fMRI of Prose Comprehension in High- and Low-Performing Older Adults

Characterization and clinical detection of early Alzheimer's disease is difficult due to significant neurocognitive variability present in both healthy and pathological aging. This poses a problem for memory and aging studies because individuals categorized as healthy may actually have an early or `preclinical' AD, which may contaminate results. This study addressed these concerns by 1) using a novel prose recall task designed to elicit subtle changes in episodic memory that occur in early AD 2) examining neural activity of high- and low-performing older adults to reduce within-group variability and differentiate healthy from pathological brain activity. The prose recall task was extremely sensitive (81.8% sensitivity and 100% specificity for mean expository and narrative recall; 100% sensitivity and 100% specificity for expository stories alone) in differentiating healthy older adults from those with very mild AD. fMRI results showed evidence that high-performers retain the ability to recruit specialized regions of the brain during encoding of prose, while low-performers overrecruit nonspecific areas and strongly resemble adults with very mild AD. This suggests that high-performers engage in compensatory brain activity which may reflect a healthy aging process, while low-performers exhibit signs of dedifferentiation which may reflect a disease process