Consciousness Flashcards
What is consciousness
The state of being aware and responsive to one’s surrounding’s
What are the elements of consciousness
Level
Content
Self
Describe the reticular activating system
Reticular formation (RF) regulates many vital functions. The degree of activity in the reticular system is associated with alertness/levels of consciousness
Where does the reticular activating system project to
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
Describe the areas of the brain where consciousness is controlled
No single brain region
Feed-forwards processing (subliminal or non-conscious)
Top-Down recurrent processing (conscious access)
How is brain complexity quantified
transcranial magnetic stimulation and EEG – pertubational complexity index (PCI)
What are neural correlates of consciousness (NCC)
The minimum neuronal mechanisms jointly sufficient for any one specific conscious experience.
Primarily localized to a posterior cortical hot zone that includes sensory areas
What are some common disorders of consciousness
Coma - absent wakefulness and absent awareness
Vegetative state - wakefulness with absent awareness
Minimally conscious state - wakefulness with minimal awareness
Describe a coma
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
Describe vegetative state
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
Describe minimally conscious states
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
Describe the brain in locked-in syndrome and brainstem death
Locked-in = intact cortex and ascending reticular activating substance. Damage to the ventral pons
Death - immediate damage to brainstem
Describe how EEGs can be interpreted
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
Describe the assessment of coma
Glasgow coma scale
score of 3 - severe brain injury and brain death
What are the metabolic causes of coma
Drug overdose
hypoglycaemia
diabetes
hypercalcaemia
What are the diffuse intracranial causes of coma
Head injury Meningitis SAH Encephalitis Epilepsy Hypoxic brain injury
How can a hemisphere lesion lead to a coma
Cerebral infarct
Cerebral haemorrhage (Subdural, Extradural)
Abscess
Tumour
How can brainstem damage lead to a coma
Brainstem infarct Tumour Abscess Cerebellar haemorrhage Cerebellar infarct
Describe extradural haemorrhage
Initial loss of consciousness
Lucid period then eventual second phase of consciousness loss
Describe subdural haemorrhage
Often presents in a crescent moon shape
Describe diffuse axonal injury
Disorder of the white matter tracts
Describe poster fossa lesions
Can damage the brainstem
Descrive bilateral medial thalamic infarcts
May be caused by stroke
Which projections are most important in regulating level of arousal
Cholinergic projections
What are the three mechanisms by which these projections regulate the level of arousal?
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
What are some causes of coma
Metabolic alteration e.g. hypoglycaemia, hypoxia, intoxication
Bilateral lesions in the cerebral hemispheres
Lesions in the thalamus or brainstem
What causes a persistent vegetative state
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
Describe brain death
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
