EEG, Sleep and Circadian Rhythms

Question 1

What is sleep

Answer 1

State of unconsciousness in which we can be aroused

Question 2

Describe sleep

Answer 2

Cyclical and predictable

Question 3

What is the theory of sleep?

Answer 3

Sleep occurs due to active inhibitory processes that originate in the pons. Something below the level of the mid-pons must be actively sending inhibitory impulses to the cortex

Evidence suggests the activity originates in the Reticular Formation of the brain stem, an area now known to be closely associated with controlling the state of consciousness. It sends projections to the thalamus and higher cortical areas.

Sleep inducing peptides can be isolated from the CSF of sleep deprived animals and when injected into the brains of different animals induce a “natural” sleep almost immediately.

Question 4

How is the hypothalamus related to sleep?

Answer 4

Evidence also supports involvement of the hypothalamus, and it’s suprachiasmatic nuclei (SCN), in induction of sleep

SCN activity demonstrates ~24hr circadian rhythm and controls release of melatonin from the pineal gland

Inhibitory neurons in SCN are stimulated by light and act to inhibit pineal gland. Darkness therefore corresponds with decreased activity in the SCN and increased melatonin release and feelings of sleepiness in humans

Question 5

What does the SCN control?

Answer 5

demonstrates ~24hr circadian rhythm and controls release of melatonin from the pineal gland

Question 6

What is the pineal gland?

Answer 6

produces melatonin, a serotonin-derived hormone which modulates sleep patterns in both circadian and seasonal cycles

Question 7

What does light and darkness do to the SCN?

Answer 7

Inhibitory neurons in SCN are stimulated by light and act to inhibit pineal gland

Darkness corresponds with decreased activity in the SCN and increased melatonin release and feelings of sleepiness in humans

Question 8

What is the circadian rhythm of melatonin release likely linked to inhibition of what?

Answer 8

orexin

Question 9

What is orexin?

Answer 9

an excitatory neurotransmitter released from hypothalamus - required for wakefulness

Orexin neurons are active during the waking state and stop firing during sleep

Defective orexin signalling causes narcolepsy; individual will suddenly fall asleep, sometimes even when talking

Question 10

How does serotonin relate to sleep?

Answer 10

Many neurons within the reticular formation are serotonergic; drugs that block serotonin formation inhibit sleep suggesting serotonin must be critical to sleep induction

These effects may be related to melatonin production as serotonin is a precursos

Question 11

What are the 2 ways of assessing the level of consciousness in an awake person?

Answer 11

1. Look at their behaviour, general alertness, speech patterns, speech content, reading, writing and calculating skills. Spell words backwards or count backwards
2. Record patterns of brain activity using ElectroEncepheloGram (EEG). EEG uses electrodes placed on the scalp to record activity of underlying neurons

Question 12

EEG recordings show wave patterns that reflect the electrical activity of the brain

How can these waves be analysed?

Answer 12

1. Amplitude: the size of the wave (ranges from 0-200 µV) - tends to decrease with increasing neuronal excitation
2. Frequency: number of waves per second (ranges from 1-50+) - In general frequency increases with neuronal excitation

Question 13

What are the 4 main type of wave patterns seen?

Answer 13

1. Alpha
2. Beta
3. Theta
4. Delta

Question 14

When are alpha waves seen?

Answer 14

In the relaxed, awake state, EEG is characterised by high frequency, high amplitude waves termed a waves

Question 15

When are beta waves seen?

Answer 15

In the alert, awake state the EEG is characterised by even higher frequency, low amplitude asynchronous waves termed b waves

Low amplitude comes about, not because of low activity, but precisely the opposite

However this increase in activity is asynchronous as brain is doing so many things at once, and opposing polarities of the signals cancel each other out and do not get recorded on EEG

Question 16

When are theta waves seen?

Answer 16

Theta waves are characterised by low frequency waves which can vary enormously in amplitude

They are common in children, and during times of emotional stress and frustration in adults

They also occur during sleep in both adults and children

Question 17

When are delat waves seen?

Answer 17

Delta waves have very low frequency but high amplitude

They occur in deep sleep

Question 18

How many stages are there in the sleep cycle?

Answer 18

5

Question 19

What is the sleep cycle?

Answer 19

Stage 1 - Slow wave, non-REM, S-sleep. Slow eye movements. Light sleep. Easily roused. High amplitude, low frequency theta waves

Stage 2 – Eye movements stop. Frequency slows further but EEG shows bursts of rapid waves called “sleep spindles” (clusters of rhythmic waves, ~12-14Hz)

Stage 3 – High amplitude, very slow (2Hz) delta waves interspersed with short episodes of faster waves, spindle activity declines

Stage 4 – exclusively delta waves. Very difficult to rouse from stage 3 and 4 sleep. Known as Deep Sleep. Sleep walking/talking occurs during these stages

REM sleep - during which there are rapid eye movements. Dreams occur during REM sleep. 25% of sleep is REM - may look like stage 1 sleep in diagrams but it is not the same thing

Question 20

When does amplitude increase in the sleep cycle?

Answer 20

in deep sleep

Question 21

When are slow and fast sleep waves seen in the sleep cycle?

Answer 21

stages 1-4 = slow wave sleep

REM sleep is characterised by fast waves, eerily similar to those of the awake sleep

Question 22

What percentage of sleep is REM sleep?

Answer 22

25%

Question 23

What is the typical pattern of a nights sleep?

Answer 23

stage 1 to stage 2 to 3 to 4 then back to 3 then 2 then REM then up to 4 and back down to REM and continues like that

Question 24

When does deep sleep normally occur?

Answer 24

in the first hours of sleep

Question 25

What is the most restful type of sleep?

Answer 25

deep sleep

Question 26

What is deep sleep associated with?

Answer 26

Associated with decreased vascular tone (and therefore BP), respiratory and basal metabolic rate (hence drop in BT)

Question 27

How does the REM waves as seen on a EEG differ from deep sleep

Answer 27

waves are desynchronized, high frequency, low amplitude, very like the awake state hence aka. paradoxical sleep

Question 28

How often does REM sleep occur?

Answer 28

lasts 5-30 mins every 90 mins

more frequent as the night progresses and rest and recovery are established

Question 29

WHat stage of sleep do dreams often occur?

Answer 29

REM sleep

Question 30

Do any muscles move in REM sleep?

Answer 30

Eye muscles show bursts of rapid activity. Profound inhibition of all other skeletal muscles due to inhibitory projections from pons to spinal cord. Prevents acting out of dreams

_{(This inhibition is lacking in REM Sleep Behavioural Disorder and people may act out their dreams, sometimes with disastrous consequences)}

Question 31

WHat happens to your HR/RR and brain metabolism during REM sleep and what is seen on a EEG?

Answer 31

HR/RR become irregular and brain metabolism

EEG pattern mimics beta waves associated with highly alert, awake state

Question 32

Is it easy or hard to wake someone in REM sleep?

Answer 32

Very difficult to arouse an individual from REM sleep

Question 33

If someone is deprived of REM sleep do they need to catch up on it?

Answer 33

yes

there is always a catch up when able to sleep again indicating that REM sleep must have an important physiological function

Question 34

What symptoms would a person have if they were sleep deprived?

Answer 34

impairment of cognitive function

impairment of physical performace

sluggishness

irritability

Question 35

What does sleep help support in humans?

Answer 35

1. Neuronal plasticity - allows changes in brain and to function properly
2. Learning and memory
3. Cognition
4. Clearance of waste products from CNS
5. Conservation of whole body energy (although cerebral O2 consumption may actually increase, esp. during REM sleep)
6. Immune function (reason sleep increases when ill?)

all are comprimised when sleep deprived but mechanism is unclear

Question 36

How does lseep change over a life time?

Answer 36

total sleep time decreases through child and tennage years and percentage of REM sleep also decreases

total sleep time is highest during development when brain maturation and synaptic formation is occuring rapidly

so why is it needed in adults? - sleep may be needed in any situation where synaptic plasticity is important e.g. memory

Question 37

What is insomnia?

Answer 37

a “chronic inability to obtain the necessary amount or quality of sleep to maintain adequate daytime behaviour”, very subjective, very common. Affects » 33% of adults

Question 38

What are the 2 types of insomnia that may be seen?

Answer 38

chronic, primary insomnia where there is usually no identifiable psychological or physical cause

temporary, secondary insomnia in response to pain, bereavement or other crisis. Usually short lived

Question 39

What is the treatment of insomnia?

Answer 39

barbiturates (Stops deep and REM sleep which are the most important parts of sleep and increases time to fall asleep) and benzodiazepines (addictive and cause problems on withdrawl) used to be used but are not anymore as they have been proven to have negative effects

preferred approach to help treat insomnia is a change in behaviour to support induction of sleep, promote habits that are conducive to sleep promotion

Question 40

What are nightmares?

Answer 40

a strong visual component and are seen during REM sleep, typically occurring quite far on through the night

Waking will stop the nightmare and the individual will have a clear recollection of the “dream”

Question 41

What are night terrors?

Answer 41

occurs in deep, delta sleep and are common in children 3-8 years, typically occurring early in the night

Children thrash and scream and may sit or stand up with their eyes open but are not properly awake and often fail to recognise their parents

The child does not remember the episode on waking the following morning

Question 42

What is another name for Somnambulism?

Answer 42

sleep-walking

Question 43

What is sleep-walking?

Answer 43

Somnambulists walk with their eyes open, can see and will avoid objects, can carry out reasonably complex task such as prepare food and will often obey instructions but have no recall of the episode when woken

Question 44

When does sleep-walking occur?

Answer 44

occurs exclusively in non-REM sleep, mainly in Stage 4 sleep and is more common in children and young adults, probably due to the decline in Stage 4 sleep with age

Question 45

What is narcolepsy?

Answer 45

1:2000 suffer from narcolepsy

Enter directly into REM sleep with little warning - suddenly flling asleep

Symptoms could be interpreted as intrusion of REM sleep characteristics onto the waking state

Very dangerous because of accident risk if e.g. driving

Linked to dysfunctional orexin release from the hypothalamus (see earlier).