The contribution of executive control to semantic cognition: Convergent evidence from semantic aphasia and executive dysfunction

Abstract

Semantic cognition, as described by the controlled semantic cognition (CSC) framework (Rogers et al., 2015, Neuropsychologia, 76, 220), involves two key components: activation of coherent, generalizable concepts within a heteromodal 'hub' in combination with modality-specific features (spokes), and a constraining mechanism that manipulates and gates this knowledge to generate time-and task-appropriate behaviour. Executivesemantic goal representations, largely supported by executive regions such as frontal and parietal cortex, are thought to allow the generation of non-dominant aspects of knowledge when these are appropriate for the task or context. Semantic aphasia (SA) patients have executive-semantic deficits, and these are correlated with general executive impairment. If the CSC proposal is correct, patients with executive impairment should not only exhibit impaired semantic cognition, but should also show characteristics that align with those observed in SA. This possibility remains largely untested, as patients selected on the basis that they show executive impairment (i.e., with 'dysexecutive syndrome') have not been extensively tested on tasks tapping semantic control and have not been previously compared with SA cases. We explored conceptual processing in 12 patients showing symptoms consistent with dysexecutive syndrome (DYS) and 24 SA patients, using a range of multimodal semantic assessments which manipulated control demands. Patients with executive impairments, despite not being selected to show semantic impairments, nevertheless showed parallel patterns to SA cases. They showed strong effects of distractor strength, cues and miscues, and probe-target distance, plus minimal effects of word frequency on comprehension (unlike semantic dementia patients with degradation of conceptual knowledge). This supports a component process account of semantic cognition in which retrieval is shaped by control processes, and confirms that deficits in SA patients reflect difficulty controlling semantic retrieval.This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. Successful retrieval of semantic knowledge in a context-specific and timely manner depends on the interaction of multiple processes, including (1) the conversion of sensory input into meaning (Sharp, Scott, & Wise, 2004), (2) generalizable conceptual representations (Lambon Ralph, Sage, Jones, & Mayberry, 2010;Patterson, Nestor, & Rogers, 2007), and (3) flexible control over the retrieval of knowledge, such that semantic processing focuses on information appropriate to the context even when this is not necessarily the dominant feature or association ). An interaction between these components is envisaged within the controlled semantic cognition ( , 2010). However, the mechanisms underpinning semantic control are underspecified; in particular, it is unclear the extent to which this capacity draws on domain-gene...

Controlled semantic cognition relies upon dynamic and flexible interactions between the executive ‘semantic control’ and hub-and-spoke ‘semantic representation’ systems

“…This network constantly interacts with the hub-and-spokes structure to promote efficacious selection of task-relevant knowledge from a multitude of information in the representational database. These two neural systems can be selectively lesioned, causing double dissociation : Whereas ATL atrophy leads to semantic dementia (erosion of semantic memory with preserved capability of semantic control), frontoparietal stroke leads to semantic aphasia (inability to select appropriate pieces of semantic information, exacerbated by infrequent or unfamiliar meaning, while semantic memory per se is intact; for example, see Thompson et al., 2018 , Thompson et al., 2017 ). It is noteworthy that we chose to focus on the IFG in the present study owing to its established role in selecting context-relevant semantic information, particularly under unfamiliar or ambiguous situations.…”

Settling Into Semantic Space: An Ambiguity-Focused Account of Word-Meaning Access

“…Under this view this region is not the site for storage of amodal lexical-semantic knowledge, instead, it is hypothesized to store information regarding "the relation (or correspondences) between phonologic information on the one hand and conceptual information on the other" (Hickok & Poeppel, 2015). Other researchers have argued that the posterior regions of the middle temporal lobe supports the control processes that operate on semantic knowledge that is assumed to be stored in more anterior regions of the temporal lobe (Jefferies, 2013;Jefferies & Lambon Ralph, 2006;Noonan, Jefferies, Visser, & Lambon Ralph, 2013;Ralph, Jefferies, Patterson, & Rogers, 2016;Thompson et al, 2018). It is therefore premature to make strong claims about the neurobiological substrate of the distributed lexicalsemantic knowledge that is accessed in response to spoken and written words, except to say that these representations are likely to be (i) widely distributed across brain regions, (ii) incorporate diverse aspects of meaning, and (iii) should not be viewed as a discrete, localised 'module' of the brain.…”

How right hemisphere damage after stroke can impair speech comprehension

“…For some language tasks, right-hemisphere activation may be driven by non-linguistic perceptual processing ( Baumgaertner et al , 2013 ), or the recruitment of attention and working memory ( Vigneau et al , 2011 ). It has also been argued that increased right inferior frontal activation in patients recovering from aphasia after left hemisphere stroke may be the result of upregulating non-linguistic cognitive processing ( van Oers et al , 2010 ) and the control of semantic retrieval ( Thompson et al , 2016 , 2018 ).…”