Consciousness Flashcards
Define consciousness
Definitions are 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
Essentially, the subjective experience of reality
What is consciousness distinct from
This is distinct from the autonomic behaviours that occur in an unconsciousness manner (i.e. breathing).
Compare the presentation of neurological events to anxiety or panic attacks
Things that occur randomly and occur in discrete episodes are likely to be neurological events- stereotyped
anxiety and panic attacks are longer-lasting
When can seizures commonly happen
During sleep
What is a key symptom of temporal lobe epilepsy
Depersonalisation- altered state of consciousness- it can run on different programs
Describe Dysembryoplastic neuroepithelial tumour (DNET)
Benign tumour of the temporal lobe- common cause of epilepsy and focal lesions in adolescents and young adults
What do some people call our normal perception
A controlled hallucination
What can consciousness be divided into
Essentially a qualitative first world experience
Can be divided into the external world or the world within yourself
Compare the easy problem vs the hard problem
The easy problem vs. the hard problem (Chalmers)
• When I am in a conscious mental state, how can the structure and dynamics of the brain, in connection with the body and environment, account for the subjective phenomenological properties of consciousness? (Seth et al, 2015)
Easy problem- consciousness can be explained by the circuitry and stricture of the brain
Hard problem- but why should this circuitry lead to something that we can experience and feel, and why should it evolve in the first place
On what 3 levels can we consider consciousness
Level
Content
Self
Describe how we can visualise consciousness
graph of awareness (level, content and awareness) vs vigilance (awake behaviour, eyes open)
Vegetative state- eyes open- respond reflexively to pain- but won’t follow people around the room or have any consciousness
Minimally conscious state (dementia) - eyes may be open- but will follow people around the room- some cortical processing and consciousness- will recognise people- reproducible
What is important to remember about the reticular activating system
it is not where consciousness sits- but it is the system that enables consciousness to take place- through its projections.
- What structure within the brain is heavily involved in regulating alertness?
The reticular activating system
Essentially, what is the reticular formation
Once all the nuclei and tracts have been identified in the brainstem, a central core of cells remains. This loosely arranged network is called the brainstem reticular formation. Cellular connectivity in the reticular formation is characterized by a considerable degree of convergence and divergence such that a single cell may respond to many different sensory modalities.
What is the reticular formation
A core of grey matter passing through the midbrain, pons and upper medulla – it is a polysynaptic network that regulates the activity of the cerebral cortex
Reticular formation has many functions besides control of alertness, eg. centres which regulate body systems such as cardiovascular, respiratory, bladder, motor patterns.
What are the sensory inputs to the reticular formation
The RF receives information from ALL sensory pathways:
o Touch and pain – from ascending tracts.
o Vestibular – from medial vestibular tracts.
o Auditory – from inferior colliculus.
o Visual – from superior colliculus.
o Olfactory – from medial forebrain bundle.
How does the reticular formation modulate cerebral activity
N coeruleus – noradrenergic neurons project directly to cerebral cortex
Ventral tegmental N – Dopaminergic neurons project directly to cortex
Cholinergic neurons – project to thalamus
Raphe nuclei – in midline, main source of serotonergic projections to brain and spinal cord
The cholinergic neurons seem to be the most important for regulating the level of arousal, as they increase the level of activity in cerebral cortex via the thalamus
Summarise the reticular activating system
- The reticular formation (RF) regulates many vital functions. The degree of activity in the reticular system is associated with alertness/levels of consciousness
- RF projects to the hypothalamus, thalamus and the cortex
- Ventral tegmental area (dopaminergic neurones) (midbrain)
- Locus coeruleus (noradrenergic neurones) (pons)
What is important to remember about the location of consciousness
No single region for consciousness- thalami-cortical system is where it takes place and the interactions between many cortical regions (directly or through the thalamus)
Explain the mechanism of consciousness
Mechanisms: no single brain region, with feed-forward processing for subliminal action and top-down recurrent processing for conscious access; thalamocortical activity and interaction
Define the levels of consciousness
Levels of consciousness: alertness - involving reticular formation to control vital functions
Define the contents of consciousness
Contents of consciousness: subjective experience
Compare the levels of consciousness to the content of consciousness
o Alertness involves the reticular formation; this regulates vital functions. It projects into the thalamus and the cortex (allowing it to ‘control’ whether or not sensory signals reach cortical sites of conscious awareness – such as the posterior parietal cortex).
Which interactions are important for problem solving
Occipital- parietal interactions
Describe the ‘default-state’ of the brain
High levels of activity in many brain regions when people are awake and aware, but without pursuing any particular goal, thought, or task.
On the basis of neuroimaging studies, neuroscientists have come to call this the default state of brain activity.
Some regions including the posterior cingulate cortex, the ventral anterior cingulate cortex, the medial prefrontal cortex, and the cortex at the junction between the temporal and parietal lobes, show consistently greater activity during resting states than during processing of specific cognitive tasks.
What are the mechanisms of consciousness likely due to
The location of neurons?
• The number of neurons?- probably not- cerebellum has lots of neurones- if you remove cerebellum- still have consciousness
• The dynamics of neuronal activity- the interactions between different neurones
Describe integration
Where brain activity over time- becomes collecitivley similar, combined and correlated
Can’t have consciousness if each neurone does one thing that nothing else can
need unification of brain activity- to experience reality as a whole- although each component comes from a different part.
For example, combining sound with vision
Describe differentiation
Brain activity across the brain must be doing different things- we need variation in activity
if every neurone does the same thing- this is a seizure- perfectly synchronised.
Need different activities to account for the range of motions and experiences.
need a mixture of integration and differentiation for consciousness.
How can you quantify complexity
Quantifyingbrain complexity using transcranial magnetic stimulation and EEG (to measure brain activity) – pertubational complexity index (PCI)- measure of how conscious the patient is
Essentially, apply TMS to the patient- then look at the complexity of their brain activity- how long the activity lasts- how many different regions it involves
Not much complexity in a seizure- perfectly synchronised- no diversity- not having a rich experience
What is the CRS-R
Clinical assessment of the consciousness of patients in the vegetative state
3-23
What is UWS and EMCS
Unresponsive wakefulness syndrome
Emerging from minimally conscious state
How does the complexity vary in these patients
Complexity: will be reduced when asleep or unconscious, and higher when awake
increases from UWS/VS to LIS
and from NREM/anaesthesia to wakefulness
What is the difference between wakefulness and awareness
Wakefulness: ability to open your eyes and have basic reflexes such as coughing, swallowing and sucking
Awareness: more complex thought processes
Although being awake is clearly a prerequisite to being conscious in the sense of being normally aware of the self and the world, the functions are not equivalent.
A brain state must have a more subtle signature than wakefulness, since one can be awake and yet be unaware of some ore even most aspects of the internal and external environments.
Describe the different projections of the cholinergic nerves involved in consciousness
o Cholinergic neurones – project to the thalamus.
These have the most important role in regulating level of arousal, which involves 3 mechanisms:
• Excitation of individual thalamic relay nuclei activation of the cortex.
• Projections to intralaminar nuclei project to all areas of the cortex.
• Projections to reticular nucleus regulates flow of information through thalamic nuclei to cortex.
o Raphe nucleus – in the midline and is the main source of serotonergic projections to the brain and spinal cord.
Define what is meant by coma
A state of unarousable unresponsiveness, lasting more than 6 hours in which a person:
cannot be awakened
fails to respond normally to painful stimuli, light or sound
lacks a normal sleep-wake cycle
does not initiate any voluntary actions.
Define vegetative state
A state of wakefulness without awareness in which there is preserved capacity or stimulus-induced arousal, evidenced by sleep-wake cycle and a range of reflexive and spontaneous behaviours.
VS is characterised by complete absence of behaviour evidence for self- or environmental awareness.
Describe minimally conscious state (wakefulness with minimal awareness)
A state of severely altered consciousness in which minimal but clearly discernible evidence of self- or environmental awareness is demonstrated.
Characterised by inconsistent, but reproducible responses above the level of spontaneous or reflexive behaviour, which indicate some degree of interaction with their surroundings.
Which disorders are not disorders of consciousness
Brainstem death
Locked in syndrome
Describe the pathophysiology of the vegetative state
destruction of cortex and hemishpheres- damage to thalami-cortical neurones
Intact ascending RAS.
Describe the covert awareness that may exist in disorders of consciousness
Patient in coma
Ask them to imagine performing a task (e.g playing tennis)
Spatial navigational imagery shows activity in PMC, PPC and PPA indicating activity and awareness (although covert)
Describe the key features of the vegetative state
Forms of coma:
o Persistent vegetative state – irreversible coma due to disconnection of cortex from brainstem or widespread cortical damage.
Brainstem still functions therefore there are reflexes, postural movements and sleep-wake cycle may be present.
Thought to differ from patients in coma as the former can be aroused eventually yet both groups are thought to be unconscious.
Describe the key features of brain death
o Brain death – irreversible coma due to brainstem death – body kept alive artificially.
Decision to cease treatment depends on demonstration of absence of brainstem reflexes and response to hypercapnia.
Spinal reflexes and some postural movements may be present.
Describe how brain lesions can alter the contents of consciousness
Brain lesions alter contents of consciousness – e.g. lesions to extra-striate cortex eliminates awareness of colour (Achromatopsia).
Left visual neglect – breakdown of consciousness awareness after right parietal damage, affects as many as 40-60% of patients following right hemisphere stroke.
o Patients remain unconscious of information from left visual field (despite primary visual cortex being intact in the occipital lobe).
o The damage to the parietal cortex means information does not reach awareness as the RF is disrupted.
o Investigation:
Star cancellation test – patient cancels fewer left stars.
Visual exploration – patient will not cross midline to look left.
Describe how fMRI can be used to study consciousness
fMRI can be used to study consciousness. It can take pictures of the brain as patients carry out certain tasks therefore holding certain pieces of information in their mind which activates certain areas (more blood flow).
o Rees et al (1993) – visual neglect patients performed a face/house detection task inside a fMRI scanner and indicated when they see objects. Study showed activity in the right occipital lobe and so the information was being received but not processed, therefore they cannot “see” the objects.
Conclusion - Activation of primary visual cortices may not be sufficient for visual consciousness.
What is blind sight
Blind-sight – patients that are perceptually blind of their visual field due to occipital damage but can respond to visual stimuli.
o They can demonstrate responses to visual stimuli so can manually interact with “unseen” objects.
Describe visual neglect vs hemianopia
Hemianopia would cause the patient to not see half their field of vision and they’d know it too.
Visual neglect would cause the patient to ‘think’ they see their whole field of vision whereas they actually cannot see half their field of vision.
Describe how an EEG can be used to monitor arousal
Delta waves - often seen during sleep - >4Hz.
Theta waves – associated with drowsiness – 4-8Hz.
Alpha waves – subject relaxed with eyes closed – 8-13Hz.
Beta waves – subject is awake with normal consciousness (mental activity) – 13-30Hz.
Higher frequency waves (gamma range) – associated with creation of conscious contents in the focus of the mind’s eye, via the recurrent thalamo-cortical feedback loops. - ~40Hz.
Alpha wave frequency may decrease in frequency when eyes open
What is important to remember about EEGs
Absence of alpha and decrease in frequency (to delta and Theta waves) is bad
What does a score of 15 on the Glasgow coma scale indicate
severe brain injury and brain death.
see medlarn!
Describe the metabolic causes of coma
Metabolic
– Drug overdose – hypoglycaemia – diabetes
– “the failures”
– hypercalcaemia
Describe the diffuse intracranial causes of coma
Diffuse intracranial – head injury
– meningitis – SAH
– encephalitis – epilepsy
– hypoxic brain injury
Describe the brainstem causes of coma
Brain stem – brainstem infarct – tumour – abscess – cerebellar haemorrhage – cerebellar infarct
Describe the hemispheric lesions that can cause a coma
Hemisphere lesion – cerebral infarct – cerebral haemorrhage • subdural • extradural – abscess – tumour
Describe Bilateral medial thalamic infarcts
Stroke on both sides to thalamus- leads to coma
Which structure is vulnerable to damage in posterior fossil lesions
brainstem
Describe diffuse axonal injury
Damage to white matter tracts
shearing forces due to displacement of hemisphere- tears the white matter
can be detected by gradient echo or susceptibility weighted imaging (SWI)- white spots indicate blood which shows damage.
What is a key feature of extradural haemorrhage
Lucid Interval
How do we quantify brain complexity
Quantifyingbrain complexity using transcranial magnetic stimulation and EEG – pertubational complexity index (PCI)
What are the 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 (Koch et al., 2016)
fMRI can be used to study consciousness. It can take pictures of the brain as patients carry out certain tasks therefore holding certain pieces of information in their mind which activates certain areas (more blood flow).
o Rees et al (1993) – visual neglect patients performed a face/house detection task inside a fMRI scanner and indicated when they see objects. Study showed activity in the right occipital lobe and so the information was being received but not processed, therefore they cannot “see” the objects.
Conclusion - Activation of primary visual cortices may not be sufficient for visual consciousness.
Describe some altered states of consciousness
Altered states of consciousness:
o Contusion – a bruise localised bleeding within the brain.
o Concussion – diffuse, widespread homogenous impairment of brain tissue due to brain trauma.
o Delirium – or acute confusion – sustained disturbance of consciousness, where mental processes are slowed. Subject may be inattentive, disorientated or have difficulty carrying out simple commands.
o Stupor – lack of critical cognitive function and consciousness – only responsive to pain.
Summarise coma
Coma – damage to the RF/thalamus can lead to this:
o A state of unconsciousness in which the subject cannot be roused even by strong sensory stimuli. Different from sleep as the metabolic activity of the brain is depressed.
o Causes:
Metabolic alteration – e.g. hypoglycaemia, hypoxia.
Bilateral lesions in cerebral hemispheres.
Lesions in thalamus or brainstem (raised ICP).
o GCS – Glasgow Coma Scale – lowest score is 3.
3 sections – eyes, verbal response, motor response.
Differentiate between content and levels
There is a distinction between levels (alertness) vs. contents (subjective experience) of consciousness.
o Alertness involves the reticular formation; this regulates vital functions. It projects into the thalamus and the cortex (allowing it to ‘control’ whether or not sensory signals reach cortical sites of conscious awareness – such as the posterior parietal cortex).
