What is consciousness?
Consciousness is a very elusive and broad concept.
What are the clinical components that distinguish consciousness from unconsciousness?
Arousal and awareness.
What is wakefulness?
Wakefulness is a state of arousal.
How is wakefulness measured?
It can be assessed by the presence of eye-opening, and brainstem responses.
What are the neurobiological markers for wakefulness?
- Passage of sensory information from the brainstem to the cortex. Activation of the cortex occurs with the passage of sensory information from the upper brainstem through the reticulothalamcortical and extrathalamic pathways.
- The conscious awake state is associated with high energy demand and electrical activity within the corticothalamic system.
What does the ascending reticular activation system in the brainstem do?
It sends projections throughout the cortex directly, or through the thalamus or hypothalamus. It is an important pathway for assessing consciousness.
What is awareness?
Awareness refers to the ability of an individual to respond to both external and internal stimuli in an integrated manner. Command following is a tool used during the neurobehavioural assessment for rehabilitation).
What are the neurobiological markers of awareness?
Anatomical and functional connectivity of the frontoparietal networks and the thalamus. The thalamus is a relay station for all sensory impulses (except smell) to the cortex. It has recognition for pain, temperature, touch, and pressure.
What is a disorder of consciousness?
An altered state of prolonged pathologic consciousness.
What are the three disorders of consciousness?
Coma, vegetative state, and minimally conscious state.
What is the commonality in all these disorders?
Withdrawal of excitatory synaptic activity across the cerebrum as a result of disfacilitation of neocortical, thalamic, and striatal neurons.
Low metabolic rate in the cortex.
What is a coma?
A state of unconsciousness characterized by a lack of arousal and awareness.
What are the clinical symptoms of a coma?
- Complete loss of spontaneous or stimulus-induced arousal.
- No eye-opening.
- No sleep-wake cycles.
What are the neurobiological symptoms of a coma?
- Diffuse cortical or white matter damage.
2. Brainstem lesion (results in the massive loss in arousal and awareness.)
What is rehabilitation like?
Those who survive this stage will begin to awaken and transition into a VS or MCS within 2-4 weeks.
What is a vegetative state?
An unconscious, dissociative state of wakefulness without awareness.
What is seen clinically in a vegetative state?
Eyes can open spontaneously and sleep-wake cycles are present. Patients can be aroused externally with no signs of conscious perception. They may also act spontaneously (yawn, or smile) out of context.
What are the neurobiological symptoms?
- Presence of wakefulness show preservation of brain stem functioning, but lack of awareness shows cortical dysfunction.
What regions do the sensory stimuli activate?
Cortical areas but not high cortical areas needed for awareness.
What is rehabilitation like?
With proper medical care, a patient in a VS can remain in this state for many years, or they can progress and continue to recover.
What is a minimally conscious state?
Severe impairments of consciousness with evidence of wakefulness and partial awareness.
What do we see clinically?
Purposeful behaviours. Reproducible but inconsistent command following.
What are the neurobiological symptoms?
- Some cognitive processing due to preservation or corticothalamic connections.
- They may exhibit visual pursuit, emotional responses, gestures to appropriate environmental stimuli.
They cannot communicate their thoughts and feelings.
Why were MCS and VS categorized separately?
MCS has evidence that they comparatively had meaningful improvement in outcomes.
