Parkinson's disease and pathological oscillatory activity: is the beta band the bad guy? - New lessons learned from low-frequency deep brain stimulation.

A number of studies have identified pathological neural oscillations in Parkinson's disease and it is widely agreed that these excessive synchronizations are linked to the motor symptoms of Parkinson's disease (PD). However, it is still under debate if there exists a single frequency having a critical negative influence on PD symptoms and what this frequency might be. To provide experimental evidence for a causal link between beta oscillations and bradykinesia, C. C. Chen and coauthors stimulated patients with Parkinson's disease with different low frequencies while the patients were performing a grip force task [C. C. Chen, W. Y. Lin, H.L. Chan, Y.T. Hsu, P.H. Tu, S.T. Lee, S.M. Chiou, C.H. Tsai, C.S. Lu, P. Brown: Stimulation of the subthalamic region at 20 Hz slows the development of grip force in Parkinson's disease, Exp. Neurology, 2011]. In their study the authors could demonstrate a 15% slowing in the grip force task during 20 Hz stimulation, but not during stimulation with other frequencies. The finding of 20 Hz being the driving pathological frequency contrasts with previous studies using e.g. finger tapping, where 5 and 10 Hz had the largest influence. Thus, this study provides evidence that there is no single pathological oscillation frequency that is responsible for all Parkinsonian symptoms. Instead, the results indicate that the modulation of very specific frequencies leads to changes in specific performance parameters evaluated in particular tasks. In this respect, this study also provides more physiological evidence on the involvement of the STN in dynamic force production. Taken together, the study adds a further piece to the puzzle of understanding the pathophysiology of Parkinson's disease and the mechanisms of deep brain stimulation.