Sleep
Sleep as an altered state of consciousness: purpose, characteristics and patterns of the stages of
sleep including rapid eye movement (REM) and the non-rapid eye movement (NREM) stages of
sleep.
Sleep: a regularly occurring altered state of consciousness that typically occurs spontaneously and is primarily
characterised by a loss of consciousness that typically occurs spontaneously and is primarily characterised by a loss
of conscious awareness.
The purpose of sleep
1. Restoration theory: this theory proposes that sleep is necessary to give the body and mind time to repair
and replenish. NREM sleep restores the body and REM sleep restores the mind.
2. Survival theory: this theory proposes that sleep is necessary to aid survival. Species sleep at times when they
are least vulnerable to attack from predators. Also known as ‘adaptive theory’.
Characteristics of sleep
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There are two types of sleep: Non-rapid eye movement (NREM) and Rapid Eye Movement (REM).
NREM sleep has four stages, ranging from being drowsy and in a light sleep in Stage 1, through to deep sleep
in Stage 4. Physiological functioning slows down during NREM sleep.
REM sleep is associated with dreaming and shows a marked increase in physiological functions, however the
muscles of the body are paralysed.
A sleep cycle consists of both NREM and REM sleep and lasts approximately 90 minutes. As the night’s sleep
progresses, there is an increase in REM sleep and decrease in NREM sleep.
 Activity 2.4 (page 40) Student Activity Manual
 Activity 2.5 (page 43) Student Activity Manual
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Non-rapid Eye Movement (NREM) Sleep
NREM sleep is a dreamless sleep, where heart rate and breathing decrease and muscle tension decreases as well.
NREM sleep consists of four distinct stages.
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Stage 1: The lightest stage of sleep that lasts for approximately 2-10 minutes. We are easily awakened from
this stage. Heart rate and breathing start to slow down and muscles relax. As the muscles relax, hypnic jerks
may occur. Hypnic jerks are muscle spasms (contractions) that can wake a person from stage 1 sleep. Brain
waves begin to slow and change from alpha to theta waves.
Stage 2: As sleep deepens, heart rate and breathing continue to slow, muscles continue to relax and body
temperature decreases. In stage 2 it is still relatively easy to wake a person from sleep. Theta brain waves
are dominant and sleep spindles (bursts of high frequency brainwaves) and K-complexes (bursts of high
amplitude brainwaves) can be seen. Stage 2 lasts for approximately 20-30 minutes and accounts for 50% of
total sleep time.
Stage 3: This stage lasts for approximately 3-10 minutes and is the transition in deep sleep (slow wave
sleep). Heart rate and breathing is slow and regular and muscles are relaxed. It is much more difficult to
wake a person. Delta waves begin to replace theta waves.
Stage 4: This stage lasts for approximately 20-30 minutes, but this shortens as the night progresses.
Brainwaves are almost exclusively delta waves and it is very difficult to wake a person in this stage and they
will be disoriented for several minutes upon waking.
During stages 3 and 4 of NREM sleep, sleepwalking and night terrors can occur. Sleep talking can occur during any of
the stages.
Rapid Eye Movement (REM) Sleep
REM sleep is at the end of the first cycle of sleep. During the stage the eyeballs can be observed moving around in a
rapid, jerky manner. Brainwaves are a saw-tooth pattern that closely resembles beta waves. Therefore it appears as
if the person may be awake.
Physiologically, heart rate and breathing increase and arousal of the genitalia occurs. However, muscles are in a state
of paralysis. Internally the body is highly active, while externally it appears there is no activity going on.
During REM sleep, dreaming occurs and these periods increase in frequency as the night progresses. REM sleep is
vital for restoring the mind and is important in the consolidation and storage of memories.
Initially REM sleep may last for a couple of minutes, but by the last sleep cycle of the night, REM sleep may last up to
an hour.
Differences between NREM and REM Sleep
NREM Sleep
REM Sleep
Eye Movements
Non-rapid eye movements
Rapid, jerky eye movements
Brainwaves
Alpha to delta waves
Beta-like waves
Physiological Arousal
Decreases
Increases
Muscles
Hypnic jerks and some small
movements
Atonia – muscle paralysis
Dreams
Not common
Common
Duration
Decreases as the night
progresses
Increases as the night
progresses
Purpose of sleep
Restores the body
Restores the mind
 Activity 2.6 (page 44) Student Activity Manual
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Methods used to study the level of alertness in normal waking consciousness and the
stages of sleep:
– measurement of physiological responses including electroencephal ograph (EEG),
electrooculargraph (EOG), heart rate and, body temperature
Electroencephalograph (EEG)
EEG: Detects amplifies and records the electrical activity of the brain in the form of brainwaves.
There are four distinct brainwave patterns that we go through form being awake and alert to dreaming. These
brainwave patterns are called Alpha, Beta, Theta and Delta.
Brainwaves are described using frequency and amplitude.
Alpha waves: medium frequency, low amplitude
Beta waves: High frequency, low amplitude
Theta waves: medium frequency, medium amplitude
Delta waves: low frequency, high amplitude
The frequency is used to describe the number of brainwaves per second. Beta, for example, is high frequency as the
brain is very active.
The amplitude is used to describe the intensity (height) of the brainwaves. Delta, for example, is high amplitude.
Stage of sleep and brainwave patterns.
Stage of Sleep
Type of brainwave
Awake and alert
Beta waves
Awake and resting
Alpha waves
Stage1 NREM
Alpha and theta waves
Stage 2 NREM
Theta waves
Stage 3 NREM
Theta and delta waves
Stage 4 NREM
Delta waves
REM
Beta-like waves (saw-tooth)
Electroocularograph (EOG)
EOG: detects, amplifies and records the electrical activity of the muscles that control eye movements.
As a person progresses through stages 1-4 of NREM sleep, the EOG would record a decrease in electrical activity (less
movement of the muscles controlling the eye).
When a person goes into REM sleep, the EOG would record a high level of electrical activity (increase movement of
the muscles controlling the eye).
Electromyograph (EMG)
EMG: detects, amplifies and records the electrical activity of muscles.
As sleep progresses the muscles relax, recording less activity, until REM sleep where there is little to no activity at all.
 Activity 2.7 (page 46) Student Activity Manual
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Heart rate and body temperature
Heart rate and body temperature both decrease as sleep progresses. However, as a person enters REM sleep there
can be a sharp increase in heart rate.
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Methods used to study the level of alertness in normal waking consciousness and the
stages of sleep:
– the use of sleep laboratories, video monitoring and self reports
Sleep Laboratory: a place used for scientific research on sleep.
A sleep lab usually resembles a bedroom. The participant stays one or more nights and connected to devices such as
the EEG, EOG and EMG. Heart rate and body temperature may also be recorded. Video monitoring is also used and
researchers can observe the participant from another room as well.
A sleep lab enables researchers to control sleeping conditions to identify sleep difficulties or sleep phenomena.
Video monitoring: cameras, usually infrared, record the person during sleep for analysis.
Video monitoring can be used in sleep labs or by people at home to monitor sleep patterns and difficulties with
sleep.
Self-reports: statements and answers to questions made by the participants concerning their thoughts and feelings.
Self-reports can be in the form of questionnaires, diary entries or interviews.
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