1. Differences in the Anatomical Connectivity of the Lateral Geniculate Nucleus in Dyslexia
Mónica G. Chica1, Keith A. Schneider2
1Department of Psychiatry, Vanderbilt University (USA), 2Department of Biology, York University (Canada)
• Dyslexia is a specific learning disability of reading and
spelling affecting around 5% of the population [1].
• Dysfunction of the magnocellular system and brain areas
involved in the normal acquisition and achievement of
reading has been previously reported in subjects with
dyslexia [1–5].
• Diffusion tensor imaging (DTI) studies of white matter
pathways and structural MRI studies suggest that there are
differences in connectivity between subjects with dyslexia
and controls [2].
• The anatomical connectivity of the LGN with the optic chiasm is
reduced in dyslexia.
• The anatomical connectivity of the LGN with the visual cortex is
reduced in dyslexia
• The anatomical connectivity between the LGN and V5 is reduced
in subjects with dyslexia compared to controls.
BACKGROUND
HYPOTHESES
Segmentation of the LGN
The LGN were manually traced on the PD images by six independent experimenters who were blind to the
subjects’ group membership. The median of these measurements was calculated to create LGN ROI masks for
each subject. They were transformed to FreeSurfer space via nonlinear registration using FNIRT.
1. Katia L, Frank R, Nadege V, Denis S, Anne-Lise G. 2011. Altered Low-Gamma Sampling in Auditory Cortex Accounts for the Three
Main Facets of Dyslexia. Neuron.
2. Eckert M. 2004. Neuroanatomical Markers for Dyslexia: A Review of Dyslexia Structural Imaging Studies. The Neuroscientist.
3. Stein J. 2001. The Magnocellular Theory of Developmental Dyslexia. DYSLEXIA.
4. Marie T.B, Molly A.M. 2012. Mind, Brain and Language: Multidisciplinary Perspectives. Taylor & Francis.
5. Stein J, Walsh V. 1997. To See but not to Read; The Magnocellular Theory of Dyslexia. Trends in Neurosciences.
6. Bethycotter.wdfiles.com
• Using probabilistic tractography we found differences in the anatomical
connectivity of the LGN between subjects with dyslexia and controls.
• The ipsilateral connections between LGN and V1/optic chiasm were reduced in
dyslexia.
RESULTS
CONCLUSIONS REFERENCES
Brain regions with
substantial
magnocellular input:
Lateral geniculate
nucleus (LGN),
primarily visual cortex
(V1), middle temporal
(MT/V5) [6].
11 adults with dyslexia (5 female) and 13 controls (3 female) were
scanned with a Siemens Trio 3 T MRI scanner. For each subject:
• 40 proton density (PD) weighted images with a resolution of 0.75
× 0.75 × 1 mm3, which were registered, averaged and
interpolated to twice the resolution in each dimension.
• Diffusion weighted data with 68 directions and a resolution of 1.56
× 1.56 × 3 mm3.
• 1 structural T1-weighted scan, 1 mm3 isotropic resolution.
SUBJECTS AND DATA ACQUISITION
This research was funded by The
Dana Foundation and NSERC.
METHODS
Anatomical connectivity of the LGN with the optic chiasm
p= .002 p= .032
Segmentation of the other brain regions
The corpus callosum and optic chiasm was drawn by hand on the T1 images. We
used FreeSurfer to segment MT and the Julich histological atlas for V1 and V2.
The linear registrations from FreeSurfer and MNI to diffusion space were
computed using FLIRT.
Segmentation of the visual cortex.
Segmentation of the optic chiasm
Segmentation of corpus callosum.
Estimation of the connectivity between brain regions
The diffusion parameters for each voxel were calculated using
BEDPOSTX including the local fibre direction. Using these
parameters, we estimated the global connectivity between each pair
of segmented regions using PROBTRACKX from FSL.
Probability map (red) of the connectivity between the
LGN (green) and V1 (blue) for one subject.
Z=100 Z=101
Anatomical connectivity of the LGN with the ipsilateral V1
p= .001 p= .017 p< .001
Anatomical connectivity of the LGN with the contralateral V5
• The contralateral connections between LGN and V5 were
increased in dyslexia.
• The morphology of the LGN is significantly different in both
groups.