Objective: To assess the effects of deep brain stimulation (DBS) on effort and reward processing for self-benefitting and prosocial behavior in people with Parkinson’s Disease (PwPD).

Background: Reward and effort evaluation is integral to healthy decision-making. Computing this trade-off becomes further complex in prosocial contexts, when the expended effort yields a benefit for others rather than for oneself. Reward processing is altered in neuropsychiatric conditions like PD. DBS provides well-established treatment for PD via stimulation of the basal ganglia structures implicated in reward processing. However, whether and how DBS affects reward and effort evaluation in prosocial contexts remains unknown.

Method: 18 PwPD with DBS (age=62.3±10.4, 17 M, 2 F, 13 STN, 5 GPi) completed a prosocial motivation computer task. Participants chose between winning one point for no physical effort or more points for more effort (5 reward and 5 effort levels), with half of trials for themselves and half for another participant [1]. Subjects completed one session DBS on and one DBS off, with 150 trials in each session. Wilcoxon signed rank tests were used to compare group level behavior between self/other choices. A generalized linear mixed effects model (GLMM) further assessed the effects of DBS, effort, reward, and recipient and their interaction on choice.

Results: Participants accepted more trials that won points for themselves than trials that benefitted another person (p=0.01), exerted less force when deciding to help others (p=0.02), and took longer to make a choice when the reward benefitted another person (p<0.01). The GLMM revealed PwPD accepted more trials as the reward increased (p<0.001) and rejected more trials as the effort increased (p<0.001). These results corroborate what has been found previously in both healthy controls and PwPD [1,2]. DBS significantly affected the relationship between reward and acceptance (Fig. 1), showing people were more likely to accept trials with increasing reward when DBS was on (p<0.001). DBS did not alter behavior on self-benefitting vs. prosocial choices (p=0.76).

Conclusion: PwPD off DBS exhibit typical behavior, accepting more trials as reward increases. When DBS is on, it enhances the likelihood of accepting high reward trials. These findings further our understanding of how DBS affects reward evaluation and highlight the need to elucidate the neural mechanisms of these effects.

Percentage of trials accepted for DBS on and off.

References: [1] Lockwood, Patricia L., et al. “Distinct neural representations for prosocial and self-benefiting effort.” Current Biology 32.19 (2022): 4172-4185
[2] Talbot, Jamie, et al. “Dopamine boosts motivation for prosocial effort in Parkinson’s disease.” Journal of Neuroscience (2025)

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MDS Abstracts - https://www.mdsabstracts.org/abstract/deep-brain-stimulation-increases-motivation-to-obtain-larger-rewards-in-parkinsons-disease/