Lecture on Sleep and Circadian Rhythms

Brain Activity During Sleep

• The brain remains active during sleep.
• Sleep is essential for performing normal functions when awake.

Stages of Sleep

• Sleep occurs in approximately 90-minute cycles.
• Four main stages:
  1. N1 (Non-REM 1)
     • Transition between wakefulness and sleep.
     • Brain produces theta waves.
     • Experiences: Hypnagogic hallucinations (e.g., seeing light, hearing a phone ring).
     • Tetris effect: Visual images of repetitive tasks experienced before sleep (e.g., Tetris blocks).
     • Hypnic jerks: Muscle twitches due to a sensation of falling.
  2. N2 (Non-REM 2)
     • Deeper sleep than N1.
     • Presence of theta waves, sleep spindles, and K-complexes.
     • Sleep spindles: May inhibit cognitive processes to maintain tranquility.
     • K-complexes: Suppress cortical arousal, aid memory consolidation.
  3. N3 (Non-REM 3)
     • Also called slow-wave sleep.
     • Characterized by delta waves (0.5 to 2 Hz).
     • Difficult to wake; sleepwalking occurs here.
  4. REM (Rapid Eye Movement) Sleep
     • Eyes move rapidly under lids.
     • Muscle paralysis occurs.
     • Most dreaming occurs here.
     • Known as paradoxical sleep due to active brain but inactive body.

Sleep Cycle

• A complete cycle takes about 90 minutes.
• Order: N1 → N2 → N3 → N2 → REM → N1.
• More N3 in initial sleep hours, more REM before waking.

Circadian Rhythms

• Bodily rhythms over a 24-hour period; internal biological clock.
• Control body temperature and sleep cycle.
• Daylight and artificial light influence circadian rhythms.
  • Adjustments needed during travel due to jet lag.
• Circadian rhythms change with age:
  • Younger individuals often night owls.
  • Older individuals tend to rise and sleep early.

Factors Influencing Sleep Patterns

• Biological clock regulates metabolism, body temperature, and sleep cycles.
• Difficulty in sleeping in on weekends due to adjusted biological clock.