Executive Control Mediates Memory's Association with Change in Instrumental Activities of Daily Living: The Freedom House Study

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Abstract
To assess the relative independent contribution of changes in executive control function (ECF) and memory to changes in functional status. Three-year longitudinal cohort study. A comprehensive care retirement community. Five hundred forty-seven noninstitutionalized people aged 70 and older. The California Verbal Learning Test (CVLT) and Executive Interview (EXIT25). Functional status was assessed using instrumental activities of daily living (IADLs). Latent growth curves of CVLT, EXIT25, and IADLs were modeled. The rate of change in IADLs (adjusted for baseline IADLs and cognition) was regressed on the rate of change in each cognitive measure. Models were also adjusted for baseline age, level of care, and comorbid illnesses. There was significant variability around the baseline means and slopes for all variables. The rate of change in EXIT25 was independently correlated with the rate of change in IADLs (correlation coefficient (r)=-0.52, P<.001). This remained significant after adjusting for baseline EXIT25 scores, IADLs, age, comorbid disease, and level of care. The EXIT25's effect on the rate of change in IADLs was stronger than those of age, baseline IADLs, comorbid disease, or level of care. The rate of change in CVLT scores was not significantly associated with the rate of change in IADLs. ECF is a strong, significant, and independent correlate of functional status in normal aging. In contrast, decline in memory, as measured using the CVLT, has no independent association with the rate of change in functional status. This suggests that amnestic mild cognitive impairment can be associated with dementia only though the subsequent or comorbid development of ECF impairment.