last updated:

April 6, 2021

[Brain Image]    

PSY 340 Brain and Behavior

Class 24: Why Sleep? Why REM? Why Dreams? (OUTLINE)


A. Functions of Sleep

Why do we sleep?  Short answer: we do not know (though we are getting closer)

[Animal Sleep Times]

1. Sleep and Energy Conservation

Analogous to Sleep: Hibernation = body temp to just above freezing, brain activity almost nothing
Alternative sleep strategies in animals

2. Sleep and Memory

                Cycle and Memory
> long-term memories are strengthened (consolidation).
Some imaging studies suggest a replaying of learning sequences from the daytime and "weeding out" or pruning
 less important memory connections in brain
Sleeping after learning something usually results in memory gain upon awakening

Synapse formation in sleep   Dendritic
Sleep may promote the development of new dendritic spines (new synapses) (see figures above)
Stage N2 sleep spindles (12-14 Hz): communication between thalamus & cerebral cortex associated with new learning. r = 0.7 with nonverbal IQ (i.e., explains 49% of variation!)
[Glymphatic Sytem]

3. Sleep and Toxic Waste Removal (New, not in book)

B. Functions of REM Slee;p

C. Biological Perspectives on Dreaming

There is no single theory of dreaming which is now currently accepted by most psychologists.

Consider these five theories of what dreaming is about

Sigmund FreudFreud's Psychoanalytic Theory (1899/1900)
  • Dreams as wish fulfillment
    • Unconscious process constructs wish
    • Censorship process distorts the wish via symbols et al.
  • Each dream has two aspects
    • Manifest content = what is remembered
    • Latent content = underlying meaning of dream
  • Dreams are interpreted within psychoanalytic therapy
Freud's Interpretation of Dreams
J Allan HobsonActivation-Synthesis Hypothesis
J. Allan Hobson Initial theory (1997)
  • Activation = during REM sleep, different brain areas, particularly the limbic system, become active under stimulation from the brain stem. These areas involve circuits related to emotion, memories, and sensations. 
  • Synthesis = the brain creates a story to make sense of the activity
Protoconsciousness Theory
J. Allan Hobson more recent theory (2000s)
  • Brain activation in sleep allows the development & maintenance of circuits necessary for higher brain functions including consciousness
  • In dreaming, we are getting ready to behave
  • Dreams have more in common than not across individuals
  • REM sleep = protoconscious state = provides a virtual reality model of the world that is of functional use to the development & maintenance of waking consciousnes
Activation-Synthesis Hypothesis Brain Image

DomhoffNeurocognitive Theory of Dreaming
William Domhoff
  • Underlying neural substrate for dreaming = Default Mode Network (DMN)
  • Just as the DMN develops, so too do dreams develop as cognitive abilities mature, e,g., narrative or story abilities
  • Adolescent/adult dreams reflect many of the real-life aspects of individuals, e.g., social networks or life settings

                Emergence of Dreaming

Clinico-Anatomical Hypothesis
  • Derived from studies of brain damaged patients
  • Dreaming is a kind of quasi-hallucinatory or unusual form of thinking
  • Stimulation (either internal or external) activates parietal, occipital, & temporal cortex.
  • No visual information contradicts the stimulation
  • Lowered prefrontal cortical activity leads to lowered censorship of stimulation (dreams can violate logic or contain contradictory materials)