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Poster E25, Friday, November 10, 10:00 – 11:15 am, Harborview and Loch Raven Ballrooms

Reconfiguration of the semantic and default mode networks induced by variations of semantic context during comprehension of written narratives

Francesca Martina Branzi1, Gina F. Humphreys1, Paul Hoffman2, Matthew A. Lambon Ralph1;1University of Manchester, 2University of Edinburgh

In everyday settings, such as watching a movie or listening to a talk, it is necessary to accumulate and integrate information over time. Importantly, despite integration processes requiring reconfiguration of semantic context to encode information about the changing environment, the neural foundations of this phenomenon are still largely uncharacterised. In this functional magnetic resonance imaging (fMRI) study, we investigated whether and how areas of the semantic control network (SCN) and the default mode network (DMN) reconfigure when participants are processing variations of semantic context during comprehension of written narratives. Twenty-two healthy volunteers were asked to read short narratives divided in two paragraphs. For each narrative, the same second paragraph (target) was preceded by different first paragraphs (prime) that could be either high-congruent or low-congruent with the target in terms of meaning. Both high- and low-congruent primes could be integrated with the target and allow a coherent narrative representation to emerge, though a greater reworking of the evolving semantic context was required after low-congruent primes. Therefore, by comparing brain responses for the same target preceded by low- vs. high-congruent primes, we measured integration processes triggered by variations of semantic context. In order to tease apart domain-general and semantic-specific control processes recruited when shifting between different mental representations, we also measured brain responses for the same target preceded by a different cognitive context/task (i.e., string of numbers that participants had to read silently). We hypothesized that changes of semantic context would induce increased demands on controlled semantic integration processes within the SCN. In accord with this prediction, we found that when the semantic context changed (low-congruent condition) reading times were slower than in high-congruent conditions and SCN areas (e.g., inferior frontal gyrus, posterior middle temporal gyrus) were extensively recruited. When the task context changed (control condition) reading times were similar to those of low-congruent conditions, but brain activations revealed a reduced involvement of SCN areas and an increased involvement of some areas of the saliency network. We also tested one hypothesis that some parts of the DMN (e.g., the posterior angular gyrus, see Andrews-Hanna et al., 2010) would be recruited as a function of the degree of change of the cognitive context/task (see Crittenden et al., 2015). If correct, we expected to observe maximal recruitment of these areas in the control condition (change from the number task to the semantic task) as compared to low- and high-congruent conditions (no variation of task context). However, we found an opposite pattern of results, suggesting that rather than being sensitive to control demands, these areas support semantic context integration processes. In summary, these results reveal that some areas of the DMN and SCN support integration processes induced by variations of semantic context that allow complex semantic representations to emerge.

Topic Area: Meaning: Combinatorial Semantics

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