T50. Freezing of gait does not modulate neural oscillations in motor cortices

Abstract

Introduction Walking abilities are severely affected in patients with freezing of gait (FOG), a common phenomenon in advanced stages of Parkinson’s disease (PD). Despite the high occurrence of FOG, little is known about the underlying mechanisms. Interestingly, it was reported that patients with FOG are still able to ride a bike (Snijders AH et al., Bicycling breaks the ice for freezers of gait, Mov Disord 2011). While similar brain networks are involved in walking and bicycling (Fukuyama H et al., Brain functional activity during gait in normal subjects: A SPECT study, Neurosci Lett 1997; Christensen LOD et al., Cerebral activation during bicycle movements in man, Exp Brain Res 2000), it is not completely understood why both types of movement are differently affected in PD patients with FOG. A recent study from our group demonstrated that the oscillatory activity within the subthalamic nucleus (STN) differs between patients with and without FOG (Storzer L et al., Bicycling suppresses abnormal beta synchrony in the Parkinsonian basal ganglia, Ann Neurol 2017). In particular, it was shown that patients with FOG present a characteristic increase of oscillatory activity at ∼18 Hz. The aim of the study was to examine movement-associated cortical oscillatory activity in PD patients with and without FOG. Methods We analyzed EEG data of 19 PD patients with FOG (65.5 ± 7.2 years), 13 PD patients without FOG (61.6 ± 8.1 years), and 16 healthy controls (63.3 ± 7.3 years). Patients were recorded OFF dopaminergic medication using a portable EEG system (Porti, TMSi, Enschede, The Netherlands). Data were recorded during unconstrained walking and bicycling on a stationary bicycle. Measurements consisted of a baseline rest period, continuous movement, and an alternating sequence of rest and movement, i.e. bicycling or walking, for 10 s each. Furthermore, measurements included 180° turns around the body axis during walking condition. Turns were rated for the occurrence of FOG episodes by two different raters. Analyses were focused on oscillatory activity in the beta band and the Cz electrode overlying the leg area of both motor cortices. Statistical testing was performed by fitting linear mixed models using package lme 1.1–13 for R. Results Bicycling and walking were associated with beta power suppression (13–35 Hz). This suppression was stronger for bicycling than for walking ( β = −0.37, p β = −0.11, p = 0.72). Furthermore, within the group of Freezers we did not find cortical differences between turns with FOG and turns without FOG either( β = 0.66, p = 0.4). Conclusion We did not observe cortical beta power changes specifically related to freezing. This finding does not support the notion that the primary motor cortex is crucially involved in generating freezing.