M9, T2, unpacking visuospatial neglect

Question 1

Hemispatial neglect

Answer 1

• Hemispatial neglect is a syndrome where an individual fails to pay attention to objects presented to one side of the body and where they may even deny connection with that side.
• It is most common following damage to the right hemisphere (however, neglect from left hemisphere damage can also occur).
• Damage is contralateral to neglected space
• Overall, it impacts about 40% of those with right hemisphere lesions and 20% of those with left hemisphere lesions.

Question 2

Common symptoms following a right hemisphere lesion

Answer 2

• Deviation of the head towards the right side (ipsilateral to the lesion)
• If addressed from the left, they may ignore the person or turn their head to the right
• Will not pick up food from the left half of their plate
• Only complete the right side of a crossword puzzle
• If walking, they might systematically turn to the right
• They may not use their left-sided limbs (even if all motor processing is intact)
• Ignore the left half of the body

Question 3

Assessing spatial neglect

Answer 3

Line Crossing and Cancellation Tasks
Line Bisection Tasks
Dissociations between Cancellation and Bisection Tasks

Question 4

Line crossing task (Albert, 1973)

Answer 4

• 40 black lines that are 2cm long arranged roughly in rows
• Examiner asks patient to cross out lines
• Scored by counting how many uncrossed lines there are and seeing if they are mostly on one side of the paper

Question 5

Cancellation task (Albert, 1973)

Answer 5

• Versions of the crossing task including distracting information have also been developed (Wilson, Cockburn and Halligan, 1987)
• Task requires visual selection
• Participants cross out smaller stars
• Thought to be better at detecting more subtle cases of visual neglect

Question 6

Line bisection tasks (Heilman and Valenstein, 1979)

Answer 6

• Patients asked to mark with a pencil the centre of lines
• Examiner measures how far away from the true centre of the line the patient marks
• The direction of the bisection indicates the direction of neglect (i.e. if the line is to the right they are showing left neglect)

Question 7

Dissociations for line crossing v bisection tasks

Answer 7

Line bisection = perception of the length of a single stimulus
Cancellation = visual search processes among many stimuli

“A patient who fails to response to stimuli located on the contralesional side…may not necessarily have a deficit in the estimation of object size, whereas a patient with a deficit in size perception does not need to exhibit spatial neglect”
-> Patients without neglect but with visual field defects perform poorly on bisection tasks.

Question 8

What test is best to use for neglect? Ferber and Karnath (2001), participants

Answer 8

• N = 35 (med age 68) with right side brain damage resulting in unilateral spatial neglect
  All patients showed:
  -> Spontaneous deviation of the head and eyes toward the ipsilateral side of the lesion
  -> Orienting to the ipsilateral side of the lesion when addressed from the front or left
  -> Ignoring objects and people on the contralateral of the lesion
  -> Performed poorly on bedside clinical tests (e.g., clock test)

Question 9

What test is best to use for neglect? Ferber and Karnath (2001) line bisection and cancellation methods

Answer 9

Line bisection: mark 10 lines at the point where they were divided into two equal halves. Scored positive and negative deviations from the centre of each line

Cancellation tests: patients not able to move the paper. No time limit – patient stopped when they felt the tasks were completed. Recorded % of omissions in the task.

-> Bells and letter cancellation test show highest number of omissions
-> may be most sensitive for detecting neglect

Question 10

Ferber and Karnath (2001) diagnosis results from various cancellation tests

Answer 10

• On average, older adults will miss some targets in cancellation tasks even if they do not show neglect (around 15% of targets)
• To diagnose neglect, omission scores in cancellation tasks should be higher than 15% cut-off
  Using this cut-off:
  -> Letters diagnosed 94% patients
  -> Bells diagnosed 94% patients
  -> Stars diagnosed 87% patients
  -> Lines diagnosed 71% of patients

Question 11

Ferber and Karnath (2001) diagnosis results from line bisection test

Answer 11

To diagnose neglect, in bisection tasks, average percentage deviations should greater than 14%

Using this cut-off:
Diagnosed 60% of patients

Question 12

Spatial attention and cortical networks

Answer 12

Spatial attention is implemented at the cortical level by networks linking the posterior parietal cortex, frontal eye fields, ventral frontal cortex and the right temporoparietal junction

*look up image
Dorsal network (blue) = underlies top-down, goal directed attention, sends signals to the ventral network and visual areas to restrict activation to behaviourally important stimuli
Ventral network (yellow) = underlies bottom-up, stimulus driven attention, sends reorienting signals to the dorsal network to help orient attention towards salient stimuli currently outside of the attention focus
-> Both networks are connected

Question 13

Spatial attention and expected damage

Answer 13

• Might expect neglect patients to have damaged dorsal attention networks
• BUT, the lesion anatomy of spatial neglect does not closely match the pattern of brain activation associated with spatial attention and visuomotor behaviour
• The dorsal frontoparietal network which governs spatial attention and visuomotor control and is involved in goal directed stimulus and response selection doesn’t match the anatomy of neglect!
• The ventral temporoparietalnetwork for target detection, reorienting, vigilance and arousal matches the anatomy of neglect

Question 14

Corbetta et al (2005) hypothesis for neglect, dorsal and ventral networks

Answer 14

• “We hypothesize that spatial attention deficits in neglect arise from the structural or functional dysfunction of both dorsal and ventral attention networks.
• A stroke in ventral cortex (either frontal or parietal) should interfere with attentional reorienting.”
• “Moreover, as the ventral network normally sends the dorsal network a ‘circuit-breaking’ signal during target detection, a ventral lesion should also decrease activity of the (ipsilateral) right dorsal network.
• The resulting hemispheric imbalance could produce a rightward spatial bias in visual processing.”

Question 15

Right hemisphere damage of ventral system

Answer 15

Right hemisphere damage of ventral system means that there is a relative decrease in the activation of the IPS, TPJ and visual areas of the right hemisphere

• There will be a relative increase in the IPS and visual area activation of the left hemisphere
• Contralateral connections means there will be a dominance in right side processing

Question 16

Corbetta et al (2005) functional MRI

Answer 16

• functional MRI with 11 neglect patients tested at acute and chronic stages of recovery
• All had lesions localised to the ventral attention network
• Patients completed cueing tasks to measure voluntary attention (dorsal network)
• Ventral lesions in frontal or temporoparietal cortex cause dysfunction of dorsal parietal areas that seem to mediate a rightward bias during spatial attention.