12 - EEG, Sleep and Circadian Rhythms

what is sleep

state of unconsciousness from which an individual can be aroused by normal stimuli, light, touch, sound etc

cyclical

what is coma

state of unconsciousness from which and individual cannot be aroused and does not respond to stimuli

what does circadian rhythm control

melatonin release by pineal gland

why does darkness allow sleep

inhibitor neurones in suprachiasmatic nuclei (SCN) are stimulated by light and inhibit pineal gland from releasing melatonin

darkness removes inhibition

stimulation of pineal gland

more melatonin

sleepiness

what causes narcolepsy

loss of orexin (hypocretin) neurones

-transitions from being awake directly into REM sleep

EEG waves - alpha waves

RELAXED AWAKE state

- high frequency medium amplitude

EEG waves - beta waves

ALERT AWAKE

- very high frequency low amplitude

EEG waves - theta waves

EARLY SLEEP

- low frequency varied amplitude

EEG waves - delta waves

DEEP SLEEP

- very low frequency high amplitude

N1

stage 1 NREM sleep

slow wave non-REM S-sleep

- absent/slow eye movements

- low muscle tone

-low voltage

HIGH AMPLITUDE LOW FREQUENCY THETA WAVES

N2

no eye movements

very low tone

frequency slows

EEG shows sleep spindles - clusters of rhythmic waves and K complexes

N3

deep sleep

slow wave sleep

no eye movement

low tone

- HIGH AMPLITUDE SLOW DELTA WAVES - interspersed with short episodes of faster waves

sleep cycle state R

delta waves ONLY

rapid eye movement

very low tone

low voltage, mixed frequency

when does sleep walking/talking occur

stages 3 and 4 deep sleep

when do dreams occur

REM

types of waves seen in REM

LOW AMPLITUDE HIGH FREQUENCY - similar to awake state

how does the sleep cycle go through the stages

1, 2, 3, 4 and cycle back through 4, 3, 2 then REM

when does deep sleep occur

first few hours of sleep

- most restful

what is deep sleep associated with

decreased vascular tone and therefore lower BP, respiratory and basal metabolic rates

what part of the brain is active during deep sleep

hippocampus - hence creating of new memories of dreams

how long is each sleep cycle

90 mins

what happens to eye muscles during REM

bursts of rapid activity

why do we not "act out" dreams during REM

there is profound inhibition of skeletal muscles due to inhibitory projections from pons to spinal cord (descending)

REM promoting pathways inhibit motor neurones which is why no movement during sleep

what is REM dependent on

cholinergic pathways within reticular formation and projections to thalamus, hypothalamus adn cortex

what increases REM time

anti-cholinesterases drugs

what does REM waves mimic

beta waves associated with alert awake state

W state

wakefulness

EEG - alpha rhythm first then low voltage

EOC - variable eye movements - both rapid and slow

EMG - normal or high muscle tone

significance of amplitude and frequency of EEG waves

Useful for diagnosis of epilepsy and altered states of consciousness, measures brain electrical activity 

polysomnography

sleep study measures:

Brain activity – EEG electroencephalogram 

Eye movement – EOC electro-oculogram 

Muscle tone – EMG electromyogram 

typical pattern of a night’s sleep in an adult

On falling asleep – transition is from wakefulness → non-REM sleep 

Non-REM sleep alternates with REM sleep 

Sleep cycles take about 90 min 

With each cycle the NREM becomes lighter and REM periods become longer 

Vivid dreams during REM sleep 

People usually wake up spontaneously from an episode of REM sleep 

with age there is less…

REM sleep

glymphatic hypothesis

NREM sleep allows clearance of metabolites from the brain, remodelling of synapses, preserve energy 

homeostatic sleep drive

substance (somnogen) accumulates during wakefulness, induces sleep, is degraded during sleep, best known candidate is adenosine 

circadian regulation

24-biological clock, endogenous cycles of physiology and behaviour with a period of 24 hours 

Circadian system requires light 

Circadian rhythms regulate the timing of the function, not the function itself 

where do EEG rhythms in non-REM sleep result from?

cortico-cortical and thalamo-cortical oscillations 

When awake cells active – inhibit asleep cells 

Asleep cells activate – inhibit awake cells 

symptoms of narcolepsy

• Chronic disease 

• Daytime sleepiness 

• Cataplexy (loss of muscle control - not always)

sleep stages in narcolepsy

• Non-REM sleep fragmentation 

• Reduced wakefulness 

• Sleep-onset REM 

Transitions from being awake directly into REM sleep 

obstructive sleep apnoea

Pharyngeal collapse during sleep, leads to oxygen desaturation, hypercapnia and sleep fragmentation 

symptoms of obstructive sleep apnoea

• Snoring 

• Witness apnoeas 

• Waking up with choking sensation 

• Excessive daytime sleepiness 

consequences of obstructive sleep apnoea

• Cardiovascular 

• Metabolic 

• Neurocognitive 

diagnosis of obstructive sleep apnoea is done by?

polysomnography

-SOA more common than narcolepsy

what is circadian rhythm

endogenous cycles of physiology and behaviour with a period of about 24 hours 

role of suprachiasmatic nucleus in circadian rhythmicity

Circadian rhythms regulated by the suprachiasmatic nucleus 

The removal of SCN abolishes circadian rhythms, transplanted SCN restores rhythms, SCN cells maintain rhythm in vitro 

circadian rhythms are the…

results of feedback loops in clock genes and SCN output coordinates local clocks 

what type of disorder is chronic insomnia disorder

insomnia disorder

what type of disorder is obstructive sleep apnoea and obesity hypoventilation syndrome

sleep related breathing disorders

what type of disorder is narcolepsy

central disorders of hypersomnolence

what type of disorder is jet lag and shift work disorder?

circadian rhythm sleep-wake disorders

what type of disorder is sleepwalking, sleep terrors, recurrent isolated sleep paralysis, exploding head syndrome

parasomnias

what type of disorder is restless leg syndrome, sleep-related bruxism

sleep related movement disorders