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| âWhat a delightful thing rest is! The bed has become a place of luxury to me. I would not exchange it for all the thrones in the world.â âNapolĂŠon Bonaparte | Cycles, Naps, Dreams, and Nightmares |
A good nightâs sleep should be declared a basic human right. Research is growing nearer to establishing the purpose of sleep. For example, Robert Stickgold (1998), reviewing studies on sleep and memory, points out that among rats, sleep deprivation prevents memory formation. This chapter reviews findings that may be helpful in understanding both what a good nightâs sleep is and how we can manage to get one.
| TOPIC 16.1 | | The Sleep Cycle |
The infant averages 14 hours of sleep, the mature adult 7½ hours, and the senior adult (over 75) averages 6. Before the invention of electric lights, typical adults slept for 9 hours. When all cues to time of day are removed, typical adults will average 10.3 hours of sleep daily, similar to their cousins, the apes and monkeys. However, studies show that the length of sleep is not what causes us to be refreshed upon waking. The key factor is the number of complete sleep cycles we enjoy. Each sleep cycle contains five distinct phases, which exhibit different brain wave patterns (see more in chapter 2):
Pre-sleep: beta waves, or normal alertness.
Phase 1 sleep: alpha waves, the mind at rest, eyes closed, breathing slowed, images beginning to appear; these images can be voluntarily controlledâyou are at this point still conscious.
Phase 2 sleep: theta waves, or light sleep.
Phase 3 sleep: delta waves, or deep sleep.
Phase 4 sleep: rapid eye movement (REM) sleep, or dreaming.
Phase 5 sleep: theta waves, or light sleep, signaling the end of a cycle.
Phases 1â3 together average 65 minutes, followed by an average of 20 minutes for phase 4 (REM) sleep, with phase 5 lasting only 5 minutes on average. For a complete description, see The Mind in Sleep (Arkin, Antrobus, and Ellman, 1978) or Sleep: The Gentle Tyrant (Webb, 1992). For our purposes, it suffices to say that one sleep cycle lasts an average of 90 minutes (see figure 16.1).
Figure 16.1. The Sleep Cycle
If we were to sleep completely naturally, with no alarm clocks or other sleep disturbances, we would wake up, on the average, after a multiple of 90 minutesâfor example, after 4½ hours, 6 hours, 7½ hours, or 9 hours, but not after 7 or 8 hours, which are not multiples of 90 minutes. In the period between cycles we are not actually sleeping; this is a sort of twilight zone from which, if we are not disturbed (by light, cold, a full bladder, noise), we move into another 90-minute cycle. A person who sleeps only four cycles (6 hours) will feel more rested than someone who has slept for 8â10 hours but who has not been allowed to complete any one cycle because of being awakened before it was completed. Within a single individual, cycles can vary by as much as 60 minutes from the shortest cycle to the longest one. For example, someone whose cycles average 90 minutes might experience cycles that vary in length from 60 to 120 minutes. The standard deviation for adult length of sleep is 1 hour, which means that roughly two-thirds of all adults will sleep between 6½ and 8½ hours, based on an average of 7½ hours.
A friend once told me, âAll this stuff about cycles is a bunch of bunk. I wake up every morning when the sun rises.â After talking about his sleep patterns, he discovered that he was self-disciplined in such a way that his bedtime was consistently about 7½ hours before sunrise. He was waking between cycles, and the song of a bird, the cry of a baby, or the pressing of a full bladder could have been equally as effective as the sunrise in waking him. All it takes to awaken someone between cycles, especially if he has had sufficient sleep, is a gentle stimulus.
When my alarm goes off during the last half of my cycle, for a few hours I feel as if a truck has hit me. When it goes off during the first half of my cycle, it is like waking after a 15- to 20-minute nap, and I feel refreshed. Our motor output system from the brain is completely shut down during REM sleep; that is why we dream we are moving but donât actually move and why we feel so lifeless when we wake during REM sleep. Our motor output system hasnât kicked back in yet!
Applications
Keep a sleep journal. Record the beginning and waking times for each natural sleep episode that is uninterrupted by an alarm or any other disturbance. Find the common multiple. For example, if your recorded sleep periods were 400, 500, 400, 200, and 700 minutes, the common multiple is 100, so you would conclude that your personal sleep cycle typically lasts for 100 minutes, or about 1.6 hours.
Once you know the length of your typical sleep cycle (if you havenât kept a journal, you might assume 90 minutes), then, where possible, plan your waking accordingly. For example, my cycle is 90 minutes. If I am ready for bed at 11:00
P.
M. and I know that I must rise at 6:00
A.
M. in order to make a 7:00 breakfast meeting, I read for about 45 minutes to avoid having the alarm go off during the last half of my cycle. Conversely, if I go to bed at midnight, I set my alarm for 6:30
A.
M. and rush to get ready, rather than being interrupted toward the end of my fourth cycle.
In support of waking naturally, William Moorcroft, professor emeritus at Luther College, reported that if we get the same amount of sleep each night, we donât really need an alarm clock, except as a backup (
Sleep, January 1997). Subjects who were asked to visualize their time of waking on an imaginary clock face were generally able to rise at the desired time without an alarm. The key techniques: get the same amount of sleep nightly, choose your own time, visualize before sleep onset, and use a backup (a clock set 15 minutes later than your target rising time).
We all are awake between cycles. However, most of us are not aware of this, because we go straight into the next cycle. When we âwake upâ during the night, it is because some sensory stimulus (e.g., cold, heat, noise, or light) has penetrated our consciousness between cycles. It only
appears that our âsleepâ has been disturbed, when in fact we were not asleep at all. Many people worry about these âinterruptionsâ of sleep. Donât. Realize that being awake between cycles is perfectly normal, and just surrender to your next cycle. As we age, it is even more common to be aware of being awake between cycles. Again, donât let it cause worry, as it is perfectly normal.
For an intriguing description of the biology of sleep, see chapter 5 of John Medinaâs book
The Genetic Inferno (2000).
