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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.
Contributors MF and MR contributed equally to this study. MF, MR and GG were involved in conception, organisation and execution; design and execution and writing of the first draft. SM was involved in conception; review and critique and writing of the first draft. CL was involved in conception; review and critique. DS and AF were involved in conception, organisation and execution; review and critique. CP and LR were involved in review and critique. AA, MP, GP and AP were involved in conception; review and critique.
Funding ERANET-Neuron Grant ‘PhysiolDBS’ (Neuron-48-013).
Competing interests None.
Patient consent Obtained.
Ethics approval Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico Milano.
Provenance and peer review Not commissioned; externally peer reviewed.