Consciousness

Question 1

What are the difference between the medical and philosophical definitions of Consciousnesses

Answer 1

• Medical approach is objective: relies on the response to stimuli
  
  • Alertness
  • Verbal
  • Pain
  • Unresponsive
• Philosophical approach is subjective: relies on the experience of the above
  
  • sensation of pain touch proprioception and interoception
  • experience of emotion, memory, though, self and non-self etc.

Question 2

What are the aspects and & requirements of full human consciousness

Answer 2

• Arousal/ activation
• Connectivity
• Input
  
  • Sense organs
  • Proprioception
  • Interoception/ emotion
• Output/Control
  
  • Motor: speech, locomotion, dexterity, eye/ head movements and other orientating movements
  • Attention
  • Cognition
  • Emotional

Question 3

What are the physiological states of consciousness and disorders of consciousness

Answer 3

• Sleep (various stages)
• Psychedelic states
• General Anaesthesia
• Coma
• PVS
• MCS
• Locked-in Syndrome
• (Death)

Question 4

Give an overview of Sleep and it’s different stages

Answer 4

• state of decreased arousal
• physiological, reversible, cyclical and active process
• Awake: high-frequency, low amplitude beta activity
• Stage 1-4 Sleep: reducing frequency, increasing amplitude
  
  • Stage II: sleep spindles- 10-20Hz oscillations
  • Stage III-IV: slower delta waves
• REM Sleep: low-voltage, high frequency similar to the awake state

Question 5

What is a Coma?

Answer 5

• this is a pathological complete prolonged loss of wakefulness and awareness (eyes usually closed)
• there is unresponsiveness to external stimuli but is often reversible

Question 6

Causes of a Coma

Answer 6

• Sedation / anaesthesia
• Epilepsy
• Electrolyte / metabolic disturbance
• Disturbance of thermoregulation
• Raised intracranial pressure
• Structural damage to brainstem / thalamus / cortex
  
  • Stroke
  • Trauma (brain injury)
  • Tumour (compressive)
  • Inflammation
  • Infection

Question 7

What is a metabolic coma?

Answer 7

• more likely to have associated brain seizures and usually leave pupillary light reflexes intact
• Triphasic theta waves

Causes

• hepatic
• uraemia
• diabetic
• pancreatic
• adrenocorticoid failure

Question 8

What are the typical outcomes of comas?

• and what assessment can be done to distinguish them?

Answer 8

• Reversal and recovery
• Survival into vegetative state or minimally conscious state
• Irreversible cessation of function
• of
  
  • Brainstem (brainstem death)
  • Cerebral cortex (neocortical death)
• Glasgow coma scale: max 15, min 3
  
  • absent eye-opening distinguishes coma/ brainstem death from PVS and MCS

Question 9

What is a Vegetative State

• description
• causes
• permenance

“Unresponsive Wakefulness Syndrome”

Answer 9

• Wakefulness
• Preserved arousal (preserved sleep/wake cycle)
• Absent awareness (& hence consciousness)
• Unresponsiveness:
  
  • No voluntary response to environment
• Variably preserved reflex responses to environment
• Cause: widespread damage to cerebral cortex (esp anoxia, head injury) – Neocotical Brain death
• Persistent Vegetative State >4 weeks, can be permanent:
  
  • After a non-traumatic Brain Injury
    
    • 6 months in the UK
    • 3 months in the US
  • After Traumatic Brain Injury
    
    • 1 year

Question 10

What is a Minimally Conscious State?

Answer 10

A state of severely altered consciousness in which minimal but clearly discernable behavioural evidence of self or environment awareness is demonstrated

Like Vegetative State, but with at least one of 11 items

1. consistent movement to command
2. reproducible movement to command
3. object recognition
4. object localization
5. reaching
6. visual pursuit
7. fixation
8. automatic motor response
9. object manipulation
10. localization to noxious stimulation
11. intelligible but non-functional verbalization

• Emergence from MCS signalled by at least one of 2 items:
  
  • functional communication
  • object use.

Question 11

How can you detect awareness in VS (and MCS)

Answer 11

• Tennis: supplementary motor area activity
• Imaging moving around a house:
  
  • Parahippocampal gyrus (PPA)
  • Posterior Parietal Lobe (PPC)
  • Lateral premotor cortex (PMC)

Question 12

What is Locked-in Syndrome?

Answer 12

• Conscious (aroused & aware)
• Unable to respond (de-efferented)
• Most cases are partially locked in:
  
  • preserved vertical eye movements
  • reserved eye-opening
• Causes
  
  • Ventral Pontine Damage
  • Severe Guillain Barre Syndrome

Question 13

What is Brain Stem death?

Answer 13

• Irreversible cessation of brainstem function
• Such that consciousness could never be regained
  
  • Absent Reflexes
    
    • Pupils, Corneals
    • Ice Calorics: slow deviation of eye towards ear that is being irrigated shows an intact brainstem
    • Pain
    • Gag
    • Cough
• Apnoea
  
  • 5 min test after pre-oxygenation and allowing CO2 to reach 6Kpa
• No arousal

Question 14

What are the legal requirements to call brainstem death?

Answer 14

• Presence of an irreversible cause (eg anoxia, structural damage)
• Absence of reversible cause; drugs, hypothermia, alcohol, poisons, metabolic (pupils react) or electrolyte disturbances
• Irreversible cessation of function of
  
  • Brainstem (brainstem death) – confirmed by 2 doctors
  • Cerebral cortex (neocortical death)
  • Body
• Must be repeated after 24 hours
• Ongoing life support?
• Organ donation

Question 15

What anatomical structures correlate to consciousness?

• Macro and Micro

Answer 15

Macroscopic Structures

• Cerebral Cortex
• Reticular activating system
• Thalamus
  
  • Motor & sensory nuclei (cortical relay)
  • Thalamic reticular nucleus (gabaergic, indirect: inhibitory on thalamus)
  • Intralaminar nucleus esp centro-median nucleus
• Claustrum
• Default Mode Network (subjective consciousness)
• Anterior Cingulate Cortex
• Prefrontal Cortex
• Inferior Temporal Cortex

Microscopic Structures

• Von Economo Neurones
• Crown of Thorns Neurones

Question 16

What are Von Economo Neurons?

Answer 16

• Large spindle-shaped soma (or body) that gradually tapering into a single apical axon, there is only a single dendrite facing opposite. F
• Found in 2 very restricted regions in the brains of hominids (humans and other great apes)
  
  • Anterior cingulate cortex (ACC)
  • Fronto-insular cortex (FI)
• Found in the dorsolateral prefrontal cortex of humans.
• Also found in the brains of the humpback whales, fin whales, killer whales, sperm whales, bottlenose dolphin, Risso’s dolphin, beluga whales, African and Asian elephants, to a lesser extent in macaque monkeys and raccoons
• 3 times higher concentrations of VENs in cetaceans in comparison to humans
  
  • potentially represents convergent evolution due to adaptation to larger brains
• allow rapid communication across relatively large brains

Question 17

the Claustrum

• 2014 stimulation

Answer 17

• a thin layer of grey matter in each cerebral hemisphere between the lentiform nucleus and the insula
• Electrode between the left claustrum & anterior-dorsal insula stimulation reproducibly resulted in:
  
  • complete arrest of volitional behaviour
  • unresponsiveness
  • Amnesia
  • No negative motor symptoms or mere aphasia.
  • Disruption of consciousness did not outlast the stimulation
  • No epileptiform discharges (usually seen in destructive structural lesions of the cortex)

Question 18

What is the clinical significance of the Intralaminar Thalamic Nuclei and the Centro-median nucleus?

Answer 18

• General anaesthetics suppress activity in ILN
• Bilateral lesions of C-M nucleus result in
  
  • Coma or severe delirium
  • Death
  • Persistent vegetative state
  • Mutism
• Unilateral lesions of C-M nucleus
  
  • unilateral neglect

Question 19

What makes up the Ascending Reticular Activating System?

Answer 19

The ascending system is seen to contribute to wakefulness as characterised by cortical and behavioural arousal and regulating sleep-wake transitions

• Serotonergic nuclei: dorsal raphe & median raphe
• Dopaminergic nuclei: ventral tegmental area & substantia nigra pars compacta
• Noradrenergic nuclei: locus coeruleus & related brainstem nuclei
• Histaminergic nuclei: tubero-mamillary nucleus
• Cholinergic nuclei
  
  • Basal Nucleus of Meynert (attention)
  • Pontine tegmentum: laterodorsal tegmental nucleus & pedunculopontine nucleus

Question 20

What are the arousal systems in the Midbrain?

• structures and transmitters

Answer 20

• Dorsal raphe nucleus: 5HT
• Parabrachial nucleus: glutamate, CRGP, dynorphin
• Pretectal area
• Periaqueductal grey
• Ventral Tegmental area: Dopamine

Question 21

What are the arousal systems in the Pons?

• structures and transmitters

Answer 21

• Locus coeruleus – Noradrenaline
• Latero-dorsal tegmental nucleus – Acetyl Choline
• Pedunculopontine nucleus – Acetyl Choline
• Pontine raphe nuclei – 5HT
• Intralaminar centromedian nucleus - glutamate

Question 22

What are the arousal systems in the Hypothalamus and the Basal Forebrain?

Answer 22

Hypothalamus

• Tuberomammillary nucleus - Histamine
• Lateral hypothalamus – Hypocretin, glutamate

Basal Forebrain

• Substantia Innominata - Acetyl Choline

Question 23

What is the role of the Anterior Cingulate Cortex in consciousness?

Answer 23

• Error detection and conflict monitoring
• Sense of volition
• Registration of pain
• Social evaluation
• Reward-based learning

Question 24

What is the resting brain activity like in disorders of consciousness?

Answer 24

Reduced activity within

• bilateral medial dorsal thalamic nucleus
• left cingulate
• posterior cingulate (DMN)
• precuneus (DMN)
• middle frontal gyri
• medial temporal gyri

Question 25

What is the Default Mode Network (DMN)

Answer 25

* A large-scale brain network primarily composed of * medial prefrontal cortex * posterior cingulate cortex/precuneus * angular gyrus (part of the TPJ) * hippocampus and para-hippocampus * DMN activity negatively correlated with activity in attentional and other networks * Active when not focused on the outside world: **Self-reference and reference to other conscious entities** * autobiographical information (episodic memory), self-reference traits etc. * reflecting about one's own emotional state, remembering the at and envisioning the future * Theory of mind, moral reasoning, social evaluation & social categorization/ status * story comprehension

Question 26

How do Brain Networks fair in Disorders of Consciousness according to scans?

Answer 26

* PET * Global brain metabolism not a sensitive marker of consciousness * fronto-parietal networks and their connectivity with thalamus breaks down in disorders of consciousness * fMRI * there is connectivity within DMN * Connectivity between DMN & ECN breaks down in disorders of consciousness

Question 27

What physiological measures can be used to correlate to consciousness?

Answer 27

* Event-Related Potentials: measurable stereotyped electro-magnetic brain correlates of sensory, cognitive, or motor events (EEG averaged)

Question 28

What functional measures can be used to correlate to consciousness?

Answer 28

* TMS with MEG or EEG * Perturbational Complexity Index (PCI) * Lempel-Ziv Complexity (LZc) - quantifies the number of distinct patterns present in data * Amplitude Coalition Entropy (ACE) - reflects the entropy over time in set of most active channels * Synchrony Coalition Entropy (SCE) - reflects the entropy over time of the constitution of the sets of synchronous channels.