Notes on Sleep Measurement, Stages, and Cycles

Sleep Measurement

  • Conducted using polysomnography in sleep laboratories.
  • Measures brain activity (EEG), eye movement (EOG), and muscle activity (EMG).

Brain Activity Monitoring

  • EEG (Electroencephalogram): Measures brain activity; key features are wave shape, frequency (>13 Hz for Beta, 8-13 Hz for Alpha).
  • EOG (Electrooculogram): Records eye movements; changes in voltage reflect movements.
  • EMG (Electromyogram): Detects muscle activity; muscle tension correlates with electrical activity.

EEG Patterns During Wakefulness

  • Beta Waves: Irregular, low-amplitude, >13 Hz - indicates alertness and active thinking.
  • Alpha Waves: Regular, moderate intensity, 8-13 Hz - indicates relaxation.

Sleep Stages

  • NREM Sleep (Stages N1-N3):
    • Stage N1 (NREM 1): Transition phase; characterized by theta waves (4-7 Hz).
    • Stage N2 (NREM 2): Irregular EEG; includes sleep spindles (12-14 Hz) and K complexes.
    • Stage N3 (NREM 3): Deep sleep; characterized by delta waves (<4 Hz).
  • REM Sleep (REMS):
    • Occurs ~80 minutes after falling asleep; characterized by sawtooth waves, rapid eye movement, and muscle paralysis.
    • Involves both increased neuronal activity and loss of muscle tone.

Sleep Cycles

  • Lasts 90-120 minutes; N3 prevails earlier in the night, with REM dominating later.
  • First REM period <10 minutes, final REM may exceed 30 minutes.

Awakening Responses

  • From N3: Difficult to awaken; leads to grogginess.
  • From REM: Easier to awaken; alertness typically follows, often with reports of dreaming.