Consciousness

Question 1

Consciousness: define consciousness; explain the mechanisms, levels, and contents of consciousness; and define the concept of neural correlate of consciousness

Answer 1

Definition = difficult

• the subject experience of the mind and the world around us
• that there is “something it is like” to be in the state of the subjective or first-person point of view
• the state of being aware of and responsive to one’s surroundings
• Most definitions have an idea of the level (coma/ sleep/ wake) and content (what are you thinking about? Coma/ dementia/ awake) of consciousness and a sense of self
• The easy problem = how the neurons etc come together to produce consciousness
• The hard problem = science hits the soul and gets stumped – why do we feel that uniqueness of what it’s like to be each of us as individuals?
• Mechanisms of consciousness
  
  • Reticular Activating Ssystem = on/off switch: provides drive to other systems of brain
  • Probably to do with dynamics of neuronal activity
    
    • Can’t just be to do with synchronisation – in a seizure activity is highly synchronous, but you can’t encode thoughts or memory in that
    • Differentiation is also important – variability of brain activity is also important
  • Different mode networks light up on scan when asked to perform different actions/ are in a resting state
• Neural correlates of consciousness
  
  • The minimum neuronal mechanisms jointly sufficient for any one specific conscious experience.
  • Primarily localized to a posterior cortical hot zone that includes sensory areas

Question 2

Reticular activating system: identify the main structures of the reticular activating system, explain the function of the reticular activating system in modulating activity of the cerebral cortex and association with different levels of consciousness

Answer 2

RAS is made up of:

• Ventral tegmental Area (dopaminergic neurones)
• Locus coeruleus (noradrenergic neurones)
• Reticular formation
  
  • RF: regulation of many vital functions
    
    • degree of activity in the reticular system is associated with alertness/levels of consciousness
    • RF projects to the thalamus and the cortex, allowing sensory signals to reach cortical sites of conscious

Question 3

Electroencephalography: define the main EEG rhythms which identify different levels of arousal

Answer 3

• Can quantify brain complexity using combined transcranial magnetic stimulation and EEG
• Measure the pertubational complexity index (PTI)
  
  • Firing of magnetic pulse into brain causes a reverberation of activity around the brain
  • Measure EEG response
    
    • In awake state it bounces around the brain
    • In sleep, the peak of activity moves around less
    • Brain response to electric pulse –> measure of consciousness
• Measure electric activity on scalp that correlates to waves of brain activity that are related to brain state
  
  • Frequencies
    
    • 8-12Hz = alpha
      
      • Rhythm seen on back of brain
      • Related to attention – when you attend to something your alpha goes down
    • 4-8Hz = theta
      
      • Slower = generally bad, drowsy
    • <4Hz = delta
    • Beta = 14-30Hz, Gamma = >40Hz
      
      • Normal waking consciousness

Question 4

Altered conscious level: define the main altered states of consciousness and explain the Glasgow Coma Score (GCS)

Answer 4

• Disorders of consciousness:
  
  • Coma:
    
    • Unrousable unconsciousness
  • Vegetative state
    
    • No awareness
    • There is a sleep wake cycle
  • Minimally conscious state
    
    • May track you around the room and have self-awareness, but consciousness still severely altered
  • Locked-in syndrome
    
    • Internally awake but cannot externally see this
• Brain stem death
  
  • Is there a covert awareness that you can’t see upon clinical assessment? Has been demonstrated in some patients that they are aware
    
    • It changes things – you can’t just pull nutrition on them to let them die
• Neglect
  
  • Particularly likely to happen in stroke
  • Homonymous hemianopia is similar, neglect is a higher order than that
    
    • Unilateral loss of conscious awareness
    • Not just a visual field defect

Question 5

Coma: identify causes of metabolic and non-metabolic coma, and explain the differences between brain death, coma and persistent vegetative state

Answer 5

• Causes:
  
  • Metabolic:
    
    • Drug overdose, hypo/hyperglycaemia, diabetes, “the failures” (liver/ renal)
  • Non-metabolic
    
    • Diffuse intracranial:
      
      • Head injury, meningitis, encephalitis, epilepsy
    • Hemisphere lesion
      
      • Cerebral infarct/ haemorrhage, abscess, tumour
    • Brain stem:
      
      • Brainstem infarct, tumour, cerebellar haemorrhage/ infarct
• GCS
  
  • Clinical means of assessing conscious level
    
    • Ranges from 3 to 15
    • Eyes, voice and motor: 4,5,6

Flexor and extensor response to pain:

• Flexor = decorticate
• Extensor = decerebrate