Consciousness

Question 1

What is consciousness

Answer 1

The state of being aware and responsive to one’s surrounding’s

Question 2

What are the elements of consciousness

Answer 2

Level
Content
Self

Question 3

Describe the reticular activating system

Answer 3

Reticular formation (RF) regulates many vital functions. The degree of activity in the reticular system is associated with alertness/levels of consciousness

Question 4

Where does the reticular activating system project to

Answer 4

Thalamus and cortex → cortical projections
Ventral tegmental area → Cerebral cortex (dopaminergic neurones, midbrain)
Locus coeruleus → cerebral cortex (noradrenergic neurones, pons)
Raphe nuclei in the midline – main source of serotoninergic projections to the brain and spinal cord

Question 5

Describe the areas of the brain where consciousness is controlled

Answer 5

No single brain region
Feed-forwards processing (subliminal or non-conscious)

Top-Down recurrent processing (conscious access)

Question 6

How is brain complexity quantified

Answer 6

transcranial magnetic stimulation and EEG – pertubational complexity index (PCI)

Question 7

What are neural correlates of consciousness (NCC)

Answer 7

The minimum neuronal mechanisms jointly sufficient for any one specific conscious experience.
Primarily localized to a posterior cortical hot zone that includes sensory areas

Question 8

What are some common disorders of consciousness

Answer 8

Coma - absent wakefulness and absent awareness

Vegetative state - wakefulness with absent awareness

Minimally conscious state - wakefulness with minimal awareness

Question 9

Describe a coma

Answer 9

State of unrousable unresponsiveness, lasting more than 6 hours in which a person cannot be wakened
Fails to respond normally to painful stimuli, light or sound
Lacks a normal sleep-wake cycle
Does not initiate voluntary actions

Question 10

Describe vegetative state

Answer 10

Preserved capacity for spontaneous wakefulness or stimulus-induced arousal
Characterised by complete absence of behavioural evidence for self or environmental awareness
Destruction of cortex and hemispheres, intact ascending reticular activating substance

Question 11

Describe minimally conscious states

Answer 11

Severely altered consciousness in which there is minimal but clearly discernible behavioural evidence of awareness demonstrated
Characterised by inconsistent but reproducible responses above level of spontaneous of reflex behaviour

Question 12

Describe the brain in locked-in syndrome and brainstem death

Answer 12

Locked-in = intact cortex and ascending reticular activating substance. Damage to the ventral pons

Death - immediate damage to brainstem

Question 13

Describe how EEGs can be interpreted

Answer 13

Higher frequency neural oscillations are associated with the creation of conscious contents in the focus in the mind’s eye, via thalami-cortical feedback loops

Delta (< 4 Hz) – seen in sleep Theta (4-8 Hz) – drowsiness
Alpha (8-13 Hz) – subject relaxed with eyes closed
Beta (13-30 Hz) – mental activity and attention
Gamma range (~40 Hz) – creation of conscious contents in the focus of the mind’s eye, via the recurrent thalamo-cortical feedback

Slowing = bad

Question 14

Describe the assessment of coma

Answer 14

Glasgow coma scale

score of 3 - severe brain injury and brain death

Question 15

What are the metabolic causes of coma

Answer 15

Drug overdose
hypoglycaemia
diabetes
hypercalcaemia

Question 16

What are the diffuse intracranial causes of coma

Answer 16

Head injury 
Meningitis
SAH 
Encephalitis
Epilepsy 
Hypoxic brain injury

Question 17

How can a hemisphere lesion lead to a coma

Answer 17

Cerebral infarct
Cerebral haemorrhage (Subdural, Extradural)
Abscess
Tumour

Question 18

How can brainstem damage lead to a coma

Answer 18

Brainstem infarct
Tumour
Abscess
Cerebellar haemorrhage 
Cerebellar infarct

Question 19

Describe extradural haemorrhage

Answer 19

Initial loss of consciousness

Lucid period then eventual second phase of consciousness loss

Question 20

Describe subdural haemorrhage

Answer 20

Often presents in a crescent moon shape

Question 21

Describe diffuse axonal injury

Answer 21

Disorder of the white matter tracts

Question 22

Describe poster fossa lesions

Answer 22

Can damage the brainstem

Question 23

Descrive bilateral medial thalamic infarcts

Answer 23

May be caused by stroke

Question 24

Which projections are most important in regulating level of arousal

Answer 24

Cholinergic projections

Question 25

What are the three mechanisms by which these projections regulate the level of arousal?

Answer 25

Excitation of individual thalamic relay nuclei –> activation of cortex
Projections to intralaminar nuclei –> project to all areas of cortex
Projections to reticular nucleus– regulates flow of information through other thalamic nuclei to the cortex

Question 26

What are some causes of coma

Answer 26

Metabolic alteration e.g. hypoglycaemia, hypoxia, intoxication
Bilateral lesions in the cerebral hemispheres
Lesions in the thalamus or brainstem

Question 27

What causes a persistent vegetative state

Answer 27

Disconnection of the brainstem from the cortex or widespread cortical damage
Brainstem is still functioning so reflexes, postural movements and sleep-wake cycle may still be present

Question 28

Describe brain death

Answer 28

Immediate damage to brainstem
Irreversible coma due to brainstem death, but body kept alive artificially
NOTE: spinal reflexes and some postural movements may be present