March 06, 2025	PSY 340 Brain and Behavior Class 22: Stages of Sleep & Brain Mechanisms [OUTLINE]

A. Sleep and Other Interruptions of Consciousness

• Sleep
  
  
• Coma

• Vegetative State (aka "Unresponsive Wakefulness Syndrome" or "Persistent Visceral State")
  
  
• Some patients may actually be experiencing "cognitive motor dissociation (CMD)" in which they can perform cognitive tasks which are detected by fMRI or EEG.
  

• Minimally Conscious State

• Brain Death = no evidence of activity in cerebrum or cerebellum (see image)
  
  
• Persistent coma
• Absence of brainstem reflexes
• Lack of ability to breathe independently
  

Image from  Laureys, S. (2005). Death, unconsciousness and the brain. Nature Reviews Neuroscience, 6, 899-909, fig. 2.

B. The Stages of Sleep

electroencephalograph (EEG)
Stage W (awake) a relaxed mental state (alpha waves) or an alert mental state (beta waves)
When we are asleep, theta waves delta waves

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

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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:

C. Brain Mechanisms of Wakefulness & Arousal

	pontomesencephalon (reticular formation)	Acetylcholine (ACh) & glutamate = excitatory
	basal forebrain (anterior to hypothalamus)	Acetylcholine (ACh) = excitatory [green tracts] GABA = inhibitiory [red tracts]
	hypothalamus	Histamine Orexin (Hypocretin)
	locus coeruleus (dorsal pons)	Norepinephrine (blocks REM sleep)
	dorsal raphe nucleus	Serotonin

D. Sleep and the Inhibition of Brain Activity

• GABA inhibits signaling in localized areas of cerebral cortex
• Sleep paralysis
• Sleepwaking (somnambulism)
  

E. Brain Function in REM Sleep: PGO Waves

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 stimulates ACh Serotonin & norepinepherine interrupt or shorten REM

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 CNS problems
Narcolepsy	Includes one or more of these symptoms: Gradual/sudden onset of sleepiness Cataplexy: muscle weakness while remaining awake. Often triggered by strong emotions Sleep paralysis: inability to move when falling asleep or waking up 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	during REM sleep individual moves vigorously or violently (kick, punch, etc.); dreams of violent nature
Night Terrors	Crying & screaming but NOT usually awakening. Happens mostly to children in the first third of sleep.
Sleep Talking	We all do it
Sleepwalking	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

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  The first version of this page was posted on March 6, 2005.