Veering in hemi-Parkinson’s disease: Primacy of visual over motor contributions

Abstract

Veering while walking is often reported in individuals with Parkinson’s disease (PD), with potential mechanisms being vision-based (asymmetrical perception of the visual environment) or motoric (asymmetry in stride length between relatively affected and non-affected body side). We examined these competing hypotheses by assessing veering in 13 normal control participants (NC) and 20 non-demented individuals with PD: 9 with left-side onset of motor symptoms (LPD) and 11 with right-side onset (RPD). Participants walked in a corridor under three conditions: eyes-open, egocentric reference point (ECRP; walk toward a subjectively perceived center of a target at the end of the corridor), and vision-occluded. The visual hypothesis predicted that LPD participants would veer rightward, in line with their rightward visual-field bias, whereas those with RPD would veer leftward. The motor hypothesis predicted the opposite pattern of results, with veering toward the side with shorter stride length. Results supported the visual hypothesis. Under visual guidance, RPD participants significantly differed from NC, veering leftward despite a shorter right- than left-stride length, whereas LPD veered rightward (not significantly different from NC), despite shorter left- than right-stride length. LPD participants showed significantly reduced rightward veering and stride asymmetry when they walked in the presence of a visual landmark (ECRP) than in the eyes-open condition without a target. There were no group differences in veering in the vision-occluded condition. The findings suggest that interventions to correct walking abnormalities such as veering in PD should incorporate vision-based strategies rather than solely addressing motor asymmetries, and should be tailored to the distinctive navigational profiles of LPD and RPD.

Visual Impairment Is More Common in Parkinson’s Disease and Is a Risk Factor for Poor Health Outcomes

“…For example, postural instability in PD has been shown to be greater when visual fixation is impaired. 6 Visual impairment is also associated with physical inactivity, which is itself a risk factor for falls and hip fracture, 42,43 and physical inactivity is also negatively associated with PD-related outcomes. 44 Visual impairment may also increase the risk of hallucinations in PD, [7][8][9][10] and both hallucinations and dementia are risk factors for falls.…”

Obstacle circumvention and eye coordination during walking to least and most affected side in people with Parkinson’s disease

“…We can speculate that degeneration in the most affected brain side also occurred in perceptual brain areas. Previous studies have also indicated that veering is side affected to PD-dependent [60,61]. Perceptual/sensorial asymmetry is a characteristic in the earliest stages of the disease [54,59,62,63], which seems to be manifested depending on the basal ganglia-cortical loops activated by the visual and motor demands of the task [62].…”

Cerebral Asymmetry and Dominance in Man

“…Interventions to correct walking abnormalities such as veering in PD should incorporate vision-based strategies rather than solely addressing motor asymmetries, and should be tailored to the distinctive navigational profiles of leftside onset of motor symptoms (LPD) and right-side onset (RPD). [28] The functional organization of the pre-frontal cortex (PFC) has been explored with a considerable evidence for a left hemisphere (LH) "interpreter". Recent investigations have added evidence for several roles of the right PFC in reasoning, problem solving, and decision-making; focusing on the beneficial complementary role of the right PFC in maintaining and enhancing the role of the left PFC, the "interpreter".…”