Objective: Identifying the effect of dopamine on subthalamic theta oscillations in Parkinson’s disease (PD).

Background: Understanding the underlying electrophysiological alterations in PD is essential for the optimization of treatment options, in particular for closed loop deep brain stimulation. Many studies reported symptom-related alterations in beta (13-30 Hz) and gamma oscillations (>30 Hz) in the basal-ganglia-cortical networks. However, recent findings showed subthalamic theta oscillations (4-8 Hz) in situations of behavioural conflict suggesting that they might be implicated in movement inhibition. However, it is not yet clear, whether theta oscillations play a role for ongoing movements in PD patients and whether this oscillatory activity can be modulated by dopamine.

Methods: We recorded local field potentials (LFPs) from the subthalamic nucleus (STN) of three PD patients (1 woman; 51-63 years). Patients performed an internally paced finger tapping task with and without dopaminergic medication in a post-operative interval of several days. Trial duration was 10 s in order to enable the extraction of low frequencies. After manual artefact correction and line-noise removal, we wavelet transformed the data (4 cycles) of each trial and thereafter binned power data based on the phase of the ongoing movement. The latter was determined by the instantaneous phase of the band-pass filtered accelerometer data in the trial-specific peak tapping frequency. The data was baseline corrected with the average frequency-specific power during rest.

Results: A non-parametric cluster-based permutation analysis demonstrated enhanced STN theta power (4-6 Hz) at specific phases of the ongoing movement in each patient, which was diminished when dopamine was administered. Our data indicate that this STN theta activity was not related to tremor. First, none of the patients exhibited any resting tremor during testing, independent of dopaminergic medication. Furthermore, inspection of both, low and high frequency electromyographic activity did not exhibit any spectral peaks besides the tapping frequency.

Conclusions: In summary, our data suggest that PD-related oscillatory changes within the STN exceed the beta and gamma spectrum and pave promising avenues for future research.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/subthalamic-theta-oscillations-in-parkinsons-disease/