Neuro 15 - Sleep and consciousness

Question 1

Describe the stages of sleep

Answer 1

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

Question 2

Describe HR and Response rate in sleep

Answer 2

HR and resp rate = slow during slow wave sleep, faster during REM sleep

Question 3

How does the reticular activating system control consciousness

Answer 3

Lateral hypothalamus (linked with orexin/hypocretin system) - promotes wakefulness by stimulating RAS

Ventrolateral preoptic nucleus - promotes sleep by inhibiting RAS

Question 4

How do we achieve circadian synchronisation of sleep/wake cycle

Answer 4

Suprachiasmatic nucleus —> synchronises sleep with falling light level

Question 5

What are the effects of sleep deprivation

Answer 5

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

Question 6

What occurs after sleep loss?

Answer 6

1. Reduced latency to sleep onset i.e. fall asleep quicker/earlier
2. Increased slow wave sleep (NREM)
3. Increased REM sleep

Question 7

What are the potential functions of sleep

Answer 7

1. Energy conservation
2. Memory consolidation
3. Restoration and recovery

Question 8

Describe dreams

Answer 8

Can occur in REM and NREM sleep (more common in REM)

Higher limbic activity than frontal lobe during dreams - dreams more emotional than IRL

Question 9

What are the 2 main sleep disorders

Answer 9

1. Insomnia

2. Narcolepsy

Question 10

Describe insomnia

Answer 10

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

Question 11

Describe narcolepsy

Answer 11

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

Question 12

Consciousness can be broken down into …… and ……. .

Describe each

Answer 12

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

Question 13

Reticular formation (RF) regulates vital functions

Degree of RAS activity is associated with alertness/levels of consciousness. From where does the RF project

Answer 13

RF projects from brainstem —> thalamus and cortex

Question 14

What are the brainstem structures that project widely to cortex

Answer 14

VTA (Dopaminergic neurons)

Locus coeruleus (NA neurones)

Question 15

Explain the terms used for dynamics of neuronal activity

Answer 15

Integration - different parts of the brain working together

Differentiation - different neurones have different patterns of activity

Question 16

How can we quantify brain complexity in vivo?

Answer 16

Using TMS (transcranial magnetic stimulation) and EEG - Perturbational Complexity Index (PCI) - in sleep/anaesthesia/disorders - response to TMS less complex

Question 17

What is meant by neural correlates of consciousness

Answer 17

Minimum neuronal mechanisms jointly sufficient for a specific conscious experience

Areas are primarily localised to posterior cortical hot zone - including sensory ares

Question 18

Describe the disorders of consciousness

Answer 18

1. Coma - unresponsive, no sleep-wake cycle, lasts more than 6 hours
2. 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
3. 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

Question 19

Locked-in syndrome may be caused by damage to?

Answer 19

The ventral pons

Question 20

Distinguish hemianopia from visual neglect

Answer 20

Neglect = higher order problem - lose conscious awareness of one side

Question 21

If the optic tract is damaged, what do you get

Answer 21

Homonymous hemianopia

If chiasm damaged –> bitemporal hemianopia

Question 22

What does EEG measure

Answer 22

Measures the electrical activity on scalp using electrodes - monitors arousal/wakefulness levels

Question 23

Describe the EEG rhythms

Answer 23

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)

Question 24

What are higher frequency neural oscillations (gamma range - 40+ Hz) associated with?

Answer 24

Creation of conscious contents in minds eye, via thalami-cortical feedback loop

Question 25

What are metabolic causes of coma

Answer 25

1. Drug OD
2. Hypoglycaemia
3. Hyperglycaemia
4. Diabetes/renal/liver failure

Question 26

What are the diffuse intracranial causes of coma

Answer 26

1. Head injury
2. Meningitis
3. SAH
4. Encephalitis
5. Epilepsy
6. Hypoxic brain injury

Question 27

Describe the hemisphere lesions that may cause coma

Answer 27

1. Cerebral infarct
2. 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
3. Abscess
4. Tumour

Question 28

What brainstem lesions can cause coma

Answer 28

1. Brainstem infarct
2. Tumour
3. Abscess
4. Cerebellar haemorrhage
5. Cerebellar infarct

Stroke - doesn’t usually cause coma unless posterior circulation stroke behind brainstem

Question 29

Head injury may cause diffuse axonal injury which causes?

Answer 29

Inability ot integrate information between different brain regions

Head injuries may also produce bilateral medial thalamic infarcts in thalamus