Topological Organization of Center-of-Pressure Dynamics During Virtual Reality Walking Differs Between Individuals With Parkinson's Disease and Healthy Older Adults.

Background: Gait impairment in Parkinson's disease (PD) is multifactorial and may become more pronounced under perceptual-cognitive challenge. Virtual reality (VR) provides an altered locomotor context, yet its effects on both conventional magnitude-based Center of pressure (CoP) metrics and higher-order structural organization remain unclear. This study compared linear, nonlinear, and topological characteristics of stance-phase CoP trajectories between individuals with PD and healthy older adults during normal and VR walking, with particular emphasis on whether VR elicited group-specific differences in topological organization. Methods: Fifteen individuals with idiopathic PD and 17 age-matched controls performed overground walking under normal gait (NG) and VR conditions. Stance-phase CoP trajectories were analyzed using linear magnitude measures (path length, velocity, root mean square, ellipse area), sample entropy (SampEn), and persistent homology-derived persistence entropy (H0 and H1). Mixed-factor repeated-measures ANOVA models assessed Group and Task effects. Results: VR increased CoP path length ( Conclusions: The primary analysis showed a group-dependent H1 persistence-entropy response across normal and VR walking. However, because zero entropy represented both zero- and one-feature diagrams and robustness across alternative point-cloud densities and persistence thresholds was not examined, this finding should be considered exploratory. Conventional CoP measures did not show diagnosis-specific responses to VR. H1 persistence entropy may therefore provide complementary information about CoP trajectory organization, although its physiological and clinical significance requires further investigation.