Poster Session F, Tuesday, March 26, 8:00 – 10:00 am, Pacific Concourse
“Blurred lines” – ‘Non-episodic’ content of future thinking narratives challenges a strict episodic-semantic distinction
Cherie Strikwerda-Brown1,2,3, John R. Hodges1,2,4, Olivier Piguet1,2,3, Muireann Irish1,2,3; 1Brain and Mind Centre, the University of Sydney, Australia, 2School of Psychology, the University of Sydney, Australia, 3Australian Research Council Centre of Excellence in Cognition and its Disorders, Sydney, Australia, 4Sydney Medical School, the University of Sydney, Australia
Contemporary theoretical frameworks propose that episodic and semantic memory lie at opposite ends of a continuum. Informed by this view, we recently developed a new taxonomy (‘NExt’) for coding ‘non-episodic’ (external) content of autobiographical narratives, which revealed a spectrum of episodic and semantic elements within the external details category. The composition of these elements within other forms of episodic construction, however, has not yet been explored. Here, we employed the NExt taxonomy to examine external detail profiles in episodic future thinking narratives. Profiles in Alzheimer’s disease (AD) and semantic dementia (SD), neurodegenerative disorders with respective impairments in episodic and semantic memory, were compared with those of Controls. Within future narratives, somewhat counterintuitive profiles of external details emerged. Relative to Controls, AD patients produced increased ‘episodic’ external details, whereas elevations in ‘episodic’, ‘semantic’, and ‘general event’ (at the intersection of episodic and semantic) details were observed in SD. Voxel-based morphometry analyses of structural MRI, however, revealed an association between increased future ‘episodic’ external details in AD and the integrity of bilateral frontal regions typically associated with semantic memory. By contrast, elevated future ‘general event’ and ‘semantic’ details in SD related to preservation of right precuneus and other bilateral posterior temporoparietal regions implicated in vivid episodic retrieval. These findings reinforce the blurring of the episodic-semantic distinction, suggesting the external details category cannot be conceptualised merely in terms of ‘non-episodic’ content. Moreover, neurodegenerative populations offer unique insights into the episodic-semantic continuum, displaying compensatory reliance upon the most preserved memory system during future simulation.
Topic Area: LONG-TERM MEMORY: Semantic