Decoding the Neural Mechanisms Underlying Postural Instability and Gait Dysfunction in Parkinson's Disease

PD is a progressive neurodegenerative disorder characterized by motor symptoms including tremor, rigidity, and bradykinesia. While DBS is an effective treatment for many of these motor symptoms, postural instability and gait dysfunction (PIGD), including FOG, frequently persist and are a major source of falls, loss of independence, and reduced quality of life.

The neural mechanisms underlying PIGD and FOG remain poorly understood, particularly in real-world conditions where these symptoms are most likely to occur. Conventional clinical assessments often fail to reliably provoke these gait disturbances, limiting the ability to study their underlying neurophysiology. At the same time, recent advances in DBS technology - specifically systems capable of recording brain signals, or neural activity - provide a unique opportunity to directly examine brain signals associated with gait impairment.

This study is designed to characterize the neural mechanisms associated with PIGD and FOG in individuals with PD who have an implanted sensing-enabled DBS system (Medtronic Percept™). By integrating neural recordings from the subthalamic nucleus (STN) with detailed biomechanical measurements during walking tasks, the study aims to identify patterns of neural activity that precede, accompany, and follow gait disturbances.

To address the challenge of eliciting ecologically valid gait disturbances, participants will complete walking and balance tasks within a fully immersive virtual reality platform. This system simulates real-world scenarios that are meant to provoke FOG and PIGD, including situations involving environmental constraints, anxiety-inducing contexts, and dual-task cognitive demands.

Additional assessments will include stair ambulation and functional mobility tasks using an instrumented gait platform which provides quantitative measures of temporal, kinematic, and kinetic aspects of walking and balance.

During these tasks, neural activity recorded from the DBS device will be synchronized with motion capture and biomechanical data. This integrated dataset will allow investigators to examine how neural activity relates to gait performance and to identify neural patterns associated with FOG episodes.

Participants will undergo multiple testing sessions under varying DBS conditions, including their clinically optimized DBS therapy and other programmed conditions. These comparisons will enable evaluation of how different stimulation approaches influence neural activity and gait performance.

The knowledge gained from this study is expected to advance understanding of the neural mechanisms underlying gait dysfunction in PD and may inform the development of more personalized and adaptive neuromodulation strategies to better treat these disabling symptoms in the future.

• Multiple Deep Brain Stimulation (DBS) Conditions (Other): Participants have the Medtronic Percept DBS system implanted as part of standard clinical care. During study sessions, stimulation is evaluated under different conditions, including clinically optimized stimulation, off stimulation, and alternative stimulation paradigms. Stimulation settings are temporarily adjusted for research assessments and are returned to clinically optimized settings at the end of each session. Effects of those conditions on task performance are being assessed.
• Moving Overground in a Virtual Environment (MOVE) (Behavioral): Participants complete walking and balance tasks within a virtual reality environment designed to simulate real-world situations that provoke gait disturbances. Tasks include navigating environmental constraints, performing turning and stopping movements, and completing dual-task cognitive challenges while walking.
• Cleveland Clinic Stair Ambulation and Functional Evaluation of Gait (SAFE-Gait) (Behavioral): Participants complete stair ambulation and functional mobility tasks on an instrumented platform, including ascending and descending steps, walking, turning, and performing dual-task conditions. These assessments provide quantitative measures of gait performance, balance, and functional mobility.

Primary outcomes

• Change in STN-LFP power fluctuations from single-task walking compared to FOG episode [Five sessions completed from enrollment to the end of testing, over an average of one week.]: Participants will complete motor, cognitive and dual-task modules in a virtual reality environment that simulates a home-setting, allowing for acquisition of real-world, at-home behavior. They will also complete a stair navigation task under both single and dual-task conditions. During these assessments, neural activity (i.e., subthalamic nucleus local field potentials (STN-LFPs)) will be recorded from the Medtronic Percept Deep Brain Stimulation system. Freezing of gait (FOG) episodes will be marked by a clinician, and change in STN-LFP power fluctuations from single-task walking compared to FOG episodes will be analyzed as the primary outcome.

Secondary outcomes

• Number of FOG episodes during the MOVE system modules under each of the four DBS conditions [Five sessions completed from enrollment to the end of testing, over an average of one week.]: Participants will complete motor, cognitive and dual-task modules in a virtual reality setting, Moving Overground in Virtual Environments (MOVE). The MOVE system simulates a home-setting, allowing for acquisition of real-world, at-home behavior. It consists of four modules: 1) Reference, 2) Physical, 3) Anxiety, 4) Cognitive (dual-task). Freezing of gait (FOG) episodes usually occur under stressful circumstances which can be grouped into three broad categories: changes in physical environment, anxiety-provoking situations and dual-task environments. The modules in the MOVE system are designed to elicit FOG episodes in a research setting. FOG episodes will be marked by a clinician, and the number of episodes under each of the four DBS conditions will be compared.
• Overall time for SAFE-Gait task [Five sessions completed from enrollment to the end of testing, over an average of one week.]: Participants will complete the Cleveland Clinic Stair Ambulation and Functional Evaluation of Gait (SAFE-Gait). The SAFE-Gait test requires participants to 1) ascend 3 standard steps, 2) walk on a flat surface for 3 meters, 3) turn and 4) walk back to the starting position which requires descending 3 steps. The time to complete this task will be recorded and compared for all tested DBS conditions.

Sex: All, ages: 18 Years to any

Inclusion Criteria:

* You have been diagnosed with Parkinson's disease
* You already have a deep brain stimulation (DBS) device implanted as part of your medical care - specifically, the Medtronic Percept DBS device
* Your DBS settings have been stable for at least 3 months
* You experience freezing of gait (sudden inability to move your feet when trying to walk)
* You are able to walk on your own for at least 10 minutes without assistance
* You are willing to temporarily stop your Parkinson's medications and have your DBS settings adjusted for study testing
* You are able to understand the study and provide consent to participate

Exclusion Criteria:

* You have a neurological condition other than Parkinson's disease (such as stroke or multiple sclerosis)
* You have been diagnosed with dementia or have difficulty understanding the study or giving consent
* You currently have alcohol or substance abuse problems
* You have hearing or vision problems that would make it difficult to use a virtual reality headset
* You have any medical or mental health condition that, in the opinion of the study doctor, would make it unsafe or difficult for you to participate

• Jay L Alberts, PhD, Principal investigator, The Cleveland Clinic