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The role of white matter connections in reading development and dyslexia DYSlexia Collaboration Leuven (DYSCO) Dr. Maaike Vandermosten Prof. Dr. Pol Ghesquière Prof. Dr. Jan Wouters
The role of white matter
connections in reading
development and dyslexia
DYSlexia Collaboration Leuven
(DYSCO)
Dr. Maaike Vandermosten
Prof. Dr. Pol Ghesquière
Prof. Dr. Jan Wouters
OVERVIEW
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1. Introduction
1. Dyslexia
2. fMRI-studies on reading and dyslexia
2. Structural brain connections in reading and dyslexia
1. Diffusion Tensor Imaging (DTI) technique
2. Structural connections in adults with dyslexia?
3. Structural connections in pre-readers (at risk for) dyslexia?
1.1. Dyslexia
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• Prevalence: 5 -10%
• Severe, persistent and
specific
underachievement
• Causes?
o Phonological deficit
Inferior frontal
Temporoparietal
Occipitotemporal
= phonological aspects of reading
= Orthographic aspects of reading
= neural anomalies in dyslexics
1.2. fMRI-studies in dyslexia
See meta-analysis Jobard et al., 2003
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3. Structural reading network in dyslexia
1. DTI-technique
2. Structural reading network in adults
3. Structural reading network in children
What is DTI?
• MRI-technique that gives an
indication of white matter
organization
•White matter consists of
myelinated axons
•Function: efficient communication
between cortical areas
3.1. DTI-technique: MRI
3.1. DTI-technique: diffusion
‘free’ diffusion ‘hindered’ diffusion
D is equal in all directions D is not equal in all directions
ISOTROPIC ANISOTROPIC
3.1. DTI-technique: diffusion
gray matter white matter
6 unknowns
3.1. DTI-technique: diffusion in the brain
‘summarize’ tensor:
fractional anisotropy
DTI measures
3.1. DTI-technique: parameters
FA decrease
Myelination
Axon density and caliber
Fiber mixture
FA increase
less
less
less more
more
more
Microscopic
Macroscopic
INTERPRETATION OF FA
‘integrity of white matter’
‘efficient communication’
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3.1. DTI-technique: parameters
‘summarize’ tensor:
fractional anisotropy
DTI measures
fibertracking
3.1. DTI-technique: parameters
For details see Vandermosten et al., 2012, Neuroscience & Biobehavioral Reviews
- Quantitatively meta-analysis of 11 studies that used VBA (60 foci, 257
participants)
-272 mm³ and centred at -29, -30, 18
PREVIOUS DTI-STUDIES
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3.2. Structural reading network in adults with dyslexia
PARTICIPANTS
Dyslexic readers
M (SD)
Normal readers
M (SD)
Test statistics
N 20 20 Subject characteristics
Sex (male/female) 7/13 8/12 p = .75 Age (years) 22.1 (3.1) 21.4 (3.0) p = .51 Non-verbal IQ (WAIS) 108 (10) 106 (10) p = .59
Defining literacy measures Word reading 66.1 (1.9) 99.8 (11.4) p < .0001 Pseudoword reading 66.0 (1.8) 107.9 (9.8) p < .0001 Spelling 69.3 (6.5) 105.8 (9.6) p < .0001
Reading underlying processes
Phoneme awareness (effect size) -2.79 (1.25) 0 (1) p <.0001
Speech perception in noise (SRT in dB) -8.2 (0.9) -8.5 (1.1) p = .30
Orthographic processing (raw score) 28.2 (3.6) 34.5 (2.6) p <.0001
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3.2. Structural reading network in adults with dyslexia
Inferior frontal Temporoparietal
Occipitotemporal
fMRI DTI
= phonological aspects of reading
= Orthographic aspects of reading
= neural anomaliesin dyslexics
3.2. Structural reading network in adults with dyslexia
Arcuate Fasciculus (AFFTP)
Posterior Arcuate Fasciculus
(posterior AFTP)
Inferior Fronto-Occipital Fasciculus (IFOF)
+ right hemispheric tracts
RESULTS: GROUP COMPARISON of FA
(controlled for IQ and quality index of DTI-acquisition)
Normal Readers
Mean FA (sd)
Dyslexic Readers
Mean FA (sd)
P-value
ANCOVA
Left AFFTP 0.474 (0.017) 0.460 (0.025) .029*
Left posterior AFTP 0.455 (0.026) 0.444 (0.027) .14
Left IFOF 0.485 (0.027) 0.486 (0.024) .81
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AFFTP
posterior AFTP
IFOF
3.2. Structural reading network in adults with dyslexia
RESULTS: GROUP COMPARISON of FA
(controlled for IQ and quality index of DTI-acquisition)
Normal Readers
Mean FA (sd)
Dyslexic Readers
Mean FA (sd)
P-value
ANCOVA
Left AFFTP 0.474 (0.017) 0.460 (0.025) .029*
Left posterior AFTP 0.455 (0.026) 0.444 (0.027) .14
Left IFOF 0.485 (0.027) 0.486 (0.024) .81
Right AFFTP 0.422 (0.030) 0.426 (0.021) .68
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AFFTP
posterior AFTP
IFOF
3.2. Structural reading network in adults with dyslexia
RESULTS: CORRELATIONS with FA
Phoneme
awareness
Speech-in-noise
perception
Orthography
Left AFFTP
Left posterior AFTP
Left IFOF
(controlled for literacy, IQ and quality index of DTI-acquisition)
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3.2. Structural reading network in adults with dyslexia
AFFTP
posterior AFTP
IFOF
RESULTS: CORRELATIONS with FA
Phoneme
awareness
Speech-in-noise
perception
Orthography
Left AFFTP .33* .31(*) -.04
Left posterior AFTP .21 .42** .00
Left IFOF .04 .18 .39*
(controlled for literacy, IQ and quality index of DTI-acquisition)
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3.2. Structural reading network in adults with dyslexia
No significant correlations
in right hemispheric tracts AFFTP
posterior AFTP
IFOF
Predicting variables FA left IFOF FA left direct
AFFT
Step 1: Control Variables .04 .04 Step 2: Group variable .00 .10* Step 3a: Phoneme awareness .02 .10* Step 3b: Orthographic processing .16** .00 Total R² .21 .24
RESULTS: MULTIPLE REGRESSION
Predicting variables FA left IFOF FA left posterior
AFTP
Step 1: Control Variables .04 .02 Step 2: Group variable .00 .06 Step 3a: Speech in noise perception .01 .18** Step 3b: Orthographic processing .12* .01 Total R² .19 .26
Correlational double dissociation
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3.2. Structural reading network in adults with dyslexia
Left IFOF
- No group difference
- Corresponds to ventral
orthographical route
Left AF
- Lower FA in dyslexic adults (AFFTP)
- Corresponds to dorsal phonological route
(AFFTP & posterior AFTP)
- Right hemispheric tracts
- No FA-difference between dyslexic and typical reading adults
- No FA-relation with phonological and orthographic tasks
3.2. Structural reading network in adults with dyslexia
- No involvement of the Corona Radiata
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Which network sustains reading at the very beginning?
- Brain not genetically pre-wired for reading!
Where is the primary deficit of dyslexia?
- White matter is plastic!
Predictions developmental sequence:
Predictions dyslexia:
• Primary deficit (phonological processing) in left dorsal regions
• Secondary deficit (building up orthographic word representations) in left ventral regions
STANDARD NEUROANATOMICAL MODEL:
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3.3. Structural reading network in pre-readers at risk for dyslexia
1
2
fMRI DTI
!Validation needed, especially on connections!
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• first data collection before children are able to read
• continuous registration of developmental pathway
• direction of causal influence?
• early detection and prediction early prevention
3.3. Structural reading network in pre-readers at risk for dyslexia
• Last year of kindergarten
• 35 family-risk for dyslexia pre-readers
• at least one first-degree relative diagnosed as dyslexic
• 35 no family risk for dyslexia pre-readers
• Individual matching
• Educational environment, i.e. same school!
• Sex
• Age
• Non-verbal IQ (CPM)
• Educational level of father and mother
PARTICIPANTS:
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3.3. Structural reading network in pre-readers at risk for dyslexia
FRD+
(n = 36)
FRD-
(n = 35)
Test statistics
Demographic data
Gender (boy/girl) 23/13 18/17 Fisher’s exact test: p = .34
SES 5.3 (1.6) 5.6 (1.6) Fisher’s exact test: p = .18
ADHD 2.5 (2.2) 1.5 (1.5) Fisher’s exact test: p = .40
Handedness (left/right) 5/30 2/32 Fisher’s exact test: p = .43
Age in months 61.4 (3.1) 61.7 (3.0) F(1,27) = 0.14; p = .71
Non-verbal IQ 109.9 (13.2) 110.4 (10.0) F(1,27) = 0.01; p = .83
Cognitive predictors (composite score )
Phonological Awareness -0.06 (1.28) 0 (1) F(1,27) = 0.20; p = .66
Rapid Automatized Naming -0.46 (1.08) 0 (1) F F(1,27) = 3.41; p = .09
Letter Knowledge -0.51 (1.25) 0 (1) F(1,27) = 9.75; p = .02
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PARTICIPANTS:
3.3. Structural reading network in pre-readers at risk for dyslexia
DTI to examine ventral and dorsal tracts on:
1. pre-reading anomalies related to family-risk factors of dyslexia?
2. their specific cognitive function at that young age?
• Correlation with phonological tasks (phonological awareness)
• partial orthographic tasks (letter knowledge and rapid automatized naming)
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3.3. Structural reading network in pre-readers at risk for dyslexia
RESULTS: GROUP COMPARISON of FA
Group x Hemisphere x Tract interaction [F(2,344) = 3.17, p = .043]
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3.3. Structural reading network in pre-readers at risk for dyslexia
RESULTS: CORRELATIONS with FA
LEFT RIGHT
AFFTP Posterior
AFTP IFOF
AFFTP
Posterior
AFTP IFOF
Phonological Awareness
Rapid Automatized
Naming Letter Knowledge
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3.3. Structural reading network in pre-readers at risk for dyslexia
LEFT RIGHT
AFFTP Posterior
AFTP IFOF
AFFTP
Posterior
AFTP IFOF
Phonological Awareness 0.30* 0.24 * 0.36** 0.27* 0.19 0.37**
Rapid Automatized
Naming 0.13 0.07 0.20 0.16 -0.09 0.31**
Letter Knowledge 0.16 0.15 0.26 * 0.21 0.17 0.26 *
• phonological awareness was the only significant predictor of FA
- no unique contribution of letter knowledge & rapid automatized naming
RESULTS: MULTIPLE REGRESSION
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RESULTS: CORRELATIONS with FA
3.3. Structural reading network in pre-readers at risk for dyslexia
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IFOF
Posterior AFTP
AFFTP
Group difference high vs low risk pre-readers?
Phonological vs Orthographic function?
PHONOLOGY
PHONOLOGY
3.3. Structural reading network in pre-readers at risk for dyslexia
Preliminary conclusions
• White matter anomalies :
•predate reading causal?
•are located in left ventral and posterior dorsal connections
opposes the standard neuroanatomical model
• White matter function:
• Phonological awareness is sustained bilaterally by both dorsal and ventral tract
gradual left lateralization and a gradual phonological versus orthographic specialization
• Longitudinal follow-up needed
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3.2. Structural reading network in pre-readers at risk for dyslexia
Acknowledgments
DYSlexia COllaboration Leuven (DYSCO)
Parenting and Special Education Research Group, KU Leuven
Pol Ghesquière
Maaike Vandermosten
Jolijn Vanderauwera
Bart Boets
ExpORL, Dept. Neurosciences, KU Leuven
Jan Wouters
Heleen Luts
Hanne Poelmans
Sophie Vanvooren
Astrid De Vos
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Thank you!
