Examining Intraindividual Variability as a Predictor of Cognitive and Functional Decline in Older Adulthood

Abstract

Intraindividual variability (IIV) has recently emerged as a promising early indicator of future cognitive decline (Haynes et al., 2017). However, the literature is currently limited in that the majority of studies have only examined IIV in one cognitive domain: reaction time. Explorations into the relationship between IIV and functional status are also sparse, with only one recent study exploring this relationship (Schmitter-Edgecombe et al., 2020). The present study aimed to address gaps in the literature by examining IIV in differing cognitive domains to determine which measure(s) were the best predictors of cognitive and functional status at baseline as well as decline at a 1-year follow-up in a sample of cognitively healthy (CH) and mild cognitively impaired (MCI) individuals. 80 participants (48 CH, 32 MCI) completed a baseline visit and 62 individuals (38 CH, 24 MCI) completed a 1-year follow-up visit. Due to the coronavirus-19 disease pandemic (COVID-19), 12 individuals completed their follow-up visit via video-teleconferencing (VTC) on an iPad. Discriminant function analysis (DFA) revealed that IIV on a number-letter switching task was successful at distinguishing between CH and MCI groups at baseline. Hierarchical regressions demonstrated a pattern of lower variability on a choice reaction time measure (CRT) being associated with better cognition as measured by the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS) over and beyond baseline cognition, mood, and demographic factors at 1-year follow-up across groups. Regarding functioning, no IIV measure significantly discriminated between cognitive status groups in DFA analysis. Hierarchical regressions demonstrated differing associations of IIV measures between functional self-report measures and between cognitive status groups. Future implications and directions are discussed.