Objective: To investigate the effects of deep brain stimulation (DBS) on neural activity in patients with Parkinson’s disease (PD). Specifically, to assess the effects of stimulation of the subthalamic nucleus (STN) on phase-amplitude coupling (PAC) between electroencephalography (EEG) and STN signals, and whether this effect is only on the side of stimulation.

Background: DBS is an established treatment for PD involving implantation of electrodes in brain regions, such as the STN, to modulate neural activity. Despite the efficacy of DBS, the mechanisms underlying its therapeutic effects are not fully understood. One potential mechanism is the modulation of PAC between neural signals, which refers to the coupling between the phase of a slower oscillation and the amplitude of a faster oscillation. Previous studies have investigated the effects of DBS on PAC, but the results have been inconsistent. The findings of this study could provide insight into the mechanisms underlying the therapeutic effects of DBS and inform future interventions.

Method: Six PD patients were tested 1-3 days post DBS surgery. The data collected included EEG and LFP recordings through externalized DBS leads. PAC was measured (OFF-medication) as a function of Time (pre-stimulation, during DBS & post-stimulation) x hemisphere side (Left & Right). Pre and Post-stimulation recordings were five minutes where DBS was applied for 7 minutes. EEG was recorded from different electrodes (Cz, C3, C4, Fz, F3, F4, Pz, P3, P4). DBS was be applied to the left STN with one contact of the electrode being the cathode and a surface electrode placed on the chest wall as anode, similar to the usual monopolar therapeutic configuration. The stimulation parameters were: frequency 130 Hz frequency, pulse width 60 µs and stimulation intensity 2-5 mA. PAC in EEG, STN LFP and PAC between STN and EEG were analysed within the beta-gamma range.

Results: For EEG PAC, there was a trend towards an increase in PAC after stimulation, regardless of hemisphere. For STN PAC, there was an increase in PAC during and after stimulation, particularly on the side of stimulation (left STN). Finally, STN-EEG (Left STN- C3, Right STN- C4) analyses showed a clear trend towards increased PAC after stimulation.

Conclusion: While data collection is ongoing, the results thus far suggests that DBS changes PAC in patients. Changes in PAC may be related to the therapeutic mechanisms of DBS.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/effects-of-subthalamic-nucleus-deep-brain-stimulation-on-phase-amplitude-coupling-in-parkinsons-disease/