2 6 2 MATTHEW WALKER obvious need, then, would be for life—and healthy life. Now we discover that the average life span of these hunter-gatherers is just fifty-eight years, even though they are far more physically active than we are, rarely 0bese, and are not plagued by the assault ofprocessed f00ds that erode our health. Ofcourse, they dO not have access tO modern medicine and sanitation, bOth ofwhich are reasons that many Ofus in industrialized, first-world nations have an expected life span that exceeds theirs by over a decade. But it is telling that, based on epidemiological data, any adult sle eping an average of 6.75 hours a night would be predicted to live only int0 their early sixties: very close to the median life span of these tribespeople. More prescient, however, is what normally kills people in these tribes. SO long as they survive high rates ofinfant mortality and make it through adolescence, a common cause 0f death ⅲ adulthood is infec- tion. Weak immune systems are a known consequence Of insufficient sleep, as we have discussed in great detail. I should so note that one Of the most common immune system failures that kills individuals ⅲ hunter-gatherer clans are intestinal infections—something that shares an intriguing overlap with the deadly intestinal tract infections that killed the sleep-deprived rats in the above studies. Recognizing this shorter li 他 span, which fits well with the acclaimed shorter sleep amounts the researchers measured, the next error in logic many made is exposed by asking ル these tribes would sleep what appears t0 be t00 little, based on 心 that we 燔 ow 伝 om thousands of research studies. We do not yet ow of the reasons, but a likely contributing fac- tor lies ⅲ the title we apply t0 these tribes: hunter-gatherers. One ofthe few universal ways offorcing animals of kinds to sleep less than nor- mal amounts is to limit food, applying a degree ofstarvation. When food becomes scarce, sleep becomes scarce, as animals try tO Stay awake lon- ger tO forage. Part Ofthe reason that these hunter-gatherer tribes are not Obese is because they are constantly searching for food, which is never abundant for long stretches. They spend much of their waking lives in purslllt and preparation 0f nutrition. For example, the Hadza will face days where they obtain 1 , 400 calories or less, and routinely eat 300 to 600 fewer daily calories than those ofus in modern Western cultures. A

The lnternational Bestseller Startling, vital, a life raft' 。。 ~ ~ WhyWe 0 M AT T H E W WA L K E R Sleep The New S Cie nce ofSleep and Dreams

Chapter 1 Chapter 2 Chapter 3 Chapter 4 Chapter 5 Ch 叩 ter 6 Chapter 7 Chapter 8 Chapter 9 Chapter 10 Ch 叩 ter 11 Contents This Thing CaIIed SIeep To Sleep . Caffeine, Jet Lag, and Melatonin: Losing and Gaining Control 0fYour Sleep Rhythm Defining and Generating Sleep: Time Dilation and What We Learned 仕 om a Baby in 1952 Ape Beds, Dinosaurs, and Napping with Half a Brain: Who SIeeps, How Do We Sleep, and How Much? Changes in Sleep Across the Life Span ー 2 Why ShouId You Sleep? Your Mother and Shakespeare Knew: The Benefits of Sleep for the Brain T00 Extreme for the Guinness お 0 砒可、 WorIdRecords: Sleep Deprivation and the Brain Cancer, Heart Attacks, and a Shorter Life: Sleep Deprivation and the B0dy ー 24 3 How and Why We Dream Routinely Psych0tic: REM-Sleep Dreaming Dreaming as Overnight Therapy Dream Creativity and Dream Control 3 13 38 56 78 107 133 164 193 206 219

times it is hard tO think Of a bOOk that iS more important tO read than this one' Adam Gazzaley, co-author 0f The D な ac d Mind 、 A bursting rocket of a book ... lands shock statistics like a boxer demolishing a tottering opponent ... ・ We tend to imagine sleep as if it were not really part 0f whO we are. Walker shows, triumphantly, how dangerously wrong we can be' James McConnachie, Su れ da ァ石川ぉ 'Things have tO change in our workplace and our communities, our homes and our families ... The evidence IS enough tO send anyone early t0 bed. lt's no kind 0f choice at all' Rachel Cooke, O 伝催レ 'Startling, sobering, vital, a life raft ... A neuroscientist ShO 、 hOW a good night's shut-eye can make us cleverer, more attractive, slimmer, happier, healthier and ward 0 幵 cancer ... filled with startling information it's probably a little t00 soon tO tell you that Ⅳ We S ル印 saved my life, but I can tell you that it's been an eye-opener' Mark O'Connell, Gu 市 4 れ 'He is an expert, but more importantly, he knows hOW tO . a well-organized, explain it all clearly t0 generalreaders . highly accessible, up-to-date report on sleep and its crucial ro に in a healthy life' K た郷 Re レル Matthew WaIker's fascination with sleep has taken him from Nottingham t0 Harvard and on to the University of California, Berkeley, where he IS currently Professor Of Neuroscience and Psychology and Director of the SIeep and Neuroimaging Laboratory. He has published over 100 scientific research studies during the course of his t 、 venty-year career. W わァ We S 孕 is his first book.

W H Y W E S L E E P 5 7 mals sleep: 仕 om shrews to parrots, kangaroos, polar bears, bats, and, 0f course, we humans. Sleep iS universal. Even invertebrates, such as primordial mollusks and echinoderms, and even very primitive worms, enJOY periods Of slumber. ⅲ these phases, affectionately termed "lethargus," they, like humans, become unresponsive tO external stimuli. And just as we fall asleep faster and sleep more soundly when sleep-deprived, so, t00 , do worms, defined by their degree ofinsensitivity tO prods 仕 om experimenters. How "old" does this make sleep? Worms emerged during the Cam- brian explosion: at least 500 million years ago. That is, worms (and sleep by association) predate vertebrate life. This includes dinosaurs, which, by inference, are likely to have slept. lmagine diplodocuses and triceratopses comfortably settling in for a night 0f full repose! Regress evolutionary time still further and we have discovered that the very simplest forms of unicellular organisms that survive for pen- Ods exceeding twenty-four hours, such as bacteria, have active and pas- sive phases that correspond t0 the light-dark cycle 0f our planet. lt is a pattern that we now believe tO be the precursor Of our own circadian rhythm, and with it, wake and sleep. Many ofthe explanations for why we sleep circle around a common, and perhaps erroneous, idea: sleep is the state we must enter in order tO fix that which has been upset by wake. But what ifwe turned this argu- ment on its head? What if sleep is so useful—so physiologically ben- eficial to every aspect of our being—that the real question is:Why did life ever bother to wake up? Considering how biologically damaging the state Of wakefulness can Often be, that is the true evolutionary puzzle here, not sleep. Adopt this perspective, and we can pose a very different theory: sleep was the first state 0f life on this planet, and it was 仕 om sleep that wakefulness emerged. lt may be a preposterous hypothesis, and one that nobody is taking seriously or exploring, but personally I do not think it tO be entirely unreasonable. Whichever ofthese MO theories is true, what we know for certain is that sleep is of ancient 0 ⅱ n. lt appeared with the very earliest forms of planetary life. Like other rudimentary features, such as DNA, sleep has remained a common bond uniting every creature in the animal kingdom. A long-lasting commonality, yes; however, there are truly

Conclusion e 孕 or ル 0 0 e 孕 Within the space of a mere hundred years, human beings have aban- doned their bi010 c y mandated need for adequate sleep—one that evolution spent 3 , 400 , 000 years perfecting in service of life-support functions. AS a result, the decimation ofsleep throughout industrialized nations is having a catastrophic impact on our health, our life expec- tancy, our safety, our productivity, and the education 0f our children. This silent sleep loss epidemic is the greatest public health challenge we face ⅲ the fiventy-first century in developed nations. If we wish tO avoid the suffocating noose of sleep neglect, the premature death it inflicts, and the sickening health it invites, a radical shift in our per- sonal, cultural, professional, and societal appreciation of sleep must occur. I believe it is time for us to reclaim our right to a んⅡ night of sleep, without embarrassment or the damaging stigma of laziness. ln doing SO, we can be reunited with that most powerful elixir Of wellness and ⅵ t 曲 dispensed through every conceivable biological pathway. Then we may remember what it feels like t0 be truly awake during the day, infused with the very deepest plenitude ofbeing.

ー 5 2 MATTHEW WALKER ture described as anhedonia: the inability to gain pleasure from nor- mallypleasurable expenences, such as f00d, socializing, or sex. The one-third of depressed individuals who respond to sleep depri- vation may therefore be those whO experience the greater amplification within reward circuits ofthe brain that I described earlier, resulting in far stronger sensitivity tO, and experiencing Of, positive rewarding triggers following sleep deprivation. Their anhedonia is therefore lessened, and now they can begin t0 expenence a greater degree ofpleasure 仕 om plea- surable life experiences. ln contrast, the other two-thirds 0f depressed patients may suffer the opposite negative emotional consequences Of sleep deprivation more dominantly: a worsening, rather than alleviation, oftheir depression. lfwe can identify what determines those wh0 ⅶⅡ be responders and those whO will not, my hope is that we can create better, more tailored sleep-intervention methods for combating depression. We will revisit the effects 0f sleep loss on emotional stability and Other brain functions in later chapters when we discuss the real-life consequences Of sleep IOSS in SOCiety, education, and the workplace. The findings justify our questioning of whether or not sleep-deprived doctors can make emotionally rational decisions and judgments; under-slept military personnel should have their fingers on the triggers ofweaponry; overworked bankers and stock traders can make rational, non-risky financial decisions when investing the public's hard-earned retirement funds; and ifteenagers should be battling against impossibly early start times during a developmental phase 0f life when they are most vulnerable t0 developing psychiatric disorders. For now, however, I will summarize this section by offering a discermng quote on the topic ofsleep and emotion by the American entrepreneur E. Joseph Cossman: "The best bridge between despair and hope is a good night's sleep. TIRED AND FORGETFUL? Have you everpulled an "all-nighter," deliberately staymg awake night? One of my true loves is teaching a large undergraduate class on the sci- *Cossman had otherpearls ofwisdom, t00 , such as "The best way tO remember yourwife's birthday is to forget it once.

ー 0 8 MATTHEW WALKER lic health message. We ⅷⅡ come to learn that sleep is the universal health care provider: whatever the physical or mental ailment, sleep has a prescription it can dispense. Upon completion Of these chapters, I hope even the most ardent 0f short-sleepers will be swayed, having a reformed deference. Earlier, I described the component stages of sleep. Here, I reveal the attendant virtues Of each. lronically, most all Of the "new," twenty-first- century discoveries regarding sleep were delightfully summarized in 1611 in Macbeth, act vo , scene れ vo , where Shakespeare prophetically states that sleep is "the chief nourisher in life's feast."* Perhaps, with less highfalutin language, your mother offered similar advice, extolling the benefits of sleep in healing emotional wounds, helping you learn and remember, gifting you with solutions to challenging problems, and preventing sickness and infection. Science, it seems, has simply been evidential, providing pro of of everything your mother, and 叩 p arently Shakespeare, knew about the wonders ofsleep. SLEEP FOR THE BRAIN Sleep is not the absence Of wakefulness. lt is far more than that. Described earlier, our nighttime sleep is an exquisitely complex, met- abolically active, and deliberately ordered series ofunique stages. Numerous functions 0f the brain are restored by, and depend upon, sleep. No one type of sleep accomplishes all. Each stage of sleep—light NREM sleep, deep NREM sleep, and REM sleep—offer different brain benefits at different times of night. Thus, no one 与甲 e of sleep is more essential than another. LOSing out on any one ofthese types ofsleep will cause brain impalrment. Of the many advantages conferred by sleep on the brain, that of memory is especially impressive, and particularly well understood. Sleep has proven itself time and again as a memory aid: both before *"Sleep that knits up the ravelld sleeve ofcare, The death ofeach day's life, sore labour's bath, Balm of hurt minds, great nature's second course, Chief nourisher ⅲ life's feast,— William Shakespeare, Macbeth, Folger Shakespeare Library (NewYork: Simon & Schuster; first edition, 2 開 3 ).

WHY WE SLEEP ー 6 3 approach in medicine in the form Of prescribing statins tO higher-risk individuals in their forties and fifties to help prevent cardiovascular disease, rather than havlng tO treat it decades later. lnsufficient sleep is only one among several risk factors associated with Alzheimer's disease. SIeep alone will not be the magic bullet that eradicates dementia. Nevertheless, prioritizing sleep across the life span is clearly becoming a significant factor for lowering Alzheimer s disease risk.

WHY WE SLEEP 5 body functions. NO drugs that we currently have ⅷⅡ help the patient sleep. After twelve t0 eighteen months 0f no sleep, the patient will die. Though exceedingly rare, this disorder asserts that a lack of sleep can kill a human being. Second is the deadly circumstance of getting behind the wheel of a motor vehicle without having had sufficient sleep. Drowsydriving is the cause of hundreds of thousands of traffic accidents and fatalities each year. And here, it is not only the life of the sleep-deprived individuals that is at risk, but the lives 0f those around them. Tragically, one per- son dies ⅲ a traffic accident every hour ⅲ the United States due tO a fatigue-related error. lt is disqtneting tO learn that vehicular accidents caused by drowsy driving exceed those caused by alcohol and drugs combined. Society's apathy toward sleep has, in part, been caused by the his- toric failure Of science tO explain why we need it. Sleep remained one ofthe last great biological mysteries. 1 ofthe mighty problem-solving methods ⅲ science—genetics, molecular biology, and high-powered digital technology—have been unable t0 unlock the stubborn vault 0f sleep. Minds ofthe most stringent kind, including N0bel Prize—winner Francis Crick, who deduced the twisted-ladder structure 0f DNA, famed Roman educator and rhetorician Quintilian, and even Sigmund Freud had all tried their hand at deciphering sleep's enigmatic code, ln vam. TO better frame this state Of prior scientific ignorance, imagine the birth ofyour first child. At the hospital, the doctor enters the room and says, ℃ ongratulations, it's a healthy baby boy. We've completed 0f the preliminary tests and everything looks good." She smiles reassur- ingly and starts walking toward the door. However, before exiting the room she turns around and says,"There is just one thing. From this moment forth, and for the rest 0fyour child's entire life, he will repeat- edly and routinely lapse intO a state 0f apparent coma. lt might even resemble death at times. And while his body lies still his mind will often b e filled with stunmngt_PY@!!_e.hallucinations.This state will c onsume one-third ofhis life and I have absolutely no idea why he'll d0 it, or what it is for. Good luck! ” Astonishing, but until very recently, this was reality: doctors and sci-