Sleep and Consciousness Terms

AP Psychology

Sleep/wake cycle

The natural pattern of alternating sleep and wakefulness that repeats about every 24 hours, controlled by biological and environmental cues (like light and dark).

Circadian rhythm

The body’s internal 24-hour biological clock that regulates sleep, temperature, and other functions.

Disruptions

Things like jet lag or shift work can throw off this rhythm, causing tiredness or trouble concentrating.

EEG (electroencephalogram) – stages of sleep

A machine that records brain waves to show different stages of sleep (from light to deep sleep and REM).

NREM (Non-Rapid Eye Movement) – stages 1–3

The first three stages of sleep before REM.
Stage 1: Light sleep, may include brief images or sensations.

• Stage 2: Deeper sleep, brain waves slow, body relaxes.

• Stage 3: Deepest sleep (slow-wave sleep), important for body recovery.

Hypnagogic sensations

Vivid, dreamlike sensations or jerks that occur as you’re falling asleep (beginning of Stage 1).

REM (Rapid Eye Movement)

Sleep stage where most dreaming happens. Brain is active, eyes move quickly, but body muscles are paralyzed.

Paradoxical sleep

Another name for REM sleep because the brain is active like you’re awake, but your body is still and relaxed (paralyzed).

Dreaming

A sequence of images, emotions, and thoughts that occur mainly during REM sleep.

REM rebound

When a person is deprived of REM sleep, the next time they sleep, they spend more time in REM to make up for it.

Activation-synthesis theory

Dreams are the brain’s attempt to make sense of random neural activity that occurs during sleep.

Information-processing (consolidation) theory

Dreams help us process and store information, organizing memories and experiences from the day.

Insomnia

Ongoing difficulty falling asleep or staying asleep.

Narcolepsy

A disorder where people suddenly fall asleep at unpredictable times.

REM sleep behavior disorder

A condition where the body doesn’t stay paralyzed during REM, causing people to act out their dreams.

Sleep apnea

A disorder where breathing repeatedly stops and starts during sleep, often causing loud snoring or gasping.

Somnambulism (sleepwalking)

Walking or doing other activities while in deep NREM sleep (usually Stage 3).