EEG, Sleep and Circadian Rhythms Flashcards
What is sleep
State of unconsciousness in which we can be aroused
Describe sleep
Cyclical and predictable
What is the theory of sleep?
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.
How is the hypothalamus related to sleep?
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
What does the SCN control?
demonstrates ~24hr circadian rhythm and controls release of melatonin from the pineal gland
What is the pineal gland?
produces melatonin, a serotonin-derived hormone which modulates sleep patterns in both circadian and seasonal cycles
What does light and darkness do to the SCN?
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
What is the circadian rhythm of melatonin release likely linked to inhibition of what?
orexin
What is orexin?
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
How does serotonin relate to sleep?
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
What are the 2 ways of assessing the level of consciousness in an awake person?
- Look at their behaviour, general alertness, speech patterns, speech content, reading, writing and calculating skills. Spell words backwards or count backwards
- Record patterns of brain activity using ElectroEncepheloGram (EEG). EEG uses electrodes placed on the scalp to record activity of underlying neurons
EEG recordings show wave patterns that reflect the electrical activity of the brain
How can these waves be analysed?
- Amplitude: the size of the wave (ranges from 0-200 µV) - tends to decrease with increasing neuronal excitation
- Frequency: number of waves per second (ranges from 1-50+) - In general frequency increases with neuronal excitation
What are the 4 main type of wave patterns seen?
- Alpha
- Beta
- Theta
- Delta
When are alpha waves seen?
In the relaxed, awake state, EEG is characterised by high frequency, high amplitude waves termed a waves
When are beta waves seen?
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
When are theta waves seen?
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
When are delat waves seen?
Delta waves have very low frequency but high amplitude
They occur in deep sleep
How many stages are there in the sleep cycle?
5
What is the sleep cycle?
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
When does amplitude increase in the sleep cycle?
in deep sleep
When are slow and fast sleep waves seen in the sleep cycle?
stages 1-4 = slow wave sleep
REM sleep is characterised by fast waves, eerily similar to those of the awake sleep
What percentage of sleep is REM sleep?
25%
What is the typical pattern of a nights sleep?
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
When does deep sleep normally occur?
in the first hours of sleep
What is the most restful type of sleep?
deep sleep
What is deep sleep associated with?
Associated with decreased vascular tone (and therefore BP), respiratory and basal metabolic rate (hence drop in BT)
How does the REM waves as seen on a EEG differ from deep sleep
waves are desynchronized, high frequency, low amplitude, very like the awake state hence aka. paradoxical sleep
How often does REM sleep occur?
lasts 5-30 mins every 90 mins
more frequent as the night progresses and rest and recovery are established
WHat stage of sleep do dreams often occur?
REM sleep
Do any muscles move in REM sleep?
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)
WHat happens to your HR/RR and brain metabolism during REM sleep and what is seen on a EEG?
HR/RR become irregular and brain metabolism
EEG pattern mimics beta waves associated with highly alert, awake state
Is it easy or hard to wake someone in REM sleep?
Very difficult to arouse an individual from REM sleep
If someone is deprived of REM sleep do they need to catch up on it?
yes
there is always a catch up when able to sleep again indicating that REM sleep must have an important physiological function
What symptoms would a person have if they were sleep deprived?
impairment of cognitive function
impairment of physical performace
sluggishness
irritability
What does sleep help support in humans?
- Neuronal plasticity - allows changes in brain and to function properly
- Learning and memory
- Cognition
- Clearance of waste products from CNS
- Conservation of whole body energy (although cerebral O2 consumption may actually increase, esp. during REM sleep)
- Immune function (reason sleep increases when ill?)
all are comprimised when sleep deprived but mechanism is unclear
How does lseep change over a life time?
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
What is insomnia?
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
What are the 2 types of insomnia that may be seen?
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
What is the treatment of insomnia?
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
What are nightmares?
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”
What are night terrors?
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
What is another name for Somnambulism?
sleep-walking
What is sleep-walking?
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
When does sleep-walking occur?
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
What is narcolepsy?
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).
