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Left area 55b is the sensorimotor–semantic interface for lexical comprehension and production
Poster Session B, Wednesday, September 30, 4:30 - 6:30 pm, Wangari Maathai
Yi Du1,2, Guowei Wu1,2, Xiuyi Wang1; 1State Key Laboratory of Cognitive Science and Mental Health, Institute of Psychology, Chinese Academy of Sciences, 2Department of Psychology, University of Chinese Academy of Sciences
Human language requires the seamless integration of amodal conceptual knowledge with modality-specific sensorimotor systems. However, the precise cortical interface governing this semantic–sensorimotor transformation remains elusive. Left area 55b, situated at the junction of dorsal and ventral language pathways, is a strong candidate; yet its exact functional role—whether purely motor, purely semantic, or integrative—remains highly debated. Here, we sought to determine if area 55b acts as the dedicated cortical transition zone mediating bidirectional lexical processing. Using a highly precise individualized functional mapping approach, participants performed four lexical tasks encompassing both language comprehension (word listening, reading) and production (picture naming, writing), each contrasted with modality-matched non-lexical controls. We identified a core, format-independent lexical network (including area 55b, superior frontal language area (SFL), inferior frontal junction (IFJ), and anterior fusiform gyrus) and evaluated these candidate regions against five stringent a priori criteria defining a true sensorimotor–semantic interface. We found that only left area 55b satisfied all five requirements. First, it reliably dissociated comprehension from production across both vocal and manual modalities, demonstrating a distinct production-biased multivariate and univariate profile. Second, area 55b exhibited production-selective semantic enhancement, carrying significantly stronger semantic category representations when concepts had to be transformed into active motor outputs. Third, effective connectivity analyses demonstrated that area 55b acts as a dynamic routing hub, shifting its directed information flow from sensory and associative networks during comprehension to downstream motor effectors during production. Fourth, individualized mapping revealed a fine-grained internal anterior–posterior functional gradient within area 55b: an anterior language-network component specialized for semantic information, closely juxtaposed with a posterior somato-cognitive action network (SCAN) component carrying stronger articulatory information. Finally, this internal functional segregation systematically aligned with local structural transitions across six independent macroscale cortical hierarchies, anchoring area 55b exactly at the biological boundary between sensory and association cortex. These converging results resolve a critical gap in language neurobiology by reconciling historically divergent accounts of the dorsal frontal cortex. Rather than functioning as a monolithic motor or semantic module, area 55b acts as a highly flexible, state-dependent transition zone. By bridging macroscale language and SCAN networks, left area 55b is identified as the mechanistic sensorimotor–semantic interface that inextricably links what we mean to how we perceive and express it.
Topic Areas: Meaning: Lexical Semantics, Multisensory or Sensorimotor Integration