Abstract
The inferior frontal gyrus (IFG) plays a pivotal role in processing morphologically complex words. This study investigated the neural mechanisms underlying morpheme detection during lexical access, utilizing Korean Eojeols-morphologically agglutinated lexemes with clearly defined morphemic boundaries. By extending the traditionally recognized role of the IFG in morpho-syntactic processing, this research emphasizes its involvement in detecting structural violations within morphological categories. To explore these processes, syllables within Eojeols were transposed either across-lexico-morphemic boundaries (ACROSS: transposed-syllable-across-boundaries) or within-lexico-morphemic boundaries (WITHIN: transposed-syllable-within-boundaries). A control condition involved replaced-syllable nonwords (REPLACED). Sixty-two native Korean speakers performed a lexical decision task (LDT) while undergoing functional magnetic resonance imaging (fMRI). Behaviorally, ACROSS demonstrated faster reaction times (RT) and higher accuracy (ACC) compared to WITHIN, while showing comparable performance to REPLACED, consistent with a morpheme boundary effect. fMRI results revealed distinct neural activation patterns: ACROSS accuracy correlated with the triangular and orbital sub-regions of the IFG, whereas WITHIN accuracy was linked to the cingulate cortex. These findings provide compelling neural evidence for the essential role of the IFG in morphological decomposition and its sensitivity to structural violations within morphological categories.