The Science of Sleep: What It Is, How It Works, and Why It Matters

Science of sleepWe often hear that humans spend one third of their lives sleeping—and most of us would up that fraction if we could. Whether we’re curling up for a brief lunchtime catnap, catching a doze on a sunny afternoon, or clocking our solid eight hours at night, sleeping is normally a reliable way to rest our heads and recharge our minds. And our bodies demand it: without sufficient sleep, we experience changes in mood, memory loss, and difficulty concentrating. Symptoms of sleep deprivation can be severe, and we know that sleep is essential for restoring and rejuvenating muscles, tissue, and energy. And yet, although science is making remarkable inroads into the workings and functions of sleep, many aspects still remain a mystery.
In The Science of Sleep, sleep expert Wallace B. Mendelson explains the elements of human sleep states and explores the variety of sleep disorders afflicting thousands of people worldwide. Mendelson lays out the various treatments that are available today and provides a helpful guide for one of life’s most important activities. By offering the first scientific yet accessible account of sleep science, Mendelson allows readers to assess their personal relationships with sleep and craft their own individual approaches to a comfortable and effective night’s rest.
Addressing one of the major public health issues of the day with cutting-edge research and empathetic understanding, The Science of Sleep is the definitive illustrated reference guide to sleep science.

Praise for The Science of Sleep:
“Not only does this book remind us why we need sleep but it also tells us what happens if we don’t get enough of it.” – Euro Scientist
“Dr Mendelson provides a readable, engaging, and clearly written work concerning sleep science and medicine. His ability to explain complexities in a manner that communicates essential characteristics is truly artful. And speaking of art, the illustrations and layout make this book a joy to open and begin reading or skimming on any page. For anyone serious about sleep science, this book should sit prominently on a nearby bookshelf, assuming it ever gets off your desk.” – Max Hirshkowitz, PhD, Sleep Specialist 

Excerpt from The Science of Sleep:
Sleep means different things to different people, and indeed its meaning differs in the same person at various times. I remember, for instance, as a little boy, going to bed anticipating the presents awaiting me on Christmas morning, and thinking that since I would soon be asleep, the time would seem to pass in an instant. Then the presents would be mine. Not surprisingly, that sort of thinking led to the opposite, a long period of unhappy wakefulness. The opposite can occur as well, as in the song “The Green Green Grass of Home”, in which sleep is a time of escape into happy memories, in contrast to the very unfortunate events awaiting the sleeper in the morning. For others, sleep can become a kind of testing ground: a person who prides herself on always being the best at whatever she does can view good sleep as a challenge, something she has to work at—the result, paradoxically, being poor sleep. It can also be a time of anxiety. People for whom it is important to feel in control of things can find it worrisome to have a period each night in which they seem more vulnerable and not in charge.  For others, sleep can be a time of getting a glimpse of the “real” world; I have had patients who say that their dream experiences during sleep seem so much more real and meaningful than what they awaken to in the morning.
Sleep is also inextricably tied to the notion of restoration. After a good night’s sleep a healthy person awakens with a sense of vitality, of readiness to face the new day. As we will discuss later, no one is certain what this entails physiologically—it is not just a simple matter of increasing metabolic energy stores—but its presence (or absence) plays a role in what we think about sleep.  Related to this is the notion of sleep as a pleasurable experience, something to look forward to. Sadly, for many people the opposite is true. The genesis of this is not always clear. Some think that a lifelong feeling that sleep is an unhappy time is a derivative of childhood experiences, in which the more typical learning association of sleeping with pleasure did not take place. Others view this as a disorder of the amount of l brain chemicals that normally bring on sleep. Another view is that it may result from habits in which bedtime is used for behaviors incompatible with sleep, such as worrying and planning tomorrow’s battles.
Sleep is also inextricably tied to the environment in which we live, in a world of alternating day and night. Our bodies have developed elaborate mechanisms to help time our waking and sleep to be in conjunction with light and darkness. Sometimes this timing can go astray, either due to behaviors such as engaging in shift work or flying long distances, or due to inherent problems of the body clock. These in turn can lead to difficulties with sleeping, or at least with sleeping during the traditional hours allocated for it.
Sleep can also be a kind of social behavior, inside the species, or across species (for instance when sleeping with a pet). We often use the euphemism of sleeping together to refer to another kind of activity that can take place in bed, but this kind of delicate phraseology can obscure another aspect, which is that repetitive sharing of the sleep experience may play a role in a couple bonding together.
There is also a sense that sleep is important to health, both physical and mental. Sleep which is curtailed or disrupted can lead, for instance, to a predilection to diabetes and related disorders. It seems to be important for the formation of long-term memories. This suggests, for instance, the futility of students doing “all nighters” of studying. It turns out that getting a good night’s sleep may be the most helpful thing in preparation for  an exam in the morning.  One of the great believers in a good night’s sleep, incidentally, was Alexander the Great.  In 331 BC, before the crucial battle in which he overwhelmed a vastly larger Persian army on their own territory, he slept so deeply that his officers became worried and had to awaken him.  He got up, put on his armor, and went on to an outstanding victory which set the stage for conquering an empire.
In this book we will present the scientific understanding of sleep, beginning by describing its basic processes and how to measure them. It will be seen that sleep results from the careful orchestration of a variety of physiologic processes. As in any complex mechanism, sometimes things go awry, in this case resulting in clinical sleep disorders which are experienced as insomnia, excessive sleepiness or undesirable behaviors during sleep. We will describe some of these disorders, and some of the treatments that are available. This information is not a substitute for medical evaluation. If you think you may have a sleep disorder, you should consult your doctor for evaluation and possible referral to a sleep disorders center. It is hoped that armed with the information provided here, you will be better able to understand and discuss what is happening, and to make more informed choices in conjunction with your doctor.
Just as sleep is a universal human behavior, so is human curiosity and the desire to know more about ourselves. A number of men and women devoted themselves to learn more about sleep, long before sleep studies became an established scientific discipline. They came from a variety of unlikely backgrounds—a WW I cavalryman, and a fighter pilot, for example. One was looking for something entirely else, the basis of a supposed “psychic energy” which might let people communicate across long distances, and ended instead with the groundbreaking discovery of the human electroencephalogram. Another was a doctor faced with treating patients in a worldwide epidemic of encephalitis, who recognized a pattern to the parts of the affected brains—and learned from it the basic structures making it possible for us to be awake or asleep. Another had made his fame developing a method to precisely measure the speed of projectiles for the Army, but his curiosity led him to measurements of many other kinds of things, including electrical waveforms during the human sleep stages. If you, the reader, have picked up this book, it sounds like you, too, have curiosity about how things work, and it is my hope that here you will learn more about how we wake and sleep.

Wallace MendelsonAbout the Author:
Wallace B. Mendelson, M.D., has more than forty years of experience in sleep research and clinical care – as a Professor of Psychiatry and Clinical Pharmacology (ret), former director of the Sleep Research Laboratory at the University of Chicago, and past president of the Sleep Research Society. He has written five books and numerous scientific papers on sleep disorders. He has also been the recipient of various honors including a special award for excellence in sleep and psychiatry from the National Sleep Foundation in 2010. To learn more, go to