Global Disorders of Consciousness

Question 1

What are global disorders of consciousness?

Answer 1

Profound alteration or total loss of consciousness, where consciousness has been affected by damage to the brain. It accompanies many different neurological injuries

Question 2

What are different functional types of global disorders of consciousness?

Answer 2

Unresponsive states (coma, vegetative), states preserving minimal sensorimotor integration (akinetic mutism, hyperkinetic mutism), global behavioural disruptions that preserve a capacity for communication and goal directed behaviour

Question 3

What is the most severe state of a global disorder of consciousness?

Answer 3

Coma

Question 4

What are the characteristics of coma?

Answer 4

Unresponsiveness to internal or external stimuli. Eyes closed. Motionless. No awareness of self or environment. No cyclical state changes (eg eyes opening/closing)

Question 5

What are the 2 mechanisms of brain dysfunction in coma?

Answer 5

Diffuse injuries impairing functioning of both hemispheres (cortical and subcortical) often result of severe brain trauma or oxygen deprivation. Discrete bilateral injuries to subcortical structures

Question 6

What is the ascending reticular activating system?

Answer 6

Extends from midbrain to thalamus. Neurons project widely to the cerebral hemispheres. Involved in maintaining the alert state. Roles in arousal and motivation/circadian rhythm/controlling respiration, cardiac rhythms etc. Damage to this system results in coma

Question 7

What is the duration of coma?

Answer 7

Depends on regions and extent on damage

Question 8

What is the duration and recovery from coma due to isolated bilateral upper brainstem and paramedian thalamic injuries?

Answer 8

Can produce initial coma with a variable duration of only hours or 1-2 days at most

Question 9

What is the duration and recovery from coma due to restricted bilateral brainstem lesions?

Answer 9

Typically faster and more complete recoveries than bilateral thalamic injuries, particularly if involves midbrain. This is due to no damage to thalamus

Question 10

What happens to some patients with isolated paramedian thalamic lesions?

Answer 10

They may never recover or recover over a very long interval

Question 11

What are the characteristics of a vegetative state?

Answer 11

Recovery of irregular cyclic arousal patterns compared with coma. No behavioural evidence of awareness of self or environment. After 30 days it becomes a persistent vegetative state, which can become permanent

Question 12

What causes vegetative state?

Answer 12

Structural anatomical damage overlaps with injuries producing coma

Question 13

What causes some patients to remain in a permanent vegetative state?

Answer 13

Specific patterns of diffuse brain injury following trauma/oxygen deprivation. Widespread corticothalamic disconnections. Profound subcortical damage in both non-traumatic and traumatic injury types

Question 14

What damage occurs in non-traumatic VS?

Answer 14

Severe bilateral thalamic damage often also associated with diffuse cortical damage

Question 15

What damage occurs in traumatic VS?

Answer 15

Damage to cerebral white matter producing severe thalamic degeneration. Cortical grey matter usually spared

Question 16

What did Laureys et al 2010 suggest as a new name for vegetative state?

Answer 16

Unresponsive wakefulness syndrome. Acknowledges the problem in making strong claims about awareness in patients with severe brain damage (highlighted in fMRI studies)

Question 17

What are the characteristics of a minimally conscious state?

Answer 17

Unequivocal but inconsistent behavioural evidence of awareness of self or environment. Patients may evolves to MCS from coma or VS. Often transient but may be permanent

Question 18

What is MCS usually associated with?

Answer 18

A variety of pathologies including brain injury or congenital nervous system disorders

Question 19

What did Laureys and Schiff 2012 conclude when studying progressions in recovery of normative cognitive function?

Answer 19

Progressing from MCS includes high level behavioural responses such as command following or specific responses to linguistic content. Regressing in MCS includes low level nonreflex behaviour such as visual pursuit, localisation of pain or appropriate smiling to emotional stimuli

Question 20

What have PET studies found about brain function in vegetative state?

Answer 20

Regions in prefrontal/parietal cortices are significantly less active. Overall cerebral metabolism often reduced to 40-50% of normal levels. Though in some who subsequently recovered, their global metabolic rates did not show substantial change, some awake healthy volunteers have VS global brain metabolism values, and some VS patients show almost normal global cortical metabolism

Question 21

Are VS patients aware of pain?

Answer 21

Robust activation in brainstem, thalamus and primary somatosensory cortex (Laureys et al 2002), but higher order pain related areas were not activated

Question 22

Are VS patients aware of auditory stimulation?

Answer 22

Activated primary auditory cortices but not higher order multimodal areas from which they were disconnected (Laureys et al 2002) consistent with hypothesis that neural activity in primary cortices is necessary but not sufficient for awareness

Question 23

What was Owen et al 2006s study?

Answer 23

fMRI evidence for preserved consciousness in some VS patients. Tennis/house study. Criticised that words may have automatically triggered activation but Owen et al 2007 showed evidence against this, and the words had to be in an instructional context to cause activation

Question 24

What are the positives for using EEGs over fMRI?

Answer 24

More portable, cheaper, relatively greater availability and practicality

Question 25

What have EEG studies of VS shown?

Answer 25

Cruse et al 2012. Patient repeatedly diagnosed as VS for 12 years attempted to follow commands so was aware but not able to execute an overtly discernible action

Question 26

What are MCS patients aware of?

Answer 26

Show activation similar to controls in response to auditory, emotional and noxious stimuli (Boly et al 2005)

Question 27

What did Schnakers et al 2008 EEG study show?

Answer 27

Group of MCS patients exhibited reliably larger P3 components in EEG recording when counting number of times their own name was presented

Question 28

Can consciousness be restored?

Answer 28

Corazzol et al 2017. Patient in VS for 15 years. Implanted with vagus nerve stimulator. After 1 month, reproducible and consistent improvements in general arousal, sustained attention, body motility and visual pursuit. Scores on coma recovery scale improved, indicating a transition from VS to MCS. EEG and PET measured indicated improvements in neural functioning