7. Sleep Flashcards
Jenkins & Dallenbach (1924)
Examined the blip in Ebbinghaus data using more participants
- Between evening and morning (separated by sleep) there seemed to be less forgetting
(learning in the evening vs learning in the morning)
- Found much less forgetting following sleep
!Active role of sleep or lack of interference???
…They argued lack of interference
What is polysomnography?
- EEG
+ - EMG (electromyography - muscle tension, often on chin)
+ - EOG (electrooculography, eye movements)
Characteristics of Sleep:
Stage 1 (shallow sleep)
EEG:
- absence of alpha activity
- vertex sharp waves
EMG:
- relatively low amplitude
EOG:
- Slow eye movement
Characteristics of Sleep:
Stage 2
EEG:
- Sleep spindles (oscillating at 12-15Hz)
- K-complexes (high voltage, sharp wave)
EOG:
- no eye movements
Characteristics of Sleep:
Stages 3 & 4 (Slow wave sleep - SWS)
EEG:
- slow Delta activity (<=2Hz) with high-voltage (>=75uV)
EMG:
- low tonic activities
EOG:
- no eye movement
“Dead to the world” - very hard to be woken up from SWS
Characteristics of Sleep:
REM sleep (rapid eye movement)
EEG:
- mixed frequency (rel low voltage)
EMG:
- ironically suppressed (sleep paralysis)
EOG:
- contains rapid eye movements
Plihal & Born (1997):
Partial sleep deprivation
- suggestive evidence for the importance of SWS and REM
Took advantage of half of sleep being SWS and half being REM
Looked at effects on performance in:
- Standard procedural tasks (mirror tracing):
- People who get REM (late night sleep) do much better in mirror tracing
- Declarative memory tasks (paired-associate learning):
- People who get SWS (or early night sleep) do much better with declarative memory
Marr (1970)
System consolidation theory (computational model)
- Hippocampus stores day’s events
- subsequent transfer of info to the neocortex
- transfer based on hippocampal replay
Changes in brain representations of memories of pictures (Evidence for system consolidation theory)
Takashima et al (2006)
Longitudinal (3 month) study
Day 1:
1. Study 320 pictures (remote)
- Rest/nap
- Study 80 pictures (recent)
- Recognition test in scanner:
- 80 remote pics
- 80 recent pics
- 80 new (not seen before) pics
Results suggest that:
!SWS is important for declarative memory
!Performance on REMOTE items correlated with hippocampus activity (mediating acquisition of new memories)
!Then these memories taken over by activity in vmPFC
ACTIVE Systems Consolidation theory
Born et al (2006, 2010, 2012)
- Modification of standard model (fleshing out sleep’s role)
- Hippocampus is associated with initial learning of a new declarative memory
- Sleep is then the medium for hippocampal replay over many nights of sleep
- Then the consolidated memory becomes ingrained in the cortex without the participation of the hippocampus
Systems consolidation of memory:
Rasch & Born (2013)
(Staresina et al, 2015; electrode arrays implanted in the brain)
Role of:
- Slow-wave oscillations
- Spindles
- Hippocampal ripples
Slow-wave oscillations:
- Provide timing signal for other brain components to do their job at the right time (exchange of info between hip and cortex)
Spindles:
- Thalamo-cortical
- Are aligned with S-W oscillations
Hippocampal ripples:
- When spindle wave dips, the ripples are active (synched activity between the two) = Hippocampus sending information to the neocortex?
Targeted memory reactivation
Rudoy et al (2009)
If hippocampal replay of memories occurs in sleep, then possibly what you can do is enhance/model this replay synthetically by stimulating the brain
(using sound)
- Learning objects and their locations (cat, kettle….; declarative memory task)
- as you see the objects, their characteristic sounds are played along with them (cat + meow) - Nap (25 min)
- played sounds for half of the objects during SWS
At test after the nap:
!!!!Significantly less forgetting for items that were played during sleep
- sound MAY trigger hippocampal replay
Marshall et al (2006)
Stimulating the sleeping brain (transcranial DC stimulation)
If you can make the slow oscillations of SWS stronger with DC stimulation that would result in better memory retention for declarative memories
Ngo et al (2013)
Enhancing slow waves using sound stimuli (sleep)
Presenting sounds during the up-states (peaks) of slow wave
!!!When stimulated with sounds, the oscillation does not have greater peaks but carries on oscillating for a little longer (~3s)
!!!These longer oscillations led to better retention of information boosted by auditory stimuli in sleep
!!!Also, more SWS = better retention
Hippocampal reactivation in animals through electrodes implated into animal brains
(O’Keefe & Nadel, 1978)
place cell activation in a maze
Place cells fire when rats are in a certain location
- likely to be a form of cognitive mapping
Hippocampal reactivation in animals through electrodes implated into animal brains
Wilson & McNaughton (1994)
- Slow-wave sleep and reactivation maze navigation
Showed that place cells that fire in sequence when exploring a maze show similar firing sequences in subsequent SWS
(Suggests replay)
! These are also found in nonhuman primates and songbirds
Euston et al (2007)
Reactivation in sleep:
- multiple cell recording in mPFC and hippocampus
- found sequences of neurons firing in the mPFC and the hippocampus during maze exploring
!!!in replay during sleep, these sequences fire at a much faster rate
Beyond classical sleep consolidation
Walker (2009); Stickgold and Walker (2010)
Sleep is for more than just strengthening/stabilising memory
Unitization:
- Representations initially shared between the hippocampus and the cortex
- then the representation becomes unitized in the cortex as its own thing
Assimilation:
- Changes in the new cortical representation or pre-existing cortical representations to integrate the new representation with other ones
Abstraction:
- Being able to generalize the information like a cortical schema
- You rarely encounter exactly the same circumstances more than once, so this enables a flexibility in applying the established memory
Beyond classical sleep consolidation
Kuriyama et al (2004)
Evidence for unitization of representations into the cortex
Learning finger-tapping sequences of 9 elements (e.g. 2, 5, 3, 1, 4, 2…)
They had some evidence that during initial learning we develop “chunks” to break down the sequence
The following sleep, the sequence was unitized (instead of known in chunks, it was known as a whole)
Beyond classical sleep consolidation
Tamminen et al (2010)
Evidence for assimilation of representations in the cortex
Lexical assimilation (learning new words) is facilitated by sleep
- learning something new may influence the lexical neighbours of that word
e. g. the “Brexit effect”
- at some point in your life you encountered the word “Brexit” for the first time in your life
- Initially “Brexit” may not be linked with other words (e.g. breakfast~bread brexit)
- In the final state, it may be linked with words that you knew before (e.g. breakfast~bread~brexit) ##################
In the study they taught a new word “Cathedric”
- Similar word such as: Cathedral
Following sleep, the new word started competing with existing words
- This onset of competition was correlated with the amount of sleep spindles present during sleep
(More spindles = bigger changes how new information influenced old information)
- people getting word Brexit and breakfast mixed up after hearing it so much*
Beyond classical sleep consolidation
Payne et al (2009)
Evidence for abstraction of representations in the cortex
Hippocampal transfer may lead to reorganisation and restructuring of new knowledge
Used Deese-Roediger-McDermott (DRM) paradigm:
- “bed, rest, awake, tired, dream, wake, snooze, blanket, doze, slumber, snore, nap, peace, yawn, drowsy”
She looked into to what extent people recalled the critical word (Sleep) after period or wake or sleep.
!!!!Following sleep, people were more likely to recall the critical word (Sleep) after sleep compared to wake
