Lecture 9 - Sleep 2: Sleep, dreaming and memory Flashcards
EEG stands for
Electroencephalogram
EOG stands for
Electrooculogram
EMG stands for
Electromyogram
Electroencephalogram
gross brain electrical activity, generated by neurons that create synaptic potentials
Electrooculogram
eye movements, sits on muscles next to eyes and detect the activation of these muscles
Electromyogram
muscle activity, other muscles that aren’t captured on the EOG
EEG patterns as you sleep
Theta waves are at a lower frequency, change from random activity when someone is awake
As the sleeper progresses from stage 1 to stage 4 sleep the EEG becomes more synchronised and of higher amplitude
Then after a period of about 60 minutes the EEG begins to resemble the stage 1 or awake state, muscle tone decreases and the eyes start moving rapidly
Muscle tone decreasing means that you become very relaxed
Synchrony suggests that neurons are all firing together which means that there is the potential for larger potentials when all the neurons are firing at the same time (summate)
Yellow graph shows that there are small REM periods initially and then throughout the night the length of the REM periods increases
Awake
low voltage, high-frequency beta waves
Drowsy
Alpha waves prominent
Stage 1 sleep
Theta waves prominent
Stage 2 sleep
Sleep spindles and mixed EEG activity
Slow wave sleep (stage 3 and stage 4 sleep)
Progressively more delta waves (stage 4 shown)
REM sleep graph
Low voltage, high-frequency waves
EOG detects rapid eye movements
EMG shows loss of muscle tone
REM sleep
Rapid eye movement sleep is a unique phase of sleep, characterized by random rapid movement of the eyes, accompanied by low muscle tone throughout the body, and the propensity of the sleeper to dream vividly.
Also known as paradoxical sleep
High correlation with dreaming
80% report dreaming during REM, 7% report dreaming during slow wave sleep
Dream = a holistic mental experience (some would say hallucination) while asleep consisting of characters interacting over a period of time in a succession of several organised and apparently real, although bizarre, vivid images or scenes
Lower chance of vivid dreams when waking someone from slow wave sleep
Slow wave sleep
Slow-wave sleep (SWS) refers to phase 3 sleep, which is the deepest phase of non-rapid eye movement (NREM) sleep, and is characterized by delta waves (measured by EEG). Dreaming and sleepwalking can occur during SWS. SWS is thought to be important for memory consolidation.
Common beliefs about dreams - External stimuli can be incorporated into dreams
Plenty of information to back this statement up therefore it is true
Such as parents being able to hear their young children crying when they are seemingly in a deep sleep
Common beliefs about dreams - dreams last only an instant
Usually people guess their dream duration is similar to the amount of time they were in REM sleep, usually consistent with external time therefore this statement is false
Common beliefs about dreams - Some people do not dream
Some do not dream due to pathology but most of the time it is because people do not remember their dreams, therefore this statement is false
Common beliefs about dreams - Penile and clitorial erections indicate dreams with sexual content
Does not seem to have any relation to the dream content, it is just a physiological response
In males, erections occur 3-5 times a night roughly lasting 30 mins even if they do not have a sexual dream
Therefore this statement is not necessarily true
Common beliefs about dreams - People only dream in black and white
Can test by waking people up during REM sleep
Some dreams do not have colour but by large many of them do
Common beliefs about dreams - Eye movements in REM sleep relate to dream content
REM sleep behaviour disorder is where people go into REM sleep and usually you have a decreased muscle tone but for people with this disorder this does not occur so people start acting out their dreams and the eye movements in these cases corresponds to what is occurring in these people’s dreams
This statement is therefore possibly correct
Common beliefs about dreams - If you fall in your dream and hit the ground, you will really die
Only people that would know if this statement is true are dead people….
Plihal and Born (1977)
Paired associate word list (explicit memory) and Mirror drawing (procedural memory) tested after REM and SWS. Explicit tasks improved by SWS
Procedural memory enhanced by REM
Learn at 11pm and test after 3 hours sleep (get early sleep) OR sleep 3 hours, learn at 2 am, sleep and test at 5am (get late sleep) OR control participants stay awake during the interval
Percent improvement = performance improvement, higher up you are the better you perform
These studies suggests that: declarative memory is enhanced by early (slow wave sleep?) sleep and that procedural memory is enhanced by late (REM?) sleep
Wagner et al. 2004
The scientists provided the subjects with two rules by which to generate a second string of numerals. In addition, a shortcut, which the researchers did not divulge, could be used to arrive at the target answer. After initial training, some participants were allowed to get a good nights sleep while others remained awake. When they returned to the problem eight hours later, those who had slumbered were twice as likely to find the shortcut as were those who hadnt slept. Members of a second group that trained in the morning and attempted the problem again later that day were also slower at finding the shortcut, suggesting that tiredness was not a factor for the poor performances.
Participants presented with a sequence completion task before (training) and after (test) sleep or control condition
On each trial, a different string of eight digits was presented
Each string was composed of the digits 1, 4 and 9 e.g. 1 1 4 4 9 4 9 4
For each string, subjects had to determine what the final digit was
A solution could be arrived at by computation or insight
Computation : two simple rules
The ‘same rule’ - the result of two identical digits is just this digit
The ‘different rule’ - the result of two non-identical digits is the remaining third digit
Insight = the 2nd digit is always the same as the last Blocks = blocks of training
Experiment suggests that whilst you are asleep and not necessarily conscious of what it going on around you, sleep can help you think about problems going on in the world around you whilst asleep (the brain is training to solve them)
Rasch et al (2007) and Diekelmann and Brown (2010)
‘Cueing’ memories during slow wave sleep enhances subsequent performance
Odour of peppermint for example and odour is provided to them whilst they are asleep and the odour is either associated with it or a new odour is presented (the second one is the control variable)
Odour previously associated with a task is given during sleep
Retrival performance shows people’s ability to perform the task
Suggests there can be processing of memory during sleep, a cue is given during sleep which has been previously associated which has reactivated that pathway to memory during sleep for slow wave sleep
During REM and during waking show no difference with odour preexposure
How might memories be enhanced during sleep?
Neocortex has a lot of information stored
Possible that the hippocampus is communicating with the neocortex to consolidate new memories
The neocortex is a set of layers of the mammalian cerebral cortex involved in higher-order brain functions such as sensory perception, cognition, generation of motor commands, spatial reasoning and language.
During awake…
During awake experience the hippocampus encodes events as sequences of cell firing
In the hippocampus we know that there are cells that will fire in an order that will correspond to a particular task/sequence of experiences you are having and we know this from many years of studies on land animals running along a track and we know that there are cells that fire at a particular location on that track
It has also been found that there are cells in the hippocampus that will fire in sequence when you are performing a particular task and these cells firing are dependent on the particular timing or activity you are doing
As you are performing a task the hippocampus is encoding different aspects of a particular task which produces a sequence of activity in the cells of the hippocampus
During slow wave sleep ….
During slow wave sleep the hippocampus replays events as sequences of cell firing during sharp wave ripples
cells fire in the same sequence that they did when you are actually experiencing the event
Neocortical sleep spindles co-occur with
Sharp Wave Ripples
Sharp wave ripples occur during
slow wave sleep
SWR and hippocampal cells
Hippocampal cells fire in the same order they did during the experience, but the sequence is sped up
Neocortical sleep spindles
Neocortical sleep spindles co-occur with SWRs
In the neocortex at about the same time as the hippocampus with the SWRs, in the neocortex are the sleep spindles which seems to suggest that the hippocampus is playing back information into the neocortex and the neocortex is responding with the sleep spindles which may be the biological basis for memory consolidation during sleep - hippocampus replaying events back into the neocortex and this information is being incorporated into the semantic structure that is held in the neocortex and potentially some of the information is being fed back into the neocortex
Lewis and Durrant (2011)
Sleep spindle density predicts
memory
EEG spindle density in neocortex during sleep predicts subsequent memory performance
Saletin and Walker (2012)
Give someone a memory task, let them sleep and then look at the rate/density of sleep spindles then the more sleep spindles you have the better the memory you have for the task
Positive correlation between sleep spindle density and the percentage of total recall
Sleep spindles occur in about one second
Mechanism for memory consolidation
Experience is encoded in the hippocampus
The representation of experience is replayed at high speed during slow wave sleep
Sleep spindles may reflect engagement of that replayed experience with information in the neocortex
These events may underlie episodic memory consolidation
