This document contains a summary and elaboration of the learning goals of the first task of the course Sleep and Sleep disorders and can be used to prepare for the tutorial sessions and to study for the exam. The information comes from the recommended reading, which differs from previous years!
Task 1: Quality and Quantity
What are the different sleep stages?
Sleep consists of two main categories:
1. REM = characterized by dreaming, rapid eye movements, loss of muscle tone (muscle atonia),
irregular breathing, and poor thermoregulation.
o The brain waveform during REM sleep has mixed frequency.
2. NREM -> further divided into three stages: Stage 1 (N1), Stage 2 (N2), and Stage 3 (N3)
o Stages N1, N2, and N3 are each characterized and differentiated by unique patterns of
electrical brain activity. They also differ in the ease of being awakened and the likelihood
of being recognized as sleep by a sleeper who is awakened by an experimenter:
Stage N1 is the lightest of the three NREM stages of sleep. It is easy to be
awakened from sleep and when awakened, an individual is least likely of all NREM
sleep stages to perceive having been asleep.
Stage N3 is the deepest sleep stage, and stage 2 is intermediate
The brain activity waveform during N3 is slow (low frequency), which is
why stage N3 is sometimes referred to as slow-wave-sleep
The brain waveform during Stage N2 is characterized by sharp spikes (K-
complexes) as well as short bursts of activity (sleep spindles)
Sleep begins with the lightest of the NREM stages (N1) and proceeds through the NREM sleep stages,
including the deepest stage (N3), until the first REM episode occurs, within an average of 70 min.
The period from the onset of sleep until the first REM episode is the first sleep cycle.
The rest of the night is spent cycling between NREM and REM sleep in a similar fashion
Except for the first cycle, which lasts 70 min, the duration of subsequent cycles is roughly 90
min. Brief awakenings during sleep stage transitions are normal.
How can you measure sleep?
Sleep architecture = the electrophysiological structure of sleep
The objective measurement of the internal structure of sleep is based on a polysomnography
(PSG) recording, which consists of measuring electrical activity of the brain; muscle tones
around the eyes, chin, and legs; and breathing patterns
Objective measures:
PSG is the gold standard”of objective sleep measurement and involves collecting data on
electrical brain activities and muscle tone.
o Collected data informs about aspects of sleep quality: minutes to fall asleep, number of
awakenings, duration of each awakening, total sleep time, and sleep efficiency (defined
as the ratio between the time asleep and the time allocated for sleep).
o The most common clinical use of PSG is for the diagnosis of sleep-related breathing
disorders where PSG also includes measurements of respiration (air flow, snoring, chest
and abdominal movement), sleep position, heart rate, and oxygen saturation.
Another objective method is based on movement of the wrist. A wrist-worn device (actigraph),
which has a very sensitive motion sensor, collects movement data. Validated algorithms are
then used to score each minute as sleep or wakefulness.
o Can give information about total sleep time but not sleep stages. With multiple nights of
recording, actigraphs can also provide information on day-to-day variability in sleep,
which is not feasible with PSG
o Benefits: relatively unobtrusive nature and low cost, relative to PSG.
, Subjective measures encompass sleep diaries, which provide daily sleep data, and sleep
questionnaires, which retrospectively assess sleep behaviors and symptom severity.
Subjective measures are economical and practical, and they yield information that cannot be
captured by objective measurements, such as the refreshing value of sleep, level of distress
about poor sleep, and amount of daytime impairment
Validation studies show good agreement with PSG among healthy sleepers, but lower, yet
acceptable, agreement among individuals with disturbed sleep
Assessing daytime sleepiness is also part of a comprehensive sleep assessment because sleepiness can
constitute a safety risk and because severe sleepiness is a diagnostic symptom of some sleep disorders
Two objective measures are the Multiple Sleep Latency Test (MSLT) and the Maintenance
of Wakefulness Test (MWT).
o MSLT = a measure of physiological sleepiness
Measures sleepiness as defined by the propensity to fall asleep
Consists of 4 or more PSG-monitored daytime nap opportunities, usually 2 hours
apart. Each nap opportunity lasts 20 min.
The MSLT score is the average number of minutes to fall asleep over all nap
opportunities, in which naps that were not associated with sleep are scored as 20
-> a higher MSLT score reflects lower level of sleepiness.
Scores < 5 min are interpreted as an indication of excessive sleepiness
o MWT = a measure of a person’s ability to maintain wakefulness under conditions that
are conducive to sleep (dark, quiet, boring)
Consists of multiple PSG-monitored, 40-min trials, in which the individual is seated
in a dark and quiet room and is instructed to stay awake
The MWT score is the average time to fall asleep across the nap opportunities, in
which naps that were not associated with sleep are scored as 40 -> a higher MWT
score reflects higher level of alertness.
What are recommended sleep durations for different ages?
National Sleep Foundation’s updated sleep duration recommendations: final report –
Hirschkowitz et al.
Appropriate sleep duration ranges vary throughout the life span -> aim study: make recommendations
for daily sleep duration across the life span.
For each age group, every sleep duration from 0-24 hours was evaluated for appropriateness.
o Response options were inappropriate, scores ranging from 1 to 3; uncertain, scores
ranging from 4 to 6; or appropriate, scores ranging from 7 to 9.
Recommendations for sleep duration consider overall health and well-being, as well as cognitive,
emotional, and physical health.
Recommendations:
1. Newborns (0-3 months): 14- to 17-hour sleep
duration (weaker scientific evidence and the
experts’ own experience and/or opinion)
o Regularly sleeping longer than 19 hours
may limit a newborn’s environmental
interaction and may impede cognitive
and/or emotional development
o Sleep duration recommendations for
newborns may not apply during the first
few days of life because long sleep can be normal.
o Rapid maturational changes in sleep patterns occur in newborns, and appropriate sleep
durations may vary widely based on actual age -> during the first few days of life,
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