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Poster C35, Wednesday, August 21, 2019, 10:45 am – 12:30 pm, Restaurant Hall

A functional gradient for semantic cognition: graded transitions from default mode to executive cortex

Beth Jefferies1, Xiuyi Wang1, Daniel Margulies2, Jonathan Smallwood1;1University of York, 2Centre National de la Recherche Scientifique (CNRS) UMR 7225, Frontlab, Institut du Cerveau et dela Moelle Épinière, Paris

Semantic cognition recruits regions of default mode network (DMN) alongside semantic control and multiple demand network (MDN) regions. However, it is unclear how these networks are differentially engaged to support flexible patterns of semantic retrieval that are appropriate to the circumstances. In a verbal semantic feature matching task (which involved matching concepts on the basis of colour, shape or size features), we parametrically manipulated the global semantic similarity of the words to create a ‘psychological gradient’ varying in the need to constrain retrieval. On some trials, task demands were well-aligned with long-term memory, since the words to be matched on a specific feature, such as COLOUR, also had strong general conceptual overlap (STRAWBERRY-TOMATO). On other trials, participants were required to match words which were largely unrelated (e.g. COLOUR: STRAWBERRY-POST BOX). We tested the hypothesis that neural recruitment within this task would change lineally along a connectivity gradient from DMN to MDN as the concepts to be matched shared fewer features. In line with this hypothesis, we found semantic responses changed along the cortical surface in a graded fashion, depending on the requirement for constrained retrieval. This functional gradient within semantic cognition was apparent in data from individual runs within individual brains, suggesting it is not a product of spatial averaging. To examine whether these graded transitions capture the layout of networks involved in semantic processing, we defined DMN and MDN using non-semantic localizer tasks and established that the peak response for semantic control in previous studies fell midway between DMN and MDN in temporal and frontal cortex. Furthermore, there was an orderly decrease in values corresponding to both the connectivity gradient and the effect of the psychological gradient on the BOLD response, captured by the transition between networks from DMN, through the semantic control network, to MDN. These findings show gradual transitions between multiple networks supporting semantic cognition, which are organised along a functional gradient – with activation towards the DMN reflecting patterns of conceptual retrieval that closely align with the structure of long-term knowledge, and activation towards MDN reflecting more adaptive coding of current conceptual demands.

Themes: Meaning: Lexical Semantics, Control, Selection, and Executive Processes
Method: Functional Imaging

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