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Chapter 8: Wakefulness and Sleep

Module 8.1: Rhythms of Waking and Sleeping

• Endogenous Rhythms:

  • Definition: Internal biological clocks that govern cycles of activity and inactivity.

  • Circadian Rhythms: Approximately a 24-hour cycle; evident in sleep patterns, alertness levels.

  • Circannual Rhythms: Longer cycles related to seasons, e.g., migration behaviors in birds.

• Setting and Resetting the Biological Clock:

  • Zeitgebers: External cues like light that help synchronize internal clocks with the environment.

  • Light is the primary zeitgeber influencing circadian rhythms in animals.

  • Habituation to external schedules can lead to misalignments, especially in extreme environments (e.g., submarines, space).

• Mechanisms of the Biological Clock:

  • The Suprachiasmatic Nucleus (SCN): Main regulator of circadian rhythms, responding mainly to light inputs.

  • SCN damage leads to erratic rhythms; SCN drives the molecular feedback loops tied to PER and TIM proteins.

• In Closing: Sleep–Wake Cycles:

  • Overall dependence of sleep on intrinsic rhythms as well as environmental factors like light and social cues.

Module 8.2: Stages of Sleep and Brain Mechanisms

• Stages of Sleep:

  • Stages marked using EEG; differentiate between NREM and REM.

  • REM sleep characterized by increased brain activity, rapid eye movements, and muscle atonia.

• Brain Mechanisms of Wakefulness and Sleep:

  • The Reticular Formation: Central in regulating arousal; regulates shifts between sleep and wakefulness.

  • Neurotransmitters: GABA inhibition plays a crucial role in promoting sleep; imbalance can lead to disorders like insomnia or sleepwalking.

• Sleep Disorders:

  • Narcolepsy, Sleep Apnea, and others; characterized by specific symptoms and underlying neurobiological mechanisms.

• In Closing: Stages of Sleep:

  • Importance of understanding sleep architecture in diagnosing and treating sleep-related disorders.

Module 8.3: Why Sleep? Why REM? Why Dreams?

• Functions of Sleep:

  • Energy conservation during inefficient periods.

  • Cellular restoration processes active during various sleep stages, especially NREM.

  • Enhancement of memory consolidation; improved learning and cognitive performances noted after sleep.

• Functions of REM Sleep:

  • Possible roles in memory shaping and emotional regulation; often highest proportion seen in species with longer sleep durations.

  • Theories on REM function:

    • Activation-Synthesis Hypothesis: Dreams synthesize sensory experiences based on alterations in brain connectivity during REM.

    • Neurocognitive Hypothesis: Dreams reflect a unique form of cognitive processing during altered states of consciousness.

• Our Limited Self-Understanding:

  • Despite advancements in sleep research, many questions about the function of sleep and dreaming persist; sleep behaviors may lead to evolutionary advantages absent complete understanding.