U4 AoS1 Psychology SAC Success Criteria (2026) - SLEEP

what is sleep

sleep is an altered state of consciousness, which is a personal, internal, subjective experience that cannot be directly observed - hence is considered a psychological construct.

What does EEG measure?

An electroencephalograph (EEG) detects, amplifies and records general patterns of electrical activity of the brain.

How is EEG set?

Electrodes attached to the surface of the scalp detect electrical signals from the thousands of neurons that are active in the vicinity of the electrodes and the EEG device averages this activity out.

The EEG then amplifies and translates the activity into a visual pattern called brain waves.

what does the presence of theta brain waves indicate?

That someone is asleep.

what does the presence of delta brain waves indicate?

More delta waves will be present in the deeper stages of sleep.

What does EEG measure in terms of sleep stages?

• REM = HIGH electrical activity (HIGH frequency + low amplitude)

• NREM = lower levels of electrical activity: 

• NREM - 1 (medium frequency + low-medium amplitude) 

• NREM - 2 (medium-low frequency + medium-HIGH amplitude)

• NREM - 3 (low frequency + HIGH amplitude)

What does EOG measure?

An electro-oculography (EOG) detects, amplifies and records the electrical activity of the muscles that control eye movement.

What does EOG measure in terms of sleep stages?

• REM = a high amount of electrical activity in the muscles that control eye movement will be detected by the EOG. 

• NREM = little to no electrical activity in the muscles that control eye movement will be detected by the EOG.

What does EMG measure?

An electromyography (EMG) detects, amplifies and records the electrical activity of muscles. 

What does EMG measure in terms of sleep stages?

• NREM =  moderate or low electrical activity in the muscles will likely be detected by an EMG. 

• REM = very low electrical activity in the muscles will likely be detected by an EMG.

Brain wave patterns

Beta: High frequency, low amplitude
Alpha: Medium-high frequency, medium low amplitude
Theta: medium low frequency, medium-high amplitude
Delta: low frequency, high amplitude.

The role of the circadian rhythm in regulating the sleep-wake patterns

A circadian rhythm is a biological rhythm that involves physiological, psychological and/or behaviour changes that occur as part of a cycle that lasts approximately 24 hours.

what is SCN? Role of the suprachiasmatic nucleus (SCN) in regulating the sleep-wake patterns

The SCN is an area in the hypothalamus.

The SCN can function independently to maintain an approximately 24 hour sleep-wake pattern, however, it is also influenced by external cues (zietgebers)

How is SCN sensitive to zeitgeber light? how does it connect to the release of melatonin?

The SCN is particularly sensitive to the zeitgeber light - it receives information about the amount of incoming light from the retinas in the eyes and adjusts sleep-wake patterns accordingly. 

The SCN sends messages to the pineal gland to secrete more OR less melatonin into the bloodstream. 

what is melatonin? .

Melatonin is a hormone that reduces alertness and induces drowsiness/sleepiness.

Role of melatonin in regulating the sleep-wake patterns - when more light is detected

When more light is detected by neurons in the eyes (retina) this message is sent to the SCN. 

The SCN then sends inhibitory neural messages to the pineal gland to inhibit the release of melatonin into the bloodstream.

This increases wakefulness/alertness

Role of melatonin in regulating the sleep-wake patterns - when less light is detected

When less light is detected the retina this message is sent to the SCN. 

 SCN then sends excitatory neural messages to the pineal gland which stimulates the release of melatonin into the bloodstream.

This decreases alertness AND induces drowsiness/sleepiness.   

I can explain how sleep changes across the lifespan (from a newborn/infant, child, adolescent, adult, to an elderly person) in relation to the total amount of time spent sleeping.

• Infants: 

  • Newborns require 16 hours (50% REM; 50% NREM)

  • Older Infants require 12-14 hours (50 - 20% REM; 50- 80% NREM). 

• Adolescents require 9 hours (20% REM; 80% NREM) 

• Adults require 8 hours (20% REM; 80% NREM).

• Elderly people require 6 hours (20% REM; 80% NREM).

Infants (newborns) - circadian rhythm

Newborn infants do not have an established circadian rhythm & sleeping patterns are erratic.

• They may start their sleep cycle in REM sleep (rather than NREM). 

• Tend to sleep in multiple blocks of time - throughout the day and night.

• Wake up frequently.

Infants (newborns) - how much sleep each stage gets

In the first few weeks of life about 50% of sleep time is spent in REM -  it is unclear why this occurs, however, it is proposed that: 

• REM sleep provides stimulation that is necessary for the maturation of the nervous system/brain.

• Memories and learning may be consolidated during this time. 

• The twitches that occur during newborns REM sleep may help them develop their sensorimotor system, coordinating sensory experiences with motor actions.

Infants- as they get older by about 2-3 months.

By about 2-3 months the circadian rhythm begins to exert its influence, over time this results in:

• Longer periods of sleep at night (however, daytime sleep will also still occur). 

• More regular patterns of NREM-REM sleep emerging.

  • Sleep generally begins at NREM stage 1.

  • The proportion of REM sleep begins to decrease and shifts to the later part of the cycle. 

infants by age 2 years (end of infancy)

• total sleep time has dropped to 12-14 hours 

• REM sleep as a percentage of total sleep is about 20% (with this proportion remaining fairly consistent into old age).  

Children

During childhood total sleep time continues to decrease, this is due a number of biological and social factors, including the dropping of daytime napping, and the introduction of pre-school routines. 

Children: amount of sleep in each stage

• Up until the age of 10 about half of NREM sleep is spent in Stage 3 (deep sleep)  - this can be why young children can be extremely difficult to wake.

• In the first sleep cycle young children may also ‘skip’ their first REM sleep period entirely.

ADOLESCENCE - sleep requirement

By adolescence total sleep time drops to around 9 hours with about 2 hours of this time (20%) spent in REM sleep.

ADOLESCENCE - time spent in sleep stages

Compared to children, sleep episodes begin to more closely resemble that of adults:

• The amount of time spent in NREM Stage 3 (deep) decreases while time spent in NREM Stage 2 increases.

• The REM period on the first cycle is unlikely to be skipped.  

Research indicates the adolescents tend to get less sleep than they need to function at their best - in part this is due to a biological delay in the release of melatonin that results in sleep onset being pushed back 1-2 hours, if waking is not able to be delayed sleep deprivation occurs. 

Adulthood - sleep requirement

Most adults average about 8 hours of sleep at night (20% REM)

• During early adulthood the circadian rhythm is advanced resulting in an earlier sleep onset time than in adolescence.  

• Deep sleep (N3) continues to decrease - between 20 to 60 years of age it drops at a rate of about 2% per decade. 
  

Elderly - sleep requirement

By about age 60 total sleep time averages around 6 hours (20% REM).

Elderly - circadina rhythm and time spent in each stage

• Another circadian advance occurs resulting in a preference for earlier sleep times and earlier awakenings.

• People who are 60+ don’t spend much time in deep sleep (N3) & by age 90 it is rarely experienced at all.

• The elderly also experience more awakenings throughout the night & may find it harder to fall asleep to begin with. 

What is affective, behavioural and cognitive functioning

• affective functioning = a person's experience of their emotions (i.e. mood)

• behavioural functioning = a person’s observable actions  

• cognitive functioning = a person’s mental processes (i.e. thoughts)

Examples of affective effects of partial sleep deprivation (emotions/mood)

• Amplified emotional responses/impaired emotional regulation: emotional responses are faster, more intense or exaggerated.

• increase in negative moods: sadness, anger, hostility, irritability or short temperedness.

• Flattened mood.

Examples of behavioural effects of partial sleep deprivation

• slower performance on tasks

• slower reaction times

• increased clumsiness due to reduced hand eye coordination

• lack of regulation over behaviours (i.e increase in disruptive behaviour)

• increase in risk-taking or impulsive behaviours

• feeling fatigued/tired/excessive sleepiness

• increase in eye closures.

Examples of cognitive effects of partial sleep deprivation

• difficulty paying attention or concentrating

• reduced ability to divide attention

• difficulty processing information

• Difficulty with reasoning & decision making.

• Decreased ability to think rationally & clearly. 

• Memory impairments. 

• Reduction in creative thinking. 

• Distorted perceptions.  

• Problems performing simple monotonous tasks which require sustained attention/concentration (NOTE: more complex tasks are less likely to be affected but can still be impaired).

Partial sleep deprivation

Sleep deprivation = getting inadequate sleep in terms of quantity and/or quality.
normally required or getting poor quality sleep.

• Poor quantity sleep = not getting enough total sleep.

• Poor quality sleep = not enough deep sleep (N3) and/or REM sleep.  

How can u recover form partial sleep deprivation

MOST side effects of partial sleep deprivation are reversed by a single night of uninterrupted sleep.

• Sleep on subsequent nights after sleep deprivation might be longer than usual to recover some of the sleep debt accumulated.

• If you missed out on enough REM sleep you are also likely to experience a REM rebound - a greater amount of REM sleep than normal during the next night of uninterrupted sleep.

Describe the features of a circadian rhythm disorder

sleep disorders in which a person’s circadian rhythm (their internal biologically driven sleep-wake cycle) is disrupted.

• as a result the individual’s internal body clock is no longer in alignment with the external day-night cycle.

• this can lead to excessive sleepiness, insomnia, distress or impairments in a person’s functioning.

Insomnia

an inability to fall asleep, stay asleep, or get back to sleep after waking up too early. 

Bright light therapy

exposing a person to a bright light for a period of time in order to reset their  sleep-wake cycle/circadian rhythms.

Delayed Sleep Phase Syndrome (DSPS)

A circadian rhythm sleep disorder characterised by a delay in the time of sleep onset and awakening.

• The delay is usually 1-2 hours, with a person falling asleep later than what is required/desired & therefor needing to wake up later in order to achieve an adequate amount of sleep. 

DSPS - bright light therapy, how does it work

when using bright light therapy to treat delayed sleep phase syndrome (DSPS) exposure to light should occur in the early morning (6am to 8am)

• this can help reset the sleep-wake cycle by reducing the amount of melatonin released in the morning and inducing wakefulness.

• in turn, this prompts the suprachiasmatic nucleus to trigger the release of melatonin earlier in the evening, advancing sleepiness.

Over several weeks this can shift the circadian rhythm to induce an earlier sleep and wake onset. 

Advanced sleep phase disorder (ASPD)

A circadian rhythm sleep disorder characterised by an advance in the time of sleep onset and awakening.

The advancement is usually 1-2 hours, with a person falling asleep earlier than what is required/desired & therefor waking up earlier in the morning.

ASPD Bright light therapy

When using bright light therapy to treat ASPD exposure to light should occur in the early in the evening. 

• This can result in later melatonin release, to help delay sleep until a more appropriate time later in the evening.

• Over several weeks this can shift the circadian rhythm to delay sleep onset and waking.

what if people with DSPS and ASPD are allowed to sleep all of it?

If people with DSPS & ASPD were allowed to sleep at the time dictated by their body clock sleep deprivation (and its associated side effects) would not occur. 

Shift work

work that takes place outside normal business hours (particularly at night and in the early morning).

Night shift results in a mismatch/misalignment between an individual’s natural sleep-wake cycle (circadian rhythm) and the sleep-wake schedule required for their job.  

By sleeping during the day shift workers tend to experience a reduction in the quantity AND quality of sleep, some will experience shift work sleep disorder (SWSD). 

Shift work sleep disorder (SWSD)

Persistent insomnia and/or excessive sleepiness (causing distress and/or impairment) associated with shift work.

How to minimise the impact of shift work on sleep:

• The sleep environment should be kept dark and quiet.

• The shift worker should avoid daylight between the end of the shift and sleep time - dark sunglasses can help with this. 

• The routine of sleeping during the day should be maintained even on days off to allow the circadian rhythm to adjust (rather than going back and forth).

• New shifts should start at successively later times in the evening/night as it is easier to adjust the circadian rhythm by delaying sleep gradually.

Shift work - bright light therapy

When using bright light therapy to adjust to shift work exposure to light should occur in the evening before a night shift.

• This can help delay the releases of melatonin, helping a person feel more awake during their shift, and then sleepy when the sift is finished in the morning - this enables better sleep* to occur during the day. 

• Over several weeks this can shift the circadian rhythm to be more in line with shift work demands.

Sleep Hygiene

the sleep-related behaviours and environmental conditions that affect sleep.

Zeitgebers

external environmental cues, that can regulate the body’s circadian rhythm.

Daylight

all direct and indirect sunlight.

• When exposed to the natural light from the sun in the course of a typical day, our circadian sleep–wake cycle becomes closely synchronised with sunrise and sunset - keeping us awake during the day and sleeping when it’s dark.

• Exposure to daylight during the morning and early afternoon hours advances the sleep–wake cycle, pushing it forward to a slightly earlier time. 

• Light exposure in the late afternoon and early evening has the opposite effect, delaying the sleep–wake cycle and pushing it back to a later time.

Daylight and its effects on sleep:

It is best to sleep in as much darkness as possible (ideally pitch black). 

Sleeping in daylight, even at a low level (or with a light on), tends to interfere with sleep-cycles and adversely affects sleep quality. 

• It can cause an increase in the duration of NREM stage 1 sleep, decrease the duration of deep sleep & REM sleep, and lead to more frequent arousals.

Simply closing your eyes isn’t effective for preventing light exposure (the eyelids can’t block sufficient light to suppress melatonin production).

• If you are required to sleep in daylight, wearing a close-fitting eye mask can help avoid the effects of light and may improve sleep quality. 

Blue light

a part of the visible light spectrum, it is emitted from smartphones, screens, computer monitors, televisions, LED & fluorescent light bulbs. 

• Blue light enters the eyes and is detected by the SCN, this then sends a message to the pineal gland to delay the production and release of melatonin.  

• This decreases feelings of sleepiness which may result in sleep deprivation (i.e. quantity and quality of sleep may be affected).

Temperature

Your core body temperature (temperature of the body’s internal organs and the blood) follows a 24-hour circadian rhythm which is linked with the sleep–wake cycle. 

• Generally, about two hours before falling asleep, our core body temperature starts to decrease under circadian control, coinciding with the secretion of melatonin.

Room temperature can therefore be used as a zeitgeber to signal and help get the body ready for sleep - the bedroom should be ‘cool’ to promote sleep onset and better quality sleep.

• Research has determined that the ideal room temperature for sleep onset is 19-21 degrees celsius (i.e not to cold but not too hot).  

Eating and drinking patterns

For most people who consume food during the active, day-light phase of the 24-hour cycle the suprachiasmatic nucleus and other peripheral body clocks remain synchronized.

However, if a person begins to alter the timing, amount and composition of their meals to eat/drink more during the inactive, ‘dark phase’ of the 24-hour cycle misalignment occur - over time this can influence the sleep-wake cycle. 

Eating meals within 3-4 hours of sleep onset can negatively affect sleep quantity and quality.  

• Sleep onset can be delayed if our body is still actively digesting food at night instead of resting.

• Digestive processes can also increase awakenings which affects the quality of sleep obtained.