Introduction: Prominent beta band oscillations have been observed in Parkinson's disease (PD) in the STN and GPi, and proposed as closed-loop signal controls for DBS therapy. The GPi is a less studied target than the STN and human basal ganglia physiology has rarely been compared across different disease states. We test the hypothesis that resting state LFP characteristics distinguish the parkinsonian state from segmental and generalized dystonia.
Methods: Resting state GPi LFPs were recorded intraoperatively from DBS electrodes in 14 PD, 3 craniocervical dystonia (c-dys), and 4 generalized dystonia (g-dys) patients in the awake state. Alpha-beta power characteristics were calculated characterizing the peak power band at those frequencies. Phase-amplitude interactions (PAC) in both cortex and STN are increasingly recognized as potential disease biomarkers, we quantified the interaction between the amplitude of high frequency activity and alpha-beta phase as previously described (1,2).
Results: GPi LFPs demonstrated similar frequencies for the alpha-beta spectral peak, at 19.0 ± 5.8 Hz for PD, 20.5 ± 6.8 Hz for c-dys, and 17.6 ± 8.3 Hz for g-dys patients (p=0.79). The amplitude of the log spectral peak power was not significantly different (p=0.38). 8 PD, 2 c-dys, and 3 g-dys patients showed coupling between alpha-beta phase and the amplitude of a narrowband high frequency oscillation (280-360Hz). Coupling of beta phase to broadband power, as observed in the motor cortex in PD, was not found in GPi.
Conclusions: Direct comparison of GPi LFPs in PD, craniocervical, and generalized dystonia shows that all patients have peak spectral power in the beta band, casting doubt on the view that excessive beta band power is a specific biomarker of the parkinsonian state. Cross frequency interactions are also found in GPi and are not specific for disease state. The study reveals potential similarities between abnormal neural network activity and synchronization in PD and dystonia.
Patient Care: Discovery of disease-specific biomarkers for movement disorders will not only generate new insights into the pathophysiology of various movement disorders, but will lead to future design for a “closed loop” system whereby stimulation will be driven by the pathological signal to improve the efficacy of DBS therapy.
Learning Objectives: By the end of this session, participants should be able to:
1) describe GPi LFP power spectral characteristics in Parkinson’s disease, segmental, and generalized dystonia
2) identify phase-amplitude coupling in all 3 diseases
3) gain a better understanding of the abnormal network activity in movement disorders
References: 1) Lopez-Azcarate J, Tainta M, Rodriguez-Oroz MC, Valencia M, Gonzalez R, Guridi J, Iriarte J, Obeso JA, Artieda J, Alegre M. Coupling between beta and high-frequency activity in the human subthalamic nucleus may be a pathophysiological mechanism in Parkinson's disease. The Journal of neuroscience : the official journal of the Society for Neuroscience. 2010;30(19):6667-77.
2) de Hemptinne C, Ryapolova-Webb ES, Air EL, Garcia PA, Miller KJ, Ojemann JG, Ostrem JL, Galifianakis NB, Starr PA. Exaggerated phase-amplitude coupling in the primary motor cortex in Parkinson disease. Proc Natl Acad Sci U S A. 2013;110(12):4780-5.