Unit 1.5: Sleep

What is Consciousness?

Consciousness is our awareness of ourselves and our environment, including thoughts, feelings, sensations, and external stimuli[web:74][web:81].

Consciousness exists on a continuum from high awareness (fully awake and alert) to low awareness (deep sleep or unconsciousness)[web:81].

Levels of Consciousness

Key Point: Sleep is NOT the absence of consciousness—it's a different, altered state where the brain remains active with reduced external awareness[web:74][web:81].

What is Circadian Rhythm?

The circadian rhythm is the body's internal biological clock that operates on an approximately 24-hour cycle, regulating sleep-wake patterns, body temperature, hormone release, and alertness[web:74][web:81].

Key Control Center: The suprachiasmatic nucleus (SCN) in the hypothalamus controls circadian rhythms[web:74].

• Light exposure is the primary cue (zeitgeber) that synchronizes the internal clock with the 24-hour day
• Light → retina → SCN → pineal gland → regulates melatonin production
• Darkness triggers melatonin release → signals sleepiness
• Light suppresses melatonin → promotes wakefulness

Circadian Rhythm Effects on Behavior

Circadian Rhythm Disruptions

Sleep Cycle Structure

Each sleep cycle lasts approximately 90-110 minutes and repeats 4-6 times per night[web:74][web:78][web:81].

Important Pattern: As the night progresses, Stage 3 (deep sleep) decreases while REM sleep increases in duration[web:74][web:78].

Stage 1 NREM: Light Sleep (Transition)

Stage 1 is the lightest phase of sleep, the brief transition from wakefulness to sleep lasting only a few minutes[web:74][web:78][web:81].

Characteristics:

• EEG Pattern: Theta waves (slower brain activity than wakefulness)
• Duration: 1-5 minutes
• Easily awakened from this stage
• Hypnagogic sensations — brief, dream-like images, floating feelings, sudden body jerks (hypnic jerks), or the sensation of falling[web:74][web:81]
• Muscles begin to relax; heartbeat and breathing slow

Stage 2 NREM: Deeper Light Sleep

Stage 2 is a deeper sleep where the body prepares for slow-wave sleep, accounting for about 50% of total sleep time[web:74][web:78][web:81].

Characteristics:

• EEG Pattern: Sleep spindles (brief bursts of rapid brain activity) and K-complexes (large, slow waves)[web:74][web:78]
• Duration: 10-25 minutes in first cycle; increases with each cycle
• Body temperature drops
• Heart rate slows
• Less awareness of surroundings
• Sleep spindles help shield the brain from external disturbances and are important for memory consolidation[web:74]

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

Stage 3 is the deepest NREM sleep stage, also called slow-wave sleep (SWS), where the most restorative physical processes occur[web:74][web:78][web:81].

Characteristics:

• EEG Pattern: Delta waves (slow, high-amplitude brain waves)[web:74][web:78]
• Duration: Longest early in the night; decreases with each cycle
• Very difficult to wake someone in this stage
• If awakened, person feels groggy and disoriented (sleep inertia)
• Physical restoration: Tissue repair, muscle growth, immune system strengthening
• Energy replenishment: Body restores energy reserves
• Hormone release: Growth hormone secretion peaks

Key Functions: Stage 3 is critical for physical health, immune function, and feeling refreshed the next day. Most deep sleep occurs in the first half of the night[web:74][web:81].

Paradoxical Sleep

REM sleep is called "paradoxical sleep" because the brain is highly active (similar to waking EEG patterns) while the body is in its most relaxed state[web:74][web:78][web:81].

Characteristics:

• EEG Pattern: Beta waves (fast, low-amplitude waves similar to wakefulness)[web:74][web:78]
• First REM period: Occurs about 90 minutes after falling asleep
• REM periods lengthen as the night progresses; longest REM occurs in the early morning
• Rapid eye movements under closed eyelids
• Muscle atonia: Temporary paralysis of skeletal muscles prevents acting out dreams[web:74][web:81]
• Vivid, story-like dreams most commonly occur during REM
• Increased heart rate and breathing (can be irregular)

REM Sleep Functions

• Memory consolidation: Especially for procedural (skills) and emotional memories[web:74][web:81]
• Emotional regulation: Processing and integrating emotions from the day
• Brain development: Critical in infancy and childhood for neural connections
• Creative problem-solving: May facilitate insight and novel connections
• Dreaming: Most vivid dreams occur in REM sleep

REM Rebound

REM rebound occurs when someone is deprived of REM sleep (from alcohol, medication, or sleep disruption) and then compensates by spending more time in REM during subsequent sleep periods[web:74][web:81].

The brain prioritizes catching up on lost REM sleep, entering REM more quickly and staying in it longer, demonstrating REM's importance for cognitive and emotional functioning[web:74].

NREM vs. REM Sleep Comparison

1. Restoration Theory

Restoration theory proposes that sleep allows the body and brain to repair and restore themselves after daily wear and tear[web:74][web:81].

Key Ideas:

• Sleep repairs cells and tissues
• Sleep clears metabolic waste from the brain (including toxins that accumulate during waking hours)
• Sleep replenishes energy reserves
• Sleep strengthens the immune system
• Sleep restores neurotransmitter levels

Evidence: Sleep deprivation leads to impaired physical performance, weakened immune response, and cognitive decline[web:74][web:81].

2. Memory Consolidation Theory

Memory consolidation theory suggests that sleep helps the brain organize, process, and store memories from the day[web:74][web:81].

Key Ideas:

• During sleep, the brain replays and reorganizes daily experiences
• Neural pathways are strengthened for important memories
• Unnecessary connections are pruned to increase efficiency
• Information transfers from hippocampus to long-term cortical storage
• Emotions are integrated and regulated

Evidence: Studies show better memory retention and learning after sleep. Sleep deprivation impairs memory formation and recall[web:74][web:81].

3. Evolutionary (Adaptive) Theory

Evolutionary theory proposes that sleep evolved as an adaptive survival mechanism to keep organisms safe from predators during vulnerable nighttime hours[web:76][web:81].

Key Ideas:

• Sleep kept early humans inactive and hidden during darkness when predators were most active
• Sleep conserves energy when food-gathering isn't possible (nighttime)
• Different species have different sleep patterns based on their ecological niche

Example: Prey animals (like rabbits) sleep lightly and briefly; predators (like lions) sleep deeply and longer[web:76].

⚠️ Important Exam Note

Freud's Psychoanalytic Dream Theory (dreams as wish fulfillment, manifest/latent content) is NOT tested on the AP Psychology exam. Only focus on the two theories below[web:74].

1. Activation-Synthesis Theory

The activation-synthesis theory (proposed by Hobson and McCarley) suggests that dreams are the brain's attempt to make sense of random neural firing that occurs during REM sleep[web:74][web:79][web:81].

How It Works:

1. During REM, the brainstem (pons) generates random neural activity
2. The cerebral cortex tries to synthesize this random activity into a coherent narrative
3. The brain creates a story from scattered signals — memories, emotions, sensations
4. This explains why dreams often feel bizarre, illogical, or disjointed

Key Point: Dreams are meaningless — they're just the brain's creative response to random neural noise, not messages from the unconscious[web:74][web:79].

2. Memory Consolidation Theory (Information Processing)

The memory consolidation theory proposes that dreaming serves a purposeful function — helping the brain process, organize, and store daily experiences and emotions[web:74][web:79][web:81].

How It Works:

• Dreams help sort and file information from the day
• Important memories are strengthened; unimportant ones are pruned
• Emotional experiences are processed and integrated
• Dreams act like the brain's overnight filing system

Key Point: Dreams are meaningful — they reflect the brain actively consolidating memories and processing emotions, making sleep essential for learning[web:74][web:79][web:81].

Dream Theory Comparison

⚠️ AP Exam Coverage

The AP Psychology exam covers ONLY these five sleep disorders. Do not study others[web:74].

1. Insomnia

Insomnia is the most common sleep disorder, characterized by persistent difficulty falling asleep, staying asleep, or both[web:74][web:81].

Symptoms:

• Difficulty initiating sleep (taking more than 30 minutes to fall asleep)
• Difficulty maintaining sleep (frequent night awakenings)
• Waking up too early and unable to return to sleep
• Daytime fatigue, irritability, poor concentration

Causes: Stress, anxiety, poor sleep habits, caffeine, screen exposure before bed

Treatment: Cognitive-behavioral therapy (CBT-I), sleep hygiene, relaxation techniques

2. Narcolepsy

Narcolepsy is a neurological disorder characterized by sudden, uncontrollable sleep attacks during the day[web:74][web:81].

Symptoms:

• Excessive daytime sleepiness — overwhelming urge to sleep
• Sleep attacks — falling asleep suddenly and involuntarily (can happen while driving, eating, talking)
• Cataplexy — sudden muscle weakness triggered by strong emotions (laughter, surprise)
• Entering REM sleep abnormally quickly
• Fragmented nighttime sleep

Cause: Low levels of hypocretin (orexin), a brain chemical that regulates wakefulness

Treatment: Stimulant medications, scheduled naps, lifestyle adjustments

3. Sleep Apnea

Sleep apnea is a disorder where breathing repeatedly stops and starts during sleep, causing brief awakenings that disrupt sleep cycles[web:74][web:81].

Symptoms:

• Loud snoring (often noticed by bed partner)
• Pauses in breathing followed by gasping or choking sounds
• Frequent awakenings (person may not remember them)
• Daytime sleepiness despite spending enough time in bed
• Morning headaches, dry mouth

Effects: Fragmented sleep reduces Stage 3 and REM sleep; increases risk of heart disease, stroke, high blood pressure

Treatment: CPAP machine (continuous positive airway pressure), weight loss, oral appliances, surgery

4. REM Sleep Behavior Disorder

REM sleep behavior disorder occurs when the normal muscle atonia (paralysis) during REM sleep is absent, allowing people to physically act out their dreams[web:74][web:81].

Symptoms:

• Acting out dreams — punching, kicking, shouting, flailing arms
• Can injure self or bed partner
• Person usually remembers the dream upon waking
• More common in older adults, particularly men

Cause: Breakdown of brainstem mechanisms that normally paralyze muscles during REM

Treatment: Medications (clonazepam), safety measures (padding bed, removing dangerous objects)

5. Somnambulism (Sleepwalking)

Somnambulism (sleepwalking) involves walking or performing complex behaviors during deep NREM sleep (Stage 3) without conscious awareness[web:74][web:81].

Symptoms:

• Walking during sleep with eyes open but blank expression
• Performing activities (getting dressed, eating, leaving the house)
• Difficult to awaken; if awakened, person is confused and disoriented
• No memory of the episode upon waking
• More common in children (outgrow it in adolescence)

Triggers: Sleep deprivation, stress, fever, medications, irregular sleep schedules

Safety Note: Contrary to myth, it is NOT dangerous to wake a sleepwalker — gently guide them back to bed

Treatment: Improve sleep hygiene, maintain regular sleep schedule, secure environment (lock doors, remove obstacles)

Sleep Disorders Quick Reference

Sleep is essential for learning and memory formation. Both NREM and REM sleep play critical roles in consolidating different types of memories[web:74][web:81].

How Sleep Strengthens Memory:

• The brain replays and reorganizes daily experiences during sleep
• Neural pathways are strengthened for important memories
• Synaptic connections are pruned for unimportant information
• Waste products are cleared from the brain
• Neurotransmitter levels are restored

Effects of Sleep Deprivation

Lack of sleep severely impairs cognitive, emotional, and physical functioning[web:74][web:81].

Cognitive Effects:

• Impaired attention and focus
• Memory problems — difficulty forming new memories and recalling old ones
• Slower reaction time
• Poor decision-making and judgment
• Reduced creativity and problem-solving

Physical & Emotional Effects:

• Weakened immune system — increased illness risk
• Irritability, mood swings
• Increased anxiety and depression
• Weight gain (disrupted hunger hormones)
• Higher risk of accidents and injuries

Study Tip: Research shows it's better to review material and get sleep than to pull an all-nighter before a test. Sleep consolidates what you studied![web:74][web:81]

Multiple Choice Tips

• Master EEG patterns: theta (Stage 1), sleep spindles/K-complexes (Stage 2), delta (Stage 3), beta (REM)[web:74][web:78]
• Know sleep stage functions: Stage 3 = physical restoration, REM = memory consolidation and dreaming[web:74]
• Understand circadian rhythm disruptions: jet lag, shift work, screen exposure effects[web:74]
• Distinguish the five sleep disorders and which sleep stage each affects[web:74][web:81]
• Memorize dream theories: activation-synthesis (random) vs. memory consolidation (purposeful)[web:74][web:79]
• Remember REM rebound: increased REM sleep after deprivation[web:74]

Free Response Question (FRQ) Tips

• Use precise terminology: circadian rhythm, SCN, hypnagogic sensations, muscle atonia, REM rebound[web:74]
• Link sleep stages to functions: explain why Stage 3 is restorative and REM consolidates memories[web:74][web:81]
• Apply sleep theories: describe how restoration, memory consolidation, and evolutionary theories explain sleep's purpose[web:74]
• Explain sleep disorder effects: connect disorders to specific sleep stages and behavioral consequences[web:74][web:81]
• Use real-world examples: jet lag effects, pulling all-nighters, sleep deprivation impacts on performance[web:74]

🔑 The Big Picture

Sleep is an altered state of consciousness regulated by circadian rhythms (24-hour biological clock controlled by the SCN). Sleep cycles through NREM stages (1-3) and REM approximately every 90 minutes. NREM focuses on physical restoration while REM supports memory consolidation, emotional regulation, and dreaming. Dreams may result from random neural firing (activation-synthesis) or serve to consolidate memories. Five sleep disorders (insomnia, narcolepsy, sleep apnea, REM behavior disorder, somnambulism) disrupt healthy sleep and impair daily functioning[web:74][web:81].

💡 Essential Concepts

• Consciousness levels
• Circadian rhythm (24-hour cycle)
• SCN (suprachiasmatic nucleus)
• Melatonin regulation
• Sleep cycle (90 minutes)
• Stage 1: Theta waves, hypnagogic
• Stage 2: Sleep spindles, K-complexes
• Stage 3: Delta waves, deep sleep
• REM: Paradoxical, muscle atonia
• REM rebound
• Restoration theory
• Memory consolidation theory
• Activation-synthesis theory
• Insomnia
• Narcolepsy
• Sleep apnea
• REM behavior disorder
• Somnambulism
• Sleep deprivation effects