Neural basis of linearization in speech production

An initial stage of speech production is conceptual planning, where a speaker determines which information to convey first (the linearization problem). This fMRI study investigated the linearization process during the production of "before" and "after" sentences. In "after" sentences, a series of events is expressed in the order of event occurrence. In "before" sentences, however, the order of event mention is achieved by reversing the chronological order. We suggested that the linearization process may be supported by a neural network connecting the left middle temporal gyrus (MTG) with the medial superior frontal gyrus, left middle frontal gyrus, and left angular gyrus/inferior parietal gyrus. Within this network, regions were more activated and interregional interactions were strongly enhanced for producing "before" than "after" sentences. The left MTG was also functionally connected with the left orbital inferior frontal gyrus, contributing to the retrieval of necessary world knowledge and linguistic knowledge. Connectivity between these two regions was not different between conditions.