275: Recall the earlier discussion of alcohol killing REM sleep in fetuses?  Well, it kills REM sleep in adults, too, and as such disrupts learning and memory.  Walker recommends avoiding alcohol entirely.

Page 279: On the relationship between cold core temperature and sleep.  Interestingly, I find the opposite on hot showers/baths – for some reason, hot baths help me nap, but cold showers help me sleep at night.

Page 280: Walker notes that being woken up violently (like by an alarm clock) triggers that same stress response we were talking about.  You shouldn’t use the snooze button, because then you’re subjecting yourself to that cortisol response over and over and over…

Pages 291 – 292: He goes a bit deeper into CBT-I here.  I haven’t tried all of these (although I never had a clock face in my bedroom to begin with), but I do find that the CBT angle to reduce anxiety works pretty well.

Those who’ve read Dr. Judith Beck’s “ Cognitive Behavior Therapy ( CBT review + notes) or my model on it – cognitive behavioral therapy – may recall that CBT is equally or more effective than medication for certain kinds of depression and anxiety and other issues.  Turns out, according to Walker, that CBT-I is more effective than sleeping pills and results in sustainable long-term improvements.

Also, sleeping pills suck and are terrible for you because they just sedate you and in some senses actually impair “naturalistic” sleep.  Walker’s not anti-medication… he just doesn’t see any available that work well.

Pages 296 – 297: Walker notes that:

“A hundred years ago, less than two percent of the population in the United States slept six hours or less a night.  Now, almost 30 percent of American adults do.”

Scary.  He goes on to clarify that in most cases, it’s not that people want or need less sleep, but they’re getting less during the week and trying to catch up on weekends.  (See Roenneberg’s “ Internal Time – IntTm review + notes – for some lovely, vivid graphs of scalloped sleep-wake pattern among many people, and especially owls.)

Walker asks:

“Sleep deprivation degrades many of the key faculties required for most forms of employment.  Why, then do we overvalue employees that undervalue sleep?

[…] there remains a contrived, yet fortified, arrogance in many business cultures focused on the uselessness of sleep.  It is bizarre […] this mentality has persisted, in part, because certain business leaders mistakenly believe that time on-task equates with task completion and productivity.”

See product vs. packaging, Cal Newport’s Deep Work (DpWk review + notes), etc.  This is, in part, a salience phenomenon, wherein butts-in-chairs and hands-on-keyboards are very visible, whereas real productivity is often not.

There’s also a momentum problem relating to status quo bias. In a few pages (301), Matthew Walker cites research by Christopher Barnes, whose pieces for HBR on chronotypes (12) have been Favorite Sammy Things for years.  Managers, perversely, tend to prefer early types to late types even if they have the exact same performance.  Specifically, in the piece from 2015, Barnes summarizes:

supervisors tend to assume that employees who start and finish work late (versus early) are less conscientious and lower in performance, even if their behavior and performance is exactly the same as someone working an early riser’s schedule”

Cross-reference Roenneberg’s discussion of the culture problem in “ Internal Time” ( IntTm review + notes).  Roenneberg calls the quality of general discussion about chronotypes to be “frighteningly low and shallow.” Roenneberg also says:

“As long as all individuals have similar [chronotypes],  the earliest bird has an advantage over anyone getting up later.  This was probably true for most preindustrial societies; hence the persistence of the early-bird proverbs.  [But under modern circumstances]… the temporal chicken-and-egg problem starts to apply […] [extremely] late chronotypes would still be awake [before early birds rise].  There is no reason why these extreme late types couldn’t gather all the mushrooms before the early risers arrived […]

This myth that early risers are good people and that late risers are lazy has its reasons and merits in rural societies but becomes questionable in a modern 24/7 society.”


“I am often asked whether we cannot get used to given working hours merely through discipline and by confining our sleep habits to certain times.  The assumption inherent in this question is that the human body clock can synchronize to social cues.

I tend to find that any such questioner, who usually also displays a somewhat disdainful tone toward the weakness of late chronotypes, is an early type – someone who has never experienced the problems associated with the scallop-shaped sleep-wake behavior of late chronotypes.”  

Pages 304 – 305: Nike and Google are held up as paragons of sleep thanks to their nap pods, flexible work hours, etc.  

Pages 308 – 313: Walker here discusses some of the heartbreaking data on sleep deprivation among adolescents, courtesy of early school start times.  Roenneberg rants about this as well, but I think Walker does it better.

Walker notes that:

“Our children didn’t always go to school at this biologically unreasonable time.  A century ago, schools in the US started at nine a.m. As a result, 95% of all children woke up without an alarm clock.  

Now, the inverse is true, caused by the incessant marching back of school start times – which are in direct conflict with children’s evolutionarily preprogrammed need to be asleep during these precious, REM-sleep-rich morning hours.”

So, it’s a double whammy.  Recall from Roenneberg’s “ Internal Time ( IntTm review + notes) thatchronotypes have been getting later, thanks to the “perpetual twilight” we now live in thanks to relatively-dark mornings in offices instead of outdoors, and the bright nights thanks to indoor lighting, devices, etc.

As such, it’s very likely that teenagers’ chronotypes are later than they were a century ago, while school start times are dramatically earlier.

Walker goes on to cite studies finding massive increases in SAT scores, 70% drops in traffic collisions among 16-18 year old drivers, etc – all from just starting school an hour or two later.

Pages 316 – 319: Here is a fun and unexpected bit: doctors’ hours are notoriously brutal.

But why? Apparently it traces back to cocaine addict William Halsted, who I’d previously read about in David Oshinsky’s “ Bellevue ( BV review + notes).  Lots of good background there… this is a fascinating example of culture.

Anyway, Walker notes that:

“Residents working a thirty-hour-straight shift will commit 36 percent more serious medical errors [… and make…] 460 percent more diagnostic mistakes in the intensive care unit than when well rested.

Through the course of their residency, one in five medical residents will make a sleepless-related medical error that causes significant, liable harm to a patient.  One in twenty residents will kill a patient due to a lack of sleep.”

See also The Checklist Manifesto ( TCM review + notes), How Doctors Think (HDT review + notes), The Design of Everyday Things (DOET review + notes), and so on.  Here’s a contextualizing quote from Groopman’s How Doctors Think, on the mindset of a sleep-deprived doctor:

“McEvoy’s story of relentless work and sleep deprivation reminded me of the worst moments of my own internship and residency […] subconsciously, I found myself minimizing the severity of a symptom or assuming that an aberrant laboratory result was an artifact rather than a sign of a serious problem.”

But honestly Till Roenneberg has the best take on this  on pages 215 – 218 of Internal Time ( IntTm review + notes).  Commenting on a study finding that sleep deprivation can lead to medical interns making 36% more “serious medical errors” while providing patient care, Roenneberg notes:

“It’s not surprising that someone who works for up to seventy-two hours without noteworthy rest makes more mistakes, but what seems like common sense is worthless without a quantitative basis provided by a properly designed study.”

 I can’t tell if he’s being snarky or serious – in context, I’m guessing snarky – but it’s hilarious either way.

I know I’m making light of a serious topic, but humor is how you learn.

Pages 320 – 321: On base rates: Walker recommends you ask your surgeon how long it’s been since they’ve slept (he notes that 22 hours without sleep = legally drunk.)  If it’s too long, don’t take the surgery.

On culture perpetuation, Walker notes there’s a “I suffered, so you have to too” phenomenon that needs to go.

Page 332: Walker notes that despite the huge importance of sleep, we don’t teach kids about it.

Page 334: Walker’s advice for businesses:

“everyone would be present during a core window for key interactions – say, twelve to three p.m.  Yet there would be flexible tail ends either side to accommodate all individual chronotypes.

Owls could start work late (e.g., noon) and continue into the evening, giving their full force of mental capacity and physical energy to their jobs.  Larks can likewise do so with early start and finish times.”

Walker also makes a point I’ve made myself, before, about rush hour.

Page 337: One last example: more human lighting in NICUs (neonatal intensive care units) resulted in 50 – 60% better weight gain and higher oxygenation of blood.


First Read: summer 2018

Last Read: summer 2018

Number of Times Read: 1

Planning to Read Again?: absolutely


Review Date: summer 2018

Notes Date: summer 2018