Quantification of reading circuits in the ventral occipitotemporal cortex

Substantial evidence shows that one of the circuits supporting reading is located in the ventral occipito-temporal cortex (VOTC), a region that was first functionally identified and denominated visual word form area (VWFA). Recent evidence combining functional, structural, and quantitative MRI suggests that the VOTC can be segregated into at least two sub-regions: one involved in visual feature extraction in the posterior occipito-temporal sulcus (pOTS), and one implicated in integrating with the language network in the middle occipito-temporal sulcus (mOTS). Due to the heterogeneity of functional localizers, it is usually difficult to know if the same cortical region is being located across studies and if the results of the analyses are comparable. The aim of the present work was to develop a single-subject multimodal VOTC word recognition localizer, replicable across different labs and studies. Our experiment followed a dense-sampling (10 repetitions) strategy with 2 participants. We acquired 2 different fMRI reading region localizers, classical 8-bar retinotopy scans with different contents inside the bars (checkers, words, pseudowords, and false fonts), and structural MRI scans (quantitative and diffusion MRI, T1w, and T2w images). Our results revealed that by combining multimodal MRI measurements we can segregate two different reading regions at the individual subject level, and that with 10 repetitions, we can measure the variability of the two localizations. Furthermore, we developed and tested in different settings a shorter localizer capable of capturing similar individual variability, that will be made available to the scientific community. In sum, here we propose a new protocol to harmonize inter-lab and inter-study visual word recognition, which will be critical to advance our understanding of the role of the VOTC in neurobiology of reading.