Introduction to Sleep
- Universal behavior: Found in almost all animals, even fruit flies exhibit periods of quiescence.
- Innate: We are born with the ability to sleep; it doesn’t require learning.
- Key characteristics:
- Low motor activity: Postural muscles are relaxed.
- Low sensory reactivity: Less responsive to external stimuli.
- Reversible: Can be easily awakened.
Types of Sleep
- Slow-wave sleep (SWS):
- Neocortex is “offline”: Engaged in synchronized, slow wave activity.
- Reduced information processing due to repetitive brain wave pattern.
- Rapid eye movement (REM) sleep:
- Neocortex appears awake: Active brain activity similar to waking state.
- Motor neurons inhibited: Prevents physical action despite active brain.
- Associated with dreaming: More frequent and vivid dream recall upon waking from REM sleep.
REM Sleep Behavior Disorder
- Symptom: Acting out dreams due to lack of motor neuron inhibition during REM sleep.
- Characteristics: Primarily affects middle-aged men.
- Consequences: Disruptive to both the individual and their bed partner.
- Association: Often linked to underlying neurodegenerative disorders.
Sleep Architecture
- Sleep cycle: Alternating periods of SWS and REM sleep throughout the night.
- SWS depth: Increases initially and then decreases towards morning.
- REM duration: Short at the beginning of sleep, increasing in length as the night progresses.
Sleep Mechanism