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 subject experience of the mind and world around us, first person point of view, aware of ones surroundings.

Question 2

What structure within the brain is heavily involved in regulating alertness?

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 upper medulla – it is a polysynaptic network that regulates the activity of the cerebral cortex

Question 4

What are the elements of consciousness?

Answer 4

Level, content, self

Question 5

What does RAS enable?

Answer 5

Regulates many vital functions Degree of activity is related to alertness and levels of consciousness RF projects to the hypothalamus, thalamus and the cortex

Question 6

What are the sensory inputs to the reticular formation?

Answer 6

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 7

The RF modulates cerebral activity via various projections. What are these projections?

Answer 7

Noadrenergic projections from the nucleus coeruleus to the cerebral cortex PONS. Dopaminergic projections from the ventral tegmental area to the cerebral cortex MIDBRAIN. Cholinergic projections to the thalamus most important in regulating levels of arousal.

Question 8

What are the mechanisms of consciousness?

Answer 8

The location of neurons? The number of neurons? The dynamics of neuronal activity No single brain region for consciousness

Question 9

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

Answer 9

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 10

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

Answer 10

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 11

What is a cerebral contusion?

Answer 11

Localised bleeding in the brain (bruise in the brain)

Question 12

How can you quantify brain complexity?

Answer 12

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

Question 13

What are disorders of consciousness?

Answer 13

Coma Vegetative state Minimally conscious state

Question 14

Summarise each of the disorders of consciousness

Answer 14

Question 15

Summarise affected areas in vegatative state, locked in syndrome and brain stem death.

Answer 15

Locked in syndrome - perfect consciousness but motor impairment

Brainstem death unlike any other states.

Neglect and bitemporal hemianopia are not the same - people are aware of neglect adn can adjust

Question 16

How does EEG monitor levels of arousal?

Answer 16

Delta (< 4 Hz) – seen in sleep

Theta (4-8 Hz) – drowsiness

Alpha (8-13 Hz) – subject relaxed with eyes closed - posterior dominant rhythm loss of alpha means something not right posteriorly.

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 is bad

Question 17

What can EEG diagnose?

Answer 17

epilsepsy - few mins

Non-convulsive states - hrs/days

Question 18

Describe how the Glasgow Coma Scale is structured.

Answer 18

Eye opening = 4

Verbal responses = 5

Motor responses = 6

Question 19

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

Answer 19

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 20

State some causes of coma.

Answer 20

Metabolic - drug OD, hypoglycaemia, diabetes, hypercalcaemia

Diffsue intercranial - head injury, meningitis, SAH (subarachnoid haemorhhage), encephalitis (inflammed brain), epilepsy, hypoxic brain injury

Hemishpere lesion - cerebral infarct, subdral/extradural haemorrhage, abscess (built up collection of pus), tumour

Brain stem - brainstem infarct, tumour, abscess, cerebellar haemorrhage, cerebellar infarct

Question 21

What causes a persistent vegetative state?

Answer 21

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 22

What is brain death?

Answer 22

Irreversible coma due to brainstem death, but body kept alive artificially

NOTE: spinal reflexes and some postural movements may be present

Question 23

What would the consequences of a right parietal lesion be?

Answer 23

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 24

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

Answer 24

Functional MRI

Question 25

Define the vegetative state

Answer 25

A vegetative state is absence of responsiveness and awareness due to overwhelming dysfunction of the cerebral hemispheres, with sufficient sparing of the diencephalon and brain stem to preserve autonomic and motor reflexes and sleep-wake cycles.