Consciousness Flashcards
What do you require to be aware of particular information?
Levels of consciousness i.e. alertness
Contents i.e. subjective experience
What systems does the reticular activating system influence?
Pain perception
Cardiovascular
Sleep cycles
Respiration
Which parts of the RF system release neurotransmitters that project to the cortex?
Locus coreuleus; NA
Ventral tegmental area; Dopaminergic
From the thalamus where do the sensory projections lead to?
Anterior prefrontal cortex
What does the release of cholinergic neurons do?
Cholinergic neurones boosts the level of activity in the cerebral cortex to maintain alertness
Name the sensory pathways for; Touch and pain Vestibular Auditory Visual Olfactory
Ascending pathway (spinothalamic) Medial vestibular nucleus Inferior colliculus Superior colliculus Medial forebrain bundle
What is the purpose of the raphe nuclei?
Located in the midline, they are the main source of serotonergic projections to the brain and spinal cord
What are some of the connections of the thalamus to the cortex?
Anterior part of thalamus -> prefrontal cortex
Ventrolateral -> motor cortex
Posterior -> parietal
There are also visual cortex connections.
What is the mechanism that cholinergic neurones use to increase the activity of the cortex?
- Excitation of individual thalamic relay nuclei
- Excitation of intralaminar nuclei which project to all areas of the cortex
- Projections to the reticular nucleus which regulates flow of information through other thalamic nuclei to the cortex
What are the EEG rhythms associated with; sleep, drowsiness, relaxed with eyes closed, normal consciousness, formation of conscious content?
Sleep: delta waves, >4Hz
Drowsiness: theta waves, 4-8Hz
Relaxed with eyes closed: alpha waves, 8-13hz
Normal consciousness: beta waves, 13-30hz
Formation of conscious content (through thalami-cortical loops): gamma waves, <40Hz
What can cause a state of unconsciousness?
Damage to the RF/thalamus or bilateral cortical insult.
Persistent vegetative state: Damaged interaction between cortex and brainstem or widespread cortical damage (flat EEG, irreversible coma)
Brain death: brainstem death/lesions (raised ICP, slow wave EEG). Spinal reflexes and postural movements may still be present.
Metabolic cause: e.g. hypoxia, hypoglycaemia, intoxication
What is the difference between a coma and ‘locked-in’ syndrome?
In a coma they are generally unresponsive due to sensory input and show abnormal wake/sleep cycles.
In ‘locked-in’ syndrome they cannot responds due to motor impairments.
What are some issues with the glasgow coma scale and what does it assess?
It cannot track progression in chronic patients.
Measures eye commandments, verbal and motor responses.
Assessing verbal response will be of no use in someone with a temporal lesion.
What is a contusion and the cause of it?
Caused by a bruise (haematoma)
Localised bleed in the brain, affects the capillaries and basal cells
What is a concussion and the cause of it?
Caused by trauma to the brain, widespread
Leads to microscopic impairments -> diffuse axonal injury -> myelin damage
What is the difference in presentation of a concussion/contusion, stupor and delirium?
A concussion or contusion may cause temporary loss of cognitive function (minutes).
Stupor is a lack of critical cognitive function and lack of consciousness, only respond to pain.
Delirium is when there is sustained disturbance of consciousness, this may cause the patient to fail at performing simple tasks.
Which structures of the cortex are involved in attention and are they required for consciousness?
Prefrontal cortex and parietal cortex (mainly right side).
Necessary but not sufficient for consciousness, also need input from subcortical structures e.g. thalamus.
What type of lesion would cause visual ‘neglect’ syndrome?
Frontoparietal lesion; unaware of information coming from the contralateral side
What is the difference between a hemianopia and visual neglect syndrome?
Hemianopia; intact cortical function, disconnection with optic nerve due to impairment in relay from eye -> lateral geniculate body in thalamus
Which is the area of the brain involved with thinking about future tasks and it’s nickname?
‘The default mode network’ in the posterior cingulate cortex
What is the condition, ‘Blindsight’?
Patient has a damaged occipital visual cortex, they are perceptually blind.
Eyes-> lateral geniculate body -> superior colliculus
Able to respond to visual stimuli as subcortical regions can lead to behaviours without awareness.
What tests can you do asses visual ‘neglect’?
Star awareness test
Visual exploration
What brain region(s) do you need for consciousness?
Need communication between many brain regions -> top-down recurrent processing.
Focal processing does not lead to consciousness
