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
What is narcolepsy?
This is a PRIMARY problem with sleep regulation.
Falling asleep repeatedly during he day and d_isrupted sleep during the night._
Dysfunction of control of REM sleep.
What is narcolepsy often associated with?
Cataplexy.
What is cataplexy?
Sudden, brief loss of voluntary muscle tone, often triggered by strong emotions e.g. laughter
What is the cause of narcolepsy?
Orexin/hypocretin deficiency
What are the effects of shift work on physiology?
Physiological processes become dysregulated which can lead to:
- Sleep disorders
- Fatigue
- Increased risk of obesity, diabetes and cancer
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.
Give a definition of consciousness.
The state of being aware of and responsive to one’s surroundings.
/the subject’s exprience of the mind and the world around us.
What are the main 3 elements of consciousness?
- Level of consciousness
- Content of consciousness i.e. how rich the experience is
- Consciousness of self i.e. selfawareness
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 is the main system involved in consiousness? Describe its connections.
Reticular activating system - level of activity associated with consciousnes
- Reticular formation (RF) projects to hypothalamus, thalamus and cortex
- Other parts of the RAS include the VTA in the midbrain (sends dopaminergic neurons) and locus coeruleus in the pons (noradrenergic neurons).
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
What is the name of the brain network seen on an fMRI which is activated when someone’s mind is wandering?
Default mode network
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.
Describe the level of awareness and vigilance in a person with LIS.
They will have the same level of consciousness and arousal as someone who is fully awake BUT they have no motor outputs.
What is NCC?
Neural correlates of consciousness
This is the minimum neuronal mechanisms jointly sufficient for any one specific conscious experience.
Where have NCC primarily been shown to be localised?
In the posterior cortical hot zone that includes sensory areas
Name and describe three disroders of consciousness.
- Coma - absent wakefulness and absent awareness
- Vegetative state - wakefulness with absent awareness
- Minimally conscious state (MCS) - wakefulness with minimal awareness
What is the definition of coma?
State of UNROUSABLE unresponsiveness, lasting >6HOURS in which a person:
- cannot be awakened
- fails to respons normally to painful stimuli, light or sound
- lacks a normal sleep-wake cycle and
- does not initiate volunatry actions
Compare the characteristics of vegetative state to coma.
VS is wakefulness without awareness, whereas coma is absence of wakefulness and awareness.
In VS the patient also: … which does not happen in coma.
- has capacity for spontaneous or stimulus-induced arousal
- has sleep wake-cycles
- shows a range of reflexive and spontaneous behaviours
What are the characteristics of MCS?
Inconsistent but reproducible responses above the level of sponatneous or reflexive behaviour, which indicate some degree of interaction with their surroudnings.
Evidence of of self- or environmental awareness.
Are brainstem death or LIS examples of disorders of consciousness?
NO
Compare the levels of arousal and awareness in these conditions:
- Coma
- VS
- MCS
- LIS
What are the areas of damage in LIS, VS and brainstem death?
- VS - destruction of cortex and hemispheres
- Locked-in syndrome - damage to ventral pons
- Brainstem death - irremediable damage to brain stem
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.
What is the difference between bitemporal hemianopia and visual neglect?
Bitemporal hemianopia - loss of vision due to damage to visual pathways. Patienst are aware of this.
Visual neglect - a higher order problems which causes perception of the world to change. The patient will have a constant preference to one side of the world and neglect the other e.g. only eating food from one half of the plate. Although they have the correct stimuli.
What is EEG used for?
To monitor levels of arousal. Useful in detection of “non convulsive status” i.e. when a patient is having seizures but without the convulsions.
howName the different EEG rhythms and when they occur. How are these interpreted?
Delta waves <4Hz (4 cycles per second) = SLEEP
Theta: 4-8Hz
Alpha: 8-13 Hz
Beta: 13-30Hz
Gamma: ~40Hz = NORMAL WAKIN CONSCIOUSNESS
We usually have all these waves present at once but we care about which one is most prominent:
Which EEG rhythm is most prominent in healthy conscious individuals?
Alpha 8-13Hz
What is “non specific slowing” on an EEG?
Prominence of theta and delta waves - usually a bad sign
What are higher frequency neural oscillartions (gamma range) associated with?
Cognition and creation of conscious contents in the focus of the mind’s eye, via the thalamno-cortical loops.
Gamma range = ~40Hz
What are the 3 main areas assessed by the Glasgow Coma Scale?
- If eyes are open
- Verbal responses
- Motor responses
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.
What are the major categories of causes of coma?
- Metabolic causes
- Diffuse intracranial causes
- Hemisphere lesion
- Brain stem
What are the metabolic causes of coma?
Metabolic -
- drug overdose,
- hypoglycaemia,
- diabetes,
- “the failures”,
- hypercalcaemia.
What are the diffuse intracranial causes of coma?
Diffuse intracranial -
- head injury,
- meningitis,
- SAH,
- encephalitis,
- epilepsy,
- hypoxic brain injury.
What hemisphere lesions can lead to coma?
Hemisphere trauma -
- cerebral infarcts,
- cerebral haemorrhage (subdural, extradural),
- abscess,
- tumour
What are the brainstem causes of coma?
Brainstem -
- brainstem infarct,
- tumour,
- abscess,
- cerebellar haemorrhage,
- cerebellar infarcts.
What type of imaging can be used to view diffuse axonal injury?
- CT
- Gradient echo or susceptibility weighted imaging (SW1)
Small microbleeds can be seen as dots where the axonal injury has occurred.
Describe the pathophysiology of diffuse axonal injury.
Usually due to traumatic brain injury
Brain moves in a way that the white matter tracts get damages e.g. corpus callosum because the hemispheres can move in opposite directions. Axonal injury –> microbleeds
This changes the way different parts of the brain can communicate with each other.
Why are posterior fossa lesions dangerous?
They can cause compression of structures in the brainstem which are needed to stay alive.
Surgeons are more likely to remove bleeds in these areas than in others.
What type of stroke can lead to coma?
Bilateral medial thalamic infarcts
