Sleep is not one uniform state. Across the night, brain activity changes through distinct stages that can be identified by patterns recorded with an electroencephalogram (EEG). This lesson introduces the basic measures used to describe brain waves and explains the three stages of non-REM sleep.
An EEG records patterns of electrical activity in the brain. Two important features of a brain wave are its frequency and amplitude. Frequency is the number of waves that occur each second and is measured in Hertz (Hz). Amplitude is the height of the wave.
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What are frequency and amplitude in brain-wave descriptions?
Frequency is how many brain waves occur per second and is measured in Hertz (Hz). Amplitude is the height of a brain wave.
What happens during NREM stage 1?
Stage 1 is the transition from wakefulness to sleep. Breathing, heartbeat, muscle tension, and core body temperature decrease; alpha activity gives way to theta activity as the stage continues.
What is a sleep spindle?
A sleep spindle is a brief, rapid burst of higher-frequency brain waves that interrupts the theta activity typical of stage 2 and may support learning and memory.
What is a K-complex?
A K-complex is a very high-amplitude pattern of brain activity associated with stage 2. It may arise in response to environmental stimuli and help the brain respond to them.
Why is NREM stage 3 called slow-wave sleep?
It is dominated by delta waves with very low frequency—less than 3 Hz—and high amplitude. Heart rate and breathing slow markedly, and awakening is difficult.
Quiz questions
Why is REM sleep sometimes called paradoxical sleep?Answer: Its brain activity resembles wakefulness while voluntary muscles are temporarily paralyzed.
What is REM rebound?Answer: Spending more time in REM sleep after a period of REM deprivation.
In Freud’s account of dreams, what is latent content?Answer: The dream’s hidden meaning, distinguished from its remembered storyline.
Which account proposes that dreams reflect events important to the dreamer’s waking life?Answer: Cartwright’s account.
What makes a dream lucid?Answer: The dreamer realizes they are dreaming and may influence the dream.
Based on Psychology 2e by Rose M. Spielman, William J. Jenkins, Marilyn D. Lovett (OpenStax), licensed CC BY 4.0. Adapted into a summary, flashcards and quizzes.