Distinct cross-modal coupling between the written and auditory language networks during reading and spoken word...

Most literate individuals can perceive language through different sensory modalities, such as through hearing spoken words or reading written words. While the processing of written and auditory words is initially separated in the brain, these processing streams must converge, such as in brain areas representing high-level language processing like the inferior frontal cortex. However, given the complexities of the interactions between spoken and written language processing, there may be multiple additional interface points between networks. For instance, it is commonly assumed that during reading acquisition, the brain makes use of pre-existing auditory speech representations to aid in the learning of written words. Yet, how the written and spoken language systems are coupled in the brain is still poorly understood. In this study, we individually localized key areas in the brain's reading and auditory speech processing systems (such as the visual and auditory word form areas, VWFA and AWFA, respectively, in the "what" streams, and premotor cortex in the dorsal auditory stream) and analyzed cross-modal responses in and functional connectivity between these areas for a variety of tasks. We present evidence for multiple interaction points between the written and auditory word processing streams, including a direct connection from the AWFA to the VWFA (confirmed through re-analysis of MEG data from a large open-science database), and task-dependent engagement of the dorsal auditory stream by written words. The resulting understanding of the combined language processing network provides a novel framework for studies of reading acquisition, language impairments, and reading intervention.