Chapter 4: Stages of Sleep & Sleep Disorders

Introduction to Sleep Stages and Disorders

This lecture focuses on the detailed stages of sleep, building upon previous discussions about sleep duration and deprivation. It also addresses various sleep disorders, differentiating between normal sleep phenomena and actual medical conditions. The information presented is crucial for understanding an upcoming essay that will cover the hypnagogic state, REM, and Non-REM sleep.

Studying Sleep Stages

• Sleep and dreams are among the most researched topics in psychology, studied for many years.

• Methodology: Researchers utilize Electroencephalograms (EEGs) to monitor brain activity in participants while they sleep, correlating specific brain wave patterns to different sleep stages.

• EEG Patterns: Different EEG patterns such as alpha waves and delta waves are associated with various stages. While identifying specific wave names is not required for the essay, understanding their existence is beneficial.

The Hypnagogic State (Wakefulness)

• Definition: Referred to as "wakefulness" in some contexts, but biologically known as the hypnagogic state. It is considered a state, not a stage, as not everyone consistently experiences it.

• Characteristics:

  • High alertness – individuals can easily hear what is going on and wake up quickly.

  • Common during naps or when first falling asleep, before entering deeper sleep.

• Associated Phenomenon: Hypnic jerks are sudden body jerks experienced while falling asleep in this state. This phenomenon is why the state was historically termed "hypnagogic."

• Terminology Debate: Ongoing research battles exist regarding the nomenclature, with biology often preferring "hypnagogic state" over "wakefulness."

Rapid Eye Movement (REM) Sleep

• Definition: Characterized by rapid eye movement under the eyelids. Crucially, in REM sleep, the brain is as active as if the person is awake.

• Misconception: Despite diagrams sometimes placing it at the bottom, REM is not the deepest stage of sleep. This is a common error, particularly in AI-generated summaries, which the instructor rigorously corrects.

• Dreaming: Over $90\%$ of dreams occur during REM sleep. The active brain state during REM explains why dreaming is so prevalent.

• Dream Research: Studies involve waking participants immediately after observing rapid eye movements (indicating dreaming) and asking them to journal their dreams.

• Duration of Dreams: We do not dream for the entire duration of REM sleep, only when the eyes are actively darting.

Non-REM Sleep

• General Description: During Non-REM sleep, the brain is significantly less active than in REM sleep.

• Stages of Non-REM: There are three distinct stages of Non-REM sleep:

  • Stage 1 Non-REM (Light Sleep): Still relatively light. The remaining dreams (less than $10\%$) may occur in this stage.

  • Stage 2 Non-REM (Bridge Sleep): Acts as a bridge between light and deep sleep. Individuals can feel somewhat rested after this stage. Brain activity shows a mix of low and brief high-frequency waves.

  • Stage 3 Non-REM (Deep Sleep): This is the deepest and most restorative stage of sleep. The brain is minimally active, characterized by high-frequency delta waves. It is extremely difficult to wake someone from Stage 3 Non-REM, and if woken, they may be disoriented or lash out.

    • No Dreaming: Crucially, there should be no dreaming in Stage 3 Non-REM. Dreaming in this stage indicates a sleep disorder.

    • Restoration: Deep sleep is essential for feeling refreshed and avoiding sleep deprivation.

The Sleep Cycle Pattern

• Individuals cycle through wakefulness, Non-REM stages, and REM sleep. The pattern typically moves from wakefulness into lighter Non-REM stages, then deeper into Stage 3 Non-REM, before cycling back up into REM.

• Early Deep Sleep: The majority of deep sleep (Stage 3 Non-REM) occurs early in the sleep cycle, often within the first hour to hour and a half.

• Power Naps: A nap of approximately $20$ minutes is often recommended as a "power nap." This duration allows individuals to reach at least Stage 2 Non-REM without entering deep Stage 3, from which waking can lead to feeling worse (sleep inertia).

• Dream Frequency: On average, people experience $4$ to $6$ dreams per night, potentially totaling up to $2$ hours of dream content, even if most are not remembered.

• Dream Recall: Dreams from the last REM cycle before waking are most commonly remembered.

• REM Duration: REM cycles tend to lengthen towards the end of a sleep period, preparing the body for waking.

Sleep Schedule and Consistency

• Biological Ideal: Maintaining a consistent sleep and wake-up schedule every night is biologically optimal. If consistently adhered to, males may only need approximately $4.5$ to $5$ hours of sleep, and females $5$ to $5.5$ hours, to avoid sleep deprivation.

• Real-world Implications: Most individuals do not maintain such strict consistency, thus requiring longer sleep durations to compensate. Consistent schedules can lead to waking naturally without an alarm.

Stage 3 Non-REM Sleep Disorders

These disorders occur when an individual spends too much time, or experiences unusual activity, in Stage 3 Non-REM sleep, leading to a "dissonance" where the body may exhibit actions typically associated with REM sleep while in deep sleep.

• Sleepwalking (Somnambulism):

  • Cause: Dreaming during Stage 3 Non-REM sleep, when the brain should not be active enough to dream.

  • Characteristics: Individuals act out their dreams, are in a deep sleep state, and generally have no memory of the event the next day. They may follow routines (e.g., walking to the garage) and their sensory nerves still provide some awareness of their surroundings.

  • Safety: The long-held belief was never to wake a sleepwalker due to risks of heart attack or violence. Current understanding is that while you can wake them, it's generally advised against for their safety and yours. Redirecting them gently back to bed is preferred, as waking them abruptly can cause disorientation, panic, or even physical harm.

  • Treatment: Sleep studies can pinpoint prolonged Stage 3 Non-REM. Devices (e.g., bed alarms) can be used to emit subtle waves/pulses to gently disrupt deep sleep without full arousal, breaking the cycle.

• Sleep Talking (Somniloquy - Not a Disorder):

  • Characteristics: Talking during sleep is common and varies by sleep stage. In REM, individuals can form complete sentences; in deeper Non-REM stages, speech becomes more gibberish or single words.

  • Diagnostic Use: The clarity and complexity of speech can indicate how deep someone is in a sleepwalking episode; more garbled speech suggests deeper sleep.

• Nightmares (Not a Disorder):

  • Characteristics: Bad dreams occurring during REM sleep. They are often remembered and can cause distress, sometimes waking the individual.

  • Frequency: Most people have more "sweet dreams" than nightmares. Nightmares are often linked to stressful days and are typically singular per sleep cycle.

• Night Terrors (Pavor Nocturnus):

  • Cause: A nightmare occurring during Stage 3 Non-REM sleep.

  • Characteristics: Individuals may sit up, scream, and appear terrified, but they are still in deep sleep and will not remember the event the next day. Movement is generally confined to the bed or immediate surroundings (e.g., moving to a bathroom), less extensive than sleepwalking. There is a risk of injury if they move or are abruptly woken.

• Enuresis (Bedwetting - Not in all textbooks):

  • Cause: Primarily a Stage 3 Non-REM sleep problem where the brain fails to wake the individual to respond to bladder signals.

  • Other Causes: Can also be due to urological issues (kidney or bladder problems).

  • Prevalence: Common in children, typically resolving as they get older and their brain/body adjust to sleep changes. If it persists past age $7$, medical investigation for urological or persistent sleep-related issues is warranted.

  • Treatment: Specialized mat alarms that detect dampness can trigger a subtle alert, conditioning the child to wake and use the restroom.

• All Stage 3 Non-REM Disorders in Children: These disorders are common in children because their brains and bodies are still adjusting to major sleep pattern changes. Infants spend the majority of their early sleep in REM (essential for brain development and frequent feeding needs), and only consistently hit Stage 3 Non-REM around $18$ months to $2$ years. Most children outgrow these disorders ($80\%$ by adulthood).

Other Sleep Disorders

• Insomnia:

  • Prevalence: The most common sleep problem, and generally the most treatable.

  • Definition: Consistent difficulty falling asleep (sleep onset insomnia) or staying asleep (early awakening insomnia), regardless of exhaustion.

  • Differentiation: It's distinct from occasional sleep difficulties caused by stress or an active mind (where the individual is not truly exhausted).

  • Types & Treatment:

    • Sleep Onset Insomnia: Trouble falling asleep despite feeling exhausted. May be treated with melatonin or other relaxation aids.

    • Early Awakening Insomnia: Falling asleep easily but waking up hours later and being unable to return to sleep. Often requires a sleep study to determine the appropriate timing for time-release medication.

• Narcolepsy:

  • Rarity: Affects only about $1\%$ of the population.

  • Characteristics: Individuals experience sudden, irresistible urges to sleep, transitioning almost instantaneously from wakefulness (or the hypnagogic state) directly into REM sleep. This can happen during any activity.

  • Triggers: Arousal and excitement can often trigger narcoleptic episodes (e.g., observed in dogs when fed or excited).

  • Treatment: Identifying triggers, medication (e.g., low-dose anti-anxiety drugs), and maintaining a very strict, consistent sleep schedule.

• Sleep Apnea:

  • Nature: A respiratory problem, not a brain-activity sleep disorder.

  • Types:

    • Inherited Sleep Apnea: Typically presents in adolescence or early adulthood, often requiring a CPAP machine. A family history is common.

    • Acquired Sleep Apnea: Can develop in older adults due to factors like aging or weight gain, distinct from the inherited form.

  • Analogy: Similar to cardiovascular disease, which has both inherited and environmentally induced forms.

Upcoming Topics

• The next session will involve an in-class activity discussing the accuracy and inaccuracies of videos depicting sleepwalking.

• Further discussion will cover dream content and more details on dream research, leading to the completion of Chapter $4$ and the start of Chapter $5$.