No abstract

Understanding short-term cognitive decline in relation to Alzheimer's neuroimaging biomarkers in early stages of the development of neuropathology and neurodegeneration will inform participant recruitment and monitoring strategies in clinical trials aimed at prevention of cognitive impairment and dementia. We assessed associations among neuroimaging measures of cerebral amyloid pathology, a hallmark Alzheimer's neuropathology, hippocampal atrophy, and prospective cognition among 171 cognitively normal Baltimore Longitudinal Study of Aging participants (baseline age 56-95 years, 48% female, 562 cognitive assessments, 3.7 years follow-up). We categorized each individual based on dichotomous amyloid pathology (A) and hippocampal neurodegeneration (N) status at baseline: A-N-, A+N-, A-N+, A+N+. We conducted linear mixed effects analyses to assess cross-sectional and longitudinal trends in cognitive test z-scores by amyloid and neurodegeneration group. To investigate the effects of amyloid dose and degree of hippocampal atrophy, we assessed the associations of continuous mean cortical amyloid level and hippocampal volume with cognitive performance among individuals with detectable amyloid pathology at baseline. Individuals with amyloidosis or hippocampal atrophy had steeper longitudinal declines in verbal episodic memory and learning compared to those with neither condition (A+N- versus A-N-: β = - 0.069, P = 0.017; A-N+ versus A-N-: β = - 0.081, P = 0.025). Among individuals with hippocampal atrophy, amyloid positivity was associated with steeper declines in verbal memory (β = - 0.123, P = 0.015), visual memory (β = - 0.121, P = 0.036), language (β = - 0.144, P = 0.0004), and mental status (β = - 0.242, P = 0.002). Similarly, among individuals with amyloidosis, hippocampal atrophy was associated with steeper declines in verbal memory (β = - 0.135, P = 0.004), visual memory (β = - 0.141, P = 0.010), language (β = - 0.108, P = 0.006), and mental status (β = - 0.165, P = 0.022). Presence of both amyloidosis and hippocampal atrophy was associated with greater declines than would be expected by their additive contributions in visual memory (β = - 0.139, P = 0.036), language (β = - 0.132, P = 0.005), and mental status (β = - 0.170, P = 0.049). Neither amyloidosis nor hippocampal atrophy was predictive of declines in executive function, processing speed, or visuospatial ability. Among individuals with amyloidosis, higher baseline amyloid level was associated with lower concurrent visual memory, steeper declines in language, visuospatial ability, and mental status, whereas greater hippocampal atrophy was associated with steeper declines in category fluency. Our results suggest that both amyloid pathology and neurodegeneration have disadvantageous, in part synergistic, effects on prospective cognition. These cognitive effects are detectable early among cognitively normal individuals with amyloidosis, who are in preclinical stages of Alzheimer's disease according to research criteria. Our findings highlight the importance of e...

White matter hyperintensities are frequently detected on cranial magnetic resonance imaging (MRI) scans of older adults. Given the presumed ischemic contribution to the etiology of these lesions and the posited import of resting brain activity on cognitive function, we hypothesized that longitudinal changes in MRI-detected white matter disease, and its severity at a given time point, would be associated with changes in regional cerebral blood flow (rCBF) over time. We evaluated MRI scans and resting H(2)(15)O positron emission tomographic rCBF at baseline and after an average of 7.7-year follow-up in Baltimore Longitudinal Study of Aging participants without dementia. Differences in patterns of rCBF were evident at baseline and at follow-up between the group of subjects showing increased white matter disease over the 8-year interval compared with the group with stable white matter ratings. Furthermore, longitudinal changes over time in rCBF also differed between the two groups. Specifically, the group with progressive white matter abnormalities showed greater increase in the right inferior temporal gyrus/fusiform gyrus, right anterior cingulate, and the rostral aspect of the left superior temporal gyrus. Regions of greater longitudinal decrease in this group were evident in the right inferior parietal lobule and at the right occipital pole. Changes in white matter disease over time and its severity at any given time are associated significantly with both cross-sectional and longitudinal patterns of rCBF. The longitudinal increases may reflect cortical compensation mechanisms for reduced efficacy of interregional neural communications that result from white matter deterioration.