Lecture 4: Extra reading information

Baars and Gage chapter 13: Disorders of consciousness:

• Consciousness and unconsciousness:

• Consciousness: Awareness and wakefulness.

• Unconscious is characterised by closed eyes, lack of awareness, slowed breathing and heart rate and limited spontaneous movement.

• Two broad categories:

  • Reversible unconsciousness (sleep, anaesthesia)

  • Potentially non-reversible DOC (brain injury, disease)

Disorders of consciousness:

• DOC result from brain injury

• Diagnosis relies on observable behaviour, not subjective report.

• Clinical assessments examine arousal/wake cycles, language comprehension, eye movements/gaze, motor responses and reflexes.

Clinical states of DOC:

• Coma

• No sleep wake cycles

• Eyes closed continuously

• No purposeful movement

• No speech

• Caused by severe cortical, thalamic or brainstem damage

• Usually resolves within 2 weeks.

• Possible outcomes: Vegetative state, minimally conscious state and brain death

Clinical states of DOC:

• Vegetative state (VS):

• Eyes may open

• Sleep-wake cycles present

• No awareness

• No language comprehension

• No visual tracking

• Involuntary movements only

• High wakefulness and extremely low awareness.

• 1-12 months or may become permenant.

Clinical states of DOC:

• Minimally conscious state:

• Eye opening

• Inconsistent but definite signs of awareness

• May follow simple commands

• Limited speech

• Visual tracking

• Emotional responses to family.

• Behaviour is inconsistent

• Often a transitional state during recovery

Clinical states of DOC:

• Posttraumatic confusional state:

• Extended wakefulness

• Confused, disoriented

• Consistent one step command following

• Sentence-level speech

• Functional object use.

• Represents further recovery toward full consciousness.

Locked in syndrome (not a DOC):

• Caused by brainstem damage

• Cortex intact

• Full awareness and normal cognition.

• Near total paralysis

• Only voluntary movement: Eye movements.

• High awareness and wakefulness but inability to communicate.

• Metabolism is near normal.

Brain metabolism and consciousness:

• In normal consciousness there is high global metabolism and highest activity in praecuneus and posterior cingulate cortex (PCC).

• Across states:

  • Deep sleep, anaesthesia, coma, reduced metabolism.

  • Permanent VS → Very low metabolism

  • MCS → Moderate

  • Locked in → Near normal.

• Praecuneus metabolism strongly correlates with awareness.

Ethical and end of life decisions:

• Major issue: Should life support be withdrawn in chronic VS or MCS?

• European survey (~2500 healthcare professionals):

  • 66% support withdrawal in chronic VS

  • 28% support withdrawal in MCS

  • Only 18% would want to be kept alive in chronic VS themselves

• Regional differences:

  • Northern Europe → more likely to support withdrawal

  • Southern Europe → less likely