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  • Deep Brain Stimulation of the Subthalamic Nucleus in Parkinson's Disease Induces Impulsivity through Modulation of the Value of Sensory Information

    Final Number:

    Dennis London M.D.; Michael Pourfar MD; Alon Y. Mogilner MD

    Study Design:

    Subject Category:

    Meeting: Congress of Neurological Surgeons 2017 Annual Meeting

    Introduction: In addition to its motor functions, the subthalamic nucleus (STN) has a cognitive role in inhibiting impulsivity. Previous studies have suggested that the STN raises the evidence threshold for making decisions.

    Methods: We tested this theory in 8 patients receiving bilateral DBS of the STN using an auditory task (n=5085 trials) in which subjects listen to bilaterally presented “clicks” and decide which side has more. Subjects’ decision-making could be interrupted prior to reaching their evidence threshold, resulting in non-reaction time (non-RT) trials. Non-interrupted trials are RT trials. The statistics of stimulus presentation and trial ending were designed so that subjects could not predict when these events would occur, resulting in evidence accumulation to a bound.

    Results: We expected performance to decline in the DBS ON compared to the OFF condition on trials where subjects hit their decision bound (RT trials). However, DBS caused a performance decrease in only leftward RT trials (p=1.82 * 10-4, Fisher’s exact test). Drift-diffusion modeling showed that DBS caused 6/8 subjects to increase the value of clicks that occur temporally close to other clicks. There was no clear effect on decision bound. Using model-free analysis, we found that subjects responded impulsively to bursts of evidence that were associated with high levels of conflicting evidence. In addition, DBS caused subjects to paradoxically become more likely to hit their decision threshold after an error; there was an increased likelihood that an RT trial followed an incorrect RT trial when DBS was ON (p=0.0050, Fisher’s exact test), but errors did not cause a difference when DBS was OFF (0.58, Fisher’s exact test).

    Conclusions: While DBS of the STN may lower the decision bound, our data suggests that it may also prevent premature responses to bursts of evidence that portend conflict. It likely also has a role in preventing post-error impulsivity.

    Patient Care: This research will allow a better understanding of the effect of DBS on impulsive decision-making. It will allow future exploration of how the cognitive side effects of DBS can be mitigated.

    Learning Objectives: By the conclusion of this session, participants should be able to: 1) understand that DBS of the STN can cause impulsivity, 2) understand what decision-making parameters can be altered by DBS, and 3) understand how DBS can affect how patients react to errors.

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