The ventral visual stream for reading converges on the transmodal language network

Abstract

Reading bridges sensation and cognition. To derive meaning from written words, visual input is first processed in unimodal (i.e., sensory-specific) visual streams and then engages a distributed language network (LANG) that includes classic perisylvian language areas and supports transmodal (i.e., sensory-nonspecific) functions. A reading-relevant region in the inferotemporal cortex (ITC), sometimes called the visual word form area (VWFA), has been the subject of controversy because it displays properties of both systems: it responds to meaningless written pseudowords, implying a unimodal visual function, but also responds to meaningful speech, implying a transmodal function. We investigated whether precision functional mapping could help clarify this regions role in reading. We characterized a stream of visual regions along the ITC that responded preferentially to visual orthographic forms (i.e., written pseudowords, consonant strings, and real words). Network mapping revealed that only the most anterior region of this "orthographic stream" was connected to the LANG network and accordingly showed responses to meaningful speech. Furthermore, this anterior region was more selective, responding preferentially to text-based stimuli, whereas the more posterior regions of the stream were additionally activated by perceptually similar images (i.e., number strings, foreign script). Our results support that connections to the LANG network may drive specialization along the orthographic stream for writing. This basal language network region may represent an interface between visual and transmodal language systems, thus serving as a critical nexus for reading.