Perception of whole-body motion during balance perturbations is impaired in Parkinson\'s disease and is associated with balance impairment

Background: In addition to motor deficits, Parkinson9s disease (PD) may cause perceptual impairments. The role of perceptual impairments in sensorimotor function is unclear, and has typically been studied in single-joint motions. Research Question: We hypothesized that perception of whole-body motion is impaired in PD and contributes to balance impairments. We tested 1) whether directional acuity to whole body perturbations during standing was worse in people with PD compared to neurotypical older adults (NOA), and 2) whether balance ability, as assessed by the MiniBESTest, was associated with poor directional acuity in either group. Methods: Participants were exposed to pairs of support-surface translation perturbations in a two-alternative forced choice testing paradigm developed previously in a young healthy population. The first perturbation of each pair was directly backward and the second deviated to the left or right (1 degree-44 degrees). Participants judged and reported whether the perturbations in each pair were in the "same" or "different" direction. This information was used to calculate directional acuity thresholds corresponding to "just-noticeable differences" in perturbation direction. Linear mixed models determined associations between directional thresholds and clinical variables including MDS UPDRS-III score, age, and MiniBESTest score. Results: 20 PD (64+/-7 y, 12 male, >=12 hours since last intake of antiparkinsonian medications) and 12 NOA (64+/-8, 6 male) were assessed. Directional thresholds were higher (worse) among PD participants (17.6+/-5.9 degrees vs. 12.8+/-3.3 degrees, P