Transcript Week 14 The Memory Function of Sleep

Week 14
The Memory Function of Sleep
Group 3
Tawni Voyles
Alyona Koneva
Bayou Wang
11. Tell the class about oscillatory behavior during
sleep, and what this has to do with consolidation and
with SWS. Be complete, and discuss Figure 1
thoroughly.
NonREM
Sleep
Stages
Stage 1
&2
Stage 3
&4
Field potential oscillations
Function
Slow
oscillation
Redistribute memories for
long-term storage
LSS
Thalamocortical
spindles
SWS
Hippocampal
ripples
REM
Function
Coordinate the bidirectional
information flow between the
neocortex and the hippocampus
Prime cortical networks for
the long-term storage of
memory representations
Promote synaptic
potentiation
Fine-tuned temporal
relationship
Memory re-activation during slow wave sleep
Part a
• Key point: similarity of the temporal firing sequences
• Illustration: Neuronal re-activation of ensemble activity
mostly occurs during SWS and almost always occur in
the order in which they were experienced.
Memory re-activation during slow wave sleep
Part b
• Key point: Odour re-exposed during SMS can potentiate memroy.
• Illustration: Hippocampal networks are particularly sensitive to
inputs that can re-activate memories during SMS, which supports
the causal role of re-activation during SWS in memory
consolidation.
Memory re-activation during slow wave sleep
Part c
• Key point: left anterior hippocampus and certain
neocortical regions were activated specifically during SMS
compared to other conditions.
• Illustration: Support the theory that SMS’s function is to
transfer memory between hippocampus and neocortex.
12. First, show us a diagram of “phase.” . . .
Explain “there is a fine-tuned temporal relationship between the occurrence
of slow oscillations, spindles, and sharp wave-ripples during SWS that
coordinate the bidirectional information flow between the neocortex and
the hippocampus.” Explain how “up-states” play a role here, and the
excitatory phases of the spindle cycle.
• The most prominent oscillations during SWS are slow oscillations,
spindles, and sharp-wave ripples.
•Down-State – neurons’membranes are hyperpolarized, results in
neuronal silence with an absence of spiking activity.
•Up-State – neurons’membranes are depolarized, resulting in strongly
increased wake-like firing of large neuronal populations.
… continued
• In humans, cats, and rats, spindle activity and ripples increase during
the up-state, and become suppressed during the down-state of a
slow oscillation.
• Sharp-wave ripple complexes are also temporally coupled to
spindles.
• These ripple-spindle events provide a mechanism for hippocampalneocortical information transfer.
• Ripples and associated hippocampal memory re-activations feed into
the excitatory phases of the spindle cycle.
• During the up-state, the feed-forward control of slow oscillations over
ripples and spindles allows transferred information to reach the
neocortex.
Where are CA1 and CA3?
•The hippocampal formation is composed of the dentate gyrus and the
cornu ammonis (CA1, CA2, CA3, CA4).
•The CA areas are all filled with densely packed pyramidal cells similar to
those found in the neocortex.
What happens to coherence in CA1 and CA3, and what might that
mean? What IS coherence?
• Coherence describes all properties of the correlation between
physical quantities of single or multiple waves. There is both spatial
and temporal coherence.
• During REM sleep, there is reduced coherence between CA 1 and
CA 3.
• This suggests that the different memory systems (declarative &
procedural) become disengaged during REM sleep.
• This may be necessary for establishing effective local processes of
synaptic consolidation in these different systems.
13. What sort of oscillatory neural activity is
connected with consolidation during REM?
Pontogeniculo-occipital (PGO) waves and the EEG
theta rhythm support REM sleep-dependent
consolidation processes.
In rats:
• an increase in REM sleep PGO-wave density for 3–4
hours following training on an active avoidance task.
• Improvement in post-sleep task performance
• Increased activity of plasticity-related IEGs and
brain-derived neurotrophic factor (Bdnf) in the dorsal
hippocampus (within 3 hours following training).
Do theta (4–8 Hz) oscillations contribute to
consolidation?
Assumption:
Theta activity during waking occurs during the encoding
of hippocampus-dependent memories.
Evidence:
• neuronal re-play of memories in the hippocampus
during REM sleep-associated theta activity.
• place cells encoding a familiar route re-activated
preferentially during the troughs of theta oscillations
during post-training REM sleep.
• cells encoding novel sites fired during the peaks.
Conclusion?
REM sleep de-potentiates synaptic
circuits that encode familiar events but
potentiates synaptic circuits that
encode novel episodes.
14. Why do the authors say the specific
contribution of theta is obscure at the moment?
In humans:
• neocortical theta activity enhanced during REM sleep
following learning of word pairs.
• theta activity (especially in the right prefrontal cortex)
was correlated with the consolidation of emotional
memories.
In mice:
• reduced REM sleep theta activity after fear
conditioning.