Cortical Rhythms (L12-13) Flashcards
Name the machine that studies the stages of sleep.
The Electroencephalogram (EEG).
What is sleep characterised by?
- Loss of behavioural control
- Loss of consciousness
Which 2 types of memory is sleep especially important for?
- Declarative memory
- Procedural memory
Name the types of sleep and the stages at which they occur.
Light sleep - stage 1 and 2
Slow wave sleep (SWS) – stage 3 and 4
Rapid eye movement sleep (REM)
Non-REM
Describe the oscillations that occur during slow wave sleep and the Hz of each.
(3)
- Slow oscillations – in humans ~0.8 Hz.
- Spindles (10-15 Hz), waxing and waning oscillation – arise from the thalamus – stage 2 and SWS.
- Hippocampal sharp waves – depolarisation with very fast 100-300 Hz
Describe the oscillations that occur during REM and the Hz of each.
(3)
- Ponto-geniculo-occipital (PGO) waves that propagate from the
pontine nucleus in the brainstem to lateral geniculate nucleus and visual cortex - Theta oscillations – hallmark of REM sleep – mainly in the hippocampus
- Gamma 30-80 Hz oscillations
Read:
What is sleep for?
- Consolidation of memories = active re-processing of new memories within the networks that encoded them.
- Occurs best during sleep so consolidation and encoding don’t interfere with each other.
During consolidation newly encoded memory traces are
reactivated in the fast learning store and that then drives the slow learning store.
Representations in the slow learning store are gradually strengthened.
Fast learning store = ___1___
Slow learning store = ___2___
- Hippocampus
2. Neocortex
Read:
Place cell firing.
Place is partly coded by an increase in firing rate. Different hippocampal neurons respond to different parts of a spatial field.
_____ means replaying during sleep the sequence of firing in hippocampal cells that occurred while encoding. Episodic events need a sequential structure.
Reactivation.
Which parts of the brain are activated as a human navigates through a maze?
Occipito-parietal and hippocampal regions.
Read:
Reactivation.
- Occurs during SWS – only in a minority of neurons recorded
- Reactivations occur in the order they were experienced
- Reactivations are noisier and less accurate
- Happens at a faster firing rate
- Promotes the gradual redistribution and reorganisation of memory to a site for long-term storage (system consolidation)
- Promotes synaptic changes that are necessary to stabilize memories (synaptic consolidation) which occurs during the subsequent REM sleep
Seen in the thalamus, striatum and neocortex.
SWS = consolidation of ___1___ memories – hippocampus dependent.
REM – consolidation of ___2___ – hippocampus independent.
- Declarative
2. Non-declarative
_____ hypothesis – optimum benefit to memory consolidation when SWS and REM take place in succession.
Sequential.
Read:
How do sleep oscillations promote synaptic plasticity?
- Spindles and action potentials associated cause increases in calcium
- Repeated spindles associated with LTP
- Spindles could therefore strengthen synapses
Name the 2 main theories of memory formation.
- Synaptic homoeostasis
- System consolidation
True or false?
- During waking and encoding synapses become potentiated
- During SWS there is a global downscaling – ~1 Hz SW ideal for LTD
True.
Describe System consolidation.
3
- Events encoded in hippocampus and neocortex during awake
- Slow oscillations in SWS drive reactivations
- Synchronization of spindles and slow waves drives plasticity
Read:
Odour memory reactivation experiment.
Re-exposure to an odour during SWS leads to enhanced retention performance.
Subjects sleep in the fMRI scanner - re-exposure to the odour during SWS activated left anterior hippocampus (left) and retrosplenal cortex (right).
No activation was seen when learning not associated with the odour.
This and other studies support the system consolidation theory.
Abnormalities of sleep are associated with most _____ disease.
Neuropsychiatric.
Read: The Magnetoencphalogram (MEG).
Voltage changes are accompanied
by magnetic field changes.
MEG - measures the magnetic
field rather than electric fields.
Tiny fields but no distortion.
Keeps temporal resolution and
improves the spatial resolution - < 1cm.
Describe the main limitation of the EEG.
Poor spatial resolution (10 cm2):
- Signals distorted by blood vessels, dura, skull, scalp muscles and skin.
- Mainly samples activity from the superficial layers of the cortex.
List the pros of the EEG.
- Technically easy
- Non-invasive
- High temporal resolution
Read:
Alpha oscillations.
- 9 – 11 Hz, large amplitude.
- Associated with relaxed wakefulness.
- Seen in primary sensory neocortical areas.
- Origin – locally generated or thalamo-cortical.
- Function – Idling rhythm – preserves the pattern of connectivity formed by previous sensory inputs.
The local mean field potential of the EEG reflects the _____ behaviour of a large number of interacting neurons.
Average.
How do we process perceptions, emotions, memories that
are distributed across different brain regions so easily?
(2)
- Local interactions - ~ 1cm -
monosynaptic connections.
Large-scale synchrony
>1 cm - e.g. across
hemispheres or cortical
regions.
_____ _____ involved in executive functions such as memory, attention, planning.
Prefrontal cortex.
The _____ in humans and animals is critical for memory functions.
Hippocampus.
Read:
Different EEG signals and their respective Hz.
Slow waves < 1 Hz
Delta rhythms 0.5 - 4 Hz
Theta 3-7 Hz
Alpha 9 -11 Hz
Spindles 8-15 Hz
Beta 15 - 30 Hz
Gamma 30 - 60 Hz
High gamma > 60 Hz
Ultrafast > 100 Hz
Read:
Theta Oscillations.
4 – 7 Hz (theta 1), 7 – 12 Hz (theta 2) medium amplitude.
Theta 1 is associated with active exploratory movement.
Theta 2 is associated with passive exploratory movement.
Seen in most neocortical area, and hippocampus.
Origin – locally generated – some projections from medial septum to hippocampus.
Function – primary sensory processing and learning and recall.
Also occurs with gamma oscillations.
Read:
Beta Oscillations.
Beta 1 ( 11-20 Hz) and beta 2 ( 21-29) Hz, low amplitude.
Beta 1 - associated with intense mental activity, attention.
Seen in primary sensory areas and central fronto-parietal area.
Origin – local neocortical generator.
Function – long-range synchronisation, learning and memory.
Associated with gamma oscillation.
Read:
Gamma Oscillations.
Gamma slow 30-80 Hz, low amplitude.
Associated with sensory processing – occurs during REM sleep.
Origin – local neocortical generator.
Function – temporal code for primary sensory information.
Read:
Abnormal network synchrony in AD.
Rodent study suggests:
- Deficits in PV interneurons => deficits in gamma => deficits in memory.
Human post-mortem studies have shown decreased PV expression in humans
so same thing applies.
Means that targeting interneurons and increasing their activity could restore
function.
