Detection of very early stages of Alzheimer's Disease (AD) has been an area of difficulty for researchers due to confounds with age. Prose recall has been suggested as a diagnostically sensitive test of episodic memory declines in AD; however, the process by which this occurs has not been adequately defined. Theories of discourse processing suggest that prose comprehension can be mapped onto distinct patterns of brain activation and that the cognitive mechanisms used for comprehension are dependent on prose content; however, most studies have been limited to healthy adults. In this study we examined healthy young adults, healthy older adults, and adults with AD during comprehension of two different prose genres, expository and narrative. We found significant activation in posterior cingulate cortex for healthy older adults who read expository prose, and significant deactivation in anterior cingulate cortex for AD adults who read narrative prose. These results indicate that aging involves noncompensatory overrecruitment of cognitive control areas for long term memory, and that AD involves attentional deficits. This study further supports the sensitivity of prose comprehension as a diagnostic tool for AD.
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