Sleep Stages and EEG

• Circadian rhythm is a 24-hour bodily rhythm regulated by the suprachiasmatic nucleus (SCN) in the hypothalamus.
• The SCN responds to morning light, signaling the pineal gland to decrease melatonin production.
• Adenosine buildup during wakefulness increases sleep drive, while sleep reduces adenosine levels.
• Caffeine is an adenosine antagonist.
• DNA damage in neurons during wakefulness also increases sleep pressure, which sleep helps repair.
• Physical or mental activity during the day increases adenosine buildup, leading to more tiredness.

Electroencephalograph (EEG)

• EEG measures electrical activity in the cortex during sleep using electrodes on the scalp.
• Eye movements and muscle tension are also monitored.

Sleep Stages

• A complete sleep cycle lasts approximately 90 minutes.
• Sleep consists of repeating patterns of distinct stages (NREM 1-3 and REM).
• More time is spent in NREM-3 (deep, slow-wave sleep) during the first 3 hours of sleep.
• The latter half of the night includes longer episodes of NREM-2 and REM sleep.
• NREM-1 and NREM-2 are light stages of sleep.
• NREM-3 is a deep sleep stage.
• Most dreaming occurs during REM sleep.
• During REM sleep, an individual experiences paralyzed, zero movement

NREM vs. REM Sleep Characteristics

• REM sleep occurs about five times per night.
• Most dreaming takes place during REM.
• Physiological arousal increases (e.g., heart rate, breathing, genital arousal).
• Sleep paralysis occurs due to the pons blocking motor cortex messages.
• REM sleep behavior disorder involves acting out dreams due to neuron degeneration in the pons.
• REM is paradoxical sleep because body muscles are immobile, but the brain and sympathetic nervous system are active.
• REM is associated with fast brain-wave activity similar to an alert, waking state.
• Several brain areas become active due to increased acetylcholine levels at the onset of REM.
• During REM, the pons shut off motor neurons but send neurons to the motor cortex, visual cortex, amygdala, hippocampus, and brain stem while the prefrontal cortex is off.
• NREM sleep typically makes up about 75-80% of total sleep time.
• NREM has three stages: N1, N2, and N3.

NREM Stage 1 (N1)

• A light transitional sleep occurs as one drifts from wakefulness to sleep.
• Easily disrupted by environmental stimuli.
• Brief muscle twitching or sudden muscle contractions may occur.
• Characterized by theta brain waves (4-7 Hz).
• Typically lasts 5-10 minutes, making up about 5% of total sleep time.

NREM Stage 2 (N2)

• A slightly deeper sleep than N1.
• More difficult to awaken from than N1.
• Characterized by sleep spindles and K-complexes.
• Body temperature decreases and heart rate slows.
• Makes up about 45-55% of total sleep time.

NREM Stage 3 (N3)

• Also known as delta sleep or slow-wave sleep (SWS).
• The deepest and most restorative stage of NREM sleep.
• Characterized by delta waves.
• When sleepwalking or night terrors occur, they typically happen during this stage.
• Critical for physical restoration, immune function, and memory consolidation.
• Makes up about 15-25% of total sleep time.
• The proportion of time spent in each stage changes throughout the night.
• More N3 (deep) sleep occurs in the earlier sleep cycles.
• More REM sleep occurs in the later cycles.

Changing Sleep Cycles

• Stage 1 (Light Sleep): Transition from being awake to falling asleep, lasting a few minutes.
• Stage 2 (Light Sleep): Body temperature drops, the heart rate slows, and relaxation increases; this stage makes up about half of sleep time.
• Stage 3 (Deep Sleep): The most restful stage for body and mind recharge; it is harder to wake up during this time.
• Stage 4 (REM Sleep): Most dreaming occurs; the brain is very active, but muscles are relaxed.
• Each cycle lasts about 90 minutes.
• Early in the night, there is more deep sleep (Stage 3).
• Later on, there is more REM sleep.
• More time is spent in REM as the night goes on.

Insomnia Disorder

• Persistent difficulties with sleep quantity or quality are associated with one or more symptoms:
• Difficulty falling asleep (takes longer than 30 minutes).
• Difficulty maintaining sleep.
• Early-morning awakening with inability to return to sleep.
• Must occur at least 3 nights per week for at least 3 months.
• Often occurs with other psychological disorders.

Hypersomnolence Disorder

• Individuals fall asleep quickly and have good sleep efficiency.
• Excessive nighttime sleep (10-12 hours or more) along with significant difficulty waking up (sleep inertia).
• Excessive daytime sleepiness with long naps (>1hr) nearly every day.
• Sleep is non-restorative.

Circadian Rhythm Sleep-Wake Disorders ('Delayed Sleep Phase Type')

• A persistent inability to fall asleep and awaken at a desired time.
• Often deviates 2-4 hours from the desired sleep and wake-up time.
• Symptoms include sleep-onset insomnia, difficulty waking in the morning, and excessive sleepiness early in the day.
• Individuals often develop maladaptive behaviors (e.g., working, playing games) that further impair sleep.
• Individuals exhibit normal sleep quality and duration when allowed to set their own schedule.

Non-REM Sleep Arousal Disorders

• Symptoms occur during NREM sleep.
• Occur most commonly in childhood and diminish with age.
• Sleep terrors involve recurrent episodes of abrupt terror arousals, beginning with a panicky scream and sitting up in bed with eyes wide open.
• Sleepwalking: An individual has a blank, staring face and is unresponsive to others; can be awakened only with great difficulty and can endure injuries without pain.
• Sleepwalking can be accompanied by sleep talking, eating, or even ‘sexsomnia’ in adults.
• The individual has no memory of the episode in both disorders.

Narcolepsy

• Individuals fall asleep and quickly enter REM sleep.
• Excessive daytime sleepiness and increased need for sleep.
• Recurrent daytime sleep episodes (short naps) mimic REM sleep.
• Cataplexy: Sudden muscular weakness (loss of muscle tone) often triggered by emotion.
• Sleep paralysis: Inability to move when waking from sleep.
• Hypnagogic hallucination: Dreamlike sensations that occur with the onset of sleep (e.g., seeing vivid static images, hearing voices, or feeling weightless).
• People with narcolepsy often have efficiency i orexin (AKA hypocretin; a neuropeptide which typically promotes wakefulness)

Sleep Importance

• Sleep drive increases after strenuous exercise and wakeful activity.
• The pituitary gland releases growth hormone during sleep, especially important for babies and teenagers.
• Sleep is important for immune cell reproduction and improves immune response.
• Sleep restores and repairs the brain.
• Helps reduce DNA damage in neurons.
• Increases the production of new glial cells that form myelin.
• Maintenance of neurons in the hippocampus, amygdala, and prefrontal cortex maintains functionality in those cortical circuits.

Sleep and Memories

• Sleep strengthens neural connections that build enduring memories.
• Sleep before learning enhances the ability to encode new experiences and information.
• Sleep after learning helps consolidate those memories.
• Explicit memories: List of words, material for an upcoming exam.
• Implicit memories: Procedural memories such as playing an instrument or trying to beat a video game.
• Sleep (and dreaming) leads to improved performance.
• Better recall of lists of words, etc.
• Faster, more accurate performance of procedural memories.

Freud's Interpretation of Dreams

• Dreams are the disguised wishes and desires of the unconscious mind.
• Images in dreams (manifest content) are symbols of hidden wishes (latent content).
• Freud’s theory is not falsifiable and lacks scientific support.

Dreams and Their General Content

• Everybody dreams at night, but most are forgotten before waking up.
• Dreams during NREM sleep are often extensions of wakeful experience (‘sleep thinking’).
• Dreams during REM sleep are bizarre and vivid.
• Dreams sometimes include images from frequent experiences or particularly emotional experiences.
• Thoughts, emotions, and worries that precede sleep are most likely to be incorporated into dream content.
• About 80% of dreams include some negative event or emotion.
• Failure dreams include being pursued, attacked, rejected, or having bad luck.