17. Sleep and consciousness Flashcards
What are the behavioural criteria for sleep?
- Stereotypic or species-specific posture
- Minimal movement
- Reduced responsiveness to external stimuli
- Reversible with stimulation
What measurements can you take determine whether someone is sleeping?
- EEG - brain activity
- EOG - eye movements
- EMG - muscle activity
Describe the typical measurement findings when awake?
• Quite a fast brain rhythm in the EEG (beta rhythm)
- around 30 Hz
• Reasonable amount of muscle tone
- posture + ready for action
Describe the measurement findings in stages 1 and 2 of sleep?
• Light sleep • Non-REM • EEG activity is slowing • Beta => theta activity - 4-8 Hz • No eye movements • Muscle activity considerably reduced
Describe the measurement findings in stages 3 and 4 of sleep?
• Still non-REM sleep • Thea => delta activity - around 1 Hz • Minimal eye movement • Continued relaxation of the muscles • Very deep sleep
Describe the measurement findings in stage 5 of sleep?
- Brain activity shifts abruptly back to fast rhythm
- Rapid eye movement (REM)
- Muscle activity at its lowest - basically paralysed
How long does the sleep cycle last?
90 minutes
How do the different stages of change during a whole period of sleeping?
- REM gets longer as you have more cycles
* Other 4 stages get shorter
Apart from brain activity, eye movement and muscle tone, what else changes during sleep?
- Increase in HR and respiratory rate during REM
* May reflect what happens during dreams
Which system controls consciousness and how?
• Reticular activating system
- active when awake
• Starts in the brainstem then projects up and influences the activity of the cerebral cortex
• Can do this directly, or through the intralaminar nuclei in the thalamus
Which nuclei in the hypothalamus influence the RAS and how?
Lateral hypothalamus
• excitatory input
• active during the day
• enables higher level of activity in the cortex
• orexin (hypocretin) system within promotes wakefulness
Ventrolateral preoptic nucleus
• negative effect on RAS
• promotes sleep
• more active towards the end of the day
• each nucleus inhibits the activity of the other when active (antagonistic relationship)
What happens when you lose neurones that secrete orexin?
Keep falling asleep
What is the system that synchronises sleep with the environment and describe it
Circadian synchronisation of sleep/wake cycle
• Suprachiasmatic nucleus - synchronises sleep with falling light level
• Receives input from the retina - from specific type of ganglion cell (not rods and cones)
• Becomes more active as light levels fall
- Inhibits the LH nucleus, stimulates the VLP nucleus
- Direct effects on the RAS - reduction in traffic
• Projections also to the pineal gland (back of 3rd ventricle), activating it towards the end of the day
• Secretes a higher level of melatonin - continues throughout the night and falls at the end of the night
- adjusts various physiological processes
What are the psychiatric effects of sleep deprivation?
- Sleepiness
- Irritability
- Stress
- Mood fluctuations
- Depression
- Impulsivity
- Hallucinations
What are the neurological effects of sleep deprivation?
• Impaired: - attention - memory - executive function • Risk of errors and accidents • Neurodegeneration - sleep problems can be a warning sign for neurodegenerative disease
What are the somatic effects of sleep deprivation?
- Glucose intolerance
- Reduced leptin/increased appetite => obesity
- Impaired immunity
- Increased of cardiovascular disease and cancer
- Death
How does the body adjust to sleep loss?
- Reduced latency to sleep onset - go to bed earlier the next day
- Increased of slow wave sleep (NREM)
- Increased REM sleep - after selective REM sleep deprivation
What is the function of sleep?
- Restoration and recover (but active individuals don’t sleep more)
- Energy conservation - 10% drop in BMR, but just lying does this too
- Theory of predator avoidance? - but sleep is too complex
When do dreams occur and how does brain activity change during them?
• Occur in NREM and REM sleep - most frequent in REM
• More easily recalled in REM
• Brain activity in limbic system is higher than frontal lobe during dreams
- contents of dreams are more emotional
What are the potential functions of dreams?
- Safety valve for antisocial emotions (that are normally suppressed in real life situations)
- Disposal of unwanted memories
- Memory consolidation
How is memory consolidation different in NREM and REM sleep?
- NREM - declarative memory - facts and events
* REM - procedural memory - learning skills
What are the causes of chronic insomnia?
- Physiological - sleep aponoea, chronic pain
* Brain dysfunction - depression, fatal familial insomnia, night working
How can you treat insomnia?
- Remove cause - sleep hygiene
- Most hypnotics - enhance GAPAergic circuits
- Sleep CBT
What is narcolepsy?
- Falling asleep repeatedly during the day
* Disturbed sleep during the night
What is cataplexy?
- Sudden onset of muscle weakness that may be precipitated by excitement or emotion
- Often linked to narcolepsy
- Can be one part of body or most muscles causing collapse
What causes narcolepsy?
- Tends to be a dysfunction of control of REM sleep (one of the characteristics of REM sleep is loss of muscle tone)
- People go straight into REM sleep without going through the other stages
- Most cases seem to have an orexin deficiency - loss of effects of the RAS
- Could be genetic or autoimmune
How can you manage narcolepsy?
- Manage the patient’s sleeping patter very rigidly
- Give a framework - nap at certain times of the day
- Resort to stimulants to keep them awake
What is Lewy-Body disease?
- Type of dementia
- Sleep disorder
- Patients act out their dreams - often violently
- Partners will recall being punched in the middle of the night
What is consciousness?
- Subjective experince of the mind and the world around us
* State of being aware of and responsive to one’s surroundings
What is vigilance?
Wakefulness - level of consciousness in terms of how much your RAS is working
What is awareness?
Level and content of consciousness
What is the vigilance and awareness of someone in a vegetative state?
- High vigilance - still has sleep-wake cycle, awake behaviour, eyes open
- Awareness similar to that seen in a coma - almost nothing
What is the pertubational complexity index?
Quantifying brain complexity using transcranial magnetic stimulation and EEG
• Anaesthetise the patient
• Use transcranial MS to pulse the brain - causes reverberation of activity
• Reverberation can be measured using EEG
• Poor response in patients with disorders of consciousness
What are the neural correlates of consciousness (NCC)?
- Constitute the minimal set of neuronal events and mechanisms sufficient for a specific conscious percept
- Primary localised to posterior cortical hot zone that includes sensory areas
Describe wakefulness and awareness of someone in a minimally conscious state (MCS)
- Wakefulness with minimal awareness
- Inconsistent, but reproducible responses
- Above the level of spontaneous or reflexive behaviour
What is the difference between how arousal and awareness?
- Arousal - how awake you are
* Awareness - how conscious you are of something
What changes in the brain occur in someone in a vegetative state?
- Destruction of cortex and hemispheres
- Intact ascending RAS
- Awake but not aware
What changes occur in the brain in locked-in syndrome?
- Damage to ventral pons
- Intact cortex and RAS
- Aware but don’t appear to be awake
Do patients in a vegetative state or MCS need respiratory support?
- May need a tracheostomy
* They still have respiratory drive though
What is the brain activity of patients in a vegetative state like compared to normal people when asked the same questions?
Very similar - can be used as a form of communication
What is visual neglect?
- High order problem - lose conscious awareness of one side
- Not to be confused with homonymous hemianopia
- If the neglect is on the left side, the patient won’t attend to anything on the right side
What are the alpha waves of the brain?
- Rhythms typically seen on the back of the brain
- Related to attention
- When you attend to something, alpha waves get less prominent
- More prominent when relaxed
- Absence of waves indicates problems
Describe the speed of delta, beta and gamma waves?
- Delta - slow
- Beta - fast
- Gamma - faster
Outline the scoring of the glasgow coma scale
Eyes open
1) None
2) In response to pain
3) In response to speech
4) Spontaneous
Verbal responses
1) None
2) Incomprehensible sounds
3) Inappropriate words
4) Disorientated speech
5) Orientated speech
Motor responses
1) None
2) Extensor response to pain
3) Flexor response to pain
4) Withdrawal to pain
5) Localisation of pain
6) Obeys commands
What are the metabolic causes of coma?
- Drug overdose
- Hypoglycaemia
- Diabetes
- Renal failure, liver failure etc.
- Hypercalcaemia
What are the diffuse intracranial causes of coma?
- Head injury (trauma)
- Meningitis
- Subarachnoid haemorrhage (SAH)
- Encephalitis
- Epilepsy
- Hypoxic brain injury
What are the causes of coma, related to hemisphere lesions?
- Cerebral infarct
- Cerebral haemorrhage
- Abscess
- Tumour
- Cerebellar infarct
What are the causes of coma, related to the brain stem?
- Brainstem infarct
- Tumour
- Abscess
- Cerebellar haemorrhage
