last updated:

April 3, 2021

[Brain Image]    

PSY 340 Brain and Behavior

Class 23: Stages of Sleep & Brain Mechanisms [OUTLINE]


A. Sleep and Other Interruptions of Consciousness

brain death

Image from Laureys, S. (2005). Death, unconsciousness and the brain. Nature Reviews Neuroscience, 6, 899-909

B. The Stages of Sleep

electroencephalograph (EEG)

Stage W (awake)
  • a relaxed mental state (alpha waves) or
  • an alert mental state (beta waves)
[Brain Wave: EEG
When we are asleep,
  • theta waves
  • delta waves

A polysomnograph combines EEG, breathing monitor, O2 level, heart beat, eye movement detector (electrooculograph EOG)

[Polysomnograph Sleep Study]

Sleep Cycle (revised 2007)

This chart replaces the material from our book

Non-REM Sleep includes Stages N1 to N3
  • Stage 1 (N1): Mixed frequency, esp. theta waves
  • Stage 2 (N2): Sleep spindles and K-complex waves
  • Stage 3 (N3): Slow waves (delta) > 20%
Stage R (REM (Rapid Eye Movement) Sleep)
(= "paradoxical" sleep in animals who do not move eyes)

Real life sleep often looks a lot less regular than the chart above:

[Real Life Sleep]

C. Brain Mechanisms of Wakefulness & Arousal

Brain Mechanisms of Wakefulness & Sleep pontomesencephalon
(reticular formation) 
Acetylcholine (ACh) & glutamate = excitatory
basal forebrain
(anterior to hypothalamus)
Acetylcholine (ACh) = excitatory [green tracts]

GABA = inhibitiory
[red tracts]

Orexin (Hypocretin)
locus coeruleus
(dorsal pons)
Norepinephrine (blocks REM sleep)
dorsal raphe nucleus Serotonin
D. Sleep and the Inhibition of Brain Activity

E. Brain Function in REM Sleep

  • PGO waves (see figure on right)
  • spinal cord inhibits motor neurons associated with large muscles
  • Activity decreases in prefrontal cortex, primary visual cortex, & motor cortex, but increases in temporal & parietal cortex
  • Acetylcholine (ACh) moves sleeper into REM
    • Carbachol
  • Serotonin & norepinepherine interrupt or shorten REM
 [PGO Waves in Brain]

F. Sleep Abnormalities ("Parasomnias")

Insomnia = not sleeping enough due to (1) difficulty falling asleep (onset insomnia), (2) frequent awakening during sleep (maintenance insomnia), or (3) waking up too early (termination insomnia)
Sleep Apnea = intermittent stopping of breathing during sleep due to obstruction of the airway or central nervous system problems

Includes one or more of these symptoms:

  1. Gradual/sudden onset of sleepiness
  2. Cataplexy: muscle weakness while remaining awake. Often triggered by strong emotions
  3. Sleep paralysis: inability to move when falling asleep or waking up
  4. Hypnagogic hallucinations: dreamlike experiences at the beginning of sleep.

Equivalent to REM-like sleep intruding into the awake state

  • orexin (hypocretin) => Humans with narcolepsy do not have these cells in the hypothalamus (perhaps due to an autoimmune disorder).
Treated with stimulants, e.g., Ritalin or Cylert
Periodic Limb Movement Disorder
  • during NREM sleep individual moves legs and sometimes arms every 20-30 seconds for minutes or hours.
  • NOT "restless leg syndrome"
  • Treated with tranquilizers
REM Behavior Disorder
Night Terrors
  •  Crying & screaming but NOT usually awakening.
Sleep Talking
  •  We all do it
  • usually seen in children 2-12 years old
  • usually harmless with occasional accidents
  • no danger to wake the sleepwalking person up
  • no treatment other than making sure that the person's environment is safe

This page was first posted March 6, 2005.