Still Functional but Limited Postural Adaptation for Individuals With Parkinson's Disease in Goal-Directed Visual Tasks.

Patients with Parkinson's disease (PD) notably exhibit impairments in posture and visual attention. The objective of the present study was to determine whether PD patients were able to exhibit adaptive postural control in a goal-directed visual task. We hypothesized that the patients would reduce their centre of pressure (COP) movement and/or postural sway to a lesser extent than age-matched controls in the goal-directed visual (search) task, compared with the control free-viewing task (i.e., a lower degree of relative postural adaptation). We also expected the PD patients to sway more than controls in the goal-directed task (i.e., a lower degree of absolute adaptive postural control). The study included 39 PD patients (mean age: 59; mean Hoehn and Yahr stage: 2.1; mean Movement Disorder Society-Unified Parkinson's Disease Rating Scale score: 22; mean Montreal Cognitive Assessment score: 28 (on-drug)) and 40 age-matched adults (mean age: 62 years). The participants gazed at domestic ecological images (visual angle: 100°). Movements of the COP, head, upper back and lower back and variations in pupil dilatation were analysed. As expected, PD patients exhibited greater COP and body sway than controls in both tasks (p < 0.05). Unexpectedly, the difference in COP and/or body sway between the two tasks was greater in PD patients than in controls (p < 0.05). Our results showed that PD patients are able to exhibit adaptive postural control for goal-directed visual tasks. On a practical level and at a more general level, our findings emphasize the likely benefits of rehabilitation with goal-directed tasks requiring a visual attentional focus (walking on footprints on the ground, etc.).