Week 3 (SLEEP)
1. Describe the stages of sleep and age-related differences
2. Explain the concepts of sleep timing, social factors, diurnal preference, and
chronotype.
3. Report the criteria of all sleeping disorders described in the DSM V
(Hypersomnolence disorder, Narcolepsy, Central sleep apnea, Sleep-related
hypoventilation, Circadian rhythm sleep-wake disorders, Non–rapid eye movement
(NREM) sleep arousal disorders, Nightmare disorder, Rapid eye movement (REM)
sleep behavior disorder, Restless legs syndrome, Substance/medication-induced
sleep disorder)
4. Report in-depth knowledge of all aspects of Insomnia disorder and Obstructive sleep
apnea-hypopnea, as described in the DSM V
5. Describe the most common sleep disorders and possible treatments in children
6. Describe the most common sleep disorders and possible treatments in adults/elderly
7. Report the associations between screen time and sleep in children and adolescents
and the limitations of currents studies
Source: Chapter 2 – Normal Human Sleep: An Overview. Mary A. Carskadon, William C.
Dement
Abstract
Normal human sleep comprises two states—rapid eye movement (REM) and non–REM
(NREM) sleep— that alternate cyclically across a sleep episode. State characteristics are well
defined: NREM sleep includes a variably synchronous cortical electroencephalogram (EEG;
including sleep spindles, K- complexes, and slow waves) associated with low muscle tonus
and minimal psychological activity; the REM sleep EEG is desynchronized, muscles are
atonic, and dreaming is typical. A nightly pattern of sleep in mature humans sleeping on a
regular schedule includes several reliable characteristics: Sleep begins in NREM and
progresses through deeper NREM stages (stages 2, 3, and 4 using the classic definitions, or
stages N2 and N3 using the updated definitions) before the first episode of REM sleep
occurs approximately 80 to 100 minutes later. Thereafter, NREM sleep and REM sleep cycle
with a period of approximately 90 minutes. NREM stages 3 and 4 (or stage N3) concentrate
in the early NREM cycles, and REM sleep episodes lengthen across the night.
Age-related changes are also predictable: Newborn humans enter REM sleep (called active
sleep) before NREM (called quiet sleep) and have a shorter sleep cycle (approximately 50
minutes); coherent sleep stages emerge as the brain matures during the first year. At birth,
active sleep is approximately 50% of total sleep and declines over the first 2 years to
approximately 20% to 25%. NREM sleep slow waves are not present at birth but emerge in
the first 2 years. Slow-wave sleep (stages 3 and 4) decreases across adolescence by 40%
from preteen years and continues a slower decline into old age, particularly in men and less
so in women. REM sleep as a percentage of total sleep is approximately 20% to 25% across
childhood, adolescence, adulthood, and into old age except in dementia. Other factors
predictably alter sleep, such as previous sleep-wake history (e.g., homeostatic load), phase
of the circadian timing system, ambient temperature, drugs, and sleep disorders.
Sleep Definitions
Sleep is a reversible behavioral state of perceptual disengagement from and
unresponsiveness to the environment.
,It is also true that sleep is a complex amalgam of physiologic and behavioral processes.
Sleep is typically (but not necessarily) accompanied by postural recumbence, behavioral
quiescence, closed eyes, and all the other indicators one commonly associates with
sleeping.
In the unusual circumstance, other behaviors can occur during sleep. These behaviors can
include sleepwalking, sleep talking, teeth grinding, and other physical activities. Anomalies
involving sleep processes also include intrusions of sleep—sleep itself, dream imagery, or
muscle weakness—into wakefulness, for example.
Side note: N for NREM sleep stages and R for REM sleep stages, N1 and N2 are used instead
of stage 1 and stage 2; N3 is used to indicate the sum of stage 3 and stage 4 (often called
slow-wave sleep in human literature); R is used to name REM sleep
Within sleep, two separate states have been defined on the basis of a constellation
of physiologic parameters. These two states, rapid eye movement (REM) and non-
REM (NREM), exist in virtually all mammals and birds yet studied, and they are as
distinct from one another as each is from wakefulness.
NREM (pronounced “non-REM”) sleep is conventionally subdivided into four stages
defined along one measurement axis, the
electroencephalogram (EEG). The EEG pattern
in NREM sleep is commonly described as
synchronous, with such characteristic
waveforms as sleep spindles, K-complexes,
and high-voltage slow waves.
The four NREM stages (stages 1, 2, 3, and 4)
roughly parallel a depth-of-sleep continuum,
with arousal thresholds generally lowest in
stage 1 and highest in stage 4 sleep. NREM
sleep is usually associated with minimal or
fragmentary mental activity. A shorthand
definition of NREM sleep is a relatively inactive
yet actively regulating brain in a movable body.
REM sleep, by contrast, is defined by EEG activation, muscle atonia, and episodic
bursts of rapid eye movements. REM
sleep usually is not divided into stages,
although tonic and phasic types of REM
sleep are occasionally distinguished for
certain research purposes. The distinction
of tonic versus phasic is based on short-
lived events such as eye movements that
tend to occur in clusters separated by
episodes of relative quiescence.
The most commonly used marker of REM
sleep phasic activity in human beings is, of course, the bursts of rapid eye
movements; muscle twitches and cardiorespiratory irregularities often accompany
the REM bursts. The mental activity of human REM sleep is associated with
dreaming, based on vivid dream recall reported after approximately 80% of arousals
from this state of sleep.
, Inhibition of spinal motor neurons by brainstem mechanisms mediates suppression
of postural motor tonus in REM sleep. A shorthand definition of REM sleep,
therefore, is an activated brain in a paralyzed body.
Sleep Onset
The onset of sleep under normal circumstances in normal adult humans is through NREM
sleep. This fundamental principle of normal human sleep reflects a highly reliable finding
and is important in considering normal versus pathologic sleep. For example, the abnormal
entry into sleep through REM sleep can be a diagnostic sign in adult patients with
narcolepsy.
Definition of Sleep Onset
The precise definition of the onset of sleep has been a topic of debate, primarily because
there is no single measure that is 100% clear-cut 100% of the time. For example, a change in
EEG pattern is not always associated with a person's perception of sleep, yet even when
subjects report that they are still awake, clear behavioral changes can indicate the presence
of sleep.
Electromyogram
The electromyogram (EMG) may show a gradual diminution of muscle tonus as sleep
approaches, but rarely does a discrete EMG change pinpoint sleep onset. Furthermore, the
pre-sleep level of the EMG, particularly if
the person is relaxed, can be entirely
indistinguishable from that of unequivocal
sleep.
Electrooculogram
As sleep approaches, the electrooculogram
(EOG) shows slow, possibly asynchronous
eye movements that usually disappear
within several minutes of the EEG changes
described next. Occasionally, the onset of
these slow eye movements coincides with
a person's perceived sleep onset; more
often, subjects report that they are still awake.
Electroencephalogram
In the simplest circumstance (see Fig. 2-3), the EEG changes from a pattern of clear rhythmic
alpha (8 to 13 cycles per second [cps]) activity, particularly in the occipital region, to a
relatively low-voltage, mixed-frequency pattern (stage 1 sleep). This EEG change usually
occurs seconds to minutes after the start of slow eye movements. With regard to
introspection, the onset of a stage 1 EEG pattern may or may not coincide with perceived
sleep onset. For this reason, a number of investigators require the presence of specific EEG
patterns—the K-complex or sleep spindle (i.e., stage 2 sleep)—to acknowledge sleep onset.
Even these stage 2 EEG patterns,
however, are not unequivocally
associated with perceived sleep. A
further complication is that sleep
onset often does not occur all at
once; instead, there may be a
wavering of vigilance before
, “unequivocal” sleep ensues (Fig. 2-4). Thus, it is difficult to accept a single variable as
marking sleep onset.
As Davis and colleagues wrote many years ago: Is “falling asleep” a unitary event? Our
observations suggest that it is not. Different functions, such as sensory awareness, memory,
self-consciousness, continuity of logical thought, latency of response to a stimulus, and
alterations in the pattern of brain potentials all go in parallel in a general way, but there are
exceptions to every rule. Nevertheless, a reasonable consensus exists that the EEG change
to stage 1, usually heralded or accompanied by slow eye movements, identifies the
transition to sleep, provided that another EEG sleep pattern does not intervene. One
might not always be able to pinpoint this transition to the millisecond, but it is usually
possible to determine the change reliably within several seconds.
Behavioral Concomitants of Sleep Onset
Simple Behavioral Task
In the first example, volunteers were
asked to tap two switches alternately
at a steady pace. As shown in Figure
2-5, this simple behavior continues
after the onset of slow eye
movements and may persist for
several seconds after the EEG
changes to a stage 1 sleep pattern.
The behavior then ceases, usually to
recur only after the EEG reverts to a
waking pattern. This is an example of
what one may think of as the
simplest kind of “automatic”
behavior pattern. Because such simple behavior can persist past sleep onset and as one
passes in and out of sleep, it might explain how impaired, drowsy drivers are able to
continue down the highway.
Visual Response
A second example of behavioral change at sleep onset derives from an experiment in which
a bright light is placed in front of the subject's eyes, and the subject is asked to respond
when a light flash is seen by pressing a sensitive microswitch taped to the hand. When the
EEG pattern is stage 1 or stage 2 sleep, the response is absent more than 85% of the time.
When volunteers are queried afterward, they report that they did not see the light flash, not
that they saw the flash but the response was inhibited. This is one example of the
perceptual disengagement from the environment that accompanies sleep onset.
Auditory Response
In another sensory domain, the response to sleep onset is examined with a series of tones
played over earphones to a subject who is instructed to respond each time a tone is heard.
One study of this phenomenon showed that reaction times became longer in proximity to
the onset of stage 1 sleep, and responses were absent coincident with a change in EEG to
unequivocal sleep. For responses in both visual and auditory modalities, the return of the
response after its sleep-related disappearance typically requires the resumption of a waking
EEG pattern.
Olfactory Response
