Week 14

The Memory Function of Sleep

Group 3Tawni Voyles

Alyona KonevaBayou 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.

REM

Stage 3 & 4

Stage 1 &2

Non-REM

LSS

SWS

Slow oscillation

Hippocampalripples

Thalamo-cortical spindles

Field potential oscillations

Sleep Stages

Redistribute memories for long-term storage

Prime cortical networks for the long-term storage of memory representations

Promote synaptic potentiation

Function

Coordinate the bidirectional information flow between the neocortex and the hippocampus

Function Fine-tuned temporal relationship

Memory re-activation during slow wave sleepPart 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 sleepPart 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 sleepPart 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 hippocampal-neocortical 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.