Modeling cognitive trajectories within longitudinal studies: a focus on older adults

Abstract

The natural history of life span cognitive performance and its late-life determinants have been studied from an array of perspectives. Significant insights come from psychological disciplines, including cognitive, developmental, and neuropsychology, as well as from medical specialties, such as geriatrics, neurology, psychiatry, neuroradiology, and neuropathology, that contribute to the growing interdisciplinary scientific field: cognitive neuroscience of aging. This survey of longitudinal studies of aging suggests that disease-oriented investigations commonly do not adequately consider normative cognitive changes, whereas developmental studies do not sufficiently measure and model nonnormative cognitive aging. This article argues for an integrative perspective that considers both of these influences on cognitive trajectories and presents a series of methodological concerns that have not been addressed comprehensively. Interdisciplinary methods from longitudinal observational studies should be leveraged to enable translational interventions to promote brain longevity.

Figure 1. Spaghetti plots of memory scores as a function of age in 72 participants who developed dementia

Within-individual trajectories of Buschke Selective Reminding Test (SRT) scores for the participants in a longitudinal aging study who develop dementia as a function of chronological age (Figure 1A) and time before the clinical diagnosis (Figure 1B). Superimposed on the plots in 1B is the change-point trajectory which is apparent only when cases are aligned at time of diagnosis. Model-estimated change point was 7.6 years prior to diagnosis, with 95% confidence interval of 4.6–9.0 years. Figure adapted from Hall, et al. 2000, data are reported in Hall, et al. 2003.

Figure 2. Mean and impairment cutoff by age using conventional and robust norms

Estimates of Buschke Selective Reminding Test (SRT) scores (Figure 2A) and Wechsler Performance IQ (PIQ) scores (Figure 2B) corresponding to the mean and 2 standard deviations (SD) below the mean obtained from the conventional (dashed line) and robust (solid line) normative samples. The differences between the robust and conventional norms increase as a function of age and as scores depart from the mean. Adapted from Sliwinski, et al. 1996.