Visuospatial deficits, walking dynamics and effects of visual cues on gait regulation in Parkinson's disease (PD)
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Individuals with Parkinson’s disease (PD) present with motor and non-motor symptoms, including in the visuospatial domain. Correction of walking abnormalities through application of visual cues in the environment has been reported in PD, but the mechanisms of action are poorly understood. The present project examined competing explanations of the effects of visual guidance on multiple aspects of gait in PD. Comfortable over-ground walking was performed by 9 participants with left-side motor onset (LPD), 11 with right-side motor onset (RPD), and 13 age-matched normal control participants (NC). Study 1 examined whether veering in PD is predominantly induced by asymmetrical perception of the visual environment or by motor asymmetry between relatively affected and relatively non-affected body side. Walking conditions were eyes-open, vision-occluded, and egocentric reference point (walk toward the perceived center of a distant target). The visual hypothesis predicted that LPD, with a known tendency toward left spatial hemineglect, would veer rightward, whereas RPD would veer leftward. The motor hypothesis predicted the opposite pattern of results because the more affected body side has shorter step length. The results supported the visual hypothesis. In Study 2, visually-cued gait was examined to establish whether the key variable to improvement is attention to pattern rhythmicity, or instead if improvement may arise from perception of dynamic flow. Floor patterns included transverse lines (attention; 3 frequencies) and randomly-placed squares (dynamic; 3 densities). Relative to baseline, both transverse lines and random squares, especially at higher frequency/density, resulted in gait improvements and induced more stable interlimb coordination, especially for LPD, the subgroup known to have greater visual dependence. Effects lasted after the cues were removed. The success of the random-squares cuing indicates that the mechanism of improvement may be dynamic flow of visual texture rather than attention, and further suggests that vision-based interventions need not be restricted to transverse lines. Taken together, the studies lay the foundation for the development of treatments for walking disturbances in PD by addressing critical issues that could influence the outcomes of therapeutic interventions, including the role of visual input and the differential effects on PD subgroups.