Distinct unimodal and crossmodal regions for word processing in the left temporal cortex

How are word recognition circuits organized in the left temporal lobe? We used functional magnetic resonance imaging to dissect cortical word-processing circuits using three diagnostic criteria: the capacity of an area (1) to respond to words in a single modality (visual or auditory) or in both modalities; (2) to modulate its response in a top-down manner as a function of the graphemic or phonemic emphasis of the task; and (3) to show repetition suppression in response to the conscious repetition of the target word within the same sensory modality or across different modalities. The results clarify the organization of visual and auditory word processing streams. In particular the visual word form area (VWFA) in the left occipito-temporal sulcus appears strictly as a visual unimodal area. It is, however, bordered by a second lateral inferotemporal language area (LILA) which is multimodal. Both areas might have been confounded in past work. Our results also suggest a possible homolog of the VWFA in the auditory stream, the auditory word form area, located in the left anterior superior temporal sulcus.