Plasticity of adult brain after stroke, a study
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Transcript of Plasticity of adult brain after stroke, a study
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Outline
• Basic information
• Materials
• Methods
• Result
• Discussion
• Inference
• Take home massage
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fMRI and its principle
• fMRI is a functional neuroimaging procedureusing MRI technology .
• It measures brain activity by detectingassociated changes in blood flow.
• fMRI uses the blood-oxygen-level dependent(BOLD) contrast.
ref: wikipidea
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fMRI of visual cortex
Ref: Wikipedia
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Definitions
• Population receptive field mapping:
pRF model estimates the region of the visualfield that effectively elicits a response in a smallregion of the visual cortex (i.e., voxel).
Blood Oxygen Level dependence (BOLD) is used to estimate response in an region of interest (ROI).
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Visual field defect
Ref: clinical junior.com
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Objective
• After V1 injury recovery to some extent is wellknown. A recent study suggested, large scalereorganization occur in V1. But so far therewas no quantitative study.
• So, this study was meant look into the rangeof reorganization and its mechanism.
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Research question
1. Does visual cortex (V1) really has plasticity?
2. If have then to what extent?
3. How does that work?
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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
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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
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Anatomic Location Of the Lesion and Retinotopic Mapping.Anatomy Polar Angle Eccentricity Map Explained Variance
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Perimetry maps Vs visual field coverage maps of spared area V1
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Discussion
• Pattern 1: visual field coverage maps overlapped with perimetric scotoma.
• Pattern 2: visual field coverage maps didn’t cover the sighted quadrant of perimetricmaps.
• So , does the spared V1 changes after lesion?
• Does the position of pRF centre reorganise?
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Primary assumptions Pattern
observation assumption
1 (P1+P2+P3)
activation Invisual mapping> perimetry
-visually driven activityin spared V1 was not enough.- BOLD signal is lower.
2(P4+P5)
activation Invisual mapping< perimetry
- pRFs partially surviving island in V1 enlarged/ V1 bipassing pathways
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• After talairach coordiantes at an eccentricityof 8 deg along horizontal meridian of V1shows retinotropic representation of sparedV1 remained grossly unafffected (fovealrepresentation was in occipital pole,incresingly anterior location responded toincreasingly ant. Stimuli).
• Minor reorganization?
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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
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pRF centre distribution as a function of distance from scotoma border
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pRF size in spared V1 areas
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pRF size of the contra lesional V1
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Conclusion
1. Area V1 displays a limited degree ofreorganization in adult humans withhomonymous visual field defects
2. Reorganization is manifested in some patientsby a small shift(1-2 degree) in the pRF centerstoward the border of the scotoma and by aslight increase in V1 pRF sizes near the border ofthe scotoma.
3. Two different patterns of mismatch betweenresponses
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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.
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Take home massage
• After injury adult V1 displays palsticity.
• Reorganisation occurs through 1-2 deg shift ofpRF centre towards the border of scotomaand slight increase in the size of sparedcortical area on both hemisphere.
• A lot more has to explore –
-regarding optimal time window of plasticity.
-the mechanism and connection of V1bypass pathway.
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