Rapid plasticity in the ventral visual stream elicited by a newly learnt auditory script in congenitally blind adults

Accumulating evidence in the last decades has given rise to a new theory of brain organization, positing that cortical regions are recruited for specific tasks irrespective of the sensory modality via which information is channeled. For instance, the visual reading network has been shown to be recruited for reading via the tactile Braille code in congenitally blind adults. Yet, how rapidly non-typical sensory input modulates activity in typically visual regions is yet to be explored. To this aim, we developed a novel reading orthography, termed OVAL, enabling congenitally blind adults to quickly acquire reading via the auditory modality. OVAL uses the EyeMusic, a visual-to-auditory sensory-substitution-device (SSD) to transform visually presented letters optimized for auditory transformation into sound. Using fMRI, we show modulation in the right ventral visual stream following 2-h of same-day training. Crucially, following more extensive training (i.e., ∼12 h) we show that OVAL reading recruits the left ventral visual stream including the location of the Visual Word Form Area, a key graphene-responsive region within the visual reading network. Our results show that while after 2 h of SSD training we can already observe the recruitment of the deprived ventral visual stream by auditory stimuli, computation-selective cross-modal recruitment requires longer training to establish.