Consciousness

Question 1

Define consciousness

Answer 1

The brain state the enables us to experience the world around us and within one-self

Distinct from autonomic behaviours that occur in an unconsciousness manner (e.g. breathing)

Question 2

Elements of consciousness?

Answer 2

Distinction between LEVELS (alertness) vs. CONTENTS (subjective experience) of consciousness

Question 3

What does LEVELS incorporate?

Answer 3

Alertness invovles the RETICULAR FORMATION
o this regulates vital functions
o projects into the thalamus & cortex
o allowing it to ‘control’ if sensory signals reach cortical sites of conscious awareness e.g. posterior parietal cortex

Question 4

RAS?

Answer 4

Reticular Activating System

Question 5

What is the RAS?

Answer 5

A polysynaptic network in the core of the midbrain, pons and upper medulla

Question 6

What does the RF contain?

Answer 6

o NA neurones - locus coeruleus (pons)

o Dopaminergic neurons - ventral tegmental nucleus/area (midbrain)

o Cholinergic neurons - project into the cortex to boost the level of activity via. the thamalus (maintains awareness)

o Serotonergic projections - raphe nucleus (midline)

Question 7

Functions of the RF?

Answer 7

Besides control of awareness, also:

o centres for body systems e.g. CVS, respiratory, bladder

Degree of activity in the RS is associated with alertness/levels of consciousness

Question 8

The RF receives sensory information from ALL sensory pathways - what are they?

Answer 8

Touch & Pain
o from ASCENDING TRACTS

Vestibular
o from MEDIAL VESTIBULAR tracts

Auditory
o from INFERIOR COLLICULUS

Visual
o from SUPERIOR COLLICULUS

Olfactory
o from MEDIAL FOREBRAIN BUNDLE

Question 9

Which part of the RF has the most important role in regulating levels of arousal?

Answer 9

Cholinergic neurones!

project to thalamus

Question 10

How do the cholinergic neurones regulate level of arousal?

Answer 10

Involves 3 mechanisms!

1. EXCITATION of individual thalamic relay nuclei –> activation of the cortex
2. PROJECTIONS to intralaminar nuclei –> project to ALL areas of the cortex
3. PROJECTIONS to reticular nucleus –> regulates FLOW of information through thalamic nuclei to cortex

Question 11

How can you monitor levels of arousal?

Answer 11

via. ECG rhythms OR GCS

Question 12

What are the different waves seen in ECG rhythms of levels of arousal?

Answer 12

DELTA waves = seen during SLEEP (>4Hz)

THETA waves = associated w. drowsiness (4-8Hz)

ALPHA waves = subject is RELAXED with eyes closed (8-13Hz)

BETA waves = subject is AWAKE with normal consciousness (13-30Hz)

HIGHER Fqs waves (gamma range)
o associated with CREATION of CONSCIOUS CONTENTS in the focus of the mind’s eye
o via. the recurrent thalamo-cortical feedback loops
o ~40Hz

Question 13

GCS?

Answer 13

Glasgow Coma Scale!

Question 14

What can alter the state of consciousness?

Answer 14

o Contusions (a bruise)
 - localised bleeding within the brain

o Concussion (diffuse, widespread homogenous impairment of brain tissue due to brain trauma)

o Delirium (or acute confusion)

• sustained disturbance of consciousness, where mental processes are slowed
• subject may be inattentive, disorientated or have difficulty carrying out simple commands

o Stupor

• lack of critical cognitive function & consciousness
• only responsive to pain

Question 15

What can lead to a coma?

Answer 15

Damage to RF/thalamus

Question 16

What is a coma?

Answer 16

State of unconsciousness in which the subject cannot be roused even by strong sensory stimuli

Question 17

How is a coma different to sleep?

Answer 17

Metabolic activity of the brain is DEPRESSED in a coma

Question 18

Causes of coma?

Answer 18

1. Metabolic alteration
   o drug OD
   o hypoglycaemia
   o hypoxia
2. Bilateral lesions in cerebral hemispheres
3. Lesions in thalamus OR brain stem (raised ICP)

Question 19

What are the 2 forms of coma?

Answer 19

1. Persistent vegetative state
   - irreversible coma due to disconnection of cortex from brainstem
   OR
   - widespread cortical damage
2. Brain death
   - irreversible coma due to brainstem death
   - body kept alive artificially

Question 20

Explain the form of coma where person is in ‘persistent vegetative state’?

Answer 20

Brainstem still functions SO

• reflexes, postural movements & sleep-wake cycle may be present
• can be aroused from but are still unconscious

Question 21

Explain the form of coma where person is ‘brain dead’?

Answer 21

Decision to cease treatment depends on demonstration of absence of brainstem reflexes and response to HYPERCAPNIA

Spinal reflexes & some postural movement may still be present

Question 22

How does Achromatopsia arise?

Answer 22

Lesions to extra-striate cortex eliminates awareness of colour

Question 23

Left visual neglect in terms of disorders of consciousness?

Answer 23

Breakdown of consciousness awareness after RIGHT PARIETAL damage

o patient remain unconscious of info. from L visual field (despite 1o visual cortex being intact in occipital lobe)
- info being received by occipital lobe BUT not processed

o damage to parietal cortex means info. does NOT reach awareness as the RF is disrupted

Question 24

How can you investigate left visual neglect?

Answer 24

o Star cancellation test
- patient cancels fewer left stars

o Visual explorations
- patient will NOT cross midline to look left

Question 25

What can be used to study consciousness?

Answer 25

fMRIs!

Question 26

What is meant by blind-sight in terms of disorders of consciousness?

Answer 26

Are perceptually blind of their visual field due to occipital damage
BUT
can respond to visual stimuli

Question 27

Feed-forward processing vs. top-down recurrent processing?

Answer 27

There is NO SINGLE AREA for consciousness

o feed-forward processing (subliminal or non-conscious)
o top-down recurrent processing (conscious access)

ONENOTE!!

Question 28

Visual neglect vs. Hemianopia?

Answer 28

Hemianopia
o patient can NOT see half of their field of vision
o patient WILL KNOW

Visual neglect
o patient would ‘THINK’ they can see whole field of vision
o BUT can NOT see half their visual field