Loss of cognition in late life poses a major public health challenge. Understanding how cognition changes over time is essential to develop strategies for preventing or delaying cognitive impairment and dementia. Notably, there is substantial individual difference in cognitive aging; some older people manage to maintain their cognition, some decline slowly, and others decline much faster.
Common brain pathological conditions, such as Alzheimer's disease, infarcts, and Lewy body disease, are important contributors to decline in cognition. However, they only account for part of the variation in decline, suggesting that other factors are at play.
Yu et al., (2014) (PDF, 160KB) sought to determine whether there are distinct profiles of cognitive aging unaccounted for by common neuropathologies. Longitudinal cognitive measures were collected from approximately 900 participants of the Religious Orders Study and the Rush Memory and Aging Projects. The participants were followed annually for up to 18 years until the time of their death and subsequently underwent brain autopsy.
The analysis identified four distinct groups after controlling for indices of common neuropathologies. Specifically, 44% of the participants had little or no decline, 35% showed moderate decline, 13% showed severe decline and the rest (8%) had substantial fluctuation of cognitive measures over time. Moreover, the four groups differed on a range of psychological, experiential and neurobiologic markers of cognitive and neural reserve, including depressive symptoms, loneliness, cognitive and physical activity and neuronal density.
The study has several important implications. First, the research shows that, for many older persons, cognitive aging in the absence of neuropathology is characterized by stability in cognition. Second, the results suggest that other pathologic processes also contribute to cognitive decline and await identification. Third, the results support that behavioral and structural elements of reserve influence late life cognitive performance and contribute to individual differences in the ability to respond to accumulating damage due to common age-related brain pathology.
In summary, dissecting person-specific differences in cognitive decline offers a better appreciation of the complexity of cognitive aging and may suggest novel approaches to mitigate late life cognitive decline even in the presence of pathology.
Citation:
Yu, L., Boyle, P., Segawa, E., Leurgans, S., Schneider, J. A., Wilson, R. S., and Bennett, D. A. (2014). Residual decline in cognition after adjustment for common neuropathologic conditions. Neuropsychology. Advance online publication. http://dx.doi.org/10.1037/neu0000159
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