非常有用也比较有意思的一本书，向所有读者群推荐（NY Times Bestseller)。书以一个问题开始：我们（虫鱼鸟兽一切动物）为什么要睡觉？为什么生物经过这么漫长的进化，还一直保留着睡觉这个看起来会极大降低存活率（比如睡着了很容易被偷袭）的机制？水里需要不停游动的鱼类，或者需要跨洋级别长期飞行的鸟类都各自进化出了一些像一次只睡半边脑之类的 workaround 也无法完全避开睡觉，究竟是为什么？
当然书并没有给出答案的完整刻画，因为完整的刻画应该还是生物研究中的谜题之一，但是书给出了一个很重要的定性答案：睡觉并不（仅仅）是一种休息（比如，像电脑休眠那样，机能停止运行），而是一种 development——跟你吃饭长身体、上课长知识、闯荡江湖长人生阅历同等重要的一个环节。因此这是一个非常复杂的生理过程，所以靠酒精或者药物之类的麻醉神经等方式强行进入昏睡状态并不能有效地起到真正睡眠所起的作用。打个比方就好比每天晚上你的电脑或者手机要进入维护模式，进行磁盘碎片整理（memory 的转移和索引），安装固件更新漏洞补丁（增强免疫系统功能）之类的，喝醉昏睡过去大概就等价于强行拔掉电源——虽然两种情况电脑都黑屏了，但是第二天重启的时候立刻就会知道区别很大。而熬夜晚睡则相当于长期运行内存效率低下、没有补丁的“裸奔”系统。书中提出了一个有趣的假说：也许并不是动物进化出了睡觉这件事，而是动物最原始的状态就是睡眠状态，进化让动物能周期性地“醒过来”。
看到有一些人说书虽然观点很重要，但讲得太啰嗦，其实我觉得还好，大概是因为书里给了大量的科学实验的佐证和许多具体的实验细节的缘故吧，有点像一个 survey，我觉得特别是这方面的实验，给出细节是很好的，因为很多实验由于可行性、道德等各方面的限制，很多实验只能从侧面去验证一些假设，并且 sample size 可能会很小很小等等，只给一个结论而不描述细节的话，很容易被 over interpret，变成各种危言耸听的朋友圈文章。
从具体内容来说，书主要分为三部分：1. 睡眠本身背后的机制，比如睡眠周期是由什么控制的（可以解答比如为什么熬过了最困的点之后会有一阵反而很清醒、咖啡因是如何影响我们的清醒和睡眠的等问题），大脑的哪些部分以什么样的方式“产生”睡眠，深睡、浅睡、眼动期如何分布以及大致起什么作用等等。2. 我们为什么要睡觉，主要是一系列的关于睡眠缺失后对我们的记忆的转化和形成、免疫系统的维护以及死亡率等各方面的影响。3. 我们为什么要做梦，主要是与心理创伤的治愈和创造力的激发等相关的实验和研究。4. 睡眠相关的药物和现代社会对睡眠的影响，比如学校的早课和公司上班的时间安排，社会对于“睡很久“等于懒惰的舆论风气，电子产品对于睡眠的负面（智能手机、iPad）和正面（睡眠跟踪和管理）影响等等。
我自己几乎从来不熬夜，而且睡眠也相对比较规律一点，当然时常失眠和睡前玩 iPad 之类的问题近两年也越来越严重，开始工作之后由于通勤、交通、环境噪音等各方面的因素也导致睡眠质量下降很多，白天也开始严重依赖咖啡因来保持不睡着状态，直到最近突然觉得自己每天白天都处于困到不行的亚健康状态，不是长久之计，便开始积极地控制咖啡因摄入和管理睡眠，然后正巧看到这本书，就找来读了一下，真是有种相见恨晚的感觉。有趣的是看到睡眠与心理创伤治愈的一部分，想起来自己在最抑郁的一段时间确实是每天都一直在睡觉睡觉，哈哈，也许保持乐观的秘诀真的是睡觉呢。
有点可惜的是书里并没有提供什么特别有效的诸如“五分钟入睡”的秘诀之类的。在（遥远的）将来我们的生物学、神经科学等各方面足够发达到对睡眠机制有更全面的了解和控制之后，希望能有相应的措施出现。至于现在，大概就只能根据书里提到的关于 sleep hygiene 的十二条建议来慢慢改善了，当然如果是生理上的失眠症的话，是需要看专门的睡眠专家来治疗和调理的。希望早日出中文版可以推荐给家里的人看。
Part 1: This Thing Called Sleep
Chapter 1: To Sleep
Two- thirds of adults throughout all developed nations fail to obtain the recommended eight hours of nightly sleep.I
human beings are in fact the only species that will deliberately deprive themselves of sleep without legitimate gain.
Society’s apathy toward sleep has, in part, been caused by the historic failure of science to explain why we need it. Sleep remained one of the last great biological mysteries.
From this moment forth, and for the rest of your child’s entire life, he will repeatedly and routinely lapse into a state of apparent coma. It might even resemble death at times. And while his body lies still his mind will often be filled with stunning, bizarre hallucinations. This state will consume one- third of his life and I have absolutely no idea why he’ll do it, or what it is for. Good luck!”
“If sleep does not serve an absolutely vital function, then it is the biggest mistake the evolutionary process has ever made.” III
Chapter 2: Caffeine, Jet Lag, and Melatonin: Losing and Gaining Control of Your Sleep Rhythm
every living creature on the planet with a life span of more than several days generates this natural cycle.
Despite being cut off from the influence of light during the day, the plant still behaved as though it were being bathed in sunlight; its leaves were proudly expanded.
When cut off from the daily cycle of light and dark, would their biological rhythms of sleep and wakefulness, together with body temperature, become completely erratic, or would they stay the same as those individuals in the outside world exposed to rhythmic daylight?
humans, like de Mairan’s heliotrope plants, generated their own endogenous circadian rhythm in the absence of external light from the sun.
their reliably repeating cycles of wake and sleep were not precisely twenty- four hours in length, but consistently and undeniably longer than twenty- four hours.
It is the reason that individuals with certain forms of blindness do not entirely lose their circadian rhythm. Despite not receiving light cues due to their blindness, other phenomena act as their resetting triggers.
Wakefulness and sleep are therefore under the control of the circadian rhythm, and not the other way around. That is, your circadian rhythm will march up and down every twenty- four hours irrespective of whether you have slept or not.
An adult’s owlness or larkness, also known as their chronotype, is strongly determined by genetics.
Consequently, the group as a whole is only collectively vulnerable (i.e., every person asleep) for just four rather than eight hours, despite everyone still getting the chance for eight hours of sleep. That’s potentially a 50 percent increase in survival fitness.
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.
For these reasons, melatonin is not a powerful sleeping aid in and of itself, at least not for healthy, non- jet- lagged individuals
There may be little, if any, quality melatonin in the pill. That said, there is a significant sleep placebo effect of melatonin, which should not be underestimated: the placebo effect is, after all, the most reliable effect in all of pharmacology.
Scientists have studied airplane cabin crews who frequently fly on long- haul routes and have little chance to recover.
First, parts of their brains— specifically those related to learning and memory— had physically shrunk, suggesting the destruction of brain cells caused by the biological stress of time- zone travel. Second, their short- term memory was significantly impaired.
The second is sleep pressure. At this very moment, a chemical called adenosine is building up in your brain. It will continue to increase in concentration with every waking minute that elapses.
You can, however, artificially mute the sleep signal of adenosine by using a chemical that makes you feel more alert and awake: caffeine.
caffeine is the most widely used (and abused) psychoactive stimulant in the world. It is the second most traded commodity on the planet, after oil.
By hijacking and occupying these receptors, caffeine blocks the sleepiness signal normally communicated to the brain by adenosine.
Also be aware that de- caffeinated does not mean non- caffeinated. One cup of decaf usually contains 15 to 30 percent of the dose of a regular cup of coffee, which is far from
some people have a more efficient version of the enzyme that degrades caffeine, allowing the liver to rapidly clear it from the bloodstream.
For the entire time that caffeine is in your system, the sleepiness chemical it blocks (adenosine) nevertheless continues to build up.
scientists exposed spiders to different drugs and then observed the webs that they constructed.X Those drugs included LSD, speed (amphetamine), marijuana, and caffeine.
The researchers noted how strikingly incapable the spiders were in constructing anything resembling a normal or logical web that would be of any functional use when given caffeine, even relative to other potent drugs tested.
the twenty- four- hour circadian rhythm of the suprachiasmatic nucleus and the sleep- pressure signal of adenosine— communicate with each other so as to unite their influences. In actual fact, they don’t. They are two distinct and separate systems that are ignorant of each other. They are not coupled; though, they are usually aligned.
assessing a person’s alertness across twenty- four hours of total sleep deprivation is one way that scientists can demonstrate that the two forces determining when you want to be awake and asleep— the twenty- four- hour circadian rhythm and the sleepiness signal of adenosine— are independent, and can be decoupled from their normal lockstep.
Chapter 3: Defining and Generating Sleep: Time Dilation and What We Learned from a Baby in 1952
How do you, yourself, know that you have slept? You make this self- assessment even more frequently than that of sleep in others. Each morning, with luck, you return to the waking world knowing that you have been asleep.I
All these signals still flood into the center of your brain, but it is here, in the sensory convergence zone, where that journey ends while you sleep.
I’m sure you have had the experience of needing to wake up the next morning at a specific time. Perhaps you had to catch an early- morning flight. Before bed, you diligently set your alarm for 6: 00 a.m. Miraculously, however, you woke up at 5: 58 a.m., unassisted, right before the alarm.
time dilation in dreams, beyond sleep itself. Time isn’t quite time within dreams. It is most often elongated.
memories were being “replayed” at the level of brain- cell activity as the rats snoozed. The second, more striking finding was the speed of replay. During REM sleep, the memories were being replayed far more slowly: at just half or quarter the speed of that measured when the rats were awake and learning the maze.
Consider the creation of a piece of sculpture from a block of clay. It starts with placing a large amount of raw material onto a pedestal (that entire mass of stored autobiographical memories, new and old, offered up to sleep each night). Next comes an initial and extensive removal of superfluous matter (long stretches of NREM sleep), after which brief intensification of early details can be made (short REM periods).
This account is one reason (of many, I suspect) explaining the cycling nature of NREM and REM sleep, and the imbalance of their distribution across the night.
the most epic displays of neural collaboration that we know of. Through an astonishing act of self- organization, many thousands of brain cells have all decided to unite and “sing,” or fire, in time.
When it comes to information processing, think of the wake state principally as reception (experiencing and constantly learning the world around you), NREM sleep as reflection (storing and strengthening those raw ingredients of new facts and skills), and REM sleep as integration (interconnecting these raw ingredients with each other, with all past experiences, and, in doing so, building an ever more accurate model of how the world works, including innovative insights and problem- solving abilities).
This feature, termed “atonia” (an absence of tone, referring here to the muscles), is instigated by a powerful disabling signal that is transmitted down the full length of your spinal cord from your brain stem. Once put in place, the postural body muscles, such as the biceps of your arms and the quadriceps of your legs, lose all tension and strength. No longer will they respond to commands from your brain.
It wouldn’t take long before you quickly left the gene pool. The brain paralyzes the body so the mind can dream safely.
Chapter 4: Ape Beds, Dinosaurs, and Napping with Half a Brain: Who Sleeps, How Do We Sleep, and How Much?
Without exception, every animal species studied to date sleeps, or engages in something remarkably like it. This includes insects, such as flies, bees, cockroaches, and scorpions; I fish, from small perch to the largest sharks; II amphibians, such as frogs; and reptiles, such as turtles, Komodo dragons, and chameleons. All have bona fide sleep. Ascend the evolutionary ladder further and we find that all types of birds and mammals sleep: from shrews to parrots, kangaroos, polar bears, bats, and, of course, we humans. Sleep is universal.
What if sleep is so useful— so physiologically beneficial 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 of life on this planet, and it was from sleep that wakefulness emerged.
Elephants need half as much sleep as humans, requiring just four hours of slumber each day. Tigers and lions devour fifteen hours of daily sleep. The brown bat outperforms all other mammals, being awake for just five hours each day while sleeping nineteen hours. Total amount of time is one of the most conspicuous differences in how organisms sleep.
Every species in which we can measure sleep stages experiences NREM sleep— the non- dreaming stage. However, insects, amphibians, fish, and most reptiles show no clear signs of REM sleep— the type associated with dreaming in humans. Only birds and mammals, which appeared later in the evolutionary timeline of the animal kingdom, have full- blown REM sleep. It suggests that dream (REM) sleep is the new kid on the evolutionary block. REM sleep seems to have emerged to support functions that NREM sleep alone could not accomplish, or that REM sleep was more efficient at accomplishing.
Certain of these ocean- faring species, such as dolphins and killer whales, buck the REM- sleep trend in mammals. They don’t have any.
From one perspective, this makes sense: when an organism enters REM sleep, the brain paralyzes the body, turning it limp and immobile. Swimming is vital for aquatic mammals, since they must surface to breathe. If full paralysis was to take hold during sleep, they could not swim and would drown.
When on land, they have both NREM sleep and REM sleep, just like humans and all other terrestrial mammals and birds. But when they enter the ocean, they stop having REM sleep almost entirely.
More intriguing than the poverty of REM sleep in this aquatic corner of the mammalian kingdom is the fact that birds and mammals evolved separately. REM sleep may therefore have been birthed twice in the course of evolution: once for birds and once for mammals.
Take cetaceans, such as dolphins and whales, for example. Their sleep, of which there is only NREM, can be unihemispheric, meaning they will sleep with half a brain at a time!
Sleep is of such vital necessity that no matter what the evolutionary demands of an organism, even the unyielding need to swim in perpetuum from birth to death, Mother Nature had no choice. Sleep with both sides of the brain, or sleep with just one side and then switch. Both are possible, but sleep you must. Sleep is non- negotiable.
Birds can do it, too. However, there is a somewhat different, though equally life- preserving, reason: it allows them to keep an eye on things, quite literally. When birds are alone, one half of the brain and its corresponding (opposite- side) eye must stay awake, maintaining vigilance to environmental threats. As it does so, the other eye closes, allowing its corresponding half of the brain to sleep.
Things get even more interesting when birds group together. In some species, many of the birds in a flock will sleep with both halves of the brain at the same time. How do they remain safe from threat? The answer is truly ingenious. The flock will first line up in a row. With the exception of the birds at each end of the line, the rest of the group will allow both halves of the brain to indulge in sleep. Those at the far left and right ends of the row aren’t so lucky. They will enter deep sleep with just one half of the brain (opposing in each), leaving the corresponding left and right eye of each bird wide open. In doing so, they provide full panoramic threat detection for the entire group, maximizing the total number of brain halves that can sleep within the flock.
REM sleep is strangely immune to being split across sides of the brain, no matter who you are. All birds, irrespective of the environmental situation, always sleep with both halves of the brain during REM sleep.
the most incredible feat of deliberate sleep deprivation belongs to that of birds during transoceanic migration.
In- flight, migrating birds will grab remarkably brief periods of sleep lasting only seconds in duration.
The total amount of time we spend asleep is markedly shorter than all other primates (eight hours, relative to the ten to fifteen hours of sleep observed in all other primates), yet we have a disproportionate amount of REM sleep, the stage in which we dream.
Great apes, for example, will build an entirely new treetop sleep nest, or platform, every single night. (Imagine having to set aside several hours each evening after dinner to construct a new IKEA bedframe before you can sleep!)
a dangling limb may be all the invitation gravity needs to bring you hurtling down to Earth in a life- ending fall, removing you from the gene pool. This is especially true for the stage of REM sleep, in which the brain completely paralyzes all voluntary muscles of the body, leaving you utterly limp— a literal bag of bones with no tension in your muscles.
Part of the answer is fire. While there remains some debate, many believe that Homo erectus was the first to use fire, and fire was one of the most important catalysts— if not the most important— that enabled us to come out of the trees and live on terra firma. Fire is also one of the best explanations for how we were able to sleep safely on the ground.
Related, the REM- sleep gift of facilitating accurate recognition and comprehension allows us to make more intelligent decisions and actions as a consequence. More specifically, the coolheaded ability to regulate our emotions each day— a key to what we call emotional IQ— depends on getting sufficient REM sleep night after night.
Nevertheless, the superior emotional brain gifts that REM sleep affords should be considered more influential in defining our hominid success than the second benefit, of inspiring creativity. Creativity is an evolutionarily powerful tool, yes. But it is largely limited to an individual. Unless creative, ingenious solutions can be shared between individuals through the emotionally rich, pro- social bonds and cooperative relationships that REM sleep fosters— then creativity is far more likely to remain fixed within an individual, rather than spread to the masses.
Chapter 5: Changes in Sleep Across the Life Span
Prior to birth, a human infant will spend almost all of its time in a sleep- like state, much of which resembles the REM- sleep state.
this is true for all other mammals:I the time of life when REM sleep is greatest is the same stage when the brain is undergoing the greatest construction.
A more recent link with deficient REM sleep concerns autism spectrum disorder (ASD)
Infants and young children who show signs of autism, or who are diagnosed with autism, do not have normal sleep patterns or amounts.
Autistic individuals show a 30 to 50 percent deficit in the amount of REM sleep they obtain, relative to children without autism.III
Just because autism and REM- sleep abnormalities go hand in hand does not mean that one causes the other. Nor does this association tell you the direction of causality even if it does exist:
Alcohol is one of the most powerful suppressors of REM sleep that we know of.
The newborns of heavy- drinking mothers spent far less time in the active state of REM sleep compared with infants of similar age but who were born of mothers who did not drink during pregnancy.
In contrast to the single, monophasic sleep pattern observed in adults of industrialized nations, infants and young kids display polyphasic sleep: many short snippets of sleep through the day and night, punctuated by numerous awakenings, often vocal.
the themes of which will immediately resonate with many new parents. “I’ll read you one very last book if you swear,/ You’ll go the fuck to sleep.” (I implore you to listen to the audiobook version of the work, narrated to perfection by the sensational actor Samuel L. Jackson.)
During the fourteen hours of total shut- eye per day that a six- month- old infant obtains, there is a 50/ 50 timeshare between NREM and REM sleep. A five- year- old, however, will have a 70/ 30 split between NREM and REM sleep across the eleven hours of total daily slumber.
His findings help justify an opinion you may also hold: adolescents have a less rational version of an adult brain, one that takes more risks and has relatively poor decision- making skills.
The changes in deep NREM sleep always precede the cognitive and developmental milestones within the brain by several weeks or months, implying a direction of influence: deep sleep may be a driving force of brain maturation, not the other way around.
in studies of juvenile rats and cats at the equivalent stage to human adolescence. Scientists deprived these animals of deep sleep. In doing so, they halted the maturational refinement of brain connectivity, demonstrating a causal role for deep NREM sleep in propelling the brain into healthy adulthood.XV
That older adults simply need less sleep is a myth. Older adults appear to need just as much sleep as they do in midlife, but are simply less able to generate that (still necessary) sleep.
In contrast to REM sleep, which remains largely stable in midlife, the decline of deep NREM sleep is already under way by your late twenties and early thirties.
dozing off in the evening, which most older adults do not realize is classified as napping, can be the source of sleep difficulty, not true insomnia.
Unlike young or middle- age adults, where melatonin has not proved efficacious for helping sleep beyond the circumstance of jet lag, prescription melatonin has been shown to help boost the otherwise blunted circadian and associated melatonin rhythm in the elderly, reducing the time taken to fall asleep and improving self- reported sleep quality and morning alertness.XXI
First, the areas of the brain that suffer the most dramatic deterioration with aging are, unfortunately, the very same deep- sleep- generating regions— the middle- frontal regions seated above the bridge of the nose.
the more severe the deterioration that an older adult suffers within this specific mid- frontal region of their brain, the more dramatic their loss of deep NREM sleep.
Poor memory and poor sleep in old age are therefore not coincidental, but rather significantly interrelated.
We do not assume that older individuals need weaker bones just because they have reduced bone density.
Part 2: Why Should You Sleep?
Chapter 6: Your Mother and Shakespeare Knew: The Benefits of Sleep for the Brain
Sleep is not the absence of wakefulness. It is far more than that.
Our question was simple: Does the learning capacity of the human brain decline with continued time awake across the day and, if so, can sleep reverse this saturation effect and thus restore learning ability?
The memory refreshment was related to lighter, stage 2 NREM sleep, and specifically the short, powerful bursts of electrical activity called sleep spindles, noted in chapter 3.
The question: Which sleep period would confer a greater memory savings benefit— that filled with deep NREM, or that packed with abundant REM sleep? For fact- based, textbook- like memory, the result was clear. It was early- night sleep, rich in deep NREM, that won out in terms of providing superior memory retention savings relative to late- night, REM- rich sleep.
it is now science fact: the method is called targeted memory reactivation.
Sleep powerfully, yet very selectively, boosted the retention of those words previously tagged for “remembering,” yet actively avoided the strengthening of those memories tagged for “forgetting.” Participants who did not sleep showed no such impressive parsing and differential saving of the memories.IX
The term “muscle memory” is a misnomer. Muscles themselves have no such memory: a muscle that is not connected to a brain cannot perform any skilled actions, nor does a muscle store skilled routines. Muscle memory is, in fact, brain memory. Training and strengthening muscles can help you better execute a skilled memory routine. But the routine itself— the memory program— resides firmly and exclusively within the brain.
“As a pianist,” he said, “I have an experience that seems far too frequent to be chance. I will be practicing a particular piece, even late into the evening, and I cannot seem to master it. Often, I make the same mistake at the same place in a particular movement. I go to bed frustrated. But when I wake up the next morning and sit back down at the piano, I can just play, perfectly.”
Those who remained awake across the day showed no evidence of a significant improvement in performance. However, fitting with the pianist’s original description, those who were tested after the very same time delay of twelve hours, but that spanned a night of sleep, showed a striking 20 percent jump in performance speed and a near 35 percent improvement in accuracy.
The increases in speed and accuracy, underpinned by efficient automaticity, were directly related to the amount of stage 2 NREM, especially in the last two hours of an eight- hour night of sleep (e.g., from five to seven a.m., should you have fallen asleep at eleven p.m.).
daytime naps that contain sufficient numbers of sleep spindles also offer significant motor skill memory improvement, together with a restoring benefit on perceived energy and reduced muscle fatigue.
Chapter 7: Too Extreme for the Guinness Book of World Records: Sleep Deprivation and the Brain
First, although sleep deprivation of all these varied amounts caused a slowing in reaction time, there was something more telling: participants would, for brief moments, stop responding altogether. Slowness was not the most sensitive signature of sleepiness, entirely missed responses were.
After four hours of sleep for six nights, participants’ performance was just as bad as those who had not slept for twenty- four hours straight— that is, a 400 percent increase in the number of microsleeps.
Ten days of six hours of sleep a night was all it took to become as impaired in performance as going without sleep for twenty- four hours straight.
When participants were asked about their subjective sense of how impaired they were, they consistently underestimated their degree of performance disability.
Based on epidemiological studies of average sleep time, millions of individuals unwittingly spend years of their life in a sub- optimal state of psychological and physiological functioning, never maximizing their potential of mind or body due to their blind persistence in sleeping too little.
After being awake for nineteen hours, people who were sleep- deprived were as cognitively impaired as those who were legally drunk.
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.
Many of us think we can overcome drowsiness through sheer force of will, but, sadly, this is not true.
first appeared to be counterintuitive, but Dinges and Rosekind made a clever, biology- based prediction. They believed that by inserting a nap at the front end of an incoming bout of sleep deprivation, you could insert a buffer, albeit temporary and partial, that would protect the brain from suffering catastrophic lapses in concentration. They were right. Pilots suffered fewer microsleeps at the end stages of the flight if the naps were taken early that prior evening, versus if those same nap periods were taken in the middle of the night or later that next morning, when the attack of sleep deprivation was already well under way.
And so the “power nap” was born.
No matter what you may have heard or read in the popular media, there is no scientific evidence we have suggesting that a drug, a device, or any amount of psychological willpower can replace sleep.
neither naps nor caffeine can salvage more complex functions of the brain, including learning, memory, emotional stability, complex reasoning, or decision- making.
We have, however, discovered a very rare collection of individuals who appear to be able to survive on six hours of sleep, and show minimal impairment— a sleepless elite, as it were. Give them hours and hours of sleep opportunity in the laboratory, with no alarms or wake- up calls, and still they naturally sleep this short amount and no more. Part of the explanation appears to lie in their genetics, specifically a sub- variant of a gene called BHLHE41. III Scientists are now trying to understand what this gene does, and how it confers resilience to such little sleep.
prevailing view in psychiatry has been that mental disorders cause sleep disruption— a one- way street of influence. Instead, we have demonstrated that otherwise healthy people can experience a neurological pattern of brain activity similar to that observed in many of these psychiatric conditions simply by having their sleep disrupted or blocked.
I firmly believe that sleep loss and mental illness is best described as a two- way street of interaction, with the flow of traffic being stronger in one direction or the other, depending on the disorder.
The glial cells of the brain were shrinking in size by up to 60 percent during NREM sleep, enlarging the space around the neurons and allowing the cerebrospinal fluid to proficiently clean out the metabolic refuse left by the day’s neural activity.
Parenthetically, and unscientifically, I have always found it curious that Margaret Thatcher and Ronald Reagan— two heads of state that were very vocal, if not proud, about sleeping only four to five hours a night— both went on to develop the ruthless disease. The current US president, Donald Trump— also a vociferous proclaimer of sleeping just a few hours each night— may want to take note.
Chapter 8: Cancer, Heart Attacks, and a Shorter Life: Sleep Deprivation and the Body
For cardiovascular health, I believe that finding comes from a “global experiment” in which 1.5 billion people are forced to reduce their sleep by one hour or less for a single night each year. It is very likely that you have been part of this experiment, otherwise known as daylight savings time.
In the Northern Hemisphere, the switch to daylight savings time in March results in most people losing an hour of sleep opportunity. Should you tabulate millions of daily hospital records, as researchers have done, you discover that this seemingly trivial sleep reduction comes with a frightening spike in heart attacks the following day. Impressively, it works both ways. In the autumn within the Northern Hemisphere, when the clocks move forward and we gain an hour of sleep opportunity time, rates of heart attacks plummet the day after. A similar rise- and- fall relationship can be seen with the number of traffic accidents, proving that the brain, by way of attention lapses and microsleeps, is just as sensitive as the heart to very small perturbations of sleep. Most people think nothing of losing an hour of sleep for a single night, believing it to be trivial and inconsequential. It is anything but.
From a metabolic perspective, the sleep- restricted participants had lost their hunger control.
Sleep, it turns out, is an intensely metabolically active state for brain and body alike. For this reason, theories proposing that we sleep to conserve large amounts of energy are no longer entertained.
the less an individual sleeps, the less energy he or she feels they have, and the more sedentary and less willing to exercise they are in real- world settings.
The faces pictured after one night of short sleep were rated as looking more fatigued, less healthy, and significantly less attractive, compared with the appealing image of that same individual after they had slept a full eight hours.
Stirred by the strength of accumulating evidence, Denmark recently became the first country to pay worker compensation to women who had developed breast cancer after years of night- shift work in government- sponsored jobs, such as nurses and air cabin crew. Other governments— Britain, for example— have so far resisted similar legal claims, refusing payout compensation despite the science.
Part 3: How and Why We Dream
Chapter 9: Routinely Psychotic: REM-Sleep Dreaming
REM sleep is not the only time during sleep when we dream.
But dreams as most of us think of them— those hallucinogenic, motoric, emotional, and bizarre experiences with a rich narrative— come from REM sleep, and many sleep researchers limit their definition of true dreaming to that which occurs in REM sleep.
There were important virtues of Freud’s theory, and we will discuss them below. But there were deep and systemic flaws that led to a rejection of the theory by modern- day science.
there are four main clusters of the brain that spike in activity when someone starts dreaming in REM sleep: (1) the visuospatial regions at the back of the brain, which enable complex visual perception; (2) the motor cortex, which instigates movement; (3) the hippocampus and surrounding regions that we have spoken about before, which support your autobiographical memory; and (4) the deep emotional centers of the brain— the amygdala and the cingulate cortex, a ribbon of tissue that sits above the amygdala and lines the inner surface of your brain— both of which help generate and process emotions.
What came as a surprise, however, was a pronounced deactivation of other brain regions— specifically, circumscribed regions of the far left and right sides of the prefrontal cortex.
This region, especially the left and right sides, manages rational thought and logical decision- making, sending “top- down” instructions to your more primitive deep- brain centers, such as those instigating emotions. And it is this CEO region of your brain, which otherwise maintains your cognitive capacity for ordered, logical thought, that is temporarily ousted each time you enter into the dreaming state of REM sleep.
REM sleep can therefore be considered as a state characterized by strong activation in visual, motor, emotional, and autobiographical memory regions of the brain, yet a relative deactivation in regions that control rational thought.
The scientists were able to predict with significant accuracy the content of participants’ dreams at any one moment in time using just the MRI scans, operating completely blind to the dream reports of the participants.
Yet Freud was 50 percent right and 100 percent wrong. Things quickly went downhill from this point, as the theory plunged into a quagmire of unprovability. Simply put, Freud believed that dreams came from unconscious wishes that had not been fulfilled.
do dreams themselves, above and beyond REM sleep, actually do anything for us? As a matter of scientific fact, yes, they do.
Chapter 10: Dreaming as Overnight Therapy
Dreams, like heat from a lightbulb, may serve no function. Dreams may simply be epiphenomena of no use or consequence.
Perhaps it was not time that heals all wounds, but rather time spent in dream sleep.
In fact, REM sleep is the only time during the twenty- four- hour period when your brain is completely devoid of this anxiety- triggering molecule. Noradrenaline, also known as norepinephrine, is the brain equivalent to a body chemical you already know and have felt the effects of: adrenaline (epinephrine).
It was not, therefore, time per se that healed all wounds, but instead it was time spent in dream sleep that was providing emotional convalescence.
Those who were dreaming, but not dreaming of the painful experience itself, could not get past the event, still being dragged down by a strong undercurrent of depression that remained.
the repetitive nightmares reported in PTSD patients— a symptom so reliable that it forms part of the list of features required for a diagnosis of the condition. If the brain cannot divorce the emotion from memory across the first night following a trauma experience, the theory suggests that a repeat attempt of emotional memory stripping will occur on the second night, as the strength of the “emotional tag” associated with the memory remains too high. If the process fails a second time, the same attempt will continue to repeat the next night, and the next night, like a broken record. This was precisely what appeared to be happening with the recurring nightmares of the trauma experience in PTSD patients.
Prazosin was gradually lowering the harmful high tide of noradrenaline within the brain, giving these patients healthier REM- sleep quality. With healthy REM sleep came a reduction in the patients’ clinical symptoms and, most critically, a decrease in the frequency of their repetitive nightmares.
Looking across the life span, we have discovered that this REM- sleep recalibration service comes into its own just prior to the transition into adolescence. Before that, when children are still under close watch from their parents, and many salient assessments and decisions are made by Mom and/ or Dad, REM sleep provides less of a re- tuning benefit to a child’s brain. But come the early teenage years and the inflection point of parental independence wherein an adolescent must navigate the socioemotional world for himself, now we see the young brain feasting on this emotional recalibration benefit of REM sleep.
Chapter 11: Dream Creativity and Dream Control
It should come as no surprise by now that those participants who took a nap showed superior memory performance on the maze task. They could locate the navigation clues with ease, finding their way around and out of the maze faster than those who had not slept. The novel result, however, was the difference that dreaming made. Participants who slept and reported dreaming of elements of the maze, and themes around experiences clearly related to it, showed almost ten times more improvement in their task performance upon awakening than those who slept just as much, and also dreamed, but did not dream of maze- related experiences.
Scientists had gained objective, brain- based proof that lucid dreamers can control when and what they dream while they are dreaming.
this argument makes the erroneous assumption that we have stopped evolving. It is possible that lucid dreamers represent the next iteration in Homo sapiens’ evolution.
Part 4: From Sleeping Pills to Society Transformed
Chapter 12: Things That Go Bump in the Night: Sleep Disorders and Death Caused by No Sleep
They may sit up on the edge of the bed and begin talking. Others may attempt to put on clothes and walk out of the room. But look at the brainwave activity and you realize that the patient, or at least their brain, is sound asleep. There are the clear and unmistakable slow electrical waves of deep NREM sleep, with no sign of fast, frenetic waking brainwave activity.
As a result, you begin to wake up, but you are unable to lift your eyelids, turn over, cry out, or move any of the muscles that control your limbs. Gradually, the paralysis of REM sleep does wear off, and you regain control of your body, including your eyelids, arms, legs, and mouth. Don’t worry if you have had an episode of sleep paralysis at some point in your life. It is not unique to narcolepsy.
Chapter 13: iPads, Factory Whistles, and Nightcaps: What’s Stopping You from Sleeping?
What of a petite bedside lamp? How much can that really influence your suprachiasmatic nucleus? A lot, it turns out. Even a hint of dim light— 8 to 10 lux— has been shown to delay the release of nighttime melatonin in humans.
evening blue LED light has twice the harmful impact on nighttime melatonin suppression than the warm, yellow light from old incandescent bulbs, even when their lux intensities are matched.
A recent survey of over fifteen hundred American adults found that 90 percent of individuals regularly used some form of portable electronic device sixty minutes or less before bedtime. It has a very real impact on your melatonin release, and thus ability to time the onset of sleep.
using an iPad— an electronic tablet enriched with blue LED light— for two hours prior to bed blocked the otherwise rising levels of melatonin by a significant 23 percent.
But did reading on the iPad actually change sleep quantity/ quality above and beyond the timing of melatonin? It did,
As we have discussed, this frontal lobe region of the human brain helps control our impulses and restrains our behavior. Alcohol immobilizes that part of our brain first. As a result, we “loosen up,” becoming less controlled and more extroverted. But anatomically targeted brain sedation it still is.
Alcohol sedates you out of wakefulness, but it does not induce natural sleep.
Unfortunately, most of these nighttime awakenings go unnoticed by the sleeper since they don’t remember them. Individuals therefore fail to link alcohol consumption the night before with feelings of next- day exhaustion caused by the undetected sleep disruption sandwiched in between.
Second, alcohol is one of the most powerful suppressors of REM sleep that we know of.
More surprising, perhaps, was the realization that the brain is not done processing that knowledge after the first night of sleep. Memories remain perilously vulnerable to any disruption of sleep (including that from alcohol) even up to three nights after learning, despite two full nights of natural sleep prior.
Thermal environment, specifically the proximal temperature around your body and brain, is perhaps the most underappreciated factor determining the ease with which you will fall asleep tonight, and the quality of sleep you will obtain.
It is no evolutionary coincidence that we humans have developed the pre- bed ritual of splashing water on one of the most vascular parts of our bodies— our face, using one of the other highly vascular surfaces— our hands.
The need to dump heat from our extremities is also the reason that you may occasionally stick your hands and feet out from underneath the bedcovers at night due to your core becoming too hot, usually without your knowing.
A bedroom temperature of around 65 degrees Fahrenheit (18.3 ° C) is ideal for the sleep of most people, assuming standard bedding and clothing.
A luxury for many is to draw a hot bath in the evening and soak the body before bedtime. We feel it helps us fall asleep more quickly, which it can, but for the opposite reason most people imagine. You do not fall asleep faster because you are toasty and warm to the core. Instead, the hot bath invites blood to the surface of your skin, giving you that flushed appearance. When you get out of the bath, those dilated blood vessels on the surface quickly help radiate out inner heat, and your core body temperature plummets. Consequently, you fall asleep more quickly because your core is colder. Hot baths prior to bed can also induce 10 to 15 percent more deep NREM sleep in healthy adults.IV
Chapter 14: Hurting and Helping Your Sleep: Pills vs. Therapy
Sleeping pills do not provide natural sleep, can damage health, and increase the risk of life- threatening diseases.
No past or current sleeping medications on the legal (or illegal) market induce natural sleep.
Sleeping pills, old and new, target the same system in the brain that alcohol does— the receptors that stop your brain cells from firing— and are thus part of the same general class of drugs: sedatives. Sleeping pills effectively knock out the higher regions of your brain’s cortex.
good “sleep hygiene” practices, for which a list of twelve key tips can be found at the National Institutes of Health website; also offered in the appendix of this book.X
medical errors are the third- leading cause of death among Americans after heart attacks and cancer.