Consciousness Flashcards
What is consciousness?
- The subjective experience of the mind and the world around us
- 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
What are the elements of consciousness?
The level of consciousness: are you drowsy? Are you wide-awake?
The content of consciousness: what are you conscious of?
Conscious self: consciousness is associated with some attachment to self
What is vigilance and awareness?
VIGILANCE: wakefulness – the level of consciousness in terms of how much your RAS is working. (Awake behaviour e.g looking)
AWARENESS: level and content of consciousness. When you are in a coma, you have a low level of consciousness. A patient in the vegetative state does still have a sleep-wake cycle – nevertheless, the level of awareness is similar to that seen in a coma.
What is the reticular activating system?
The RAS is an on/off switch to awakeness
- projects to the thalamus to the cortex from the brainstem
What is the ventral tegmental area and the locus coeruleus?
- Ventral tegmental Area (dopaminergic neurones)
- Locus coeruleus (noradrenergic neurones)
They are brainstem structures that project widely into the cortex. They regulate activity in the rest of the brain.
Which parts of the brain control consciousness?
It is unlikely that there is one brain region that controls consciousness. Consciousness is an emergent property, and arises from the distributed activity of the brain.
What can an fRMI show?
- You can put people into an fMRI scan (you take pictures of blood flow, which is related to neural activity).
- You can build maps using fMRI – brain regions don’t just act on their own
- Activities are somewhat coordinated Certain networks become more active during certain tasks.
- When you are at rest, the default-mode network is more active
What is pertubational complexity index?
- Brain activity is measured in vivo
- Quantifying brain complexity using transcranial magnetic stimulation and EEG – pertubational complexity index (PCI)
How is pertubational complexity index done?
- You get an anaesthetised patient
- You use transcranial magnetic stimulation to pulse the brain -> this causes resonance of activity
- This can be measured using EEG
- In patients who have disorders of consciousness (or people who are asleep/anaesthetised), the response is not as diverse
- This measure (PCI) tracks conscious level really well
What are neural correlates of consciousness?
- The neural correlates of consciousness (NCC) constitute the minimal set of neuronal events and mechanisms sufficient for a specific conscious perception
- The minimum neuronal mechanisms jointly sufficient for any one specific conscious experience
What are some disorders of consciousnes?
Describe the awareness and wakefulness of each
coma (absent wakefulness/awareness)
vegetative state (wakefulness with absent awareness)
minimally conscious state (wakefulness with minimal awareness)
What is a coma?
- A state of unrousable unresponsiveness lasting more than 6 hrs
- Person cannot be woken
- Don’t respond to painful stimuli, light or sound
- Lack normal sleep/wake cycle
- Doesn’t initiate voluntary actions
What is a vegetative state?
- Wakeful without being aware
- Preserved capacity for spontaneous, stimulus induced arousal evidenced by sleep/wake cycle
- Complete absence of behavioural evidence for self or environmental awareness
What is a minimally conscious state?
A state of severely altered consciousness in which minimal self/environmental awareness exists.
- inconsistent but reproducible responses above level of spontaneous/reflexive behavior
What is arousal and awareness?
Arousal: the dial on how awake you are
Awareness: about being conscious of something (the content of consciousness)
In normal consciousness, a coma, MCS, vegetative state and locked in syndrome describe the arousal and awareness levels
Normal: high arousal and awareness
Coma: low arousal and awareness
Vegetative: high arousal and low awareness
MCS: high arousal, low awareness
Locked in syndrome: high arousal and awareness
What happens in brainstem death compared to in vegetative/MCS patients?
- You lose the brainstem drive of respiratory drive, brainstem reflexes and so on
- People in a vegetative state or patients who are minimally consciousness may need a tracheostomy, but they will still have respiratory drive
Where is the brain damage in vegetative patients and those with locked in syndrome?
vegetative: destruction of cortex and hemispheres
locked in syndrome: damage to ventral pons
How can awareness be tested for in patients with disorders of consciousness?
- Patients in vegetative state put in into an fMRI scanner
- Patients were asked to answer by nodding yes or shaking. If they did nothing they were classed as having a low level of consciousness
- When patients underwent fMRI, questions were asked again
- Instead of nodding yes, patients were told to imagine playing tennis. Instead of shaking no, patients were told to imagine they were walking around their house
- Brain activity was similar in both patients and controls when you asked the patient to imagine playing tennis/imagine wondering around the house
- This mechanism was used to allow patients to communicate
What is homonymous hemianopia?
When you lose half of the visual field, common after stroke.
What is neglect?
A higher order problem – you lose conscious awareness of one side.
- If the neglect is on the left side, the patient won’t attend at all to anything on the right side
- The patient has completely lost awareness of that side
- Not just a visual issue
What are EEGs?
EEG measures the electricity on the scalp, that in someway relates to brain activity
- By counting the frequency of oscillations you can work out speed of activity
- Oscillations are seen which reflect brain activity
During sleep what waves are present and what frequency?
Delta
up to 4Hz
During normal waking consciousness which waves are present and what frequency?
Baet
13-30 Hz
Describe what alpha waves are and when are they more/less prominent?
What does an absence suggest?
- Typically a rhythm that you see on the back of the brain, and is related to attention.
- When you attend to something, the alpha waves go down – they get less prominent
- When you relax, alpha rhythm is more prominent
- Absence of alpha waves indicates problems.
If a person has problems what will happen to the EEG?
it will be slower throughout
What is an EEG useful for?
epilepsy
What are gamma waves associated with and what frequency are they?
Associated with creation of conscious contents in the focus of the mind’s eye
- 40 Hz
Which waved are present when you are awake and active?
beta and gamma
How does the EEG compare in REM, nREM and when you are awake?
- The EEG seen in REM sleep is very different to the EEG seen in NREM sleep
- It doesn’t completely look like when you’re awake – but different to the rest of sleep
What is the glasgow coma scale?
- The GCS is a clinical means of assessing something about conscious level
- It ranges between 3 and 15. 3 could even apply to a dead person in situations. The lower the score, the higher the severity
- Eyes (4), Voice (5) and Motor (6)
GCS - EYES
none -1
response to pain -2
response to speech -3
spontaneous -4
GCS - VERBAL RESPONSE
none -1 incomprehensible sounds -2 inappropriate words -3 disorientated -4 orientated -5
GCS -MOTOR RESPONSE
none -1 extensor response to pain -2 flexor response to pain -3 withdrawal to pain -4 localisation of pain -5 obeys commands -6
What are some metabolic causes of coma?
- Drug overdose
- Hypoglycaemia
- Diabetes
- ‘The failures’ – renal, liver etc.
- Hypercalcaemia
What are some diffuse intracranial causes of coma?
- Head injury (trauma)
- Meningitis
- SAH (subarachnoid h)
- Encephalitis
- Epilepsy
- Hypoxic brain injury
What are some brainstem causes of coma?
- Brainstem infarct
- Tumour
- Abscess
- Cerebellar haemorrhage
- Cerebella infarct
What are some hemispheric causes of coma?
- Cerebral infarct
- Cerebral haemorrhage (subdural/extradural)
- Abscess
- Tumour
