What are the effects of lesioning V5?

Question 1

Discovery of area V5… [intro]

Answer 1

(Zeki, 1969)
In Macaque, found an area in the posterior bank of the STS which…
- Receives direct and highly convergent input from V1
- All cells are motion selective and majority are direction selective
(Allman & Kaas, 1971)
Found homologous area in New World Owl Monkey
- Most cells direction selective

Question 2

First case of human akinetopsia?

Answer 2

(Zihl et al, 1983)
Case LM - superior sagittal sinus thrombosis caused lesions to lateral temporal-occipital cortex
- Cunningham et al (1990), used PET, confirmed lesion encompassed V5

Psychophysical results…

1. Poor motion prediction
2. Poor motion detection
3. No motion after-effect or apparent motion
4. Could detect tactile and auditory motion

FOLLOW-UP (Zihl et al, 1991)
- No improvement in symptoms
Therefore, lesioning V5 causes irreversible deficits in motion perception

Question 3

Difference between LM and monkinetopia?

Answer 3

Newsome et al (1985) injected monkey v5 with ibotenic acid (yep really)

• Monkey recovered normal motion detection threshold after 5 days
• Different from LM because of specificity of lesion site
• This suggests that motion perception (or at least the maintenance/recovery of it) is supported by a distributed network extending beyond V5

Question 4

V5 lesion causes inactivation in other visual areas…

Answer 4

(Shipp et al, 1994) popped LM in fMRI while doing motion coherence task.

• No V5 activation
• No V1/V2 activation (present in controls), suggesting reciprocal connection have been lost
• THEREFORE V5 lesion = disruption of processing in areas beyond the lesion sight
• V3 activation still found (due to less reciprocal connections?)
• this may account for any preserved motion abilities (e.g. normal motion prediction at slow speeds)
• In summary, these results support the fact that motion perception is supported by a sparse set of regions

Question 5

Biological motion

Answer 5

McLeod et al (1996) found LM could identify the action of bio-motion
- However, could not identify the direction of motion

Vaina et al (1990) found patient AF (lateral parietal-temporal-occipital cortex lesion inc. V5) could perceive biological motion also - despite no perception of lower-order motion

• These results suggest motion processing is not strictly hierarchical as higher-order motion is still perceived despite no perception of lower order motion
• In fact, bio-motion relies on a cortical regions from temporal, frontal and parietal cortical regions (Rizzolatti & Sinigaglia, 2010), suggesting that motion processing may occur in a parallel fashion.

Therefore, although lesioning V5 seems to impair lower-order motion perception, it doesn’t necessarily mean the abolition of higher-order motion perception.

• Despite evidence that V5 is the most important hub of motion processing, this supports the suggestion that motion perception is supported by a sparse set of regions.

Question 6

TMS

Answer 6

McKeefry et al (2008) - PS had to judge whether a test grating moved faster or slower than a preceding grating - TMS was applied to V5 (and V3a) and V1 as control.

• Found test grating was perceived as moving slower than reference
• Found increase in discrimination threshold
• Suggests V5 lesion = impaired speed perception

Correlation between intensity of TMS and extent of deficit
- Suggests a clear functional role of V5

TMS to V5 resulted in deficit to speed perception and NOT spatial frequency discrimination
- Suggests selectivity of deficit that results from lesioning V5, demonstrating that V5 is primarily involved in motion processing

Question 7

Conclusion

Answer 7

Results suggests lesioning V5 has a selective impact on motion processing

A focal lesion to V5 however may result in reversible deficits
- This suggests other cortical areas may be supporting the return of motion perception in absence of V5

V5 lesion also results in inactivation of V1 to motion but not V3
- This may be an example of a region which is helping to maintain motion perception

Bio-motion perception is preserved following V5 lesion

• Suggests lesioning V5 doesn’t destroy higher-order motion perception despite deficits in lower-order motion
• Again, most likely due to other regions supporting motion perception

In summary, although lesioning v5 results in deficits in motion perception, evidence suggests that a V5 lesion alone doesn’t result in the permanent abolition of all motion processing abilities
- This suggests that while motion processing primarily occurs in V5, there are other areas that can support the ability