Poster Session 06 Program Schedule
02/15/2024
04:00 pm - 05:15 pm
Room: Shubert Complex (Posters 1-60)
Poster Session 06: Aging | MCI | Neurodegenerative Disease - PART 2
Final Abstract #55
Deconstructing Semantic Contributions to Imagination – Novel Insights From Semantic Dementia
Muireann Irish, The University of Sydney, Sydney, Australia
Thanh Cao, The University of Sydney, Sydney, Australia
Category: Memory Functions/Amnesia
Keyword 1: semantic processing
Keyword 2: hippocampus
Keyword 3: neuroimaging: structural
Objective:
The capacity to imagine richly detailed scenes in the mind’s eye is posited to underlie many sophisticated expressions of cognition including autobiographical memory, episodic future thinking, and spatial navigation. While significant advances have been made in terms of understanding the neurocognitive mechanisms of scene construction, few studies have explored the contribution of semantic memory to this process. Semantic dementia (SD) is a rare neurodegenerative disorder characterised by profound semantic impairments, in the context of relatively intact visuospatial processing and episodic new learning. A recent case study suggests that scene construction might remain relatively intact in this syndrome, although the mechanisms underpinning this spared capacity remain unclear. The objective of the present study was to explore the cognitive and neural bases of scene construction performance in a well-characterised cohort of SD.
Participants and Methods:
Fourteen patients with a clinical diagnosis of left-predominant SD and 24 age- and education- matched healthy older Control participants were recruited. Participants completed a comprehensive battery of neuropsychological tests assessing episodic and semantic memory, visuospatial processing, and executive function, and underwent 3T structural MRI. Scene construction was assessed using the Hassabis et al. (2007) scene construction task, which requires individuals to mentally construct and describe a series of commonplace scenarios (e.g., Beach, Forest, Museum) in rich detail. Narratives were scored in terms of the level of contextual detail generated, the spatial integration of the scenes, and subjective ratings of vividness, difficulty, and sense of presence. Whole-brain voxel-based morphometry explored brain-behaviour associations between scene construction performance and grey matter intensity, with significant clusters extracted voxel-wise, corrected for False Discovery Rate at q <.05.
Results:
Relative to Controls, scene construction performance was significantly compromised in SD [F(1,36)=50.1; p<.001], driven by the impoverished provision of contextual details [F(1,36)=36.2; p< .001], which spanned all detail subcategories (all p values >.01). Controlling for language function ameliorated these group differences (p >.8). Crucially, subjective ratings of vividness, sense of presence, and task difficulty did not differ between the two groups (all p values >.05), and the scenes generated by SD patients were as spatially integrated as those generated by Controls (p >.05). Correlation analyses in the SD group suggested that overall task performance was strongly associated with measures of semantic processing and executive function (all r values >.68) while spatial coherence was significantly correlated with non-verbal episodic memory retrieval and visuo-constructive abilities (all r values >.64). Voxel-based morphometry analyses indicated significant involvement of the left posterior hippocampus and bilateral anterior temporal cortices in modulating overall scene construction performance, with additional involvement of the left angular gyrus for the provision of contextual details.
Conclusions:
Deterioration of the semantic knowledge base in SD disrupts the verbal description of internally generated scene representations of commonplace scenarios but not the subjective mental experience of spatial coherence or vividness. Future studies employing non-verbally demanding tasks will be required to determine the extent to which complex expressions of mental construction remain intact in this syndrome and the role of posterior parietal cortical regions in supporting these capacities.
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