Ch 2: 2-Minute Neuroscience: Stages of Sleep

Overview of Sleep Stages Sleep is categorized into four stages based on electrical activity in the brain, measured by an electroencephalogram (EEG). The American Academy of Sleep Medicine defines these stages as follows:

  1. Stage 1: Drowsiness and Light Sleep

    • This is the transition phase when a person begins to fall asleep.

    • EEG shows low-amplitude waves with mixed frequencies, primarily high frequencies. 9

  2. Stage 2: Light Sleep

    • Characterized by sleep spindles (high-frequency wave trains) and K complexes (biphasic waves that stand out on the EEG).

    • This stage marks deeper relaxation compared to Stage 1. 10

  3. Stage 3: Slow-Wave Sleep (Deep Sleep)

    • Dominated by delta waves, which are low-frequency and high-amplitude, making up at least 20% of brain activity.

    • This stage is crucial for overall restfulness and recovery. 11

  4. Rapid Eye Movement (REM) Sleep

    • EEG activity resembles that of Stage 1 or waking state.

    • Muscles are relaxed, and rapid eye movements occur; this is when vivid dreams typically happen. 11

Sleep Cycle

  • A typical sleep cycle lasts about 90-110 minutes, and most people experience 4-5 cycles per night.

  • After REM sleep, individuals may briefly awaken before cycling back through the stages in order. 12

Key Points to Remember

  • Sleep is essential for physical and mental health, with each stage serving unique functions.

  • Understanding these stages can help improve sleep quality and overall well-being.

This guide provides a concise overview of the stages of sleep, their characteristics, and the sleep cycle, making it easier to study and understand the importance of sleep in neuroscience.