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CLINICAL NEUROLOGY :pencil2: B+B2 LECTURE 5 - Coggle Diagram
CLINICAL NEUROLOGY
:pencil2:
B+B2 LECTURE 5
Clinical Neurologist
Diagnoses patients.
Most stroke patients recover functions months/years after the trauma.
Small number of patients who have very specific deficits after the trauma.
Ventral Pathway
Object recognition, or "what" pathway. (E.g. Faces)
If you have a lesion in the ventral pathway, maybe you can’t recognise faces if you become prosopagnosic, but you can still walk around the world and interact with people by recognising their voice, for example.
Runs along the ventral surface of the brain, visual recognition system.
Has connections to the ACN
Need to direct attention towards something to recognise it.
The output for the ventral stream, which is the FFA, the PPA, etc., is the hippocampus (the memory area) and the anterior temporal lobe.
Dorsal Pathway
"Where' pathway
Locates objects in physical space.
Enables us to say where things are in relation to each other.
"Vision for action" pathway
The parietal lobe itself feeds into the motor cortex, which comes across the top of the brain diagram (black line coming down from the top to the middle of the brain = central sulcus), the motor cortex is just in front of the central sulcus. Somatosensory cortex is just behind that.
The motor cortex is where we plan all of our motor movements.
Parietal lobe - enables us to act in space.
The parietal lobe feeds into the frontal lobe.
The output for the dorsal stream, the vision for action stream, is the frontal cortex and the motor cortex.
The output of the dorsal stream is decision and action.
Attentional Control Network (ACN)
Decisions about interactions we make with the things we recognise.
A disorder in the attentional control network/lesion in the parietal lobe or frontal lobe (somewhere on top of the brain) is going to be more disruptive to daily life.
If you have a lesion in the attentional control network (ACN), the effects can be widespread and much more severe.
Think of the attentional control network as being like air traffic control.
Lesions in the ACN (dorsal pathway, parietal and frontal lobes) can cause real problems with interacting with the physical world.
Parietal Cortex
Input from V1
Functionally distinct areas.
V1 = Early Visual Cortex
IPS = Intraparietal Sulcus - the sulcus that goes into the parietal lobe,
IPS1, IPS0, IPS2, IPS3 are all subdivisions of that particular area of the brain based on Retina-topic mapping (how they respond to different parts of the visual field)
Functions
Space based attention - the world around us.
Object-based attention - attending to an object.
Reaching and grasping - reaching for an object.
Magnitude processing - how many objects? (see dyscalculia - problem processing numbers)
Feature based attention - attend to parts of an object.
Neuropsychological Disorders of the Parietal lobe
Lesions
These disorders depend on the location and hemisphere of the lesion.
On Structural MRI scans, big black spots represent space that has been filled with cerebral-spinal fluid.
Blood flow has not reached that part of the brain for an extended period of time (30 minutes or more).
When the cortex doesn’t receive blood, that part of the brain dies, and is gone forever.
Can map whereabouts the lesion is with structural MRI.
Lesions can extend across the whole of the parietal lobe and in some cases into the frontal lobe.
Lesion overlap analysis
Data from a number of patients (e.g. 100 patients)
All of their structural MRI scans have been overlapped into one common space.
If you have a lesion in the white dotted area of the right hemisphere, you are very likely to have hemispatial neglect.
Hemispatial Neglect
One of the most famous disorders of the parietal lobe.
Sometimes also called visual neglect.
Damage to the right parietal lobe.
Patients don’t attend to the left side of space.
But they can attend when objects are pointed out to them.
This means that neglect is not a problem in the visual cortex - it’s a problem of attention, not of visual perception.
Neglect, perception and mental imagery
Very simple tests that you can do with neuropsychological patients.
Bisect the line task
- Patients don’t see the left side of the line, so bisect it ¾ of the way along (½ way along the right side).
Cancel the line task
- Ignored all of the lines on the left hand side of the page.
Copy the picture of this house
- They miss the left side of the house
Draw a clock from memory
- Can’t imagine the left hand side of space.
Assessing Neglect: Eye-tracking tasks
The patient is being asked to look at a picture and describe what is going on in the picture (a scene of some kind).
Only look at the right side of space.
Piazza del Duomo, Milan (Bisiach & Luzzatti, 1978)
Patients described buildings in “minds eye”
Neglected left side of space regardless of viewpoint
Left side of space was unavailable.
Cortical Damage in Neglect
More common in the right than left hemisphere.
Right hemisphere is dominant for visuo-spatial attention.
Right hemisphere represents contralateral and ipsilateral space.
Left hemisphere represents contralateral space only.
Summary of Hemispatial Neglect
Patients neglect objects / people / environment in the left visual field.
They also have problems imagining the left visual field.
Patients can attend to objects in the left visual field when they are directed to them.
This pattern of impairments shows that neglect is a problem with attention and not with perception.
The left side of space is unavailable to neglect patients.
Neglect - Recovery
Patients do recover from neglect.
Patients start to get better a number of months later (Diaschisis)
The brain compensates for some of the deficits and rewires itself.
Sometimes a good thing, sometimes a bad thing.
Balint's Syndrome
What is it?
Bilateral damage to parietal and occipital lobes
Three distinct impairments:
simultagnosia, optic ataxia, oculomotor apraxia
Have to have
all three
to be diagnosed with Balint’s Syndrome.
But can display these deficits individually.
Simultagnosia
If two objects are presented, the patient can only see one of them at a time.
If the unseen object is jiggled then the patient will see it but they will then lose perception of the first object.
This happens anywhere in the visual field (not like neglect)
Optic Ataxia
A disorder of reaching and grasping.
Lesions can be in the left or right Inferior Parietal Lobule
(Karnath & Perenin, 2005)
Goodale et al (1994)
Case RV - bilateral damage affecting dorsal visual stream (Optic Ataxic).
Lesion to the parietal lobe.
Case DF - bilateral damage affecting ventral visual stream (Visual Agnosic)
Lesion to the frontal lobe.
Damage to the bilateral ventral occipital cortex (LO).
She can’t see objects and recognise them.
But she can reach out and grasp them.
RV should see the shape of these objects - he could mostly tell them apart.
DF performed at chance.
Although RV could see the shape of these objects, he grasped them at inappropriate points.
DF was able to grasp them successfully.
Perenin & Vighetto (1988)
Posting task.
Post hand through the slot in the wood.
Oculomotor Apraxia
A problem making planned and purposeful eye movements.
May happen in patients with Balint’s Syndrome due to deficit in a circuit between the parietal lobe and the Frontal Eye Fields (FEF)
Fronto-parietal Attention Network:
(Dorsal pathway) Parietal lobe feeds into the motor system which enables me to make planned movements.
That then feeds into the frontal cortex, which enables me to control and plan those movements.
Summary
Patients with Balint’s Syndrome show all three impairments.
Simultagnosia
Optic Ataxia
Oculomotor Apraxia
But each disorder can also occur on its own - these patients will not be diagnosed with Balint’s Syndrome.
Dyscalculia
A disorder of magnitude processing
Dyscalculia is typically a developmental disorder.
Patients tend to have a problem understanding and manipulating numbers (e.g. arithmetic, multiplication, etc.)
Neuroimaging studies suggest that the deficit may be localised in the right inferior parietal lobule.
Numerical distance effect: easier to identify the larger of two numbers when there is a greater numerical distance between them.
Controls show more BOLD activity in the right intraparietal sulcus on numerical distance effect.
Impairments
Difficulty reading analog clocks
Difficulty stating which of two numbers is larger
Difficulty with multiplication-tables, and subtraction-tables, addition tables, division tables, mental arithmetic, etc.
Difficulty with conceptualising time and judging the passing of time.
Problems with differentiating between left and right
Inability to visualise mentally
Difficulty with choreographed dance steps
Difficulty working backwards in time, (e.g. What time to leave if needing to be somewhere at 'X' time)
Difficulty navigating or mentally "turning" the map to face the current direction rather than the common North=Top usage
A Theory Of Magnitude (ATOM)
Time, space and number all require us to compare size or “magnitude”
Time, space and number share a common neural in the right intraparietal sulcus.
Dyslexia is a left parietal lobe function as well.
Dyscalculia is a disorder of magnitude.
A theory of magnitude:
If you see damage to the parietal lobe, they have problems with time, space, reaching out and grasping, arithmetic.
Things that require us to compare size.
Idea that these things all share a common substrate which is magnitude.
Magnitude is calculated in the parietal lobe → that information is then sent to the frontal cortex, and between them is the motor output, which is when I decide what I am going to do.
Damage to the parietal lobe = difficulty calculating magnitude.
ATOM: Summary
Time, Space and Number share a common neural substrate in the right intraparietal sulcus
Similar cognitive functions are likely to processed in the same brain area to save on “wiring costs”
What does this tell us about how we think?
Remember that we use cognition to understand the brain AND the brain to understand cognition