Plasticity of adult brain after stroke, a study

2. Outline
• Basic information
• Materials
• Methods
• Result
• Discussion
• Inference
• Take home massage

3. fMRI and its principle
• fMRI is a functional neuroimaging procedure
using MRI technology .
• It measures brain activity by detecting
associated changes in blood flow.
• fMRI uses the blood-oxygen-level dependent
(BOLD) contrast.
ref: wikipidea

4. fMRI of visual cortex
Ref: Wikipedia

5. Definitions
• Population receptive field mapping:
pRF model estimates the region of the visual
field that effectively elicits a response in a small
region of the visual cortex (i.e., voxel).
Blood Oxygen Level dependence (BOLD) is used
to estimate response in an region of interest
(ROI).

6. Visual field defect
Ref: clinical junior.com

7. Objective
• After V1 injury recovery to some extent is well
known. A recent study suggested, large scale
reorganization occur in V1. But so far there
was no quantitative study.
• So, this study was meant look into the range
of reorganization and its mechanism.

8. Research question
1. Does visual cortex (V1) really has plasticity?
2. If have then to what extent?
3. How does that work?

9. Materials and methods
• Control: 8 male + 1 female (age: 26-65 y)
ID Sex Age t Defect
P1 M 49 7 LUQ
P2 F 27 10 RUQ
P3 M 33 0.5 RUQ
P4 M 54 7 RUQ
P5 F 64 9 LUQ

10. Materials and methods (cont.)
• Visual field tests: Humphrey type
• Scanning: Structural and functional MRI
• Stimuli: moving square checker board bars
(radius 11.25 degree)
• Infrared eye movement tracker

11. Anatomic Location Of the Lesion and Retinotopic Mapping.
Anatomy Polar Angle Eccentricity Map Explained Variance

12. Perimetry maps Vs visual field coverage maps of spared area V1

13. Discussion
• Pattern 1: visual field coverage maps
overlapped with perimetric scotoma.
• Pattern 2: visual field coverage maps didn’t
cover the sighted quadrant of perimetric
maps.
• So , does the spared V1 changes after lesion?
• Does the position of pRF centre reorganise?

14. Primary assumptions
Patte
rn
observation assumption
1
(P1+P
2+P3)
activation In
visual
mapping>
perimetry
-visually driven activity
in spared V1 was not
enough.
- BOLD signal is lower.
2(P4+
P5)
activation In
visual
mapping<
perimetry
- pRFs partially surviving
island in V1 enlarged/
V1 bipassing pathways

15. • After talairach coordiantes at an eccentricity
of 8 deg along horizontal meridian of V1
shows retinotropic representation of spared
V1 remained grossly unafffected (foveal
representation was in occipital pole,
incresingly anterior location responded to
increasingly ant. Stimuli).
• Minor reorganization?

16. Methods (cont.)
• Methods to find minor degree reorganization:
1. pRF centre distribution as a function of
distance from the scotoma
2. population receptive field size

17. pRF centre distribution as a function of distance from
scotoma border

18. pRF size in spared V1 areas

19. pRF size of the contra lesional V1

20. Conclusion
1. Area V1 displays a limited degree of
reorganization in adult humans with
homonymous visual field defects
2. Reorganization is manifested in some patients
by a small shift(1-2 degree) in the pRF centers
toward the border of the scotoma and by a
slight increase in V1 pRF sizes near the border of
the scotoma.
3. Two different patterns of mismatch between
responses

21. Evaluation
• The paper is precise and relevant for
answering questions about plasticity in adult
V1.
• Patient selection could have been better. (P3)
• Some hypotheses are still unexplained.

22. Take home massage
• After injury adult V1 displays palsticity.
• Reorganisation occurs through 1-2 deg shift of
pRF centre towards the border of scotoma
and slight increase in the size of spared
cortical area on both hemisphere.
• A lot more has to explore –
-regarding optimal time window of plasticity.
-the mechanism and connection of V1
bypass pathway.