Disentangling perceptual judgment and online feedback deficits in Parkinson's freezing of gait.

Although the underlying mechanisms of freezing of gait in Parkinson's disease (PD) are not fully understood, impaired sensory-perceptual processing has been proposed as an important contributor to freezing episodes. The aims of this cross-sectional study were to disentangle how sensory-perceptual deficits involved in planning (prior to movement) and sensory-perceptual feedback processing (during movement execution) contribute to freezing of gait in narrow spaces. Thirteen PD participants with freezing (PD FOG), 14 PD participants without freezing (PD non-FOG), and 15 healthy individuals made a perceptual estimate of the width of the distal opening of a corridor in two conditions: parallel and narrowing walls. Gait characteristics and number of freezing episodes were then compared while participants walked in baseline (no corridor), and through parallel walls and narrowing walls corridors. Visuospatial abilities were also assessed using neuropsychological tests. PD FOG had lower scores in the copy of the pentagons (p = 0.044) and had greater error variability in the perceptual judgment task (p = 0.008) than healthy participants. Although a similar number of freezing episodes occurred in both corridor conditions, PD FOG had greater step length variability while walking through the parallel walls corridor compared to healthy (p < 0.001) and PD non-FOG (p = 0.017) participants. Regression analysis revealed that error variability in perceptual judgment predicted the percentage of time spent in double support (R (2) = 0.347) only in the narrowing walls condition for PD FOG. These results support the notion that sensory-perceptual deficits both prior to movement planning and during movement execution are important factors contributing to freezing of gait.