Traditional analyses of autobiographical construction have tended to focus on the ‘internal’ or episodic details of the narrative. Contemporary studies employing fine-grained scoring measures, however, reveal the ‘external’ component of autobiographical narratives to contain important information relevant to the individual’s life story. Here, we used the recently developed NExt scoring protocol to explore profiles of external details generated by patients with Alzheimer’s disease (AD) (n = 11) and semantic dementia (SD) (n = 13) on a future thinking task. Voxel-based morphometry analyses of structural MRI were used to determine the neural correlates of external detail profiles in each patient group. Overall, distinct NExt profiles were observed across past and future temporal contexts in AD and SD groups, which involved elevations in external details, in the context of reduced internal details, relative to healthy Controls. Specifically, AD patients provided significantly more General Semantic details compared with Controls during past retrieval, whereas Specific Episode external details were elevated during future simulation. These increased external details within future narratives related to grey matter integrity in medial and lateral frontal regions in AD. By contrast, SD patients displayed an elevation of Specific Episode, Extended Episode, and General Semantic details exclusively during future simulation relative to Controls, which related to integrity of medial and lateral parietal regions. Our findings suggest that the compensatory external details generated during future simulation comprise an array of episodic and semantic details that vary in terms of specificity and self-relevance. Moreover, these profiles appear to be differentially affected depending on the locus of underlying neuropathology in dementia. Adopting a fine-grained approach to external details provides important information regarding the interplay between episodic and semantic content during future stimulation and highlights the differential vulnerability and preservation of distinct components of the constructed narrative in clinical disorders.
Human ESCs predisposition to karyotypic instability: Is a matter of culture adaptation or differential vulnerability among hESC lines due to inherent properties?
