Comparing intra‐individual variability on executive functioning tasks in individuals with Mild Cognitive Impairment and Dementia of the Alzheimer Type: Results from the ARMADA Study

Abstract

AbstractBackgroundCognitive decline is most often assessed mean group differences on static measures of cognitive abilities (MacDonald et al., 2009). Another, perhaps more dynamic, method to understanding cognitive functioning is to evaluate variability in performance within an individual, termed intraindividual variability (IIV), which has been associated with reduction in gray matter and less efficient cognitive processing. Using results from a multi‐site, longitudinal ARMADA study that validated NIH Toolbox across the cognitive aging spectrum, we investigated whether IIV in reaction time processing can differentiate between older adults with normal cognition, mild cognitive impairment (MCI), or dementia of the Alzheimer type (DAT), as well as the relative magnitude of differences between groups.MethodAs part of the Advancing Reliable Measurement in Alzheimer’s Disease and cognitive Aging study (ARMADA; Weintraub et al 2020), participants completed the NIH Toolbox Cognition Battery, including two measures of executive functioning, Dimensional Change Card Sort and Flanker Inhibitory Control, which include granular reaction time data in milliseconds. We analyzed standard deviation and mean absolute deviation of item‐level data of all trials, correct trials only, and incorrect trials only for three groups: normal controls, those with amnestic MCI, and those with mild DAT.ResultWe observe large effect sizes of reaction time by clinical group, with the mild DAT group demonstrating mean standard error across trials of approximately .5 seconds throughout, compared with .25 seconds for MCI and .10 seconds for the control group (Figure 1). This translates to an approximate 5‐fold increase in processing speed in the most severe clinical group. Examining time trends, we see that while the NC and MCI group were faster as the test progressed; there is no similar learning effect for the mild DAT group. Similar effect sizes were observed for the Flanker test.ConclusionThis study represents one of the first studies to examine clinical performance using process data from two executive functioning measures on the NIH Toolbox across the cognitive aging spectrum. Future work will explore more definitions of IIV to determine which measure will maximally differentiate between established clinical groups and examine longitudinal differences.