Syrkin-Nikolau J, et al. - The clinicians examined subthalamic (STN) neural features of Freezers and Non-Freezers with Parkinson's disease (PD), while freely walking without freezing of gait (FOG) and during periods of FOG, which were better obtained during a novel turning and barrier gait task than during forward walking. Compared to FW, a novel turning and barrier course was superior in eliciting FOG. In Freezers, greater unpredictability in subthalamic beta rhythms was evident during stepping without freezing episodes than Non-Freezers, while greater unpredictability in alpha rhythms was evident in Freezers during FOG. During gait in freely moving people with PD, non-linear analysis of dynamic neural signals could yield greater insight into the pathophysiology of FOG; whether the increases in STN entropy were causative or compensatory remained to be determined. For rhythmic, symmetric gait and DBS parameters, some beta local field potential (LFP) power could be useful, which completely attenuated STN beta power possibly worsened FOG.

• Using an investigative, implanted, sensing neurostimulator (Activa PC + S, Medtronic, Inc.), the clinicians measured synchronous STN local field potentials (LFPs), shank angular velocities, and ground reaction forces in 14 PD subjects (8 Freezers) off medication, OFF deep brain stimulation (DBS).
• For this study, tasks included standing still, instrumented forward walking, stepping in place on dual forceplates, and instrumented walking through a turning and barrier course.

• Compared to Non-Freezers, Freezers demonstrated lower beta (13–30 Hz) power (P = 0.036) and greater beta Sample Entropy (P = 0.032) as well as greater gait asymmetry and arrhythmicity (P < 0.05 for both) during locomotion without FOG.
• At rest, no differences in alpha/beta power and/or entropy were evident.
• Freezers indicated greater alpha (8–12 Hz) Sample Entropy (P < 0.001) during periods of FOG, than during walking without FOG.