Objective: To test the hypothesis that higher neuronal density in brainstem aminergic nuclei contributes to neural reserve.Methods: Participants are 165 individuals from the Rush Memory and Aging Project, a longitudinal clinical-pathologic cohort study. They completed a mean of 5.8 years of annual evaluations that included a battery of 19 cognitive tests from which a previously established composite measure of global cognition was derived. Upon death, they had a brain autopsy and uniform neuropathologic examination that provided estimates of the density of aminergic neurons in the locus ceruleus, dorsal raphe nucleus, substantia nigra, and ventral tegmental area plus summary measures of neuronal neurofibrillary tangles and Lewy bodies from these nuclei and medial temporal lobe and neocortex.Results: Neuronal densities in each nucleus were approximately normally distributed. In separate analyses, higher neuronal density in each nucleus except the ventral tegmental area was associated with slower rate of cognitive decline, but when modeled together only locus ceruleus neuronal density was related to cognitive decline (estimate 5 0.003, SE 5 0.001, p , 0.001). Higher densities of tangles and Lewy bodies in these brainstem nuclei were associated with faster cognitive decline even after controlling for pathologic burden elsewhere in the brain. Locus ceruleus neuronal density, brainstem tangles, and brainstem Lewy bodies had independent associations with rate of cognitive decline. In addition, at higher levels of locus ceruleus neuronal density, the association of Lewy bodies with cognitive decline was diminished. ) or their components (synapses 8,9 ) in key locations. This approach allows collection of neuronal and pathologic data from the same brain regions, facilitating examination of their conjoint correlations with cognition. ConclusionThe present study examines the associations among neuronal density, neurodegenerative lesions, and change in cognitive function. We assessed neuronal density in brainstem aminergic nuclei (i.e., locus ceruleus, dorsal raphe nucleus, substantia nigra, and ventral tegmental area) because these nuclei support multiple cognitive processes, synthesize important monoamines that function as neurotransmitters and neuromodulators, are therapeutic targets for cognitive enhancement, 10 and bear a disproportionate burden of age-related neurodegeneration. 11,12 Participants from the Rush Memory and Aging Project had annual cognitive testing for a mean of 5.8 years, died, and underwent a neuropathologic examination that yielded neuronal counts for each brainstem nucleus From the Rush Alzheimer's Disease

The study aim was to describe the temporal course of cognitive decline in Alzheimer‘s disease (AD). We selected 226 persons from 2 longitudinal clinical-pathological studies who were cognitively healthy at baseline, followed at least 4 years (mean = 10.2, SD = 3.5), and clinically diagnosed with AD at some point during follow-up. Each evaluation included a battery of 17 cognitive tests from which a previously established composite measure of global cognition was derived. In those who died, a uniform neuropathologic examination established the pathological diagnoses of Alzheimer's disease and other common conditions that impair cognition. Mixed-effects models with 2 change points were used to assess trajectories of cognitive decline. In the main analysis, there was no change in cognitive function until a mean of 7.5 years before dementia was diagnosed (95% confidence interval [CI]: -8.3, -6.7). The global cognitive measure declined a mean of 0.087-unit per year (95% CI: -0.099, -0.073) until a mean of 2.0 years before the diagnosis (95% CI: -2.2, -1.7) when it increased more than fourfold to a mean loss of 0.370-unit per year (95% CI: -0.417, -0.334). Of 126 individuals who died and underwent autopsy, 101 (80%) met pathologic criteria for AD of whom 67 had at least one other pathologic condition. Pathologic measures of AD and cerebral infarction were not strongly related to cognitive trajectories. The results indicate that cognitive decline in AD begins many years before dementia is diagnosed and accelerates during the course of the disease.

In old age, depressive symptoms have an association with cognitive decline that is independent of the neuropathologic hallmarks of dementia.

In the last years of life, covariation among cognitive abilities sharply increases consistent with the cognitive dedifferentiation hypothesis.