Phases of Sleep

• Polysomnogram


  Measures heat rate, blood pressure and oxygenation level, respiratory depth + pattern, and brain waves while a person is asleep
• Sleep is characterized by:

  • Decrease in physical activity
  • Decoupling from external outputs
  • Changes in brain wave activity
• Somnambulism


  Sleepwalking. Full-on awake behaviors completely in the absence of input or recall
• Most of our dreams happen during REM sleep
• REM sleep happens for about 20 minutes starting 3 hours after you fall asleep, then once every hour for 20 minutes after that
• Beta range of frequencies is between 13 and 30 Hz and is what we are in when awake
• NREM1


  First stage of sleep where you are basically just restfully awake. Might respond to questions, and eyelids might occasionally open or close. Waves go from alpha to theta as you go deeper into this phase (lower frequency)
• Alpha waves are between 8 and 13 Hz
• Theta waves are between 4 and 8 Hz
• NREM2

  50% of sleep is in this phase, which sticks mostly in the beta range, but has K-complexes and sleep spindles around once a minute
• K-complex


  Large-amplitude brain wave events that are the largest observed in healthy humans. Happens about once a minute during NREM2
• Sleep spindle


  High-frequency burst of rapid activity in the low beta range that lasts for about a second
• NREM3


  Deep sleep phase. When a person's metabolism, breathing, and respiration are all at a minimum. Here many cortical neurons fire in synchronicity, leading to large amplitude deflections on an EEG. It's also called slow wave sleep
• REM


  When brain waves have a lot of low amplitude events at a high frequency that look similar to wakefulness
• We go into REM sleep on average 4 times a night, mostly towards the end