Consciousness Flashcards
What is consciousness?
Processes that enable us to experience the world around us This is distinct from automatic behaviours that occur in a rather unconscious manner subject experience of the mind and world around us, first person point of view, aware of ones surroundings.
What structure within the brain is heavily involved in regulating alertness?
Reticular Activating System
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
What are the elements of consciousness?
Level, content, self
What does RAS enable?
Regulates many vital functions Degree of activity is related to alertness and levels of consciousness RF projects to the hypothalamus, thalamus and the cortex
What are the sensory inputs to the reticular formation?
Sensory and pain from ascending pathways Vestibular information from medial vestibular nucleus Visual from superior colliculus Auditory from inferior colliculus Olfactory via the median forebrain bundle
The RF modulates cerebral activity via various projections. What are these projections?
Noadrenergic projections from the nucleus coeruleus to the cerebral cortex PONS. Dopaminergic projections from the ventral tegmental area to the cerebral cortex MIDBRAIN. Cholinergic projections to the thalamus most important in regulating levels of arousal.
What are the mechanisms of consciousness?
The location of neurons? The number of neurons? The dynamics of neuronal activity No single brain region for consciousness
What are the three mechanisms by which these projections regulate the level of arousal?
Excitation of individual thalamic relay nuclei - activation of cortex Projections to intralaminar nuclei - project to all areas of cortex Projections to reticular nucleus – regulates flow of information through other thalamic nuclei to the cortex
What are the different waveforms seen on an EEG and what levels of arousal do they represent?
Delta (< 4 Hz) – seen in sleep Theta (4-8 Hz) – drowsiness Alpha (8-13 Hz) – subject relaxed with eyes closed Beta (13-30 Hz) – mental activity and attention Gamma range (~40 Hz) – creation of conscious contents in the focus of the mind’s eye, via the recurrent thalamo-cortical feedback
What is a cerebral contusion?
Localised bleeding in the brain (bruise in the brain)
How can you quantify brain complexity?
using transcranial magnetic stimulation and EEG – pertubational complexity index (PCI)
What are disorders of consciousness?
Coma Vegetative state Minimally conscious state
Summarise each of the disorders of consciousness
Summarise affected areas in vegatative state, locked in syndrome and brain stem death.
Locked in syndrome - perfect consciousness but motor impairment
Brainstem death unlike any other states.
Neglect and bitemporal hemianopia are not the same - people are aware of neglect adn can adjust
How does EEG monitor levels of arousal?
Delta (< 4 Hz) – seen in sleep
Theta (4-8 Hz) – drowsiness
Alpha (8-13 Hz) – subject relaxed with eyes closed - posterior dominant rhythm loss of alpha means something not right posteriorly.
Beta (13-30 Hz) – mental activity and attention
Gamma range (~40 Hz) – creation of conscious contents in the focus of the mind’s eye, via the recurrent thalamo-cortical feedback
Slowing is bad
What can EEG diagnose?
epilsepsy - few mins
Non-convulsive states - hrs/days
Describe how the Glasgow Coma Scale is structured.
Eye opening = 4
Verbal responses = 5
Motor responses = 6
Damage to the reticular formation can lead to coma. What is a coma?
State of unconsciousness in which the subject cannot be roused even by strong sensory stimuli
Different from sleep – metabolic activity of the brain is depressed and there is total amnesia for this period
State some causes of coma.
Metabolic - drug OD, hypoglycaemia, diabetes, hypercalcaemia
Diffsue intercranial - head injury, meningitis, SAH (subarachnoid haemorhhage), encephalitis (inflammed brain), epilepsy, hypoxic brain injury
Hemishpere lesion - cerebral infarct, subdral/extradural haemorrhage, abscess (built up collection of pus), tumour
Brain stem - brainstem infarct, tumour, abscess, cerebellar haemorrhage, cerebellar infarct
What causes a persistent vegetative state?
Disconnection of the brainstem from the cortex or widespread cortical damage
Brainstem is still functioning so reflexes, postural movements and sleep-wake cycle may still be present
What is brain death?
Irreversible coma due to brainstem death, but body kept alive artificially
NOTE: spinal reflexes and some postural movements may be present
What would the consequences of a right parietal lesion be?
Hemispatial neglect – the patient will not pay attention to the left visual field
Information from the left visual field is reaching the primary visual cortex but because of the parietal damage, the patient is not conscious of this visual field
What imaging technique can be used to study consciousness in health and disease?
Functional MRI
Define the vegetative state
A vegetative state is absence of responsiveness and awareness due to overwhelming dysfunction of the cerebral hemispheres, with sufficient sparing of the diencephalon and brain stem to preserve autonomic and motor reflexes and sleep-wake cycles.
