Transcript What are the Memory Sources of Dreaming?

What are the Memory
Sources of Dreaming?
Rebecca Dai
Nicole Garces
Joanna Wong
Overview
• Examine the relationship between dreaming,
memory, and the hippocampus
• Combined research of how episodic memory is
consolidated over time and how that may be
modified during dreaming
– Episodic memories:
Memories
of personally lived
experiences
History
• Freud and “day residues”
– Elements of dreams connected to experiences of the
previous day
– Became central to psychoanalytic theory and therapy
Psychophysiological Methods introduced
to study dreaming
• REM and NREM sleep stages identified
– Pre-sleep stimulation
– Sensory stimulation during sleep
– Subjects’ post-hoc identification of memory sources
of dream elements
Recent Studies
• Suggests complete episodic memories
are shown in dreams only 1.4%
• Isolated fragments of memories occur
in 28-38% of reports
• 65% of dream elements are linked to
features of waking events
• Very emotional dreams can become
highly episodic (nightmares)
Dreams and Simulation of Reality
• Dreams contain spatially-coherent
enviroments
Contradiction:
•The lack of a fully
episodic structure
but the portrayal
of coherent virtual
worlds in dreaming
Hippocampus and Episodic
Memories in Dreaming
• Consensus: Hippocampal changes
contribute to the unique characteristics
of dream content
-Increased activity in
hippocampal region
during REM
-Rhythmic slow activity
during REM in humans
Question?
• How can this activity be linked
specifically to changes in episodic
memory organization?
First Line of Inquiry: The Here
and Now of Dream Experience
• Hypothesis: A type of
spatial and temporal
binding underlies dreaming
that is analogous to the
perceptual binding thought
to underlie waking
consciousness
•Dream-related binding sustains
illusion that dream takes place “here”
and “now”
• Hippocampus in temporal and spatial
pattern processing
– Animal Studies
• Suggested research
• Subject training in dream reporting
• Evaluate contributions of other hippocampaldependent cognitive systems
• Hippocampal damaged patients
• Dream characteristics
• Implications
2nd Inquiry: Memory Source of Dreaming
Governed by Temporal Mechanisms May
Obscure their Epsiodic Orgins
• Selection of memory sources are
influenced by chornobiological factors
– Chronobiological factors
• 90 min REM/NREM sleep cycle -> selection of
episodic memory
• Circadian cycle -> selection of dream elements
• Interval timers with a fixed duration
– Influences selection of dream memory
source
• 12 hours before dream
• A week before dream
• Observation: longer interval delay
exists but there is a consistent
appearance of memory sources rise
from age 10-19
Mechanism
• Hippocampal model of time-related
memory consolidation
– Memories relocate over time from
hippocampus to neocortex and are
reiterated in dreams during this process
– Qualitated difference in memory sources
of dreams arise from
• Recent residue (day-residue) time period
• Delayed residue (1 week) time period
– Graph next slide
Figure 1
• Duration of this relocation process
varies for different types/attributes of
memories (may extend to years)
– Animal study: major transition takes about
1 week
– Evidence:
• Hippocampal cell excitability increase after a
learning task
• But returns to baseline level on the 7th day post
training
• However, there is no evidence that this
observation relates to delayed memory
source in dreams
• Possible connection:
– Animal study shows 3 post-learning changes
• REM sleep duration increase 5-7 days post
learning, Ach level increase during REM
• Hippocampal theta cells decrease in firing rate
after a week
• Partial REM deprivation disrupts performance
• Proposed methological improvements:
– More sophisticated methods of probing
subject’s memories
• Cued autobiographical recall
• Facilitate self-reflection
• Asses subject’s confidence in memory ability
Dreams Structured by Emotion
• Dream emotional pattern preserved
– Individual’s dominant, pre-sleep emotional concern
• Emotional dream regulation probably
controlled by amygdala
– Amygdala activity higher during REM
– Reciprocal dependence with hippocampus in encoding and
storing memories
• Amygdala capable of gating sensory
information to entorhinal cortex to
hippocampus
• Hippocampal processing is essential for
encoding fear memories in amygdala circuits
Episodic Origins of Emotional
Structures
• Emotional sources go unnoticed because they
are expressed metaphorically
– Possibly to build adaptive new contexts to
assimilate current concern
• Evidence: Assault victims who experience anxiety may not
notice the emotional connection in dream content
• Problem: Freudian idea so might be questionable
• Emotional sources of dreaming may require
development of methods that sensitize
subjects to be aware of the emotional aspect
of their dream while controlling for confounds
may affect self observations
Conclusion
• Episodic origins of dream content are
opening new research ideas
• Hypothesis
– Memory elements in dreams facilitate
learning simply by reactivating those
elements in original perception-like state
– Binding different elements around
emotionally relevant themes strengthens
and consolidates those elements
Conclusion (cont.)
• Dream related memory consolidation is
regulated by oscillatory or interval
timers of different frequencies
– analogous to hippocampal mediated waves
(zif-268 gene) cause induction of LTP
• Dreaming about new material enhances
subsequent recall
– Three studies show this:
• Interrelated dream elements are better
recalled in surprise morning task
• Pre-sleep stories are better recalled in the
morning when subjects dream about frequent
about constituents of the story
• Completion of mirror-tracing task leads to
dreams that metaphorically represents the task
– i.e. trying to stay on the road