Differences in the anatomical connectivity patterns of the lateral geniculate nucleus between subjects with dyslexia and controls

Abstract

Introduction: Dyslexia is the most common neurodevelopmental disorder. It is characterized by normal intelligence but difficulties in skills associated with reading and writing. Reading is a complex skill that requires the coordination of multiple brain regions and relies on neural systems spread across the brain. Dyslexia has been linked to abnormal connectivity patterns throughout the cortex and to morphological abnormalities of the lateral geniculate nucleus (LGN). This is the first study to compare the anatomical connectivity of the LGN between subjects with dyslexia and controls. Methods: Diffusion (TR=5300ms, TE=95ms, b=1000s/mm², resolution=1.56x1.56x3 mm³), T₁ (TR=2200ms, TE=2.96, resolution=1x1x1mm³) and proton density (PD) weighted images (TR=2970ms, TE=22ms, resolution=0.75x0.75x1mm³) were acquired in 12 subjects with dyslexia and 12 controls. Six independent experimenters manually traced the LGN on the PD. One experimenter traced the corpus callosum and optic chiasm on the T₁. This was done frame-by-frame in the coronal plane using FSLVIEW. The anatomical location of V1 and V5 was determined by transforming the 1mm MNI template to each subjects’ anatomical space using non-linear transformation (ANTS). The following steps were taken to analyze the diffusion data: eddy current and head motion correction, brain extraction, diffusion tensors fitting, and probabilistic tractography. Tractography was run in ProbtrackX between the LGN and the optic chiasm and ipsilateral and contralateral V1/ V5. Results: The anatomical connectivity of the LGN with the optic chiasm and ipsilateral V1 was significantly reduced in subjects with dyslexia (p< .005). The contralateral connections between the LGN and V1/V5 were higher in dyslexia (p< .005). Conclusion: The results obtained using probabilistic tractography provide the first evidence of changes in the anatomical connectivity of the LGN in subjects with dyslexia. We demonstrated that differences in the anatomical connectivity patterns can be found from the chiasm to V1. The functional implications of these changes are unknown.

Meeting abstract presented at VSS 2015