Discrepancies between Fluid and Crystallized Ability in Healthy Adults: A Behavioral Marker of Preclinical Alzheimer’s Disease

• Published in: Neurobiology of aging Vol. 46; pp. 68 - 75
• Main Authors: McDonough, Ian M, Bischof, Gérard N, Kennedy, Kristen M, Rodrigue, Karen M, Farrell, Michelle E, Park, Denise C
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.10.2016
• Subjects: Ability discrepancy; Aged; Aged, 80 and over; Aging; Aging - pathology; Aging - psychology; Alzheimer Disease - diagnostic imaging; Alzheimer Disease - metabolism; Alzheimer Disease - pathology; Alzheimer Disease - psychology; Amyloid beta-Peptides - metabolism; Amyloid-beta; Biomarkers; Cerebral Cortex - diagnostic imaging; Cerebral Cortex - metabolism; Cerebral Cortex - pathology; Cognition - physiology; Cortical thickness; Dementia; Female; Humans; Internal Medicine; Magnetic Resonance Imaging; Male; Neuroimaging; Neurology; Positron-Emission Tomography; Preclinical; Recognition (Psychology) - physiology; beta-amyloid; ability discrepancy; dementia; aging; preclinical; cortical thickness; Aging; Cortical thickness; Preclinical; Ability discrepancy; Amyloid-beta; Dementia
• ISSN: 0197-4580; 1558-1497
• DOI: 10.1016/j.neurobiolaging.2016.06.011

Abstract Measures of core cognitive processes (fluid abilities) are highly correlated with measures of knowledge (crystallized abilities) in healthy adults. In early stages of Alzheimer’s disease (AD), fluid abilities, however, decline more rapidly than crystallized abilities. We hypothesized that cognitively-normal older adults who evidenced lower fluid ability compared with crystallized ability (an ability discrepancy) would show evidence of early AD neuropathology indexed via in vivo measures of beta-amyloid (Aβ) deposition and cortical thickness in AD-vulnerable regions. A sample of older adults ( n = 112) aged 65 to 89 underwent a cognitive battery, structural MRI, and a subset ( n = 75) also completed PET scanning to measure Aβ deposition using F-18 Florbetapir. Of this sample, 60 older adults (43 with available PET scans) evidenced a discrepancy where fluid ability was lower than crystallized ability. The magnitude of the ability discrepancy was independently associated with a greater Aβ deposition and thinner cortex in AD-vulnerable regions, as well as age. The data suggest that such a discrepancy may be a marker of preclinical AD.