Disorders of the Parietal Lobe

Question 1

what is clinical neuroscience?

Answer 1

neuroscientific approach to disorders of the brain and central nervous system

Question 2

what does clinical neuroscience do?

Answer 2

• allows clinical neuroscientists work to understand the brain bases of a number of condiitons
• problems arise due to abnormalities in the brain/nervous system like epilepsy
• problems can be acquired after brain injury (TBI or stroke)
• contributes neurobiological factors to psychiatric conditions i.e. depression, anxiety and PTSD

Question 3

where is the parietal lobe?

Answer 3

behind the frontal lobe with a boundary called the central sulcus separating the two lobes. The parietal lobe also sits above the temporal lobe, with the Sylvian fissure, or lateral sulcus, separating the two.
* important in the dorsal ‘where’ pathway

Question 4

what does ventral ‘what’ pathway?

Answer 4

understanding what objects are/object perception

Question 5

what is the dorsal ‘where’ pathway?

Answer 5

understanding where things are and how an individual can act on them

Question 6

where does the parietal cortex sit?

Answer 6

in part of the attentional control network (half parietal cortex, half frontal cortex)
* includes top down where you make decision on how to act on things, feeding into bottom-up stimulus processing

Question 7

what are the functions of the parietal cortex?

Answer 7

• space-based attention (the world around us)
• object-based attention (attend to an object and shifting attention)
• reaching and grasping (for an object)
• magnitude processing (how many objects, how far away, how quickly)
• feature based attention (attend to parts of an object)

Question 8

how do neuropsychological disorders differ?

Answer 8

• differ dependent on location and hemisphere of the lesion
• following events like a stroke, you rarely see specific impairments and generally people recover functions after a period of time (especially with habilitation)
• still have poor working memory of space even when trained
• can also be caused by Alzheimer’s

Question 9

what is hemispatial neglect?

Answer 9

a disorder of space-based attention

Question 10

describe hemispatial neglect

Answer 10

• associated with damage to the right parietal lobe
• patients don’t attend to the left side of space (cannot see the left hand side visually or feel the left - their midpoint is the left)
• but patients can attend to objects when pointed out to them (they can actively look to the left)
• neglect is NOT a problem with the visual cortex

Question 11

what are some tests that individual’s with hemispatial neglect can do?

Answer 11

• draw an image that specifically has a left and a right side
• give them a bisect a line task (hemispatial neglect present if there’s a right way bias on the line instead of the line being bisected on the middle)
• test if individual only attend to the right side of the activity (i.e. right side of a plate, right side of a hose, right side of a clock)

Question 12

what about semantic knowledge in hemispatial neglect?

Answer 12

semantic knowledge is unaffected.
* patients are unaware they are experiencing hemispatial neglect, and not necessarily release they are losing their right space

Question 13

how can we use eye-tracking to assess hemispatial neglect?

Answer 13

track someone’s eye movements, if the target only searches the right side and middle of the visual field than it’s likely they have right bias and hemispatial neglect

Question 14

describe Pizza del Duomo (in Milan)…

Answer 14

• patients are asked to describe buildings in ‘mind’s eye’
• it was found that patients neglected the left side of space regardless of the viewpoint

Question 15

what’s the difference between right and left when it comes to hemispatial damage?

Answer 15

neglect is far more common in the right hemisphere than the left hemisphere

Question 16

neglect is far more common in the right hemisphere than the left hemisphere, why is this?

Answer 16

• right hemisphere dominant for visuospatial attention and represents contralateral and ipsilateral space
• left hemisphere only represents contralateral space
• right hemisphere covers full range of visual space and therefore is more dominant whereas the left hemisphere only represents the right visual field

Question 17

what happens when individuals have hemispatial neglect and cannot attend to a side of space?

Answer 17

• patients neglect objects / people / environment in the left visual field
• have problems imagining the left visual field
• 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

Question 18

apart from recognising objects in the neglected visual field, what other problems might you predict?

Answer 18

• neglect patients may sometimes respond to voices/sounds originating from the affected hemispace as if they occurred in the ipsilesional side of space
• neglect patients show poorer audio location compared to patients with right brain damage without neglect – and these deficits are specific to the contralesional side of space

Question 19

how to recover some attentional functions, when affected by neglect?

Answer 19

• really damaged parietal cortex = doesn’t grow back
• but recovery can happen if other regions take over cognitive functions of the parietal cortex or the patient has developed cognitive strategies to help them attend to the left side of space

Question 20

what is baliant syndrome?

Answer 20

bilateral damage to parietal and occipital lobes causing a disorder of object-based attention

Question 21

if you have balint’s syndrome, you MUST have three distinct impairments (**although each disorder can occur on their own, the patient won’t have balint), what are they?

Answer 21

• Simultanagnosia
• Optic Ataxia
• Oculomotor Apraxia

Question 22

what is simultanagonsia a disorder of?

Answer 22

• spatial disorder of attention (issues with motor and attention)

-> NO ISSUE WITH VISION

Question 23

what is simultanagonsia?

Answer 23

• if two (or more) objects are presented the patient can only see one of them at a single time
• if unseen objects is jiggled, the patient will see it but then lose perception of the first object
• can happen anywhere in the visual field

Question 24

describe simultanagonia…

Answer 24

• disorder of visual perception characterised by the inability to interpret complex visual arrays despite preserved recognition of single objects
• suggested impairment in the process by which activated structural descriptions are linked to information coding the location of the object

Question 25

what’s the issue with collinear test trials when examining simultanagonsia?

Answer 25

will still count the two as one object (the tear is too small for the brain to count it as two separate shapes so the brain only treats it as one)

Question 26

what is optic ataxia?

Answer 26

disorder of reaching and grasping

Question 27

describe goodie et al. (1994) study of optic ataxia…

Answer 27

RV: bilateral damage affecting dorsal visual stream (parietal lobe lesions)
DF: bilateral damage affecting ventral visual stream (ventral occipital lesions)

• Presented both with pairs of cut out shapes (job was to find the shapes which looked the same)
• RV could see the shape of these objects - she could mostly tell them apart.
• DF performed at chance (ventral occipital is really important for object perception).
• Although RV could see the shape of these objects, she grasped them at inappropriate points.

Question 28

what is the postbox test?

Answer 28

testing to see if a patient can put their hand through a slot.
* those with optic ataxia tend to put their hands in the wrong way/will put their hand over to the side and miss the box

Question 29

what is oculomotor apraxia?

Answer 29

a problem making planned and purposeful eye movements
* patients have problems with saccade initiation and accuracy, and smooth visual pursuit (tracking an object)
* happen due to a deficit in a circuit between the parietal lobe and the frontal eye fields (FEF)

Question 30

what is dyscalculia?

Answer 30

developmental disorder affecting magnitude processing
* when caused by acquired damage, referred to as ‘acalculia’

Question 31

what happens when an individual has dyscalculia?

Answer 31

• problems with understanding and manipulating numbers (e.g. arithmetic, multiplication etc.)
• prevalence estimates around 3–6%
• neuroimaging suggest that the deficit may be localized in the right inferior parietal lobule

Question 32

describe the numerical distance effect…

Answer 32

*easier to identify the larger of two numbers when there is a greater numerical distance between them
* 8 children with Developmental Dyscalculia (DD) and 8 controls completed a task tapping this distance effect during scanning
* Controls showed greater changes in BOLD activity in right intra parietal sulcus (particular groove) when working with close or far number distances while DD group did not show this effect

Question 33

what is the impact of dyscalculia?

Answer 33

• 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 conceptualizing time and judging the passing of time
• problems with differentiating between left and right
• inability to visualize 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)

Question 34

describe a theory of magnitude (ATOM)…

Answer 34

• time, space and number all require us to compare size or ‘magnitude’
• time, space and number share a common neural in right intraparietal sulcus
• judgements about time, space and number have consequences for our actions (in order to help us plan our actions)…
  e.g. Me trying to leave my office at different times of day/in the face of undergrads moving at different speeds
• 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

Question 35

where is the parietal lobe situated?

Answer 35

in our brain’s vision for action stream, the dorsal stream

Question 36

what is the key functions of the parietal lobe?

Answer 36

directing attention, directing reaching, grasping and our eye movements, in processing of magnitude

Question 37

what is object agnosia?

Answer 37

deficit in object recognition despite intact intelligence

Question 38

does the brain have a ‘consciousness’ area outside of the visual cortex?

Answer 38

conscious area is perhaps independent of the our visual cortex