Objective: To compare the effects of levodopa and subthalamic nucleus stimulation (STN-DBS) on decision-making tasks for distal (hand) and axial (speech) efforts in Parkinson’s disease (PD).

Background: PD is a particularly relevant model to explore the neurobiology of decision-making. Several studies used effort-based designs to understand the effects of levodopa and STN-DBS on decision-making. However, many of these studies used hand movements, which are globally improved by treatments, and can modify attribution of subjective cost. To go beyond our previous results (Atkinson-Clement et al., submitted), we chose to include in our protocol a “speech effort”, because dysarthria in PD is usually less responsive to treatments.

Methods: We studied 9 patients with PD, who performed effort- (6 levels) and reward-based (3 levels) decision-making tasks, with both hand and speech modalities. They performed the tasks under 4 treatment conditions: on STN-DBS/on levodopa, on STN-DBS/off levodopa, off STN-DBS/on levodopa, and off STN-DBS/off levodopa. For statistics, we used generalized linear model weighted by the reward and effort values; considered variables were the following: acceptance rate, decision time, time to complete each trial and the maximal effort produced for each trial.

Results: First, patients off levodopa, with and without STN-DBS, accepted more hand efforts than speech efforts; the opposite was found under Levodopa, with and without STN-DBS. Second, shorter decision times for hand efforts were observed in comparison to speech efforts, without any effect of condition treatment. Regarding the time to complete each trial, patients without treatment needed more time to complete speech trials than hand trials; under both levodopa and STN-DBS, they needed more time for hand efforts. Finally, the maximal hand effort was increased under treatments, whereas the maximal voice effort was increased only under both levodopa and STN-DBS.

Conclusions: Our results suggest that levodopa and STN-DBS do not have the same influence on hand and speech cost valuation. Levodopa decreases the subjective cost of speech effort, without inducing any improvement of decision time or maximal effort. The condition with both STN-DBS and levodopa was the sole associated with speech production improvement (maximal effort and exerted force). In summary, brain networks of effort-based decision-making seem to depend partly on the effort nature.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/levodopa-and-subthalamic-stimulation-do-not-have-the-same-effect-on-subjective-cost-for-distal-and-axial-efforts-in-parkinsons-disease/