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 A beta amyloid is indicative of incipient Alzheimer's disease (AD), yet MCI with low A beta amyloid may reflect other neurode-generative processes. We aimed to determine the extent to which high A beta 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 A beta 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 A beta performed worse than MCI with high A beta on measures of executive function, attention, visuoconstruction and language. No differences were observed between HC high and low A beta groups. When compared with HC with low A beta, both MCI high and low A beta groups performed worse on measures of episodic memory. However, only the MCI low A beta group performed worse than HC low A beta on measures of executive function, attention, visuoconstruction, and language. Conclusions: When compared with HC with low A beta amyloid, MCI with high A beta amyloid present with impairments restricted to episodic memory, and the episodic memory impairments in MCI with low A beta amyloid were accompanied by impairments in executive function, attention, visuoconstruction, and language, suggesting that MCI with high A beta amyloid reflects prodromal AD, although further longitudinal data is required to confirm this.