Lecture 9 - Sleep 2: Sleep, dreaming and memory

Question 1

EEG stands for

Answer 1

Electroencephalogram

Question 2

EOG stands for

Answer 2

Electrooculogram

Question 3

EMG stands for

Answer 3

Electromyogram

Question 4

Electroencephalogram

Answer 4

gross brain electrical activity, generated by neurons that create synaptic potentials

Question 5

Electrooculogram

Answer 5

eye movements, sits on muscles next to eyes and detect the activation of these muscles

Question 6

Electromyogram

Answer 6

muscle activity, other muscles that aren’t captured on the EOG

Question 7

EEG patterns as you sleep

Answer 7

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

Question 8

Awake

Answer 8

low voltage, high-frequency beta waves

Question 9

Drowsy

Answer 9

Alpha waves prominent

Question 10

Stage 1 sleep

Answer 10

Theta waves prominent

Question 11

Stage 2 sleep

Answer 11

Sleep spindles and mixed EEG activity

Question 12

Slow wave sleep (stage 3 and stage 4 sleep)

Answer 12

Progressively more delta waves (stage 4 shown)

Question 13

REM sleep graph

Answer 13

Low voltage, high-frequency waves
EOG detects rapid eye movements
EMG shows loss of muscle tone

Question 14

REM sleep

Answer 14

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

Question 15

Slow wave sleep

Answer 15

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.

Question 16

Common beliefs about dreams - External stimuli can be incorporated into dreams

Answer 16

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

Question 17

Common beliefs about dreams - dreams last only an instant

Answer 17

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

Question 18

Common beliefs about dreams - Some people do not dream

Answer 18

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

Question 19

Common beliefs about dreams - Penile and clitorial erections indicate dreams with sexual content

Answer 19

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

Question 20

Common beliefs about dreams - People only dream in black and white

Answer 20

Can test by waking people up during REM sleep

Some dreams do not have colour but by large many of them do

Question 21

Common beliefs about dreams - Eye movements in REM sleep relate to dream content

Answer 21

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

Question 22

Common beliefs about dreams - If you fall in your dream and hit the ground, you will really die

Answer 22

Only people that would know if this statement is true are dead people….

Question 23

Plihal and Born (1977)

Answer 23

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

Question 24

Wagner et al. 2004

Answer 24

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)

Question 25

Rasch et al (2007) and Diekelmann and Brown (2010)

Answer 25

‘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

Question 26

How might memories be enhanced during sleep?

Answer 26

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.

Question 27

During awake…

Answer 27

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

Question 28

During slow wave sleep ….

Answer 28

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

Question 29

Neocortical sleep spindles co-occur with

Answer 29

Sharp Wave Ripples

Question 30

Sharp wave ripples occur during

Answer 30

slow wave sleep

Question 31

SWR and hippocampal cells

Answer 31

Hippocampal cells fire in the same order they did during the experience, but the sequence is sped up

Question 32

Neocortical sleep spindles

Answer 32

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)

Question 33

Sleep spindle density predicts

Answer 33

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

Question 34

Mechanism for memory consolidation

Answer 34

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