Sleep – Unit 4 AOS 1

Sleep

A regularly occurring altered state of consciousness characterised by reduced awareness and unique brain-wave patterns.

Consciousness

Awareness of internal and external stimuli, existing on a continuum from focused wakefulness to deep sleep.

Normal Waking Consciousness (NWC)

The state of being awake and aware of one’s thoughts, feelings and environment.

Altered State of Consciousness (ASC)

Any state distinctly different from NWC in awareness, thinking, emotions or self-control.

Naturally Occurring ASC

An altered state that happens without external aid, e.g., sleep, dreaming, daydreaming.

Induced ASC

An altered state intentionally produced by aids such as drugs, meditation or hypnosis.

Psychological Construct

A concept created to describe processes that are inferred from behaviour or measurements but not directly observable.

Electroencephalography (EEG)

Technique that detects, amplifies and records electrical activity of the brain via scalp electrodes.

Electromyography (EMG)

Recording of electrical activity of muscles to monitor changes in movement and tone during sleep.

Electro-oculargraphy (EOG)

Method for measuring eye movements by tracking electrical activity of eye muscles.

Sleep Diary

A self-report log of sleep and waking activities kept over several days to assess sleep patterns.

Video Monitoring

Visual recording of a sleeper to observe posture, movements, breathing or parasomnias.

Brain Waves

Rhythmic electrical impulses of the brain, measured in frequency and amplitude.

Beta Waves

High-frequency, low-amplitude brain waves typical of alert wakefulness and REM dreaming.

Alpha Waves

Moderate-frequency brain waves present during relaxed wakefulness with closed eyes.

Theta Waves

Medium-frequency waves associated with drowsiness, early sleep (N1) and creative wake states.

Delta Waves

Low-frequency, high-amplitude waves dominant in deep NREM stage 3 sleep.

Circadian Rhythm

A biological cycle lasting about 24 hours, e.g., the sleep–wake cycle.

Ultradian Rhythm

A biological cycle shorter than 24 hours, such as the 90-minute sleep cycle.

Suprachiasmatic Nucleus (SCN)

‘Master clock’ in the hypothalamus that regulates circadian rhythms using light information.

Melatonin

Hormone from the pineal gland that promotes sleepiness; secretion peaks at night.

REM Sleep

Rapid Eye Movement sleep with brain activity resembling wakefulness and muscle atonia; most dreaming occurs here.

NREM Sleep

Non-Rapid Eye Movement sleep comprising stages 1-3, with progressively deeper physiological relaxation.

Sleep Cycle

A roughly 90-minute sequence of NREM followed by REM sleep that repeats through the night.

Hypnogram

Graphical representation of sleep stages across a sleep episode.

Sleep Onset

Transition from wakefulness to sleep; often begins with NREM stage 1.

Sleep Latency

The time taken to fall asleep after intending to sleep.

NREM Stage 1 (N1)

Light sleep lasting 1–7 minutes; easily awakened; may include hypnic jerks.

NREM Stage 2 (N2)

Moderate sleep marked by sleep spindles and K-complexes; forms about 50% of total sleep.

NREM Stage 3 (N3)

Deep sleep dominated by delta waves; highest arousal threshold; critical for restoration.

Sleep Inertia

Grogginess and impaired performance immediately after waking, especially from deep sleep.

Partial Sleep Deprivation

Getting less sleep (quantity or quality) than needed over one or more nights.

Total Sleep Deprivation

Going without any sleep for 24 hours or longer.

Sleep Debt

Cumulative loss of sleep that must be ‘repaid’ to return to baseline functioning.

Affective Functioning

The ability to regulate and express emotions, impacting mood, emotional reactivity, and social interactions; often impaired by sleep deprivation.