The Memory Function of Sleep
Week 14
Group 4
Kindra Akridge
Kimberly Villalva
Zhiheng Zhou
16. Explain the synaptic homeostasis theory of consolidation….
(18. Figure 2a)
Synaptic Homeostasis- idea that information encoding during wakefulness leads to
an increase in synaptic strength in the brain.
Sleep downscales synaptic strength to a sustainable level in energy and tissue
volume demands that allows reuse of synapses for future encoding.
Figure 2: Encoding information during waking, synapses become widely potentiated
(large yellow nerve ending), resulting in an increase in synaptic strength. (W=
strength). Small nerve ending represents a new synapse and the unfilled ending
is not activated, thus does not increase in weight.
Slow oscillations during SWS serve to downscale synaptic strength. Weak
connections are reduced, where the relative strength of the remaining
connections is preserved.
16.... Cover each of the findings mentioned, and explain the
conclusions that can be drawn from them.
•
•
•
•
•
•
Slow oscillations associated with downscaling show maximum amplitudes at the
beginning of sleep when overall synaptic strength is high. Also showed a decrease
in amplitude across SWS cycles from the gradual synaptic depotentiation.
Memories become enhances as downscaling is assumed to be proportional in all
synapses, improving the signal to noise ratio for synapses that were strongly
potentiated during prior waking.
No evidence in how slow oscillations can induce synaptic downscaling. The low
levels of excitatory neurotransmitters during SWS and sequences of hyper- and depolarization might promote the depotentiation of the synapses.
Expression of synaptic potentiation is globally reduces after a period of sleep and
is increased if specific regions. Mainly if sleep was precede a learning experience
(meaning potentiation might take place during sleep still).
Neuroimaging studies show reduced task-related activity in cortical regions after
sleep, but also had increased activity in other regions.
Global synaptic downscaling implicates that weak encoded memories are
forgotten , thus downscaling does not really explain a key feature of sleep
dependent consolidation. But it does explain second memory-related function of
sleep, that pro-activity facilitates encoding of new information during wakefulness.
16.... Cover each of the findings mentioned, and explain the
conclusions that can be drawn from them.
•
•
•
•
•
•
Slow oscillations associated with downscaling show maximum amplitudes at the
beginning of sleep when overall synaptic strength is high. Also showed a decrease
in amplitude across SWS cycles from the gradual synaptic depotentiation.
Memories become enhances as downscaling is assumed to be proportional in all
synapses, improving the signal to noise ratio for synapses that were strongly
potentiated during prior waking.
No evidence in how slow oscillations can induce synaptic downscaling. The low
levels of excitatory neurotransmitters during SWS and sequences of hyper- and depolarization might promote the depotentiation of the synapses.
Expression of synaptic potentiation is globally reduces after a period of sleep and
is increased if specific regions. Mainly if sleep was precede a learning experience
(meaning potentiation might take place during sleep still).
Neuroimaging studies show reduced task-related activity in cortical regions after
sleep, but also had increased activity in other regions.
Global synaptic downscaling implicates that weak encoded memories are
forgotten , thus downscaling does not really explain a key feature of sleep
dependent consolidation. But it does explain second memory-related function of
sleep, that pro-activity facilitates encoding of new information during wakefulness.
17. Explain the active system hypothesis. Connect it with
behavioral research
• Active system consolidation: the waking brain events are initially encoded in
parallel in neocortical networks and in the hippocampus.
• The newly acquired memory traces are repeatedly re-activated and thereby
become gradually redistributed such that connections within the neocortex are
strengthened, forming more persistent memory representations in the SWS.
• Linking to behavioral studies:
– During SWS, the post-learning sleep not only strengthens memories but also
induces qualitative changes in their representations and so enable the
extraction of invariant features from complex stimulus materials, the
forming of new associations and insights into hidden rules.
– SWS facilitates declarative, hippocampus-dependent memory
18. Explain Figure 2b
Active system consolidation model- events during waking are encoded in both
neocortical and hippocampal networks.
During SWS, slow oscillations drive the repeated re-activation of representations in
the hippocampus in synchrony with sharp wave ripples and thalamo-cortical
spindles.
Slow oscillations support the formation of ripple-spindle events, enabling as
effective hippocampus-to-neocortex transfer of the re-activated information.
Hippocampal memory output at cortical networks match with spindle activity
during deplarizing slow oscillation. Which predisposes these networks to
persisting synaptic plastic change that are supported by REM sleep.
18. Box 3 - Neuromodulators
• SWS
– Increasing cholinergic (and also glucocorticoids) tone
during SWS blocked the sleep-depend consolidation of
hippocampus-dependent memory.
– Blocking cholinergic tone during awake improves memory
consolidation, but encoding of new information would be
impaired.
– Noradrenergic, which is at intermediate level during SWS,
stabilizes newly formed memory representation.
18. Box 3 - Neuromodulators
• REM sleep
– Cholinergic is similar or higher during REM than during
waking. It promotes synaptic consolidation and enhancing
cholinergic tone during REM improves consolidation of
motor skill.
– Noradrenergic and serotonergic reaches a minimum during
REM. However, the role of noradrenergic in memory
consolidation is under debate.
19. What might REM sleep have to do with
synaptic changes? What role do spindles
play?
• REM sleep promotes
synaptic consolidation
• It is associated with up
regulation of plasticityrelated IEG relief. The up
regulation depends on
learning during waking
hours
• Spindles do not induce IEG
activity, but might prime
certain brain regions for it.
20. Explain Figure 3
• All memories have the potential to be either temporary or long term.
• Next the active system consolidation takes place during SWS. (Repeated
re-activation of memories)
• The active system consolidation promotes new
memories to integrate into the networks of old ones.
• REM “disentangles” the connection between long
term and short term memories.
21. Cover the conclusion: summarize the findings and
theories in this review
Both SWS and REM sleep have function to optimize memory
consolidation
- SWS active system consolidation integrates newly encoded memories
with pre-existing long-term memories (inducing conformational
changes in the respective representations). System consolidation acts
with global synaptic downscaling, serving to prohibit the saturation of
synaptic networks.
- REM sleep acts to stabilize the transformed memories by enabling
undisturbed synaptic consolidation. REM sleep has been thought to
have key role in memory consolidation.
This article points out the idea the contribution of sequential SWS and
REM sleep to memory consolidation by indicating an essential role of
SWS in system consolidation might be completed by the synaptic
consolidation taking place during REM sleep.