Cognitive consequences of high Aβ amyloid in mild cognitive impairment and healthy older adults: implications for early detection of Alzheimer's disease

Background: It has been proposed that only mild cognitive impairment (MCI) with high Aβ amyloid is indicative of incipient Alzheimer's disease (AD), yet MCI with low Aβ amyloid may reflect other neurode-generative processes. We aimed to determine the extent to which high Aβ amyloid influenced cognitive function in healthy older adults and adults with MCI. Method: Healthy controls (HC; n=178) and adults with MCI (n = 56) enrolled in the Australian Imaging, Biomarkers, and Lifestyle study, underwent positron emission tomography neuroimaging for Aβ amyloid and completed an extensive neuropsychological battery, assessing the cognitive domains of verbal and visual episodic memory, executive function, visuoconstruction, attention and processing speed, and language at baseline. Results: MCI with low Aβ performed worse than MCI with high Aβ on measures of executive function, attention, visuoconstruction and language. No differences were observed between HC high and low Aβ groups. When compared with HC with low Aβ, both MCI high and low Aβbeta groups performed worse on measures of episodic memory. However, only the MCI low Aβ group performed worse than HC low Aβ on measures of executive function, attention, visuoconstruction, and language. Conclusions: When compared with HC with low Aβ amyloid, MCI with high Aβ amyloid present with impairments restricted to episodic memory, and the episodic memory impairments in MCI with low Aβ amyloid were accompanied by impairments in executive function, attention, visuoconstruction, and language, suggesting that MCI with high Aβ amyloid reflects prodromal AD, although further longitudinal data is required to confirm this.