The Promise of Sleep
As
you may have seen mentioned elsewhere on this site, I subscribe to the web site
Audible.com allowing me to download and burn to CD two audio books each month.
The book discussed here, The Promise of Sleep, is
the sort of book I'd probably never read, because reading is a bit of a chore
for me, so it was a pleasure to be able to listen to it.
Below are some of my favorite quotes from it. My hope is that you'll find enough of interest here to take the time to pick up a copy and read it.
Below are a few of the passages I highlighted as I read this book.
Special
Note: I'm still in the process of pulling quotes from this book. You might want
to check this page out again in a couple of days!
Chapter 1: Long Night's Journey into Day
The Definition of Sleep
What is sleep? I define sleep in terms of only two essential features. The first, and by far the most important, is that sleep erects a perceptual wall between the conscious mind and the outside world. The second defining feature of normal sleep is that it is immediately reversible. Even when someone is deeply asleep, intense and persistent stimulation will always awaken the sleeper. If not, the person is not asleep, but unconscious or dead. [page 17]
Chapter 3: Sleep Debt and the Mortgaged Mind
"How Tired Are You? The Multiple Sleep Latency Test
The objective measure of daytime sleepiness that had never before existed was staring us in the face — sleep latency, or the length of time it takes to fall asleep. [page 57]
Mary and I dubbed the new test the Multiple Sleep Latency Test, or MSLT. We arbitrarily decided to measure the speed of falling asleep every two hours during the daytime, and to minimize the possible horrendous boredom of lying in bed awake for long periods, we decided that the maximum duration of a single test would be limited to 20 minutes. [page 58]
We scored the test by noting the number of minutes it took the subject to get to sleep, from 0 to 20. If the person did not fall asleep in 20 minutes, we ended the test and gave him or her a score of 20… Individual sleep latency measurements were taken at 10, 12, 2, 4 and 6 o'clock. [page 59]
We often refer informally to the range of scores from 0 to 5 minutes as the "twilight zone," because in this range, physical and mental reactions often are very impaired. A score of 5 to 10 minutes is borderline, while a score of 10 to 15 indicates a manageable sleep load. A score of 15 to 20 represents excellent alertness. [page 60]
Sleep Debt: Nature's Loan Shark
We use the term "sleep debt" because accumulated lost sleep is like a monetary debt: It must be paid back…Until proven otherwise, it is reasonable and certainly safer to assume that accumulated lost sleep must be paid back hour for hour. [page 60]
People also sometimes ask me if the exact accounting could mean that they are still carrying around sleep debt from all those all-nighters years earlier in college. Wed don't know what happens to sleep debt in the long term. You may have paid off those sleep-deprived periods when you got sick shortly afterward and slept 18 hours at a stretch. Or the brain may lose track of sleep debt accumulated months or years earlier. [page 63]
Arousal: The Mask of Sleep Debt
Because the alertness-sleepiness continuum is a complex function of sleep debt, biological alerting, and environmental stimulation, we are generally very bad judges of our sleep tendency. How likely we are to fall asleep is the combination of two opposing forces: our sleep load minus our level of alerting. We may be so excited or stressed by external stimulation that we don't perceive a huge sleep debt. [page 65]
In population surveys carried out by the National Sleep Foundation, 75 percent of adults said they experience daytime sleepiness and 34 percent said sleepiness interfered with their daytime activities. [page 65]
Likewise, we cannot feel sleepy in the daytime if we do not have a sleep debt, but we may not feel sleepy if we are doing something that excites us. If we have a very strong tendency to fall asleep and we reduce the stimuli that are keeping us awake, we will very soon begin to feel sleepy and will inevitably fall asleep, intentionally or otherwise. [page 67] [JE: This is why someone sleep deprived might fall asleep in a boring meeting.]
When the [test] subjects were given the low dose of alcohol after the 8-hour [sleep] schedule, they became slightly more sleepy than when given placebo. After the schedule of 2 nights with little sleep, the exact same dose of alcohol the next morning made them severely sleepy, barely able to stay awake. However, the exact same dose of alcohol after 10 hours of sleep every night for a week had no discernible effect. In other words, alcohol may not be a potent sedative by itself, but it becomes very sedating when paired with sleep debt. [page 68]
A fact little known by the public at large is that in nearly every accident linked to alcohol consumption, sleep debt almost certainly plays a major role. [page 68]
…a small amount of sleep debt is good, indeed is necessary, for sleeping efficiently. As [test] subjects sleep debt was paid back, it took them longer and longer to fall asleep. Furthermore, as their sleep debt became very low, the subjects tended to wake up in the middle of the [night] and like awake for 4 hours until they accumulated sufficient debt to fall asleep again. Most likely we need [some] sleep debt…in order to fall asleep in 5 or 10 minutes and sleep through the night. [page 71]
In an experiment mentioned earlier, Roth and crew tested the mental performance of some of his subjects who had scored near zero on the MSLT. Then they required the subjects to spend 10 hours in bed for seven consecutive nights in order to pay off their debts. Afterward the subjects were retested. Low and behold, their mental performance improved. The results showed a direct correlation between the quality of mental performance and the level of sleep debt. What this means to me is that millions of us are living a less than optimal life and performing at less than optimal level, impaired by an amount of sleep debt that we're not even aware we carry.
Chapter 4: The Human Animal and the Biological Clock
Over millions of years, our bodies have developed a remarkably precise biological clock that ticks like a metronome to regulate sleeping and waking. From my personal perspective, by far the most important function of this biological clock is that it is a major determinant of our daily cycle of sleep and wakefulness. [page 75]
Our understanding of both clock-dependent alerting and sleep debt has provided the pillars for a very simple and elegant model of what governs why we are awake during the day and asleep at night; in fact, it can further account for periods of alertness or drowsiness whenever they occur. [page 76]
This was a stunning result, because it meant not only that the biological clock is not necessary for sleep, but that it normally promotes wakefulness and actively opposes sleep. In faact, we could conclude that the only role played by the biological clock in our daily cycle is to promote and maintain alert wakefulness. Furthermore, this role is expressed only at certain times. The Stanford group has designated this profound function as clock-dependent alerting. At certain times each day, our brains are powerfully stimulated by our biological clocks. At other times, the stimulation subsides or is turned off. [page 79]
...the clock-dependent alerting process is active in the daytime and inactive at night, with lowered activity in the early afternoon. In summary, the main reason we do not fall asleep as soon as we have been awake for a few hours is that the homeostatic sleep drive is strongly held at bay by the independent internal stimulation of the biological clock. [page 80]
[The] Stanford group postulate that the daytime clock-dependent alerting occurs in two waves, one in the morning (starting when you wake up) and the other late in the day (starting typically in the late afternoon, around 4:00 or 5:00 P.M.). We further postulate that clock-dependent alerting is substantially stronger during the evening period than in the morning. [page 81]
In early afternoon, between the two peaks of heightened clock-dependent alerting, the clock slacks off in its efforts to keep us awake. The result is drowsiness, which most people wrongly attribute to the aftereffects of eating lunch. In reality, people are only feeling their accumulated sleep debt, unopposed by clock-dependent alerting. Some of us completely "bottom out" during this time. In many cultures, people cope with this early-afternoon dip by retiring immediately after lunch for an afternoon nap. [page 81]