Sleep and Consciousness Flashcards
What are the different ways of defining sleep?
Behavioural criteria e.g. posture, movement, responsiveness to stimuli, reversibility.
Physiological criteria e.g. from EEG, EOG (electrooculogram), EMG (electromyogram), heart rate and respiration.
What is the behavioural criteria of sleep?
- Stereotypic posture
- Minimal movement
- Reduced responsiveness to external stimuli
- Reversible stimulation unlike coma, anaesthesia or death
Describe the changes in EEG during the 5 phases of sleep.
- In NREM generally becomes slower i.e. there is a lower background frequency.
- Sleep spindles can also emerge in NREM sleep.
- In REM the EEG readings become more like those when awake i.e. faster
At what stage of sleep does REM sleep occur?
Stage 5
(there are 5 stages and stages 1-4 are NREM sleep)
Describe the changes on EOG during the stages of sleep.
EOG - No movement during stages 1-4 then movement of eyes increases in REM sleep (stage 5)
Describe the changes in EMG during the stages of sleep.
EMG - tone is generally reduced when you are asleep, this stops you acting out what you are doing in your dreams.
How long is each cycle of sleep? What changes occur to the cycles as you sleep?
- Stages of sleep are tightly regulated into 90min cycles.
- You go through the 5 stages of sleep continuously during the time that you are asleep
- Early on in your sleep the NREM stages take up more of the sleep cycle but later REM sleep is longer.
What is the system in charge of maintaining arousal?
Reticular activating system - controls consciousness
Found in the brainstem and projects to the thalamus, hypothalamus and cortex.
They are necessary but not sufficient for conscious awareness. The playing out of consciousness probably does not reside in the RAS alone but it gates the activity in the cortex.
Describe the hypothalamic systems in charge of controlling sleep/wake cycles.
In the lateral hypothalamus - orexin/hypocretin promote WAKEFULNESS
The anterior hypothalamus/ventrolateral preoptic nucleus promotes SLEEP
What are the relative effects of the lateral hypothalamus and ventrolateral peoptic nucleus on the RAS?
LH pathways promote the activity of the RAS
VLP pathways inhibit activity of the RAS.
Name a hypothalamic hormone that promotes wakefullness.
Orexin/hypocretin
What controls the circadian synchronisation of the sleep/wake cycle?
Suprachiasmatic nucleus - synchronises sleep with falling light level.
When patients are constantly in a dark room they won’t be able to sleep at night as easily because the SCN is confused and not sending as many signals.
What are the effects of the suprachiasmatic nucleus on other systems affecting sleep?
SCN connects to the retina directly - this brings in signals about the light
SCN then interacts with the VLP and LH systems, and RAS.
It also sends information to the pineal glansd –> melatonin release
What are the effects of sleep deprivation?
- -Psychiatric and neurological
- Sleepiness, irritability, stress, mood fluctuations, depression, impulsivity, hallucinations
- -Neurological
- Impaired attention, memory, executive function
- Risk of errors and accidents
- Neurodegeneration (?)
- -Somatic
- Glucose intolerance
- Reduced leptin/increased appetite
- Impaired immunity
- Increased risk of cardiovascular disease and cancer
- Death
What imaging technique can be used to show that sleep deprivation affects brain function?
fMRI
Describe the accurate regulation of sleep after sleep loss.
- Reduced latency to sleep onset - takes you less time to fall asleep
- Increased slow wave sleep (NREM)
- Increase in REM sleep (after selective REM sleep deprivation - almost as if the body is keeping a tally and trying to catch up)
What are the functions of sleep?
- Restoration and recovery – but active individuals do not sleep more
- Energy conservation – 10% drop in BMR – but lying still is just as effective
- Predator avoidance – but why is sleep so complex?
- Specific brain functions – memory consolidation …
When does dreaming occur?
Mostly in REM sleep but also in NREM
When are dreams most easily recalled?
When the person has been woken up from REM sleeo
What are dreams likely to be like? Where is brain activity higher during dreaming?
- Dreams are more likely to be emotional than “real life”
- Brain activity in limbic system is higher than in frontal lobe during dreams.
What are the functions of dreams?
Possible functions:
- Safety valve for antisocial emotions – getting out your emotional distresses
- Disposal of unwanted memories
- Memory consolidation(perhaps)
What are the causes of chronic insomnia?
Causes of chronic insomnia:
-
physiological e.g.
- sleep apnea,
- chronic pain
-
brain dysfunction eg.
- depression (if depressed or anxious –> a phenomenon of early morning wakening)
- fatal familial insomnia (prion disease)
- night working
How is insomnia treated?
- Sleep hygiene
- Hypnotics
- Sleep CBT
Descirbe steps which can be taken to improve “sleep hygiene”.
Improving sleep quality: sleep hygiene
- establishing fixed times for going to bed/waking up
- creating a relaxing bedtime routine
- only going to bed when you feel tired
- maintaining a comfortable sleeping environment
- not napping during the day
- avoiding caffeine, nicotine and alcohol late at night – some people metabolise caffeine more quickly than others
- avoiding eating a heavy meal late at night
- don’t use back-lit devices shortly before going to bed – light that comes from screens disrupts sleep wake cycle
What is hypersomnia?
Excessive daytime sleepiness
Name some primary causes of hypersomnia.
- Narcolepsy
- Idiopathic hypersomnolence
- Post-traumatic brain injury
Name some secondary causes of sleep hypersomnia.
Secondary = due to poor quality overnight sleep.
Common causes:
- Obstructive sleep apnoea
- Restless legs syndrome and periodic limb movements of sleep
- Nocturnal pain – for examples diabetic neuropathy or arthritis.
- Neurodegenerative diseases – for example parkinsonism
- Medication (hypnotic misuse)
- Environmental factors like noise
- Anxiety
Rare:
- Oesophageal acid reflux
- Severe bruxism
What subjective test can be used to assess sleepiness? Descirbe it briefly.
Epwoth Sleepiness Scale
- Rate the likelihood of dozing in different situations e.g. watching TV, sitting and reading.
- Patient rates each item as 0 (would never dose) to 3 (high chance of dozing).
- ESS score is a total of 0-24. Higher score = more sleepiness
Describe the links between sleep and neurological diseases.
There is an increasing link between neurodegenerative diseases and sleep.
However it is unclear whether neurodegenerative diseases early on cause a lack of sleep or if it is the lack of sleep causing the neurodegenerative diseases.
Which two dimensions can consciousness sometimes be divided into? Describe where these would fall in relation to these dimensions:
- General anaesthesia
- Locked-in syndrome(LIS)
- vegetative state
- Coma
- Generalised seizures
Vigilance (wakefulness, eyes open)
Awareness (level/content of consciousness)
What two mechanisms govern consciousness in the brain (in terms of the dynamics of neuronal activity)? Explain this mechanism.
Differentiation and integration - you are conscious when you brain activity is both integrated and differentiated
Explanation:
-
Differentiation - conscious experience needs to be broken up into pieces.
- E.g. if you disconnected different parts of the brain, although there would be differnetiation there would be no integration of information so no conscious experience.
-
Integration - fragments of conscious experience need to be unified.
- E.g. in a generalised seizure brain activity is highly synchornous so highly integrated but there is no differentiation (no variability) so no conscious experience.
What are the two types of processing of consciousness in the brain? What are the each involved in?
- Feed-forward processing - involved in subliminal or non-conscious throught
- Top-down recurrent processing - conscious access
Name a technique (other than GCS) which can be used to assess a person’s level of consciousness.
Pertubational complexity index (PCI) - transcranial magnetic stimulation (TMS) adnd EEG.
- You administer TMS, triggering a response in the cortex then you measure the brain activity with EEG afterwards - you look at the complexity of the activity afterwards.
Compare the levels of arousal and awareness in these conditions:
- Coma
- VS
- MCS
- LIS
Which areas of the brain light up when you imagine yourself playing tennis? Which light up in spatial navugation imagery? Why was this useful?
This was used as a “yes” and “no” signal in vegetative state patient who were asked different questions and asked to respond by imagining these which would then cause changes on an fMRI.
Which EEG rhythm is most prominent in healthy conscious individuals?
Alpha 8-13Hz
Describe the GCS classification of consciousness.
What is decorticate and decerebrate posturing? Which gets a lower/worse score on the GCS? Why?
Difference between decorticate and decerebrate posturing is in the arms.
- Decorticate posturing = arms are flexed
- Decerebrate = arms are extended
Decerebrate is much worse as whole brain affected not just the cortex so you score worse i.e. lower. Different lesions can affect the posture in different ways.
