Interpretation-mediated changes in neural activity during language comprehension

Abstract

Using functional magnetic resonance imaging (fMRI), we identified cortical regions mediating interpretive processes that take place during language comprehension. We manipulated participants' interpretation of texts by asking them to focus on action-, space-, or time-related features while listening to identical short stories. We identify several cortical regions where activity varied significantly in response to this attention manipulation, even though the content being processed was exactly the same. Activity in the posterior and anterior sections of the left inferior frontal gyrus (IFG), which are thought to have different sensitivities to high-level language processing, was modulated by the listeners' attentional focus, but in ways that were quite different. The posterior left IFG (Pars Opercularis) showed different activity levels for the three conditions. However, a population coding analysis demonstrated similar distributions of activity across conditions. This suggests that while the gain of the response in the Pars Opercularis was modulated, its core organization was relatively invariant across the experimental conditions. In the anterior left IFG (Pars Triangularis), the analysis of population codes revealed different activity patterns between conditions: there was little similarity between activity during time–attention and action- and space–attention, however there were similar activity patterns while attending to space and action information. In addition, both the left superior temporal gyrus and sulcus showed greater activity in the space and action attention conditions when contrasted with time attention. We discuss these findings in light of work on the role of left IFG in processing semantic information in language, and in light of theories suggesting that temporal information in language is processed in the brain using similar mechanisms as spatial information. Our findings suggest that a substantial source of variance in neural activity during language comprehension emerges from the internally-driven, information-seeking preferences of listeners rather than the syntactic or semantic properties of a text.