Why We Sleep

“Everyone generates a circadian rhythm (circa, meaning ‘around,’ and dian, derivative of diam, meaning ‘day’). Indeed, every living creature on the planet with a life span of more than several days generates this natural cycle. The internal twenty-four-hour clock within your brain communicates its daily circadian rhythm signal to every other region of your brain and every organ in your body.” 

This passage provides the definition of the circadian rhythm, which controls the sleep-wake cycle. As the formulation indicates, the circadian rhythm rises and falls every 24 hours. While all individuals generate the circadian rhythm, the timing varies. This explains why some people are night owls and others morning larks. 

“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 passage provides the definition of the wake and NREM and REM sleep states. The reception of information and experiences from the outside world characterizes the waking state. The deep NREM slow-wave sleep transfers these recent experiences from a short-term storage site to a long-term storage site. The faster-frequency brainwaves of REM sleep build connections between old and new memories generating innovation and problem-solving abilities. Both NREM and REM sleep are critical to a diversity of brain and body functions. 

“Sleep is universal.” 

All animals sleep. Even aquatic mammals, who must constantly stay moving in their environment to survive, develop behavioral and physiological patterns that enable them to sleep when they need to. Despite this universality of sleep, Walker notes the irony that humans are the only animal known to intentionally disrupt their own sleep needs. 

“REM-sleep dreaming therefore represents a tenable new contributing factor, among others, that led to our astonishingly rapid evolutionary rise to power, for better and worse—a new (sleep-fueled), globally dominant social superclass.” 

Walker posits that the two primary benefits of REM sleep dreaming propelled humans to the top of the evolution pyramid. REM sleep dreaming facilitates an individual’s ability to decode emotions, especially related to the face. By becoming emotionally astute, humans could live in complex social and emotional communities. Living in these communities enabled humans to share creative solutions to problems. Working in conjunction with one another, these two benefits enabled human ingenuity, the likes which no other species replicates.

“Charged with such a herculean task of neuro-architecture—establishing the neural highways and side streets that will engender thoughts, memories, feelings, decisions, and actions—it’s no wonder REM sleep must dominate most, if not all, of early developmental life.” 

REM sleep facilitates the promotion of brain maturation in fetuses and newborns, which is why they spend most of their sleep time in this sleep stage. Recent research illustrates that disruptions to or impairments of this sleep state during infant brain development has life-long consequences. For example, some researchers are linking deficient REM sleep to autism.  

“I have recently given presentations to a number of national basketball and football teams in the United States, and for the latter, the United Kingdom. Standing in front of the manager, staff, and players, I tell them about one of the most sophisticated, potent, and powerful—not to mention legal—performance enhancers that has real game-winning potential: sleep.” 

Walker looks at various professions, including athletes, and explains how sleep deprivation can impair individual’s abilities to satisfactorily fulfill those roles. Scientific studies have investigated the relationship between sleep and athletic performance, with all proving that sleep deprivation correlates to impairments in respiratory, cardiovascular, and metabolic capabilities. Chronic poor sleep also increases the risk of injury—the greatest fear for coaches and athletes alike. Walker reiterates that all of these impairments are preventable with eight hours of natural sleep each night. 

“Drowsy driving alone is worse than driving drunk.”

This statement might surprise some readers, yet accidents caused by drowsy driving exceed those caused by both alcohol and drugs. Drowsy driving is significantly different than drunk driving. In the former, individuals who microsleep stop reacting altogether, whereas the latter have delays in their reactions. Falling asleep at the wheel results in the car becoming an uncontrolled, one-ton missile. Walker argues that governments should spend more money on campaigns educating the populace about the dangers of driving drowsy, similar to drunk-driving campaigns. 

“Inadequate sleep and the pathology of Alzheimer’s disease interact in a vicious cycle.” 

Alzheimer’s disease is one of the largest public health and economic challenges of modern society, with 10 percent of adults over the age of 65 suffering from it. Inadequate sleep leads to the buildup of beta-amyloid, a toxic protein, in the brain, and individuals with Alzheimer’s have abnormally high amyloid amounts. These proteins accumulate in specific regions of the brain, including where deep NREM sleep brainwaves originate. Deep NREM sleep helps to purify the brain of these proteins. Inadequate sleep means the brain cannot expel these toxins, and more continue to accumulate. As a result of the interaction between poor sleep and these toxins, individuals are stuck in this “vicious cycle,” increasing the risk of developing Alzheimer’s disease. 

“Like water from a burst pipe in your home, the effects of sleep deprivation will seep into every nook and cranny of biology, down into your cells, even altering your most fundamental self—your DNA.”

One of the main purposes of Why We Sleep is to raise awareness for how insufficient sleep proves catastrophic to major bodily functions. In Chapter 8, Walker discusses the impact of sleep deprivation on the major physiological systems of the body. Sleep deprivation, akin to water from a burst pipe in one’s home, infiltrates the entire human body system from the heart, to blood vessels, to blood sugar, to hormones, to fertility, to cells necessary for killing off foreign elements, and to DNA. Sleep neglect literally alters the very essence of an individual.  

“Last night, you became fragrantly psychotic. It will happen again tonight.” 

This passage describes dreams. There are five reasons for why Walker describes them as “flagrantly psychotic,” including: the fact that individuals hallucinate during dreams, become delusional, lose the sense of time, place, and being, experience extreme emotional swings, and wake up forgetting most of the dream. To Walker, if individuals experienced any of these symptoms during waking hours, they would need to seek psychological treatment. Yet dreams are essential biological and psychological processes that produce a host of adaptive advantages and emotional benefits.

“Dreams are not the heat of the lightbulb—they are no by-product.” 

Dreams were originally thought to be byproducts of REM sleep, like heat is the byproduct of lightbulbs. In this scenario, dreams serve no function. However, advances in sleep science illustrated that REM sleep and dreaming together produce adaptive advantages beyond just REM sleep alone. Thus, dreams are not “byproducts of REM sleep.”

“The brain’s emotional navigation system had lost its true magnetic north of directionality and sensitivity: a compass that otherwise guides us toward numerous evolutionary advantages.” 

REM sleep gifts two emotional advantages, one of which is the ability to read and interpret the value and meaning of emotional signals, including faces. Walker argues this benefit is survival-relevant for humans because it helps steer us through the complex emotional world around us. Sleep deprivation cuts short critical stages of REM. Individuals who lack good REM sleep quality cannot accurately decode emotional signals from the outside world, including other humans. These individuals slip into a fear-bias default. Without REM sleep, individuals lose their guiding North Star, or their ability to read the social world. 

“Upon awakenings from NREM sleep, participants did not appear to be especially creative, solving few of the anagram puzzles. But it was a different story when I woke them up out of REM sleep, from the dreaming phase. Overall, problem-solving abilities rocketed up, with participants solving 15 to 35 percent more puzzles when emerging from REM sleep compared with awakenings from NREM sleep or during daytime waking performance!” 

Walker is describing one of his scientific studies, which confirmed REM sleep and dreaming fostered a key benefit: problem solving abilities. During the study, Walker woke individuals up from different sleep stages throughout the night and asked them to complete an anagram task. When awoken from the dreaming phase, participants solved more puzzles compared with awakenings from NREM sleep or performance during daytime waking hours. The REM-sleep dreaming brain builds connections between pieces of information that are not obviously related in during waking hours. 

“Like an insightful interviewer, dreaming takes the approach of interrogating our recent autobiographical experience and skillfully positioning it within the context of past experiences and accomplishments, building a rich tapestry of meaning.” 

Scientific studies found that dreams were not an exact replay of the initial learning experience during waking hours. Rather, the dreaming experience cherry-picks aspects of the learning experience and then tries to place those new experiences within the context of past knowledge, accomplishments, and experiences. This aspect of the dreaming mind generates creative and novel ideas, which have led to incredible advances to human progress.

“Approximately one out of every nine people you pass on the street will meet the strict clinical criteria for insomnia, which translates to more than 40 million Americans struggling to make it through their waking days due to wide-eyed nights.” 

This passage supports Walker’s claim that insomnia is the most pressing and prevalent medical issue facing 21st-century society. Americans spend an astonishing amount of money on over-the-counter and prescription sleep remedies. While genetics play a role in causing insomnia, there are other physical, medical, psychological, and environmental triggers. Many of these triggers, such as alcohol, smartphone and laptop usage, and warmer indoor temperatures, stem from modern advances. By addressing these triggers, individuals will often get better sleep, without the aid of sleeping pills.

“Perhaps you have seen that small plastic red box on the walls of extremely hazardous work environments that has the following words written on the front: ‘Break glass in case of emergency.’ If you impose a total absence of sleep on an organism, rat or human, it indeed becomes an emergency, and you will find the biological equivalent of this shattered glass strewn throughout the brain and body, to fatal effect.” 

The evidence for whether lack of sleep will kill a human remained inconclusive. However, recent studies on the impact of sleep deprivation on rats provided definitive evidence that lack of sleep is deadly. Sleep deprivation caused ghastly external and internal damages to the rats, akin to bodily damages caused by shattered glass. The rat’s weakened immune, specifically its inability to fight off bacteria from its own gut, dealt the final blow. The sleep-deprived rats succumbed to septicemia. While similar studies have obviously not been conducted on humans, sleep deprivation is just as deadly for humans as it is for rats.  

“We are the only species that has managed to light the night to such dramatic effect.” 

Before gas and oil lamps and electric light, most human activities stopped post-dusk. Because these activities were based on vision, supported by sunlight, humans had no choice. The invention of artificial light—especially incandescent and LED lights—significantly altered our sleep-wake patterns and sleep quantity/quality. Individuals now lose significant amounts of REM sleep, feel less rested throughout the next day, and experience delays in the release of melatonin.

“No other species demonstrates this unnatural act of prematurely and artificially terminating sleep, and for good reason.” 

Walker notes the irony that humans are the only known animal to intentionally deny or disrupt their sleep habits. Even dolphins, who have natural predators that constantly threaten their existence, sleep when they need to. Alarm clocks, and particularly the snooze button, are one of the worst ways that humans disrupt their sleep. Being artificially awoken results in the body activating the flight-or-flight response. Using the snooze feature means this assault is recurring in a short time frame. Doing this every day during the work week leads to multiplicative abuse of the heart and nervous system.

“More alarming was the mortality risk for people who only dabbled in sleeping pill use. Even very occasional users—those defined as taking just eighteen pills per year—were still 3.6 times more likely to die at some point across the assessment window than non-users.” 

Walker cautions his audience against using sleeping pills. This scientific study he references supports his claim of their harmful effects. Sleeping pill usage—even for occasional users—results in higher mortality rates over the study period compared to the control participants who were not using them. 

“Taken as a whole, one out of every to adults across all developed countries (approximately 8 million people) will not get the necessary sleep they need this coming week.” 

This statistic reinforces that lack of sleep across developed nations is a global health epidemic. Sleep deprivation degrades physical and cognitive abilities, with massive societal consequences. Insufficient sleep costs most nations a portion of their GDP, undermines the next generation’s learning potential, and results in serious and often deadly medical errors. These societal tragedies are entirely preventable: Individuals just need eight hours of nightly sleep opportunity.

“More generally, I feel we as a society must work toward dismantling our negative and counterproductive attitude toward sleep: one that is epitomized in the words of a US senator who once said, ‘I’ve always loathed the necessity of sleep. Like death, it puts even the most powerful men on their backs.’”

While this quote is from Frank Underwood, a fictional television character from the House of Cards series, it encapsulates the modern world’s sleep-deprivation problem. Many individuals view sleep as a nuisance. Yet, evidence shatters this notion. There are likely no biological functions that do not benefit from good sleep quantity/quality. In fact, prolonged sleep-deprivation causes death. Thus, it will literally put individuals “on their backs.” 

“When it comes to the quantified self, it’s the old adage of ‘seeing is believing’ that ensures long-term adherence to health habits.” 

Educating people about sleep is not enough to combat sleep deprivation. These newly realized healthy habits must become permanent lifestyle changes. One practice known to convert habits to permanent practices is showing individuals their own health data. By seeing these data, individuals can explicitly see connections between the healthy new habits and changes to their mental and physical well-being. Consequently, individuals are more apt to maintain this positive way of life. Walker argues that the fast-emerging sleep trackers—using smartphones as the central health data hub—will lead to radical attitude and behavioral changes towards sleep in individuals and society writ large.  

“In just the last few months, we have preliminary research findings from several NICUs that have implemented dim-lighting conditions during the day and near-blackout conditions at night. Under these conditions, infant sleep stability, time, and quality improved.” 

This passage illustrates why sleep needs to be part of patient care. The lighting in most neonatal intensive care units is strong, preventing infants—who are at their most vulnerable stage—from getting their normal quantity and quality of sleep. Implementing lighting changes in these units results in higher sleep quality for infants. Improvements to sleep result in infants gaining weight and having higher oxygen levels in their bloodstream. Moreover, hospitals discharged these infants sooner than those who were in units with traditional lighting.