George G. Monroe v. Carolyn W. Colvin
Filing
OPINION ATTACHMENTS. [15-1098]
Natural Patterns of Sleep | Healthy Sleep
Appeal: 15-1098
Doc: 48-2
Filed: 06/16/2016
Pg: 1 of 4
Natural Patterns of Sleep
At a Glance
What is Sleep?
The Characteristics of Sleep
Natural Patterns of Sleep
Sleep Lab
How is Sleep Regulated?
Variations in Sleep
Features on this page
Sleep was once considered an inactive, or passive, state in which both
the body and the brain "turned off" to rest and recuperate from the day's
waking activities.
REM and NREM Sleep
Sleep Patterns Across the Night
Scientists have since found that the brain goes through characteristic
patterns of activity throughout each period of sleep, and that it is
sometimes more active when we're asleep than when we're awake.
Understanding these patterns, and the factors that affect them, may help
in making choices that will lead to better quality sleep.
Waking up to Sleep
Our bodies require sleep in order to maintain proper function and
health. In fact, we are programmed to sleep each night as a means of
restoring our bodies and minds. Two interacting systems—the internal
biological clock and the sleep-wake homeostat—largely determine the
timing of our transitions from wakefulness to sleep and vice versa.
These two factors also explain why, under normal conditions, we
typically stay awake during the day and sleep at night. But what
exactly happens when we drift off to sleep?
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Prior to the era of modern sleep research in the early 1920s,
scientists regarded sleep as an inactive brain state. It was generally
accepted that as night fell and sensory inputs from the environment
diminished, so too did brain function. In essence, scientists thought
that the brain simply shut down during sleep, only to restart again
when morning came.
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In 1929, an invention that enabled scientists to record brain activity
challenged this way of thinking. From recordings known as
electroencephalograms (EEGs), researchers could see that sleep was
a dynamic behavior, one in which the brain was highly active at
times, and not turned off at all. Over time, sleep studies using EEGs
and other instruments that measured eye movements and muscle
activity would reveal two main types of sleep. These were defined by
characteristic electrical patterns in a sleeping person's brain, as well
as the presence or absence of eye movements.
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The two main types of sleep are rapid-eye-movement (REM) sleep
and non-rapid-eye-movement (NREM) sleep. On an EEG, REM sleep,
often called "active sleep," is identifiable by its characteristic
low-amplitude (small), high-frequency (fast) waves and alpha
rhythm, as well as the eye movements for which it is named. Many
sleep experts think that these eye movements are in some way
related to dreams. Typically, when people are awakened from REM
sleep, they report that they had been dreaming, often extremely vivid
and sometimes bizarre dreams. In contrast, people report dreaming
far less frequently when awakened from NREM sleep. Interestingly,
during REM sleep muscles in the arms and legs are temporarily
paralyzed. This is thought to be a neurological barrier that prevents
us from "acting out" our dreams.
NREM sleep can be broken down into three distinct stages: N1, N2,
and N3. In the progression from stage N1 to N3, brain waves become
slower and more synchronized, and the eyes remain still. In stage N3,
the deepest stage of NREM, EEGs reveal high-amplitude (large), lowfrequency (slow) waves and spindles. This stage is referred to as
"deep" or "slow-wave" sleep.
http://healthysleep.med.harvard.edu/healthy/science/what/sleep-patterns-rem-nrem[06/02/2016 1:36:34 PM]
EEGs are used in sleep studies to
monitor brain activity during various
stages of sleep.
An EEG of typical REM sleep.
Natural Patterns of Sleep | Healthy Sleep
Appeal: 15-1098
Doc: 48-2
Filed: 06/16/2016
Pg: 2 of 4
REM and NREM Sleep (1:21)
Dr. Thomas Scammell describes the different stages of
sleep and their characteristics.
watch video
Cycling at Night
In healthy adults, sleep typically begins with NREM sleep. The pattern
of clear rhythmic alpha activity associated with wakefulness gives way
to N1, the first stage of sleep, which is defined by a low-voltage,
mixed-frequency pattern. The transition from wakefulness to N1
occurs seconds to minutes after the start of the slow eye movements
seen when a person first begins to nod off. This first period of N1
typically lasts just one to seven minutes. The second stage, or N2,
which is signaled by sleep spindles and/or K complexes in the EEG
recording, comes next and generally lasts 10 to 25 minutes. As N2
sleep progresses, there is a gradual appearance of the high-voltage,
slow-wave activity characteristic of N3, the third stage of NREM sleep.
This stage, which generally lasts 20 to 40 minutes, is referred to as
"slow-wave," "delta," or "deep" sleep. As NREM sleep progresses, the
brain becomes less responsive to external stimuli, and it becomes
increasingly difficult to awaken an individual from sleep.
EEG recordings showing all three
stages of typical NREM sleep.
Sleep Patterns Across the Night (0:46)
Dr. Thomas Scammell describes the cycles of REM and
NREM sleep that occur throughout the night.
watch video
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Following the N3 stage of sleep, a series of body movements usually
signals an "ascent" to lighter NREM sleep stages. Typically, a 5- to
10-minute period of N2 precedes the initial REM sleep episode. REM
sleep comprises about 20 to 25 percent of total sleep in typical
healthy adults.
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NREM sleep and REM sleep continue to alternate through the night in
a cyclical fashion. Most slow-wave NREM sleep occurs in the first part
of the night; REM sleep episodes, the first of which may last only one
to five minutes, generally become longer through the night. During a
typical night, N3 sleep occupies less time in the second cycle than the
first and may disappear altogether from later cycles. The average
length of the first NREM-REM sleep cycle is between 70 and 100
minutes; the average length of the second and later cycles is about
90 to 120 minutes. The reason for such a specific cycling pattern of
NREM and REM sleep across the night is unknown. Some scientists
speculate that specific sequences of NREM and REM sleep optimize
both physical and mental recuperation as well as some aspects of
memory consolidation that occur during sleep, but this has not been
confirmed.
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Shifting Sleep Patterns
Sleep patterns can be affected by many factors, including age, the
amount of recent sleep or wakefulness, the time of the day or night
relative to an individual’s internal clock, other behaviors prior to sleep
such as exercise, stress, environmental conditions such as
temperature and light, and various chemicals.
For example, for the first year of life, sleep often begins in the REM
state. The cyclical alternation of NREM-REM sleep in newborns is
present from birth but at 50 to 60 minutes is much shorter than the
90-minute cycles that occur in adults. Consolidated nocturnal sleep
and fully developed EEG patterns of the NREM sleep stages emerge
only after two to six months. Slow-wave sleep is greatest in young
children and it decreases steadily with age, even if sleep duration
does not change. This may be related to changes in the structure and
function of the brain.
http://healthysleep.med.harvard.edu/healthy/science/what/sleep-patterns-rem-nrem[06/02/2016 1:36:34 PM]
This hypnogram shows the typical
patterns of REM and NREM sleep
throughout the night.
Natural Patterns of Sleep | Healthy Sleep
Appeal: 15-1098
Doc: 48-2
Filed: 06/16/2016
Pg: 3 of 4
Sleep history—the quantity and quality of an individual’s sleep in
recent days—can also have dramatic effects on sleep patterns.
Repeatedly missing a night’s sleep, an irregular sleep schedule, or
frequent disturbance of sleep can result in a redistribution of sleep
stages, for instance, prolonged and deeper periods of slow-wave
NREM sleep. Drugs may affect sleep stages as well. For example,
alcohol before sleep tends to suppress REM sleep early in the night.
As the alcohol is metabolized later in the night, REM sleep rebounds.
However, awakenings also become more frequent during this time.
To learn more about the many factors that affect sleep patterns, see
External Factors That Influence Sleep.
Daytime Napping
Although it is common for people in many western societies to sleep
in a single consolidated block of about eight hours during the night,
this is by no means the only sleep pattern. In fact, following this
schedule and foregoing an afternoon nap would seem highly abnormal
to many people around the world.
In many cultures, particularly those with roots in tropical regions,
afternoon napping is commonplace and is built into daily routines.
And although the exact timing of naps is not officially scheduled, it is
not uncommon for stores and government offices to close and for
many activities to stop for an hour or two every afternoon.
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Afternoon naptime typically coincides with a brief lag in the body's
internal alerting signal. This signal, which increases throughout the
day to offset the body's increasing drive to sleep, wanes slightly in
mid-afternoon, giving sleep drive a slight edge. Napping also typically
happens during the warmest period of the day and generally follows a
large mid-day meal, which explains why afternoon sleepiness is so
often associated with warm afternoon sun and heavy lunches.
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Afternoon naps for most people typically last between 30 and 60
minutes. Any longer and there is a risk of falling into deep sleep and
having a difficult time waking. Following a nap, having dissipated
some of the accumulated sleep drive, many people report feeling
better able to stay awake and alert in the late afternoon and evening.
This increased alertness typically causes people to go to bed later and
generally to sleep less at night than people who do not take naps.
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According to sleep experts, napping can be a good way for people
who do not sleep well at night to catch up. They do caution, however,
that people with insomnia may make their nighttime sleep problem
worse by sleeping during the day. Otherwise, they generally
recommend naps for people who feel they benefit from them.
To learn more about other patterns associated with sleep, go to the
Sleep Lab
, The Characteristics of Sleep, and Changes in Sleep with
Age.
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This content was last reviewed on December 18, 2007
A resource from the Division of Sleep Medicine at
Harvard Medical School
Produced in partnership with WGBH Educational Foundation
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http://healthysleep.med.harvard.edu/healthy/science/what/sleep-patterns-rem-nrem[06/02/2016 1:36:34 PM]
Daytime napping helps to restore
one’s energy and alertness.
Bookshelf
Aserinsky E, Kleitman N. 1953.
Regularly occurring periods of eye
motility, and concomitant
phenomena, during sleep. Science.
118:273-274.
Iber Ancoli-Israel S, Chesson AL,
Quan SF. 2007. The AASM Manual for
the Scoring of Sleep and Associated
Events: Rules, Terminology and
Technical Specification. American
Academy of Sleep Medicine:
Westchester, IL.
Natural Patterns of Sleep | Healthy Sleep
Appeal: 15-1098
Doc: 48-2
Filed: 06/16/2016
Pg: 4 of 4
Feedback | Credits | Disclosures | Disclaimers | Understanding Sleep
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