The medial temporal lobes (MTLs) are widely held to support a range of constructive endeavors including remembering the past, envisaging the future, and imagining hypothetical scenarios. While right MTL structures have been ascribed a prominent role in the construction of spatial contexts, lesion evidence to directly test this hypothesis is lacking. To this end, we assessed scene construction performance in two cases, GC and DF, who presented with left- and right-lateralized presentations of semantic dementia, respectively. GC displayed characteristic semantic processing difficulties in the context of marked left anterior and medial temporal lobe atrophy. Despite significant volume loss across the entire length of the left hippocampus, GC was capable of generating richly detailed, spatially coherent scenes, most likely reflecting the preservation of his right anterior MTL. In contrast, DF's cognitive profile was one of dense prosopagnosia, with subjectively reported gaps in autobiographical memory and wayfinding difficulties. Formal testing on the scene construction task revealed striking deficits, with DF producing impoverished descriptions of spatially fragmented scenes. We attribute DF's inability to construct spatially contiguous scenes to the degeneration of right-sided MTL structures, most prominently the right anterior hippocampus (19% volume loss) and right parahippocampal cortex (23% volume loss). Our findings complement the extant fMRI literature to suggest a fundamental role for right medial temporal regions in the construction of rich detailed spatial arrays.
Keywords: episodic memory; hippocampus; imagination; mental time travel; semantic dementia.
© 2017 Wiley Periodicals, Inc.