The cortical dynamics of speaking: Lexical and phonological knowledge simultaneously recruit the frontal and temporal cortex within 200 ms
Résumé
Language production models typically assume that retrieving a word for articulation is a sequential process with substantial functional delays between conceptual, lexical, phonological and motor processing, respectively. Nevertheless, explicit evidence contrasting the spatiotemporal dynamics between different word production components is scarce. Here, using anatomically constrained magnetoencephalography during overt meaningful speech production, we explore the speed with which lexico-semantic versus acoustic-articulatory information of a to-be-uttered word become first neurophysiologically manifest in the cerebral cortex. We demonstrate early modulations of brain activity by the lexical frequency of a word in the temporal cortex and the left inferior frontal gyrus, simultaneously with activity in the motor and the posterior superior temporal cortex reflecting articulatory-acoustic phonological features (+LABIAL vs. +CORONAL) of the word-initial speech sounds (e.g., Monkey vs. Donkey). The specific nature of the spatiotemporal pattern correlating with a word's frequency and initial phoneme demonstrates that, in the course of speech planning, lexico-semantic and phonological-articulatory processes emerge together rapidly, drawing in parallel on temporal and frontal cortex. This novel finding calls for revisions of current brain language theories of word production.
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