Objective: To investigate how impulsive decision making is modulated by regular dopaminergic medication and by switching between active contacts of subthalamic nucleus stimulation

Background: Impulsive behavior is a potential side effect of both dopaminergic treatment and deep brain stimulation (DBS) of the subthalamic nucleus (STN) in patients with Parkinson’s disease (PD). Impulsive decisions underlying such behavior, may be driven by increased risk taking and/or hasty decisions. We hypothesized that changes in both stimulation and medication may result in higher risk taking and faster decisions depending on the presented odds.

Method: We studied twenty-five participants with PD who underwent DBS surgery. Six to twenty-four months postoperatively, participants underwent repeated assessments of the Cambridge Gambling Task, a paradigm suited to assess decision making under uncertainty and risk taking behavior. On two days, patients performed the paradigm under five different medication/stimulation settings: without medication and active (MED OFF STIM ON) or inactive stimulation (MED OFF STIM OFF), as well as with medication and active stimulation (MED ON STIM ON) or standardized stimulation of the most ventral (MED ON STIM V) or most dorsal contact (MED ON STIM D). The dependent variables were decision times (in ms) and risk taking, described as the mean proportion of current points gambled by the participant. We applied a linear mixed models for repeated measures using STIMULATION, MEDICATION, and the presented ODDS (i.e. 9:1, 8:2, 7:3, 6:4, 5:5) as fixed factors.

Results: We found a significant effect of CONDITION and ODDS on risk taking, while no significant interaction was found. Planned post-hoc analysis revealed significantly higher bets in the MED ON STIM ON vs. MED OFF STIM ON condition. Further, higher bets were placed in the MED ON STIM V conditions compared to MED ON STIM D. Risk taking gradually decreased with more even odds. Further, a significant effect of ODDS and CONDITION on decision time was observed. Post-hoc analysis showed increased decision latency in the MED ON STIM V compared to all other conditions.

Conclusion: Our results show that both dopaminergic medication and DBS of the STN, especially under ventral stimulation, can increase task-based risk taking. Unexpectedly, the latency to take decisions was pronouncedly increased with ventral stimulation.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/influence-of-dopaminergig-medication-and-subthalamic-nucleus-deep-brain-stimulation-on-impulsive-decision-making-in-parkinsons-disease/