Naturalistic Assessment of Reaction Time Variability in Older Adults at Risk for Alzheimer’s Disease

Abstract

AbstractBackgroundBreakdowns in attentional control may underscore cognitive changes seen in the earliest stages of Alzheimer’s disease (AD). One way to measure these changes is to assess variability in cognitive performance. Variability in cognition may be most evident when repeatedly sampled over hours or days and in different environmental contexts or at different times of day. We analyzed data from an ongoing smartphone‐based study of cognition in AD which utilizes extremely brief cognitive tests taken remotely over several days in natural environments.MethodOlder adults (N = 319, aged 75 +/‐ 5 years) completed repeated cognitive testing on the Ambulatory Research in Cognition (ARC) platform and had CSF or PET amyloid biomarkers and APOE genotype available. RTSD was assessed in a brief processing speed task by taking the SD of correct RTs. All models adjusted for baseline age, education, and gender.ResultAveraging across sessions, symptomatic participants (indicated by Clinical Dementia Rating® (CDR®) > 0) showed more variability than asymptomatic (CDR 0) participants (p = 0.009). APOE ε4 carriers showed more variability than non‐carriers, although this was not significant (p = 0.067). More fine‐grained models considered RTSD within each session (e.g. from trial‐to‐trial) using mixed effects models. Symptomatic participants exhibited greater trial‐to‐trial RTSD compared to asymptomatic participants (p = 0.001). APOE ε4 carriers also exhibited greater trial‐to‐trial RTSD compared to non‐carriers (p = 0.004). When limiting the sample to asymptomatic participants to determine if there were changes in the preclinical stage of AD, there remained a strong APOE ε4 effect, with carriers exhibiting greater trial‐to‐trial RTSD than non‐carriers (p = 0.005). Interestingly, amyloid was not significant in any models.ConclusionOlder adults at risk for AD show increased RTSD even in brief assessments. These subtle fluctuations in attention were most evident in APOE e4 carriers at very short time intervals, and less so when averaged across trials and sessions. Overall, these findings suggest that fluctuations in attention in preclinical AD are most evident from moment to moment, highlighting the need for fine‐grained and repeated assessment of attentional control.