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Pathological gambling (PG) is an impulse control disorder that manifests in 2.2–7% of patients with Parkinson's disease (PD). Although the underlying neural mechanisms remain controversial, parkinsonian patients with PG show enhanced risk propensity, especially when assuming dopamine agonist drugs.
The dopaminergic reward circuit, a neural network that participates in developing and monitoring motivated behaviours,1 includes the subthalamic nucleus (STN). Local field potentials (LFPs) recorded from macroelectrodes implanted in the STN for deep brain stimulation (DBS) show specific low-frequency oscillations in patients with PD with impulsive control disorders at rest and in patients with PG during the preparation of conflictual economics decisions.2 ,3 No study has yet investigated STN involvement in monetary reward processing, namely the phase that follows economics decisions, when participants face the outcome of their choice in patients with PD. Besides helping to understand the mechanisms underlying PG, this knowledge could promote the optimisation of therapies for impulse control disorders.
We investigated the STN's role in risk-related monetary reward in parkinsonian patients. To do so, we studied the reward-related STN LFPs changes in patients with PD with and without PG engaged in an economics decision task.
Materials and methods
We enrolled 12 patients with PD 4 days after STN DBS macroelectrode positioning surgery as described elsewhere3 (for clinical details, see table 1 from Ref. 3, patients number 1–4, 8–12, 14, 15, 17). Of the 12 patients, 6 met the criteria for PG according to the Diagnostic and Statistical Manual of Mental Disorders (DSM IV-TR). All patients gave informed consent. The study was conducted in accordance with the Declaration of Helsinki and was approved by the institutional review board. Patients were tested with the economics decision task (figure 1A,C) during bilateral STN LFP recording from DBS macroelectrode contact pair 0–2.