Visuomotor control of walking in Parkinson’s disease: Exploring possible links between conscious movement processing and freezing of gait

Abstract Introduction Changes in visual attention have been argued to influence freezing of gait (FOG) in people with Parkinson’s Disease (PD). However, the specific visual search patterns of people with FOG pathology (PD + FOG) and potential underlying mechanisms are not well understood. The current study explored visual search behavior in PD + FOG while walking on a pathway featuring environmental features known to exacerbate FOG (e.g., narrow doorway and tripping hazards). Potential attentional underpinning mechanisms were also assessed, such as conscious movement processing. Methods Visual search behavior of twelve people with PD + FOG tested in ON-state (Mage = 74.3) and twelve age-matched healthy controls (Mage = 72.5) were analysed during a complex walking task. The task required participants to step over an obstacle and navigate through a narrow doorway, surrounded by clutter. Results People with PD + FOG more frequently directed visual attention to ongoing and imminent steps compared to healthy controls (Mdn = 26% vs Mdn = 14%, respectively; p = 0.042). Self-reported conscious movement processing was also significantly higher in people with PD+FOG. The one participant who froze during the walking task fixated the future trip hazard (obstacle, approximately 6 steps ahead) almost exclusively during freezing trials (i.e., 60-100% of the trial). In contrast, during ‘non-freeze’ trials, this participant increased the duration of fixations towards ongoing and imminent steps. Conclusion Results suggest that people with PD + FOG strongly monitor/control ongoing and immediately upcoming stepping movements. However, prolonged fixations towards threats to future movements might prevent people with PD + FOG from processing the visual information needed to do this, thereby provoke freezing episodes.