Objective: To study the differential effects of dorsal and ventral Subthalamic nucleus (STN) stimulation on perseveration and evidence accumulation in patients with Parkinson’s disease (PD).

Background: Deep brain stimulation (DBS) of the STN is a gold standard to treat refractory PD patients. It also provides a unique opportunity to investigate the role of STN in executive functioning ranging from choice behaviour to value evaluation. Stimulation of STN has shown to induce impulsivity, in terms of response in the context of conflict and risk-aversive behaviours in highly uncertain environments. In this study, we differentially stimulate the dorsal and ventral parts of STN and investigate their effects on decision making.

Method: Twenty PD patients with electrodes implanted in the STN, with either dorsal or ventral contacts ‘ON’ completed two sessions (=134 trials) of the 2-step sequential learning task in a randomized order. We performed two independent computational analyses; the first to extract reinforcement learning parameters and 2) using behavioural measures (accuracy and response time) as input variables, we used hierarchical drift diffusion model (HDDM) to extract parameters of evidence accumulation in the context of conflict and uncertainty. Statistical analysis was performed using independent samples t-test on reinforcement learning variables and Bayesian factor on HDDM parameters.

Results: A paired samples t-test showed an increased perseveration (t(19)= -2.96, p = 0.008) due to stimulation of ventral STN. Additionally, we also show strong evidence for difference in drift rates across different conflict and uncertainty conditions (BF₁₀ =  35.85) and an interaction effect due to stimulation (BF₁₀ =  50.85). Independent samples t-test showed this effect to be driven by increased drift rate in high conflict-high uncertainty scenario (BF₁₀ = 17.22 x10⁴).

Conclusion: We show that stimulation of the ventral STN increases perseveration behaviours. It also increases the rate of evidence accumulation (drift rate) when the available choices are similar in value but highly uncertain. This result highlights the important of topology and how electrode position within the STN could influence the functional cortico-basal ganglia loops and eventually behaviour.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/differential-effect-of-dorsal-and-ventral-stn-stimulation-on-perseveration-and-evidence-accumulation/