1.5 - Sleep

Sleep and the Brain

• Circadian Rhythm: Our 24-hour biological clock, regulated by the hypothalamus. It controls sleep-wake cycles, body temperature, and other bodily functions.

• Sleep Cycle: Each cycle lasts about 90 minutes and includes different stages of sleep, including REM (rapid eye movement) sleep when most dreaming occurs.

Measuring Sleep: EEG and Brain Waves

• Electroencephalogram (EEG): Records brain waves using electrodes placed on the scalp. Different sleep stages have distinct brain wave patterns:

  • Awake/Alert: Beta waves

  • Relaxed: Alpha waves

  • NREM-1 (Light Sleep): Theta waves

  • NREM-2 (Sleep Spindles): Brief bursts of brain activity

  • NREM-3 (Deep Sleep): Delta waves

Stages of Sleep

1. NREM-1 (Hypnagogic State): Transitional stage, relaxed but not fully asleep. May experience hallucinations.

2. NREM-2: Deeper sleep with sleep spindles (bursts of brain activity).

3. NREM-3 (Deep Sleep): Slow-wave sleep, essential for physical restoration and growth hormone release.

4. REM (Rapid Eye Movement): Brain activity increases, vivid dreams occur, muscles are paralyzed.

Sleep Deprivation: The Consequences

Lack of sleep can lead to:

• Difficulty concentrating and reduced productivity

• Weakened immune system

• Increased risk of accidents

• Mood problems (irritability, anxiety)

• Hallucinations (in extreme cases)

Why Do We Sleep? Theories

• Protection: Sleep kept our ancestors safe from predators at night.

• Restoration: Sleep allows the body and brain to repair and rebuild.

• Memory Consolidation: Sleep helps strengthen and organize memories.

• Activation-Synthesis Theory: Dreams are the brain's attempt to make sense of random neural activity during sleep.

• Growth: The pituitary gland releases growth hormone during sleep, particularly in deep sleep.

Sleep Disorders

• Insomnia: Difficulty falling asleep or staying asleep.

• Narcolepsy: Sudden, uncontrollable sleep attacks, sometimes entering REM sleep directly.

• Night Terrors: Abrupt awakenings with intense fear and panic, usually occurring during deep sleep (NREM-3).

• Sleep Apnea: Repeatedly stopping and starting breathing while asleep.

• Sleepwalking (Somnambulism): Walking or performing complex behaviors while asleep.

• REM Behavior Disorder: Acting out dreams due to a lack of muscle paralysis during REM sleep.