Module 9: Sleep and Dreams

Biological Rhythms and Sleep

• Sleep strengthens the mind and body, impacting the ability to remember information, manage feelings, and survive.

• Recording brain waves and muscle movements, as well as observing and waking sleepers, provides biological insights beyond common sense.

• Even during deep sleep, the perceptual window remains open a crack, allowing ongoing attention to the surrounding environment.

• Electroencephalogram (EEG) recordings confirm that the brain's auditory cortex responds to sound stimuli during sleep.

• Over varying time periods, body and mind fluctuate through biological rhythms:

  • Circadian rhythm: A $24\,\text{hour}$ biological clock roughly synchronizing bodily functions with the daily cycle of day and night.

  • Sleep cycle: A repeating $90\,\text{minute}$ biological cycle traversing distinct sleep stages.

• Body temperature patterns across the circadian cycle:

  • Temperature is lowest at night.

  • Temperature rises steadily after getting out of bed.

  • Grogginess transforms into alertness throughout the morning.

  • Thinking and memory perform at their best near the daily peak in circadian arousal.

• Age and experience alter circadian rhythms:

  • Most $20\,\text{year}$ olds are evening-oriented ("night owls").

  • Older adults tend to be morning-oriented ("early birds").

Sleep Stages and Physiology

• Sleep progresses through distinct stages roughly every $90\,\text{minutes}$.

• Eugene Aserinsky discovered Rapid Eye Movement (REM) sleep.

• Awake State and Non-REM Sleep Stages:

  • Awake but relaxed state: EEG recordings show relatively slow alpha waves while resting in bed with eyes closed.

  • N1 Sleep:

  • The initial transition into sleep marked by slowed breathing and irregular brain waves.

  • Classified as the first stage of non-REM (NREM) sleep.

  • Microsleep episodes lasting around $2\,\text{seconds}$ can occur, posing catastrophic risks when driving.

  • Involves hallucinations—sensory experiences occurring without external sensory stimuli.

  • Involves hypnagogic sensations, such as feelings of falling or floating weightlessly.

  • N2 Sleep:

  • Characterized by deeper relaxation lasting approximately $20\,\text{minutes}$.

  • Defined by periodic sleep spindles—bursts of rapid, rhythmic brain-wave activity that aid memory processing.

  • N3 Sleep:

  • Slow-wave sleep lasting approximately $30\,\text{minutes}$.

  • The brain emits large, slow delta waves, making the sleeper difficult to awaken.

Rapid Eye Movement (REM) Sleep

• Approximately $1\,\text{hour}$ after falling asleep, the sleeper ascends from the initial sleep dive, returning through N2 to enter REM sleep.

• Physiological features during REM sleep:

  • Heart rate increases and breathing becomes rapid and irregular.

  • Every half-minute or so, eyes dart around in momentary bursts of activity, signaling dream onset.

  • REM sleep tricks the brain into responding to dream storylines as if real.

  • Genitals may become aroused during REM sleep regardless of dream content.

  • The motor cortex is active, but the brainstem blocks its messages, leaving voluntary muscles relaxed into near-total paralysis (except for occasional twitches).

  • Termed paradoxical sleep because the body is internally aroused with waking-like brain activity, yet externally immobile and asleep.

• Sleep cycle progression throughout the night:

  • The entire sleep cycle repeats approximately every $90\,\text{minutes}$.

  • Deep N3 sleep grows shorter and eventually disappears as the night progresses.

  • REM sleep and N2 sleep periods grow progressively longer.

  • REM sleep serves as both the stage where dreams occur and where emotional healing happens.

  • Sleepers disrupted during REM sleep show heightened emotional reactivity and reduced attunement to others' emotions.

Factors Influencing Sleep Patterns

• Individual variability in sleep duration:

  • Sleep requirements vary; not everyone needs $8\,\text{hours}$ of sleep.

  • Sleep duration and architecture are genetically influenced.

  • Cultural, social, economic, and stress factors heavily shape sleep habits.

  • Biology and environment continuously interact to affect sleep patterns.

• Circadian regulation by light:

  • Bright light activates light-sensitive retinal proteins.

  • Retinal proteins send neural signals to the suprachiasmatic nucleus (SCN), a cluster of cells in the hypothalamus.

  • The SCN controls circadian timing by signaling the brain's pineal gland:

  • Decreases production of the sleep-promoting hormone melatonin in the morning.

  • Increases melatonin production in the evening.

• Disruptions to biological rhythms:

  • Night shift workers experience chronic desynchronization, increasing their risk for fatigue, stomach problems, heart disease, and cancer.

  • Exposure to artificial light delays sleep onset and degrades sleep quality.

  • Streaming media disrupts dreaming patterns.

  • Staying up late and sleeping in on weekends, followed by sleeping early on Sunday night, causes sleep elusion.

Functions of Sleep

• Sleep serves five key adaptive and physiological functions:

  • Sleep Protects: Ancestral humans remained safe inside caves during dark hours, preventing exposure to nighttime hazards during hunting, gathering, and travel.

  • Sleep Helps Us Recuperate:

  • Provides the body and brain the opportunity to repair, rewire, and reorganize.

  • Helps the body heal from infections and restores immune system function.

  • Sleep Restores and Rebuilds Memories:

  • Consolidates fading memories of daily experiences during slow-wave deep sleep by replaying recent learning and strengthening neural connections.

  • Reactivates recent experiences stored in the hippocampus and shifts them to the cortex for permanent long-term storage.

  • Sleep Feeds Creative Thinking:

  • Dreams inspire artistic and scientific achievements (e.g., Stephanie Meyer's dream inspiring the novel Twilight).

  • Pondering a problem right before bed and sleeping on it helps the brain recognize connections and think smart.

  • Sleep Supports Growth and Development:

  • During slow-wave sleep in the first half of the night, the pituitary gland releases human growth hormone required for muscle development.

  • REM sleep and N2 sleep strengthen neural connections that construct enduring memories, including muscle memories.

Sleep Deprivation and Physiological Effects

• Sleep drive dynamics:

  • Prolonged wakefulness increases the inescapable biological drive to sleep; sleep always wins.

  • Unrestricted sleep experiments show that satisfying sleep debt leaves individuals feeling energized and happier.

• Consequences of sleep loss:

  • Leaves individuals drained of energy and diminishes their sense of well-being.

  • College and university students experience significant sleep deprivation on at least several days per week.

  • Mood effects: Tiredness triggers testiness, and reduced sleep directly predicts increased anger.

  • Psychiatric connection: Depression disrupts sleep, and sleep disturbance actively contributes to depression.

  • For individuals at risk for suicide, a single night of poor sleep increases next-day suicidal ideation.

  • REM sleep processing of emotional experiences acts as a protective buffer against depression.

  • Later school start times result in increased overall sleep for students.

• Metabolic, hormonal, and cognitive impacts of sleep debt:

  • Promotes weight gain by altering hormones, metabolism, and brain responses to food.

  • Increases ghrelin (hunger-arousing hormone) and decreases leptin (hunger-suppressing hormone).

  • Increases cortisol (stress hormone stimulating fat production) and lowers metabolic rate.

  • Disrupts gene expression, increasing risks for heart disease and other negative health outcomes.

  • Enhances limbic brain responses to visual food cues while suppressing cortical responses that resist temptation, making fatty foods more enticing to a tired brain.

  • Sickness naturally increases sleep to boost immune cell production.

  • Chronic short sleep shortens lifespan.

  • Sustained sleep deprivation causes brain cell death in mice and increases the risk of neurocognitive disorders in humans.

  • Slows reaction times and increases error rates on visual attention tasks (e.g., screening airport baggage, performing surgery, reading X-rays).

  • Daylight saving time transitions ("spring forward") lead to an immediate surge in traffic accidents due to lost sleep.

Major Sleep Disorders

• Insomnia:

  • Ongoing difficulty falling or staying asleep.

  • Fretting over insomnia aggravates the condition.

  • Common quick fixes like sleeping pills and alcohol worsen the issue by suppressing REM sleep, impairing memory and concentration, leaving next-day fatigue, and building tolerance (requiring higher doses to produce an effect).

• Narcolepsy:

  • Sudden, uncontrollable attacks of overwhelming sleepiness.

• Sleep Apnea:

  • Repeatedly stopping breathing while sleeping, leading to momentary awakenings.

• REM Sleep Behavior Disorder:

  • Dream-enacting behaviors involving loud, profane vocalizations and dramatic motor actions during REM sleep.

• Sleepwalking and Sleeptalking:

  • Engaging in normal waking activities while asleep.

  • Sleeptalking occurs during any sleep stage.

  • Sleepwalking occurs exclusively during N3 slow-wave sleep.

• Night Terrors:

  • Episodes during N3 sleep characterized by appearing terrified, talking nonsense, sitting up, or walking around.

  • Distinct from nightmares (which occur during REM sleep).

Dream Content and Environmental Processing

• Characteristics of REM dreams:

  • Vivid, emotional, and often bizarre.

  • Researchers capture exact dream content by awakening individuals during or immediately after REM sleep.

  • Most recalled dreams contain at least one negative aspect or emotion.

• Influences on dream storylines:

  • Incorporate traces of previous days' nonsexual experiences and daytime preoccupations.

  • Trauma: Exposure to trauma leads to nightmares, which function to extinguish daytime fears.

  • Music: Professional musicians report twice as many music-filled dreams as non-musicians.

  • Vision Loss: Blind individuals mostly dream using nonvisual senses, though individuals born blind can sometimes experience visual imagery in dreams.

  • Media Consumption: Viewing violent media during wakefulness increases violent dreams; viewing sexual media leads to sexual dreams.

• Environmental awareness during sleep:

  • The two-track mind continues to monitor the external environment during sleep.

  • Environmental stimuli (e.g., alarms or physical sounds) are directly woven into dream storylines.

  • Information presented in the final moments immediately before falling asleep is lost from memory.

Theories of Dreaming

• Freud's Wish-Fulfillment Theory:

  • Proposes that dreams provide a psychic safety valve discharging unacceptable feelings.

  • Manifest Content: The remembered, censored narrative storyline of a dream.

  • Latent Content: The underlying, unconscious drives and symbolic wishes that would be threatening if expressed directly.

• Information-Processing Theory:

  • Proposes that dreams help sift, sort, and fix the day's experiences into long-term memory.

  • Sacrificing sleep time to study hurts academic performance by making it harder to comprehend material or perform well on tests the following day.

• Neurocognitive Function Theory:

  • Proposes that REM sleep brain activity provides a specialized neurocognitive function to consolidate memories and process emotional information.

• Activation-Synthesis Theory:

  • Proposes that dreams erupt from neural activation spreading upward from the brainstem.

  • Dreams represent the brain's attempt to synthesize random neural activity into a coherent story.

  • Frontal lobe regions responsible for inhibition and logical reasoning remain idle, explaining lower behavioral inhibition while dreaming.

  • Damage to either the limbic system or active visual processing centers directly impairs dreaming capability.

• Cognitive Development Theory:

  • Views dreams as a reflection of brain maturation and cognitive development.

  • Prior to age $9\,\text{years old}$, children's dreams resemble static slide shows rather than active stories with the dreamer as an actor.

  • Dreams simulate reality by drawing on established concepts and knowledge using top-down cognitive control.

• REM Rebound:

  • Deprivation of REM sleep leads to REM rebound, an automatic increase in REM sleep duration during subsequent uninterrupted sleep.

  • Biological and psychological explanations work in tandem to clarify sleep and dream phenomena.