Neuro 15 - Sleep and consciousness Flashcards
Describe the stages of sleep
A single sleep cycle = 90 minutes (multiple sleep cycles during night)
Stages 1 and 2 = non REM, relatively minimal changes in EEG, EOG, EMG
Stages 3 and 4 = big EEG changes, semi-big EOG changes, EMG similar
Stage 5 = REM. Dreams + big EOG changes (eye movement) and EMG activity further decreases. EEG res again after falling
Describe HR and Response rate in sleep
HR and resp rate = slow during slow wave sleep, faster during REM sleep
How does the reticular activating system control consciousness
Lateral hypothalamus (linked with orexin/hypocretin system) - promotes wakefulness by stimulating RAS
Ventrolateral preoptic nucleus - promotes sleep by inhibiting RAS
How do we achieve circadian synchronisation of sleep/wake cycle
Suprachiasmatic nucleus —> synchronises sleep with falling light level
What are the effects of sleep deprivation
Psychiatric/neurological - sleepiness, irritability, stress, mood fluctuations, depression, etc
Neurological - impaired attention, memory, executive function. Risk of errors and accidents, neurodegeneration linked w sleep disorders (e.g. Lewy body dementia)
Somatic - glucose intolerance, obesity, diabetes, reduced leptin, impaired immunity, increased CVD/Ca risk
What occurs after sleep loss?
- Reduced latency to sleep onset i.e. fall asleep quicker/earlier
- Increased slow wave sleep (NREM)
- Increased REM sleep
What are the potential functions of sleep
- Energy conservation
- Memory consolidation
- Restoration and recovery
Describe dreams
Can occur in REM and NREM sleep (more common in REM)
Higher limbic activity than frontal lobe during dreams - dreams more emotional than IRL
What are the 2 main sleep disorders
- Insomnia
2. Narcolepsy
Describe insomnia
High prevalence - usually transient/temporary
Causes:
Physiological - sleep apnoea, chronic pain
Brain dysfunction - e.g. depression, fatal familial insomnia (FFI), night working
Treated with hypnotics - enhance GABAergic circuits
Describe narcolepsy
Narcolepsy - repeat falling asleep during day and disturbed night sleep
Associated with cataplexy (sudden, brief loss of voluntary muscle tone, often triggered by strong emotions e.g. laughter)
Dysfunction of REM sleep control - linked to orexin/hypocretin deficiency
Consciousness can be broken down into …… and ……. .
Describe each
Consciousness = vigilance (x axis) and awareness (y-axis)
Wakefulness controlled by RAS
If in vegetative state –> sleep-wake cycle still present to a degree (unlike coma)
Locked in syndrome = can’t show you’re aware/conscious
REM sleep = high level of consciousness - but not vigilant/awake
Reticular formation (RF) regulates vital functions
Degree of RAS activity is associated with alertness/levels of consciousness. From where does the RF project
RF projects from brainstem —> thalamus and cortex
What are the brainstem structures that project widely to cortex
VTA (Dopaminergic neurons)
Locus coeruleus (NA neurones)
Explain the terms used for dynamics of neuronal activity
Integration - different parts of the brain working together
Differentiation - different neurones have different patterns of activity
How can we quantify brain complexity in vivo?
Using TMS (transcranial magnetic stimulation) and EEG - Perturbational Complexity Index (PCI) - in sleep/anaesthesia/disorders - response to TMS less complex
What is meant by neural correlates of consciousness
Minimum neuronal mechanisms jointly sufficient for a specific conscious experience
Areas are primarily localised to posterior cortical hot zone - including sensory ares
Describe the disorders of consciousness
- Coma - unresponsive, no sleep-wake cycle, lasts more than 6 hours
- Vegetative state - state of wakefulness without awareness. Sleep-wake cycles present, but VS characterised by complete absence of behaviour evidence for self/environmental awareness. May also exhibit covert awareness
- Minimally conscious state (MCS) - state of severely altered consciousness - minimal (but discernible) behavioural evidence of self or environmental awareness is demonstrated
MCS characterised by inconsistent but reproducible responses above the level of spontaneous/reflexive behaviour
Locked-in syndrome may be caused by damage to?
The ventral pons
Distinguish hemianopia from visual neglect
Neglect = higher order problem - lose conscious awareness of one side
If the optic tract is damaged, what do you get
Homonymous hemianopia
If chiasm damaged –> bitemporal hemianopia
What does EEG measure
Measures the electrical activity on scalp using electrodes - monitors arousal/wakefulness levels
Describe the EEG rhythms
Awake - beta waves Drowsy/relaxed - alpha waves Stage N1 sleep = theta-waves Stage N2 sleep = sleep spindles Stage N3(/4) sleep = delta waves
REM sleep = fast, random
(alpha and beta = more conscious, awake, theta and delta = more sleepy)
What are higher frequency neural oscillations (gamma range - 40+ Hz) associated with?
Creation of conscious contents in minds eye, via thalami-cortical feedback loop
What are metabolic causes of coma
- Drug OD
- Hypoglycaemia
- Hyperglycaemia
- Diabetes/renal/liver failure
What are the diffuse intracranial causes of coma
- Head injury
- Meningitis
- SAH
- Encephalitis
- Epilepsy
- Hypoxic brain injury
Describe the hemisphere lesions that may cause coma
- Cerebral infarct
- Cerebral haemorrhage –> possibly compresses brainstem –> interferes with RAS
- Extradural = typically due to arterial bleed –> ICP rises, forms disc-shape
- Subdural - crescent shape, bright blood in CT - Abscess
- Tumour
What brainstem lesions can cause coma
- Brainstem infarct
- Tumour
- Abscess
- Cerebellar haemorrhage
- Cerebellar infarct
Stroke - doesn’t usually cause coma unless posterior circulation stroke behind brainstem
Head injury may cause diffuse axonal injury which causes?
Inability ot integrate information between different brain regions
Head injuries may also produce bilateral medial thalamic infarcts in thalamus
