EP 60. Bicycling suppresses beta power more strongly than walking in the subthalamic nucleus of Parkinsonian patients

Abstract

Introduction Walking abilities are severely affected in patients suffering from Freezing of Gait (FOG), a common phenomenon in advanced Parkinson’s disease (PD). Despite the high occurrence of the symptom in the progression of the disease, little is known about the underlying mechanisms. Remarkably, it was recently reported that patients with FOG are still able to ride a bike ( [Snijders et al., 2011] , [Snijders et al., 2012] ). While similar brain networks are involved in walking and bicycling ( [Fukuyama et al., 1997] , [Christensen et al., 2002] ), it is not understood why both types of movement are differently affected in patients with FOG. Therefore, this study aimed to investigate neural oscillations underlying bicycling and walking in PD patients. Patients and methods Seven PD patients (mean age 55.4±6.3 y) clinically selected for bilateral deep brain stimulation (DBS) therapy were included in the study. Using a portable EEG system (Porti, TMSi, Enschede, The Netherlands), local field potentials from the subthalamic nucleus (STN) were recorded using externalised leads the day after implantation of DBS electrodes. Patients were recorded while OFF any dopaminergic medication during unconstrained bicycling and walking on a stationary bicycle. The paradigm consisted of a baseline rest period, continuous movement, and an alternating sequence of rest and movement, i.e. bicycling or walking, in order to study both movement initiation and movement termination. For each STN the bipolar channel with the highest baseline beta peak power was selected for further analyses. Three of 14 STNs had to be excluded because of movement artefact contamination and a broken externalised lead in one patient. Differences were determined using cluster-based permutation tests as implemented in the FieldTrip analysis toolbox ( Oostenveld et al., 2011 ). Results Movement initiation was accompanied by power decreases in the alpha–beta range (8–35 Hz) in bicycling and walking. Contrasting both conditions revealed a stronger beta power decrease in bicycling (p 0.05). Conclusions Our finding that bicycling leads to a stronger power decrease in the beta band than walking is particularly interesting as Parkinson’s disease is generally associated with abnormally increased beta band activity in the corticobasal ganglia loop ( Oswal et al., 2013 ). The difference between oscillatory activity underlying bicycling and walking was specific to beta power suppression during movement, whereas beta rebound after movement termination was equally strong. In this sense, bicycling seems to promote the suppression of pathological oscillations in the basal ganglia, as opposed to walking. This may be due to the more continuous movement in bicycling with both legs being pushed forward permanently. In walking, stance and swing phases alternate. Therefore, one may speculate that bicycling may be less hampered in FOG because the more continuous nature of this movement promotes beta suppression and thus, facilitates movement.