Introduction to Consciousness

Question 1

What is consciousness?

Answer 1

Processes that enable us to experience the world around us

This is distinct from automatic behaviours that occur in a rather unconscious manner

Question 2

What structure within the brain is heavily involved in regulatingalertness?

Answer 2

Reticular Activating System

Question 3

What is the reticular formation?

Answer 3

A core of grey matter passing through the midbrain, pons and uppermedulla – it is a polysynaptic network that regulates the activity of the cerebral cortex

Question 4

What are the sensory inputs to the reticular formation?

Answer 4

Sensory and pain from ascending pathways
Vestibular information from medial vestibular nucleus
Visual from superior colliculus
Auditory from inferior colliculus
Olfactory via the median forebrain bundle

Question 5

The RF modulates cerebral activity via various projections. Whatare these projections?

Answer 5

Noadrenergic projections from the nucleus coeruleus to the cerebral cortex
Dopaminergic projections from the ventral tegmental area to the cerebral cortex
Cholinergic projections to the thalamus
Raphe nuclei in the midline – main source of serotoninergic projections to the brain and spinal cord

Question 6

Which of these projections is most important in regulating the level of arousal?

Answer 6

Cholinergic projections

Question 7

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

Answer 7

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 8

What are the different waveforms seen on an EEG and what levels of arousal do they represent?

Answer 8

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

Question 9

What is a cerebral contusion?

Answer 9

Localised bleeding in the brain (bruise in the brain)

Question 10

What is a concussion?

Answer 10

Diffuse, widespread, homogenous impairment of brain tissue due tobrain trauma

Question 11

What is acute confusion/delirium and stupor?

Answer 11

Acute confusion and delirium– sustained disturbance of consciousness where mental processes are slowed. Subject may be inattentive, disorientated and having difficulty carrying out simple commands or speaking
Stupor– lack of critical cognitive function and consciousness – only responsive to pain

Question 12

Damage to the reticular formation can lead to coma. What is a coma?

Answer 12

State of unconsciousness in which the subject cannot be roused even by strong sensory stimuli
Different from sleep – metabolic activity of the brain is depressed and there is total amnesia for this period

Question 13

State some causes of metabolic coma.

Answer 13

hypoglycaemia, 
hypoxia, 
intoxication/drug overdose
diabetes
hypercalcemia

Question 14

Describe how the Glasgow Coma Scale is structured.

Answer 14

Eye opening = 4
Verbal responses = 5
Motor responses = 6

Question 15

What causes a persistent vegetative state?

Answer 15

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 16

What is brain death?

Answer 16

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

Question 17

What would the consequences of a right parietal lesion be?

Answer 17

Hemispatial neglect – the patient will not pay attention to the left visual field
Information from the left visual field is reaching the primary visual cortex but because of the parietal damage, the patient is not conscious of this visual field

Question 18

What imaging technique can be used to study consciousness in health and disease?

Answer 18

Functional MRI

Question 19

What is blindsight?

Answer 19

Brain-damaged (occipito-visual cortex) patients who are perceptually blind of their visual field can demonstrate some responses to visual stimuli e.g. manually interacting with ‘unseen’ objects and avoiding ‘unseen’ objects

Question 20

What’s default mode network?

Answer 20

areas spatially differentiated that acitivate to achieve one function

Question 21

What is consciousness?

Answer 21

components distributed across the cortex, the sum of activity across the cortico-thalamic system creates consciousness

Question 22

what are the characteristics of consciousness?

Answer 22

Integration – each experience is part of a unifed whole

Differentiaton - each conscious experience is different to the other

aka: All connected to eachother but all slighty different

Question 23

What is the neural correlate of consciousness?

Answer 23

minimum neuronal mechanisms jointly sufficient for any one conscious experience

Question 24

What are some cuases of non-metabolic coma?

Answer 24

Meningitis
Hypoxic brain injury
Encephalitis
Epilepsy – including nonconvulsive seizures
Hemisphere or brainstem lesion
Bilateral lesions in the cerebral hemispheres
Lesions in the thalamus or brainstem

Question 25

What is diffuse axonal injury

Answer 25

after trauma White matter tracts damaged due to movement of hemispheres e.g. corpus callosum
Higher order cognitive functions relying on multiple brain injuries impaired