Week 5 HNN lectures Flashcards
What is attention?
- A global (superordinate) cognitive process encompassing multiple sensory modalities, operating across sensory domains
What components can attention be divided into?
Arousal, vigilance, divided attention and selective attention
What is arousal?
a general state of wakefulness and responsivity
What is vigilance?
capacity to maintain attention over prolonged periods of time
What is divided attention?
The ability to respond to more than one task at once
What is selective attention?
The ability to focus on one stimulus while suppressing competing stimuli (e.g. you are studying in a café and there is music on the radio but you wouldn’t even be able to say what song is playing because you are just completely ignoring it.)
What happens when there is impaired arousal?
Patient may be drowsy
What happens when there is impaired Vigilance?
Impersistence - The ability to sustain attention over a period of time is impaired
What happens when there is impaired divided and selective attention?
Patient is ‘Distractable’
What is the most common disturbance of mental status seen by doctors?
Delirium
What happens in delirium?
Patients are disorientated and have memory impairments
What is domain-specific attention?
Attention relating to a specific sense
What can happen in the breakdown of domain specific attention?
Visual inattention, sensory inattention, neglect
What is neglect?
When one part of the visual field is ignored
How can neglect be tested for?
If a patient is asked to draw a clock on the wall they may either miss off the numbers on one side or they might bunch all numbers onto one side of the drawing.
What are the three main systems involved in attention?
The ascending reticular activating system, the top down attention modulation system and bottom up attentional competition
What is the ascending reticular activating system?
It is responsible for sleeping and wakefulness. It is a very global system and allows us to even pay attention
What does top down attention modulation allow?
The ability to pay attention to something while ignoring other thing that are going on around you
Where does the top down attention modulation occur?
In the frontal, parietal and limbic cortices
What else will be impaired if a patient has impaired arousal?
Impaired attention as these two things are related
If a patient has impaired attention will they have impaired arousal?
Not necessarily
What can hyperarousal impair?
Attention
What part of the brain can downregulate attention?
The amygdala if we feel pain or upset
What part of the attention system is impaired if a patient has drowsiness, delirium or is in a coma?
The arousal mechanisms
What part of the attention system is impaired if a patient has inattention or neglect?
Top down attention modulation
How can attention be tested in clinical practice?
Orientation in time and place, Serial 7s, Digit span and digits backwards, Months of the year or days of the week in reverse order, Alternation tasks, e.g. ‘Trails B’, Stroop test, Star cancellation test
Where does information you pay attention to go?
Into short term memory
How long does information last in short term memory?
About 30 seconds
What happens to information that isn’t rehearsed?
It is lost from memory
What happens when people study?
We try to put the information into short term memory and then rehearse it so it moves into long term memory
How long can information that is used regularly be stored for?
Can be kept indefinitely
What is the storage of long term memory known as?
Encoding
What is taking information out of long term memory known as?
Retrieval
What is short term (working) memory?
An active storage process as it requires maintenance and manipulation of information
How many elements can be held in short term memory?
7 +/- 2 elements
What are the four different systems within working memory?
- Visual spatial sketchpad
- phonological loop
- central executive systems
- Episodic buffer
What is the visual spatial sketchbook?
This is where we can visualize or imagine visual information
What is the phonological loop?
This is where we process what we hear
What is the central executive system?
This controls and coordinates the systems of short term memory
What is the episodic buffer?
This is where we can bring in information from long term memory when we need it
What is interference?
When someone tries to learn something from one category and there is other stimuli then they will be disrupted
What is the limit on long term memory?
There is no known limit
What is the interaction between short and long term memory like?
They operate independently
What are the tow categories of long-term memory?
Explicit (declarative) and implicit (procedural)
What are the categories of explicit (declarative) memory?
Episodic and semantic
What are the categories of implicit (procedural) memory?
Motor skills and classical conditioning
What is episodic memory?
A form of explicit (declarative)memory that can be accessed and reflected upon. It is personally experienced, temporally specific episodes/ events
What is the role of the dorsolateral prefrontal cortex in episodic memory?
It is responsible for the temporal organisation of memories. It also interacts with structures in the extended limbic systems
What is temporal organisation?
the ability to place events in time
What parts of the extended limbic system are involved in episodic memory?
The medial temporal lobe and the diencephalon
How is episodic memory tested in clinical practice?
- Recall of complex verbal information (e.g. recall of stories in the Wechsler Memory scales)
- Recall of geometric figures (e.g. Rey-Osterrieth Figure test)
- Word-list learning (e.g. California verbal learning test)
- Recognition of newly encountered words and faces (Warrington’s recognition memory test)
What is semantic memory?
A form of explicit (declarative memory) that is available to access and reflect on. It is made up of factual information and vocabulary.
Where in the brain does semantic memory occur?
Left hemisphere anterior temporal lobe is a key integrative region
Anterior temporal cortex (ATC) and angular gyrus (AG) integrate incoming information
How is semantic memory arranged in the brain?
Ventral (visual) to dorsolateral (non-visual); posterior (basic objects) to anterior (complex)
There seems to be a way of organizing information based on whether it is visual or not and whether it is basic or complex. These are then stored in different regions of the brain.
What does anterior temporal cortical destruction or atrophy present with?
Damage to semantic memory
What can cause anterior temporal cortical destruction or atrophy?
- Herpes simplex encephalitis
- Trauma
- tumours
- Alzheimer’s dementia or Semantic dementia (a form of frontotemporal dementia)
What can categorical defects in semantic memory be caused by?
Can be caused by Progressive right temporal lobe atrophy (a variant of frontotemporal dementia)
What may Progressive right temporal lobe atrophy (a variant of frontotemporal dementia) also present with?
prosopagnosia - behavioural disturbance
How can semantic memory be tested in clinical practice?
- Tests of general knowledge and vocabulary (e.g. Wechsler Adult Intelligence Scale)
- Fluency – generate exemplars from specific semantic categories (e.g. name as many animals as possible in 60secs)
- Object naming to confrontation (e.g. Boston naming test – can they name frequently used objects)
- Tests of verbal knowledge (e.g. What colour is a banana?)
- Person-based tasks (e.g. naming photographs of famous people)
What is implicit (procedural) memory?
There is no conscious access to these memory stores, it is the motor skills that can be built up with practice
What are some examples of implicit (procedural) memory?
Learning to play a musical instrument, learning to ride a bike, learning to use a computer keyboard
What parts of the brain are involved in implicit memory?
basal ganglia and the cerebellum
What is the role of the eye?
detection, localisation and analysis of light in the visual field.
Where are transmitted rays of light focused to?
The retina
What do the retinal photoreceptors do with light energy?
Transduce it into changes in neuronal membrane potential
How are signals transmitted from the eye to the brain?
Via the optic nerve
What does the cornea do?
Focuses (refracts) rays of light so that they pass through the retina
Where is the retina located?
The back of the eye
What is the retina?
A multi-layered structure that converts light into neural impulses
What does the deepest layer of the retina consist of?
Photoreceptors called rods and cones
SIGHT
What is the neural signal transmitted through?
Intermediate layers of bipolar and horizontal cells
SIGHT
Where is the neural signal transmitted to?
The retinal ganglion cells
Where are the retinal ganglion cells found?
The innermost surface of the retina
Where are the cell bodies of the retinal ganglion?
The vitreous humour of the eye
Where do the axons of the retinal ganglion cells exit the eye?
The optic disc
What do the axons of the retinal ganglion cells form when they leave the eye?
The optic nerve
SIGHT
What is the pathway that the signal takes once it leaves the eye?
Optic nerve–> Optic chiasm –> optic tract –> lateral geniculate nucleus –>optic radiation –> visual cortex
What happens to the optic nerve at the optic chiasm?
There is partial decussation and 50-60% of the nerve fibres cross over
What does the partial decussation of the optic nerve at the optic chiasm allow?
The visual cortex of both the left and right cerebral hemispheres to receive visual information from BOTH eyes and permits binocular and stereoscopic vision
What does the optic tract contain?
Nerve fibres from both the left and right eyes
Where do most nerve fibres of the optic tract project to?
The Lateral geniculate nucleus
Where is the lateral geniculate nucleus?
In the dorsal thalamus
What is the dorsal thalamus?
The relay centre of the visual pathway
What does the dorsal thalamus do?
Relays sensory information from the optic nerve to the visual cortex
How is information passed from the optic tract to the visual cortex?
The nerves of the optic tract terminate within the lateral geniculate nucleus and synapse with neurons located inside it. These neurons then project to the visual cortex via the optic radiations
What is the primary visual cortex known as?
V1 (primary visual processing area) or the striate cortex (due to it’s striped appearance caused by a prominent band of myelinated nerve fibres which can be seen by the eye
what is the nasal retina?
The part of the retina on both eyes closest to the nose
where on the left eye is the light from the right visual field transmitted to?
The temporal retinal of the left eye
What is the temporal retina?
The part of the retina closer to the outside of the face
which visual cortex does the visual stimuli from the left visual field project to?
The right visual cortex
which visual cortex does the visual stimuli from the right visual field project to?
The left visual cortex
What does a partial optic nerve lesion cause?
Ipsilateral scotoma
What is ipsilateral scotoma?
A small patch where you can’t see in the middle of the eye
What does a complete optic nerve lesion cause?
Blindness in the affected eye
What does a lesion of the optic chiasm cause?
Bitemporal hemianopia
What is bitemporal hemianopia?
Blindness in the temporal visual field of both eyes
What does a lesion of the optic tract cause?
Homonymous hemianopia
What is Homonymous hemianopia?
Visual field loss on the same side in both eyes
Whar does a lesion in Meyer’s loop cause?
Homonymous upper quadrantanopia
What is homonymous upper quadrantanopia?
Loss of visual field in the upper quadrant on the same side in both eyes
What does a lesion in the optic radiation cause?
Homonymous hemianopia
What is homonymous hemianopia?
Loss of visual field over half of the eye on the same side in both eyes
What does a lesion in the visual cortex cause?
Homonymous hemianopia
What does a bilateral macular cortex lesion cause?
Bilateral central scotomas
What are bilateral central scotomas?
a circular loss of vision in the middle of the visual field
What are some causes of lesions of the optic nerve?
- Acute optic neuritis
- Indirect traumatic optic neuropathy
- Optic atrophy
What happens in acute optic neuritis?
demyelinating inflammation of the optic nerve
What can cause optic atrophy?
Ischaemia or tumours which may compress the nerve
What can cause lesions of the optic chiasm?
- Tumours (pituitary adenoma, meningioma)
- aneurysms (ACA)
What can cause lesions of the optic tract?
- tumours
- trauma
- aneurysm of post. cerebral artery
Where do nerve fibres that don’t go to the lateral geniculate nucleus go?
The superior colliculus or the pretectal area of the midbrain
What is the superior colliculus responsible for?
Eye movements
What is the pretectal area responsible for?
pupillary light reflex
What are Goldmann perimetry tests used for?
To test the extent of the visual field
How is the Goldmann perimetry test carried out?
A test light is used at the stimulus and the visual field is mapped according to the detection of light
What nervous system is responsible for pupillary constriction?
both parasympathetic and sympathetic
What is the pupil?
A hole surrounded by the iris that changes in size to regulate the amount of light falling on the retina
Why does the pupil appear black?
because light is absorbed by the retina and other tissues in the eye
How many muscles does the iris have?
two
What are the two muscles of the iris?
- sphincter pupillae
- dilator pupillae
What is sphincter pupillae?
A central sphincter that constricts the pupil
What is dilator pupillae?
A set of dilator muscles which dilate the pupil
What does the size of the pupil depend on?
The balance between parasympathetic and sympathetic stimulation
What type of fibres innervates sphincter pupillae?
Parasympathetic fibres
What type of fibres innervates dilator pupillae?
Sympathetic fibres
What does parasympathetic activity lead to in the eye?
Constriction of the pupil
What does sympathetic activity lead to in the eye?
Dilation of the pupil
Where does the pathway for pupillary constriction begin?
At the Edginer-Westphal nucleus
Where is the Edginer-Westphal nucleus?
Near the oculomotor nerve nucleus
What do the parasympathetic fibres for the eye enter the orbit with?
CNIII
Where do the parasympathetic fibres in the eye synapse?
The ciliary ganglion - the post ganglionic fibres then supply sphincter pupillae
What is the pathway for sympathetic innervation to the iris like?
It is made up of a three neuron chain
Where does the pathway for pupillary dilation begin?
In the hypothalamus and travels to the cilliospinal centre
Where is the cilliospinal centre?
In the spinal cord between the levels of C8 and T2
Where do the third neuron of the pupillary dilation pathway travel?
Through the carotid plexus
Where do the fibres innervating the dilatory muscles of the pupil enter the orbit?
The first division of the trigeminal nerve
What is the pupillary light reflex?
When the pupils constrict in response to light
What is the accommodation reflex?
The constriction and convergence of the eyes when looking from a distant object to a close one
What is the purpose of the pupillary light reflex?
It regulates the amount of light falling on the retina in different light conditions
What is the afferent pathway of the pupillary light reflex?
The optic nerve (CNII)
What is the efferent pathway of the pupillary light reflex?
The oculomotor nerve (CNIII)
How is the pupillary light reflex tested?
A torch is shone in each eye (separately) - the pupil should rapidly constrict
What does the swinging flashlight test look for?
Can identify asymmetry of afferent input in the pupillary light reflex
What would cause abnormal results in the swinging flashlight test?
Disease of the optic nerve or the retina
What is asymmetry of afferent input in the pupillary light reflex also known as?
Relative afferent pupil defect (RAPD)
What are the 3 components of the accommodation reflex?
- Pupil constriction (Constrictor pupillae)
- Lens accommodation (ciliary muscles)
- Convergence of the eyes (contraction both medial rectus muscles)
How is the accommodation reflex tested?
The patient looks at a far away image and then to a near object.
