1. Studies commissioned by the Department of Defense and the Defense Advanced Research Projects Agency found that lack of sleep degrades not only the ability of combat soldiers to identify and locate the enemy, but also—and even more disturbingly—their capacity to care whether they succeed or not.
2. “No drug has yet been invented that is a substitute for sleep,” says Dr. John A. Caldwell, principal research psychologist for the Warfighter Fatigue Countermeasures Program. The alternatives only foster a false sense of staving off the effects of fatigue, a condition I call Fatigue Denial.
3. Studies showing that sleepiness decreases attention and alertness by 50 percent.
4. After 24 hours of sleep deprivation, the impairment is equivalent to a blood alcohol alcohol content of .10, which is well past the legal limit in every state. Also, these studies warn us that the effects increase with each additional night of insufficient sleep.
5. This is because blood pressure decreases during sleep. So when you remain awake longer than normal, your blood pressure remains higher than normal. Our immune system suffers, too, since the number of natural killer cells created by our bodies to fight off invaders is reduced by sleep deprivation, leaving us vulnerable to colds and flu, allergies and asthma, and increasing our risk of many types of cancer.
6. Studies have conclusively linked sleeplessness to irritability, anger, depression and mental exhaustion. This is not only because the brain is affected; other organs and body functions are, too.
7. Both sleep deprivation and stress result in elevated levels of the hormone cortisol. Synthesized in the adrenal cortex, cortisol helps to regulate our blood pressure, heart rhythm and ability to break down carbohydrates and fats.
8. “Overtired” isn’t just a figure of speech. Going past the warning signs of fatigue can push you into a slightly manic state in which your body revs up so fast to compensate for lack of sleep that you can be too “wired” to fall asleep when you have the opportunity.
9. The most famous discovery in sleep science occurred in 1953, when University of Chicago physiology professor Nathaniel Kleitman and Eugene Aserinsky stumbled on a phenomenon that would revolutionize our understanding of how people sleep. During an experiment, they observed that the eyeballs of sleeping infants darted left and right in sporadic bursts, coupled with irregular breathing and increased heart rate. Adults, they subsequently found, did this, too. They called this strange phenomenon rapid eye movement, or REM.
10. What made this more than an “Oh, isn’t that interesting?” piece of trivia was the fact that subjects reported vivid dreaming only during this period.
11. This established once and for all that not only is sleep more than just the absence of waking—it isn’t even correct to speak of it as a single, undifferentiated unit.
12. Instead, sleep was divided into five distinct phases—now known as Stage 1, Stage 2, Stage 3, Stage 4 and REM.
13. During sleep, the electrical activity in the brain taps out a catchy but unwavering rhythm that goes 1, 2, 3, 4, 2, REM, 2, 3, 4, 2, REM, 2, 3, 4, 2, REM … and so on.
14. Each sequence is known as a “sleep cycle.” Stage 1 occurs only once—as a transition into the sleep state. We spend over half of our total sleep time in Stage 2, about 20 percent in REM and the remaining time in Stages 3 and 4. An entire cycle lasts 90 to 100 minutes, about the length of the average movie.
15. Stage 1 As you sink into your pillow and close your eyes, a medium-frequency, medium-amplitude brain wave called alpha predominates as the beta wave diminishes.
16. The identification of the alpha wave and its association with relaxation, for instance, led to biofeedback techniques that produce the same calm brain signature observed in experienced practitioners of meditation.
17. As you cross the threshold of sleep into Stage 1, alpha subsides and generalized involuntary muscle contractions occur, accompanied by surreal visual imagery such as falling off a sidewalk. You may also find yourself momentarily paralyzed.
18. Stage 1 lasts two to five minutes and is the least understood of all the components of sleep. It appears to be a quasi-REM state, involving nonlinear thoughts and associations, but it lacks REM’s trademark eye movements.
19. Stage 2 After about two to five minutes, your heart rate slows and your body temperature drops. Without noticing, you’ve slipped into Stage 2 and true unconsciousness.
20. If sleep is a soup, then Stage 2 is its stock.
21. Not only does it provide the medium in which all the other stages “float,” but it’s pretty nutritious all by itself. At the end of the 20th century, Stage 2 was still thought of as a transition phase between the so-called “real” stages of sleep (something to keep in mind before completely writing off Stage 1); today, the latest word from university laboratories is that our generous allowance of Stage 2 plays a dominant role in increasing alertness, one of the most critical benefits of sleep.
22. The ability to grasp the significance of what our senses perceive is associated with the thalamus, which forwards our raw sensations to the proper brain areas for processing. No surprise, then, that this plum-size relay operator is taking its own nap during this stage.
23. Other areas of the brain begin to take it easy, too. These include the brain stem, the ball of tissue that sits atop the spinal cord and controls breathing, heart rate, reflex response and the neuromotor aspects of speech; the prefrontal cortex, an area involved in language, abstract reasoning, planning, problem solving and social interactions; and the cingulate cortex, located just above the brain stem, which helps you override certain automatic responses for newly learned ones.
24. The defining wave characteristics of Stage 2 are spindles and “k” complexes. Spindles are lightning-quick oscillations that increase and decrease in amplitude—all in under a second.
25. Spindles also play a role in implicit learning, or the learning you do without realizing it, such as familiarizing yourself with a new neighborhood. Increased spindle production has also been correlated with higher scores on some IQ tests.
26. While we know that spindles occur only during sleep, what isn’t clear is why some things are more easily learned without sleep while for others sleep is almost essential. The best guess is that simple things tend to be more easily learned without sleep, but getting many complicated components to gel requires a sleep episode.
27. “K” complexes are large-amplitude spikes, with a slight dip at the end as seen in a cursive letter “k.” They shoot out from the cerebral cortex, an area associated with all higher-brain functions. These characters venture out only in Stage 2, appearing once every 2 to 8 minutes and lasting up to 30 seconds each time. The function of “k” complexes is still wrapped in mystery. Science’s best detective work has determined that they’re associated with changes in blood pressure and seem to be indicative of the brain’s descent into slower.
28. Stage 3 + Stage 4 = slow-wave sleep As you drift farther down the river of sleep, the temperature inside your head cools and the blood vessels constrict. An EEG will pick up the signal of the extremely slow delta wave, along with remnants of faster-frequency waves lingering from Stage 2. As you cross the threshold into Stage 3, you enter a deep, dark world known as slow-wave sleep, or SWS.
29. Low-key coughing and humming—noises that would wake you up during. Stage 2—now go unheard. It will take a loud bang or a sound of particular relevance, like your name or the cry of your baby (but, oddly, not the cry of a stranger’s child), to bring you back to the waking world. For children, the noise level can actually reach over 120 decibels (think jet plane or rock concert) before they abandon the cozy comfort of slow-wave sleep.
30. Checking your hormones now, we find that the cortisol spigot has completely shut off. This so-called “stress hormone” is no longer stripping away at your body tissue, wreaking catabolic havoc.
31. During SWS, all the critical physical benefits of sleep are delivered. Like your own internal handyman, it restores your tissue and organs to peak condition, prolonging health and youthfulness while at the same time decreasing stress, anxiety and susceptibility to illness.
32. As an added bonus, SWS has proven vital to the formation of declarative memory—new information consciously learned, such as a friend’s birthday, a phone number or the periodic table of elements.
33. While it’s tempting to regard Stage 4 as more of the same, we need to attune ourselves to a few subtle differences. The slowing of physiological processes continues, but what is unique here is the complete absence of the short, fast waves that were introduced in Stage 2. Stage 4 is our deepest sleep stage, and our systems show the greatest degree of downshifting from the waking state.
34. REM sleep After a seven- or eight-minute rebound back into Stage 2, the most exciting stage begins.
35. Unlike the more physical motor learning that results from Stage 2 spindles, the long-term potentiation of our higher-learning functions has to wait for REM.
36. Mastering anything complex, whether it be a mathematical formula, riding a bicycle or even reaching for a deeply creative solution, requires REM sleep to fuse these loose pieces of string needed to connect seemingly remote brain areas.
37. Most of the activities that require higher brain processes—memory, creativity, complex learning—depend on REM to do their business.
38. During nocturnal sleep, our trip through Stage 2, SWS and REM is preprogrammed and we’re just along for the ride. Only during a nap does the potential exist to cherry-pick stages based on the benefits we’re looking for.
39. All you need to do is calculate when a nap should contain an extra dose of any of these components and plan your nap time accordingly.
40. No biological process is an island. And sleep cycles do not end just because you’ve woken up. They continue as “shadow sleep cycles” across the day.
41. As ghostly as this sounds, these cycles are governed by two reliably scientific principles: sleep pressure, which affects SWS, and circadian rhythm, which dictates the distribution of REM. Once you learn how these components behave, the benefits of your nap are at your beck and call.
42. From the moment you wake up, your body slowly builds the urge to go back to sleep. This phenomenon, born out of an increasing need for slow-wave sleep, is known as sleep pressure.
43. In the morning, when your brain is relatively well rested, shadow sleep cycles will contain a small percentage of SWS. Later in the day, as the distance from your last sleep episode becomes greater, the amount of SWS also increases.
44. Our brains have a homeostatic drive that always endeavors to maintain a balance between SWS and waking. Indeed, the generalized feeling of true sleepiness (the kind that is not related to being bored or physically overexerted) is simply the manifestation of our body’s desire for SWS. If you stay awake indefinitely, sleep pressure intensifies until finally the urge to sleep overcomes any conscious resistance and you’re “asleep at the wheel,” or wherever you may be.
45. Once you do give in, the pressure drops with every passing cycle, much like air being allowed to intermittently escape from a balloon, so the earlier the cycle is within the nocturnal sequence, the more SWS it’s going to contain.
46. Sleep cycles generally contain the lowest amount of REM at 9 P.M., with the percentage steadily increasing until 9 A.M. It then falls off again until it reaches its 9 P.M. trough, before beginning its inevitable climb all over again.
47. The circadian phase is at its peak in the morning, with the highest concentration of REM sleep when you awake. Across the day, REM decreases.
48. In people with normal sleep/wake cycles, REM and SWS pirouette nicely across the day and night. SWS predominates in the late afternoon and evening, when REM is in its natural low phase. Then, as we move toward morning and a higher REM cycle, sleep pressure has been relieved, so SWS doesn’t hog the stage.
49. No phase of sleep can be accessed without first passing through this important and beneficial portal[Stage 2]. What is most important to remember is that the first time we enter Stage 2 in a cycle is also the longest, whether we’re napping or sleeping. It takes a minimum of 17 minutes before we can transition to our first SWS episode. This dependable phenomenon forms the basis of what is commonly known as “the power nap.”
50. The reason this 20-minute wonder leaves you feeling restored and ready to go is that it allows you to reap the benefits of Stage 2 sleep without crossing into SWS and waking up with sleep inertia symptoms (remember, you spend around two to five minutes in Stage 1).
51. Once sleep is underway, each successive appearance of Stage 2 will rarely last longer than eight minutes. In naps longer than 20 minutes, however, you can adjust the proportions of SWS and REM, depending on what time you wake up in the morning and what time you take your nap.
52. I’m often asked if a nap during the day will interfere with nocturnal sleep. The answer is a definite no.
53. Studies indicate that in a number of cases napping actually improves the ability to sleep at night.
54. After two cycles of sleep(or three hours) you will begin to cut into your nocturnal sleep, since periods of this length disrupt
your biologically programmed biphasic pattern.
55. As a rule of thumb, you can count on naps earlier in the day to be richer in REM, while late afternoon naps tend to be higher in SWS.
56. The preventive nap. This is the nap we take in anticipation of an extended period of sleeplessness. Preventive naps
work to extend a period of alertness and stamina and serve to stave off symptoms of fatigue.
57. A preventive nap is better than a recovery nap since one sleep deprivation sets in, you make your sleep work harder.
58. Hypnogogia refers to the hallucinatory state called sleep-onset dreaming that people enter into when falling asleep. In this state, dreamlike thoughts begin to mix with ideas of the day. The subconscious mind has free reign, which is why it's often used as a tool by lucid dreamers, creative thinkers and mystic seekers.