Objective: To assess EEG changes in PD patients during episodes of FOG.

Background: FOG is a paroxysmal phenomenon, a brief episodic marked reduction in forward progression of the feet despite intention to walk. Prevalence is up to 60% in advanced PD. The pathophysiology of FOG remains poorly understood, no single comprehensive model is accepted. Stepping in place (SIP) is a validated gait surrogate used for studying FOG [1].

Methods: We recruited 16 people with PD (PwP) from the Mater Misericordiae University Hospital, Dublin, Ireland. 9 PwP were diagnosed with FOG and 7 PwP formed the disease-matched control group. All PwP underwent clinical and neuro-psychological pre-assessments. PwP performed a cognitive task while navigating through a virtual reality (VR) corridor by SIP on a pressure plate. 128-channel EEG was recorded and the electrodes were grouped in multiple regions of interest (ROI). The cognitive task consisted of a visual oddball stimulus presented on the display during VR environment navigation. Reaction times and missed target rates were recorded.

Results: Reaction times did not significantly differ between the FOG+ and FOG- groups, in the seated response task. In the stepping in place VR task, the FOG+ group showed longer reaction times and a higher rate of missed targets. Analysis of the EEG data revealed no significant difference in P3 amplitude or latency between groups. The N2 response was present in the FOG+ group over the central ROI while seated but this response vanished during SIP. The FOG- group maintained the N2 response during both sitting and SIP.

Conclusions: FOG+ PwP demonstrated increased reaction times and more frequent missed targets while dual-tasking, suggesting a conflict or prioritization of gait over the cognitive task. Loss of the N2 response in FOG+ patients in the central ROI, while stepping in place, could be significant in the context of FOG, as the N2 has been associated with monitoring response conflict, which is associated with FOG[2]. Ref: 1. Nantel J, de Solages C, Bronte-Stewart H Repetitive stepping in place identifies and measures freezing episodes in subjects with PD. Gait Posture. 2011 Jul;34(3):329-33. 2. Vandenbossche J et al. Conflict and freezing of gait in PD: support for a response control deficit. Neuroscience. 2012 Mar 29;206:144-54.

April 2015: 7th Annual International IEEE EMBS Conference on Neural Engineering, Montpellier, France.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/freezing-of-gait-fog-in-pd-is-electroencephalography-eeg-a-gateway-to-elucidating-the-pathophysiology/