Right-lateralization of the visual word form area after left-hemisphere perinatal stroke

In literate adults, an area along the left posterior fusiform gyrus that is often referred to as the “visual word form area” (VWFA) responds particularly strongly to written characters compared to other visually similar stimuli. Theoretical accounts differ in whether they attribute the strong left-lateralization of the VWFA to a left-hemisphere bias towards visual features used in script, to competition of visual word form processing with that of other visual stimuli processed in the same general cortical territory (especially faces), or to the well-established left-lateralization of the language system. Here we used functional magnetic resonance imaging to test the last hypothesis by investigating lateralization of the VWFA in participants (male and female) who have right-hemisphere language due to a large left-hemisphere perinatal stroke. Demographically matched Controls were included for comparison. All participants had intact language skills and were proficient readers; age at testing ranged from 9.75 years to early adulthood. Individual whole-brain activation maps contrasting activation during rapid presentation of pseudowords and pictures of places, and analyses comparing activations during these conditions in independently defined VWFA regions of interest in left and right ventral occipitotemporal cortex, both demonstrated that while visual word form processing was left-lateralized in Controls, it was right-lateralized in participants with left-hemisphere stroke. This was despite the fact that the tissue normally occupied by the VWFA was not damaged by the stroke. This provides compelling evidence that the lateralization of the VWFA indeed follows that of the frontotemporal language system. Significance Statement The visual word form area (VWFA) in healthy adults is almost always lateralized to the left hemisphere. One hypothesis is that this is due to co-localization with the LH language network. This study provides support for this hypothesis from a rare participant group with RH language; we find that their VWFA is also right-lateralized. Our findings also support the notion that the hemispheres are equipotential early in life, with a fully functional language system – including the VWFA – able to develop in the RH if the LH is damaged. These findings contribute to our understanding of functional brain organization and plasticity, with potential implications for rehabilitation approaches for adults with reading impairments due to acquired brain injury.