Towards an aging-specific cognitive phenotype: the freedom house study.

Background/Study Context: The authors have previously reported latent growth curve (LGC) models of 3-year change in multiple cognitive measures among successfully aging volunteers. In this analysis, the authors apply growth mixture modeling (GMM) to demonstrate homogeneous subsets among them with discriminable trajectories. Only one trajectory class can be interpreted as the effect of Aging Proper. The goal of the study was to describe an aging-specific cognitive phenotype (ASCP). Methods: Five hundred forty-seven noninstitutionalized septuagenarian and octogenarian volunteers, residing in a comprehensive care retirement community, were assessed longitudinally on a comprehensive battery of brief psychometric measures. Results: All variables held more than one latent class. Members of an a priori defined "Aging Proper" class were highly concordant across measures, and allowed the aging-specific cognitive phenotype (ASCP) to be examined. The ASCP was characterized by simultaneous decline in visuospatial function, coupled with improving verbal fluency. The ASCP was not associated with decline in memory task performance. Conclusions: Previously reported age-related declines in memory are more likely to represent the effects of comorbid disease and not aging per se. The ASCP is more consistent with earlier "Right Hemisphere" models of aging and could provide clues to the mechanisms underlying true aging-related cognitive changes.