Freezing of gait-related oscillatory activity in the human subthalamic nucleus

Gait problems cause severe disability for patients with Parkinson's disease (PD), especially during the late stages of the disease. The crucial nuclei for the motor symptoms of PD are the basal ganglia and therefore investigations of the physiology of these structures during gait are warranted. We investigated electric local field potentials of the subthalamic nucleus of PD patients recorded from deep brain stimulation electrodes during walking on a treadmill. Three patients showed a normal albeit slow gait pattern, whereas three other patients displayed severe gait hesitations (freezing). Patients without freezing showed a reduction of oscillations throughout the whole beta frequency band (12-35. Hz) during walking as compared to standing or sitting. By contrast, oscillations in freezers in the lower beta frequency (12-22. Hz) were significantly enhanced during walking. Both groups displayed an increase of gamma oscillations (60-90. Hz) during walking. Our results show for the first time that an increase in lower beta band oscillation is highly correlated and possibly the causal mechanism for severe akinesia in PD. The freezing phenomenon may be based on an insufficient suppression of oscillations in the lower beta frequency range. These findings may have implications for future therapies involving closed-loop neurostimulation devices.