The purpose of this research is to determine how deep brain stimulation (DBS) for Parkinson's disease affects attention and visuospatial function. Additionally, this study will evaluate how deficits in visual attention are associated with freezing of gait (FOG) in Parkinson's disease. There is currently no reliable treatment for FOG and little is understood about the underlying reason this occurs. Some recent research has found that stimulating the right side of the brain seems to improve FOG. The right side of the brain is also paramount for visual attention, which is why investigators are conducting this study.

FOG is a common and frequently disabling symptom of PD, affecting more than half of all PwPD. It remains a complex and incompletely understood phenomenon, with no currently approved therapies. FOG is often exacerbated during dual-tasks where attention is divided to multiple tasks. A well known method of provoking FOG by PwPD and neurologists alike is to walk through doorways or through a crowded space, regions where spatial attention is necessary. Similarly, significant visuospatial attention deficits have been found in PwPD who freeze compared to those do not. Further evidence demonstrates that the STN is part of the circuit which modulates spatial attention, and that STN-DBS has a significant impact on visuospatial attention and is notably improved with right sided stimulation. Indeed, visuospatial attention is largely considered to be predominantly lateralized to the right hemisphere. Interestingly, one study showed that right STN-DBS stimulation affecting a volume of activated tissue (VAT) connected to the right sensorimotor cortex showed a significant association with reduction in FOG. The impact of STN-DBS on visuospatial attention and the degree to which this change in attention is associated with changes in FOG has not yet been studied, and may well explain part of the pathophysiology of FOG and how to treat PwPD who freeze. The present study will build on the aforementioned research by prospectively evaluating the impact of lateralized STN-DBS stimulation on visuospatial attention in PwPD, and correlating this with change in FOG.

Inclusion Criteria:

• Subjects above 18 years of age
• Subjects with freezing of gait
• Subjects with bilateral STN-DBS surgery as part of their clinical care for Parkinson's disease

Exclusion Criteria:

• Uncorrected visual or hearing impairments, as indicated by self-report
• Individuals who are pregnant or expect to become pregnant during the course of the study
• Individuals with dementia or relevant brain lesions impacting cognition or gait

Investigator will not be blinded as they will need to make adjustments to patient deep brain stimulation settings during testing.