Sleep Disorders

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%): Attenuation of the alpha rhythm, the emergence of theta activity, and slow rolling eye movements.
  • Frontocentral beta activity can increase.
  • Vertex waves and small sharp spikes can be seen.
  • Young adults spend the least amount of time in NREM stage 1 sleep.
• Stage N2 (45-55%):
  • The stage at which adults spend the most time during normal sleep.
  • Characterized by the presence of either sleep spindles and/or K-complexes with theta range background activity.
  • Positive Occipital Sharp Transients of Sleep (POSTS) are most prevalent in N2 but can also occur rarely in N1 and N3 sleep.
  • Sleep spindles are thought to be generated by the reticular thalamic nucleus.
• Stage N3 (15-20%):
  • a.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.
  • Interictal EEGs can show anterior temporal spikes especially if the EEG is performed during non-rapid eye movement (NREM) sleep.

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.