Sleep and Dreams

Biological rhythms

Natural cycles of bodily processes regulated by the body’s internal clock.

Circadian rhythm

A biological rhythm that repeats approximately every 24 hours such as the sleep-wake cycle.

Ultradian rhythm

A biological rhythm that repeats more than once in 24 hours such as the cycle of nREM and REM sleep.

Sleep-wake cycle

The daily pattern of sleeping and being awake.

nREM sleep

Non-rapid eye movement sleep characterised by slower brain activity and reduced but present muscle tension.

nREM sleep proportion

Approximately 75–80% of total sleep.

REM sleep

Rapid eye movement sleep characterised by high brain activity and temporary muscle paralysis.

REM sleep proportion

Approximately 20–25% of total sleep.

Eye movements during nREM sleep

Little or no eye movement.

Eye movements during REM sleep

Rapid movements of the eyes.

Dreams during nREM sleep

Generally less frequent and less vivid than dreams during REM sleep.

Dreams during REM sleep

Typically vivid and emotional with a story-like structure.

Sleep cycle

A repeating sequence of nREM and REM sleep lasting approximately 90 minutes.

Dreams

Thoughts and feelings alongside images and stories experienced during sleep.

EEG or electroencephalography

A method that records electrical brain activity to distinguish REM and nREM sleep.

EMG or electromyography

A method that measures muscle activity and identifies the loss of muscle tension during REM sleep.

EOG or electrooculography

A method that measures eye movements and detects rapid eye movements during REM sleep.

Dream reporting

A method in which participants describe their dreams after waking.

Qualitative dream data

Descriptive information about the content and experiences of dreams.

Exogenous cues or zeitgebers

External factors that regulate biological rhythms.

Light as a zeitgeber

An external cue that influences the biological clock and reduces melatonin production to promote wakefulness.

Darkness and melatonin

Darkness increases melatonin production and helps promote sleep.

Social cues

Daily routines such as school schedules and meal times that influence the sleep-wake cycle.

Hormones

Chemical substances released by glands into the bloodstream that affect target cells.

Melatonin

A hormone produced by the pineal gland that promotes sleepiness and helps regulate the sleep-wake cycle.

Endogenous pacemakers

Internal mechanisms that regulate biological rhythms.

SCN or suprachiasmatic nucleus

The main biological clock that receives information about light and controls biological rhythms.

Pineal gland

The gland that releases melatonin under the control of signals from the SCN.

Light and sleep regulation pathway

Light information influences the SCN which controls the pineal gland and melatonin release to regulate the sleep-wake cycle.

Jet lag

Psychological and physical effects experienced after travelling rapidly across multiple time zones.

Cause of jet lag

A mismatch between the internal circadian rhythm and local time.

Symptoms of jet lag

Tiredness and difficulty sleeping alongside poor concentration and irritability.

Shift work

Working outside normal daytime hours.

Shift work and circadian rhythms

Working unusual hours disrupts the circadian rhythm and requires sleep at biologically unusual times.

Symptoms associated with shift work

Tiredness and reduced alertness alongside poor concentration and an increased risk of accidents.

Insomnia

Difficulty falling asleep or staying asleep that results in poor-quality or insufficient sleep.

Sleep paralysis

A temporary inability to move while falling asleep or waking despite remaining conscious.

Sleepwalking

Walking or performing activities while asleep that usually occurs during nREM sleep and is often not remembered.

Screen use and sleep

Bright screen light acts as an exogenous cue that can reduce melatonin production and delay sleep.

Restoration theory of sleep

The theory that sleep restores the body and brain after the demands of the day.

Physiological restoration

The restoration of physical bodily functions associated with nREM sleep in the theory.

Psychological restoration

The restoration of mental functions associated with REM sleep in the theory.

nREM sleep and restoration

nREM sleep supports muscle and tissue repair while replenishing energy stores and releasing growth hormone.

REM sleep and restoration

REM sleep supports learning and memory alongside emotional processing and cognitive functioning.

Growth hormone

A hormone released during sleep that supports physical growth and repair.

Amygdala

A structure in the limbic system involved in processing emotions.

Sleep and the amygdala

Adequate sleep helps regulate amygdala activity and supports emotional control.

Sleep deprivation

Insufficient sleep that can impair normal physical and psychological functioning.

Sleep deprivation and emotional reactivity

Lack of sleep can make the amygdala more reactive and make emotional responses harder to regulate.

Infant sleep patterns

Infants sleep for longer each day and spend a greater proportion of sleep in REM than adults.

Adult sleep patterns

Adults sleep for fewer hours and spend a smaller proportion of sleep in REM than infants.

REM sleep and infant development

The higher proportion of REM sleep in infants is linked in the theory to brain development.

Age and sleep patterns

Total sleep time and the proportion of REM sleep generally decrease from infancy to adulthood.

Robinson et al. (2022) aim

To investigate the effects of sleep restriction on emotional functioning.

Robinson et al. method

An experiment in which participants experienced restricted sleep over several nights and completed emotional tasks.

Robinson et al. results

The notes report increased emotional reactivity and greater amygdala activity alongside less effective emotional regulation.

Robinson et al. conclusion

The notes interpret the findings as support for the importance of sleep in restoring psychological functioning and emotional control.

Research support for restoration theory

Studies linking sleep with learning and memory alongside emotional regulation support a restorative role for sleep.

Restoration theory and feeling refreshed

The theory explains why people feel physically and mentally refreshed after sleeping.

Waking rest criticism

Muscle repair also occurs during waking rest so physical restoration is not exclusive to sleep.

Species differences criticism

Restoration theory does not fully explain why different species require very different amounts of sleep.

REM brain activity criticism

High brain activity during REM sleep challenges a simple explanation of sleep as brain rest.

Sleep loss and revision

Missing sleep reduces opportunities for restoration and can impair concentration and memory alongside emotional control.

Sleep and athletic performance

Physical restoration during nREM sleep and psychological restoration during REM sleep support performance.

Repeated sleep loss and irritability

Ongoing sleep loss can increase emotional reactivity and make emotions more difficult to control.