Sleep disorders are an important part of neurology examinations as they require a strong knowledge of complex diagnostic studies such as EEG, and also of a multitude of medications. In this chapter, you will learn sleep waveforms using real EEG tracings, and review high-yield treatments for sleep disorders. Test your knowledge at the end with practice questions and flashcards!

Authors: Jody Manners MD, Brian Hanrahan MD

Circadian Rhythms

  • Defined as physical, mental, and behavioral changes following roughly a 24-hour cycle, responding primarily to light and darkness in the environment.
    • They are endogenous and self-sustained but can be modulated by external cues (zeitgebers).

Table of endogenous and self-sustained zeitgebers

      • Ultradian Rhythms occur more frequently than once every 24 hours, such as the stages of sleep, patterns of hormonal release, and appetite regulation.
      • Infradian Rhythms are less frequent than 24 hours, often weekly, monthly, or seasonally. Infradian rhythms can be associated with conditions like seasonal affective disorder (SAD) or hormone-related mood disorders.
  • The suprachiasmatic nucleus (SCN) of the hypothalamus, the central clock is responsible for synchronizing 24-hour circadian rhythms.
      • The axons of light-sensitive neurons in the retina provide information to the SCN, allowing the internal clock to be synchronized with the outside world.
      • Melatonin, secreted by the pineal gland, has a key role in sleep onset. Its secretion is inhibited by light and permitted by darkness, signaling the body when it’s night-time. 
Circadian Rhythm Pathway
  • Physiological processes influenced by circadian rhythms
      • Hormone Release
          • Cortisol: Follows a diurnal pattern, peaking in the early morning to help promote alertness and metabolic functions and gradually declining throughout the day.
          • Growth Hormone (GH): Significant releases of GH, happen in the early phases of sleep.
      • Body Temperature: Core body temperature dropping during the night and rises during the day (see graph below)
Body Temperature Changes During Sleep

Phases of Sleep

Wakefulness

  • Characterized by alpha frequency activities, sporadic eye movements, and a posteriorly dominant alpha rhythm that attenuates with eye-opening.

NREM sleep

  • Stage N1 (5% of total sleep): Associated with an emergence of theta activity, and slow roving eye movements.
    • Young adults spend the least amount of time in NREM stage 1 sleep.
  • Stage N2 (45-55% of total sleep):
    • The stage at which adults spend the most time during normal sleep.
    • Characterized by the presence of either sleep spindlesand/or K-complexes with theta range background activity.
    • Sleep spindles are thought to be generated by the reticular thalamic nucleus.
    • Stage N3 (15-20% of total sleep):
      • k.a “deep sleep” or “slow-wave sleep” (no longer called “stage 4 sleep”)
      • EEG will show slow-waves and high amplitude delta waves.
      • Parasomnias tend to occur during this stage.

REM sleep

  • 20-25% of sleep.
  • Normally occurs ~90 minutes into sleep.
  • Characterized by a desynchronized low voltage, high-frequency background.
  • There will be decreased EMG activity (REM atonia).
  • Sharply peaked irregular eye movements with lateral rectus spikes (see below) can be seen ON eeg. Note the lack of muscle artifact.
Stages of sleep over a night of sleep

 

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