16. Explain the synaptic homeostasis theory of consolidation. Cover

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.