The left inferior frontal gyrus under focus: an fMRI study of the production of deixis via syntactic extraction and prosodic focus
Résumé
The left inferior frontal gyrus (LIFG, BA 44, 45, 47) has been associated with linguistic processing (from sentence- to syllable- parsing) as well as action analysis. We hypothesize that the function of the LIFG may be the monitoring of action, a function well adapted to agent deixis (verbal pointing at the agent of an action). The aim of this fMRI study was therefore to test the hypothesis that the LIFG is involved during the production of agent deixis. We performed an experiment whereby three kinds of deictic sentences were pronounced, involving prosodic focus, syntactic extraction and prosodic focus with syntactic extraction. A common pattern of activation was found for the three deixis conditions in the LIFG (BA 45 and/or 47), the left insula and the bilateral premotor (BA 6) cortex. Prosodic deixis additionally activated the left anterior cingulate gyrus (BA 24, 32), the left supramarginal gyrus (LSMG, BA 40) and Wernicke's area (BA 22). Our results suggest that the LIFG is involved during agent deixis, through either prosody or syntax, and that the LSMG and Wernicke's area are additionally required in prosody-driven deixis. Once grammaticalized, deixis would be handled solely by the LIFG, without the LSMG and Wernicke's area.
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