14.3 Sleep and Dreaming

Sleep is a vital process that cycles through distinct stages, each with unique characteristics and functions. From light NREM sleep to deep slow-wave sleep and vivid REM dreaming, these stages repeat throughout the night, influencing our physical and mental well-being.

Understanding sleep's functions and disorders is crucial for cognitive health. While we slumber, our brains consolidate memories, regulate emotions, and restore physical energy. Sleep disorders can disrupt these processes, impacting our daily functioning and overall quality of life.

Sleep Stages and Characteristics

Stages of sleep cycle

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• Non-REM (NREM) sleep
  • Stage 1 (N1)
    • Light sleep marks transition from wakefulness to sleep lasting ~5-10 minutes
    • Easily awakened by external stimuli (noises, touch)
    • Theta waves (4-7 Hz) appear on EEG indicating decreased alertness
  • Stage 2 (N2)
    • Deeper sleep lasts ~20 minutes, harder to wake up
    • Sleep spindles (brief bursts of rapid brain waves) and K-complexes (sudden sharp waves) appear on EEG
    • Body temperature drops preparing for deeper sleep
  • Stage 3 (N3)
    • Slow-wave sleep (SWS) or deep sleep lasting ~20-40 minutes
    • Delta waves (0.5-4 Hz) dominate EEG indicating slowest brain activity
    • Difficult to awaken, may feel disoriented if woken
• REM sleep
  • Rapid eye movements occur under closed eyelids
  • Brain activity similar to wakefulness with increased glucose metabolism
  • Muscle atonia (temporary paralysis) prevents acting out dreams
  • Vivid dreaming occurs with intense emotional and visual content
• Sleep cycle
  • 90-120 minutes per cycle, varies between individuals
  • Progression through NREM stages to REM, repeats 4-6 times nightly
  • More NREM in early cycles, more REM in later cycles as night progresses

Sleep Functions and Disorders

Functions of sleep

• Memory consolidation strengthens neural connections
  • Transfer information from short-term to long-term memory
  • Slow-wave sleep aids declarative memory (facts, events)
  • REM sleep enhances procedural memory (skills, habits)
• Emotional regulation processes experiences
  • Reduces emotional reactivity to negative stimuli
  • REM sleep consolidates emotional memories, aids in coping
• Physical restoration releases growth hormone
  • Promotes tissue repair and muscle growth during slow-wave sleep
  • Enhances immune system function, increases antibody production
• Cognitive performance improves attention and concentration
  • Enhances problem-solving abilities (insight, creativity)
  • Boosts learning capacity and information retention
• Energy conservation reduces metabolic rate
  • Lowers body temperature, decreases caloric expenditure
  • Allows for energy reallocation to vital processes (cell repair)

Content and significance of dreams

• Activation-synthesis theory (Hobson & McCarley) explains random brain activation
  • Mind creates coherent narratives from neural activity
  • Dreams viewed as byproducts of sleep-related brain processes
• Threat simulation theory (Revonsuo) proposes evolutionary adaptation
  • Dreams rehearse threat-avoidance behaviors in safe environment
  • Prepares individuals for real-life dangers (predators, natural disasters)
• Freudian perspective interprets unconscious desires
  • Manifest content (remembered dream) vs latent content (hidden meaning)
  • Symbolic interpretation (water representing emotions, falling indicating insecurity)
• Cognitive theory reflects waking life concerns
  • Dreams serve problem-solving function for daily issues
  • Aids in emotional processing and regulation of mood
• Content analysis reveals common themes
  • Universal elements (flying, being chased, falling)
  • Cultural influences shape dream content (religious symbols, societal norms)
  • Individual differences based on personal experiences and personality traits

Common sleep disorders

• Insomnia involves difficulty falling or staying asleep
  • Impacts attention, memory, and mood regulation
  • Increases risk of depression, anxiety, and cardiovascular problems
• Sleep apnea causes breathing interruptions
  • Leads to cognitive deficits from oxygen deprivation
  • Increases risk of hypertension, heart disease, and stroke
• Narcolepsy results in excessive daytime sleepiness
  • Causes sudden sleep attacks in inappropriate situations
  • Disrupts nighttime sleep patterns, affects overall sleep quality
• Restless legs syndrome (RLS) creates uncomfortable leg sensations
  • Urge to move legs, especially at night, disrupts sleep onset
  • Leads to sleep disruption and daytime fatigue
• Parasomnias involve abnormal behaviors during sleep
  • Sleepwalking (somnambulism) occurs during NREM sleep
  • Night terrors cause intense fear and screaming
  • REM sleep behavior disorder involves acting out dreams
• Circadian rhythm disorders disrupt sleep-wake cycles
  • Delayed sleep phase syndrome shifts sleep later than desired
  • Advanced sleep phase syndrome causes early sleep and wake times
  • Jet lag and shift work disorder result from schedule changes
• Effects on cognitive functioning impair various abilities
  • Decreases attention span and concentration
  • Reduces working memory capacity and information processing
  • Slows reaction times, affecting driving and task performance
  • Diminishes decision-making abilities and judgment
• Impact on overall well-being affects multiple aspects of health
  • Increases susceptibility to mood disorders (depression, anxiety)
  • Compromises immune function, leading to frequent illnesses
  • Raises likelihood of accidents and injuries due to fatigue
  • Reduces quality of life, affecting work and relationships