Capturing Trial-by-Trial Variability in Behaviour: People with Parkinson’s Disease Exhibit a Greater Rate of Short-Term Fluctuations in Response Times

Average response time is frequently used to reflect executive function. Less often studied is intra-individual variability in response times (IIVRT) which reflects within-person consistency. Higher IIVRT in Parkinson’s disease (PD) has been associated with poor executive function but almost exclusively studied using standard deviations. Such linear measures cannot capture rapid and spontaneous changes in biological systems such as dopaminergic bursting activity. Therefore, nonlinear measures may provide important complementary insights into dopamine-related neurocognition. Our primary aim was to investigate nonlinear IIVRT measures in PD using graph theory, constituting the first use of this approach on RT data. As hypothesized, PD was associated with a greater rate of trial-by-trial IIVRT compared to healthy older adults. These novel results indicate that a similarity graph algorithm may be a useful tool to capture the more rapidly varying and spontaneous changes in RT behavior that result from the dysfunctional dopamine bursting dynamics present in PD.