Atypical topography of high-level visual cortex is associated with reading difficulty

Abstract

Ventral temporal cortex (VTC) contains a mosaic of regions that selectively respond to specific categories of stimuli such as faces, objects and words. The spatial arrangement of these regions relative to sulcal folding patterns in VTC is highly consistent across individuals. For example, face-selective cortex (i.e., FFA) consists of two regions located on the fusiform gyrus and word-selective cortex (i.e., visual word form area, VWFA) is positioned immediately lateral to the fusiform, within the occipitotemporal sulcus (OTS). Here we test the hypothesis that developmental dyslexia, an impairment in fluid and accurate reading, is associated with an abnormal and sub-optimal layout of these functional regions. To test this hypothesis we used functional magnetic resonance imaging (fMRI) to localize face-, object- and word-selective regions on the cortical surface in 36 children (M = 10.05 years, SD = 1.49 years, n = 16 with dyslexia). We found a canonical topography for individuals with typical reading skills: VWFA was positioned lateral to FFA and located within the OTS. Individuals with dyslexia showed a variable topography: in a subset of subjects, VWFA was was positioned medial to FFA with a variable location, and not consistently within the OTS. This atypical organization has a number of consequences that might interfere with the development of skilled reading including: (1) fewer connections between the VWFA and language cortex as estimated with diffusion MRI, (2) a predominance of peripheral, as oppose to foveal, responsivity as measured with retinotopic mapping and (3) different cytoarchitecture as elucidated from published maps of cytoarchitectonic regions in VTC.