Evidence for cortical reorganisation in macular degeneration/retinal lesions?

Question 1

Sunness et al (2004)

Answer 1

Used eccentricity mapping approach to study PS with AMD + a spared foveal region (allowed PS to fixate)

Results
No activity in LPZ

THEREFORE
No remapping

Question 2

Baseler et al (2011)

Answer 2

Phase-encoded retinotopy approach was employed to test 16 PS with JMD & AMD

Calculated the area of V1 allocated to the intact retina in each PS based on normal retinotopic mapping data sets from controls

• if the area measures in PS exceeded that predicted from the control maps it suggests reorganisation

Results
In both JMD & AMD, the area of cortex responding to the intact retina did not exceed that predicted from normal retinotopic mapping

THEREFORE
No evidence of reorganisation

Question 3

Baker et al (2005)

Answer 3

2 PS with JMD
PS had to identify which images of real world objects were repeats (active task) presented to preferred retinal locus (PRL) or lesioned foveal regions

Results
Activity in LPZ (occipital pole) due to peripheral and PRL stimulation 
Stimuli presented to fovea did not 
THEREFORE 
Reorganisation of visual processing 

HOWEVER
Top-down feedback, caused by an active task may explain the results

Question 4

Massuda et al (2008)

Answer 4

4 JMD PS completed active and passive viewing task

Results
LPZ activity in active but NOT passive task
Active task caused uniform increase in activity across the cortex

THEREFORE
LPZ activity caused by active task
Activity not specific to LPZ

Question 5

Szlyk & Little (2009)

Answer 5

Tested reading-related brain responses in 6 AMD PS

Results
AMD PS had greater activity in prefrontal, parietal and frontal eye field regions

Non Visual areas more active because the task is more difficult due to sensory loss

Large sources of brain activity may be due to task difficulty

Question 6

Baker et al (2008)

Answer 6

Tested original PS with passive task

Results
Activity still found in LPZ

THEREFORE
These individuals display reorganisation of visual processing

These PSs differ from those in Massuda et al (2008)…

Question 7

Baker et al (2008)

Complete vs partial foveal deficits

Answer 7

compared these 2 populations with an active task presented to PRL

Results
Only PS with complete central deficit elicited cortical responses in LPZ

Supported by Dilks et al (2014)

Question 8

Dilks et al (2014)

Answer 8

• tested PS who initially had foveal sparing, then lost foveal sensitivity completely

Results
Activity in LPZ seen only after complete foveal loss

THEREFORE
Remapping of visual processing only occurs after complete foveal loss

Question 9

Masuda et al (2010)

Answer 9

Tested PS with peripheral deficit (foveal vision only) in active and passive task

Results
Active task caused activity in LPZ (passive task did not)

THEREFORE
Therefore task-dependent stimulus-related activity in LPZ is not just due to absence of foveal sensitivity

LPZ activity due to foveal sensitivity being an island within visual field deficit
- so long as this island receives different input from its surroundings

Question 10

Conclusion

Answer 10

Despite contradictory results, consistency can be found when grouping studies based on active / passive tasks
- all but one study (Baker et al, 2008) that used passive viewing showed no activity in LPZ

• All studies using active task showed at least some PS with LPZ activity

Therefore, feedback mechanisms (due to task) may drive LPZ activity

If feedback is thought of as reorganisation, then the latter has occurred
- however, given that feedback is a normal observation in the visual system, it may be premature to characterise signals as reorganisation

Question 11

Baseler et al (2002)

Answer 11

Strongest evidence for remapping
Achromats (only have rods; colour blind and central field deficit)
LPZ activated by stimuli in more eccentric locations than those that drove responses in controls
V1 has reorganised by remapping representation of eccentricity

Question 12

Intro

Answer 12

What is MD: Atrophy of the macular, results in loss of central/foveal vision
Define PRL: ‘pseudo-fovea’
Define LPZ: the part of the cortex which the deafferented retina would normally project to
Present the question

Question 13

Ferreira et al (2017)

Answer 13

investigated cortical remapping in 13 PS with Retinitis Pigmentosa, a degenerative disorder leading to peripheral visual degeneration

• Found retinotopic eccentricity shift from central inputs to more peripheral locations in V1
• The shift was associated with extent of visual loss, but not with age of onset.
• Suggests that regardless of the age of onset, the visual system retains plasticity to remap even when RP symptoms started in adulthood.

Question 14

Schumacher et al (2008)

Answer 14

stimulated (checkerboards) PRL nd non-PRL regions in MD suffers
RESULTS
Stimuli presented to PRL elicited activity at occipital pole (normally representing foveal vision)
5/6 patients suffered from AMD suggesting that this cortical remapping can occur later in life after disease onset
Evidence for adult visual system plasticity/remapping