Objective: To investigate how subthalamic nucleus local field potentials (STN-LFP) and coupling between STN-LFP and electromyogram (EMG) in static and phasic movements are modulated by the dopaminergic state in Parkinson´s disease (PD).

Background: Functional neurosurgery has allowed the recording of electrophysiological signals from deep brain structures, of which the STN has exhibited exaggerated synchrony within the β-range in unmedicated PD patients. Research indicates that STN β synchronization diminishes before movement onset and subsequently exhibits a so-called rebound after the offset. However, it is not clear to what extent the STN-LFP and the EMG signals are coupled during different motor tasks in the OFF or the ON medication states.

Methods: Eight PD patients, implanted with STN deep brain stimulation electrodes according to clinical criteria and a system to record STN-LFP via telemetry performed tonic wrist extensions (IC) and alternating wrist flexion and extensions (VAM). STN-LFP and EMG from contralateral forearm extensor muscles were recorded in the unmedicated state and after an oral Levo-Dopa challenge. Fourier and wavelet methods were used to compute the global and time-dependent frequency content of the STN signals as well as coherence between the LFP and EMG.

Results: Globally, both IC and the VAM tasks show greater synchronization in the lower β range (12-17Hz) in the OFF state. Time-frequency onset and offset plots reveal that movement-related β desynchronization happens on a lower range (13-23Hz) in the ON state and at higher frequencies (20-29Hz) in the OFF state for both tasks. Movement-dependent γ synchrony, however, occurs at lower frequencies for IC in the OFF (45-60Hz) than in the ON state (65-75Hz), while for VAM there is a broadband (40-65Hz) synchrony only in the ON state. Coherence analysis yielded significantly higher values in the 13-19Hz range for IC than for VAM regardless of medication state.

Conclusions: Our results suggest a differentiated coupling of STN and EMG activity in the β and γ band frequency range relative to motor task and dopaminergic state. In particular, there was a frequency shift of movement-dependent beta desynchronization (upwards) and gamma synchronization (downwards) in the dopaminergic OFF state.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/dopamine-and-task-dependent-evolution-of-oscillatory-activity-in-the-subthalamic-nucleus-stn-and-coupling-between-the-stn-local-field-potential-and-muscle-activity-in-parkinsons-disease/