Purchase this article with an account.
Miguel Castelo-Branco, Ana Pina Rodrigues, José P Rebola, Marcelino Pereira, Marieke Van Asselen; Neural Responses of the Visual Word Form Area System in Dyslexia: Revising the Underactivation Hypothesis. Invest. Ophthalmol. Vis. Sci. 2018;59(9):4669.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
We used a neuroimaging approach to address the hypothesis that specific hypoactivation occurs in dyslexia in the ventral occipito-temporal cortex (VOTC). This region has been closely associated to reading through the extraction of a representation of words which is invariant to position, size, font or case. We addressed methodological concerns that still prevent a definitive take on the understanding of the differences between dyslexics and normal readers. These concerns are threefold. First, the activity to print stimuli is usually contrasted to fixation and not higher-level stimuli. Second, most of the previous studies are confined to the VWFA (Visual Word Form Area), when recent studies have demonstrated a posterior-to-anterior gradient of print specificity along the VOTC. Finally, up to date, no study has evaluated this region on a subject-by-subject basis, relying instead on anatomical or group regions-of-interest.
Our fMRI study tackled these problems by: 1) evaluating different control stimuli, ranging from fixation to hierarchically higher-level stimuli; 2) assessing the whole VOTC, partitioned into three main regions; and 3) performing the analyses in a subject-by-subject basis, to optimize the functional localizer.Thirty participants were included in this study (14 developmental dyslexics and 16 age and education matched controls). The design consisted of alternately viewed blocks of stimuli from a given class (words, consonant strings, phase scrambled words, phase scrambled consonant strings, small checkerboards, large checkerboards). A General Linear Model with 6 predictors was built with poshoc t-tests corrected for the number of contrasts.
Our results show that, when subject to analyses of regions of interest (ROIs) defined on a subject by subject basis, instead of a general group ROIs, dyslexics do show hypoactivation to print stimuli specifically in anterior VOTC. However, when analyzing multiple stimulus related contrasts, evidence for a general underactivation for these stimuli rather than particular stimulus specific deficits in dyslexic subjects emerges, which is spatially restricted to this region and does not include the VWFA.
We found that differences between dyslexics and controls reflect a non-stimulus specific general underactivation, that is confined to the anterior aspects of the VOTC and does not include classical VWFA.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
This PDF is available to Subscribers Only