Objective: To study the mesocorticolimbic reward system in Parkinson’s disease (PD) patients with and without REM sleep behavior disorder (RBD).

Background: RBD is a parasomnia observed in up to 60 % of PD patients.  A greater risk of impulse control disorders (ICD) has been reported in PD with RBD, suggesting a more severe mesocorticolimbic impairment in these patients (1).

Methods: Sixty six participants were included: 22 PD with RBD (PD-RBD); 22 PD without RBD (PD-noRBD) and 22 healthy volunteers,  age and sex matched [Table 1]. RBD was diagnosed by video polysomnographic recording according to the ICSD-3 criteria. Subjects with ICD, depression or apathy were excluded. We compared brain activation in the three groups using a functional MRI paradigm named “monetary incentive delay task” [Figure 1]. The latter explore the reward system during anticipation and reception of a monetary reward. Brain activation was measured by the BOLD effect, voxel by voxel in the whole brain and in regions of interest (ROI) within the reward system. ROIs are chosen from independent whole brain analysis (2): midbrain, striatum, insula, anterior cingulate cortex (ACC), orbitofrontal cortex (OFC).

Results: In whole brain analysis, reward system were found to be less activated in PD-RBD patients when a reward was anticipated or received. Significant différences were observed in the ACC, the parahippocampal gyrus, and the caudate (p <0.001 uncorrected). ROI analysis showed lower activation of reward system in PD-RBD group during the two different phases of reward. During monetary anticipation, caudate nucleus, insula, ACC and OFC were less activated in PD-RBD group than both PD-noRBD and healthy control (p<0.03) [Figure 2]. For reward outcome, nucleus accumbens and OFC were less activated in PD-RBD group (p<0.02) compared to the other groups [Figure 3].

Conclusions: The present study found a hypoactivation of the reward system in PD patients with RBD compared to those without RBD. These abnormalities may play a role in the increased risk for ICD previously observed in PD patients with RBD, further supporting the notion of an association between RBD and ICD in PD.

References: 1.         Fantini ML, Macedo L, Zibetti M, Sarchioto M, Vidal T, Pereira B, et al. Increased risk of impulse control symptoms in Parkinson’s disease with REM sleep behaviour disorder. J Neurol Neurosurg Psychiatry. 2015 Feb 1;86(2):174–9.

2.         Sescousse G, Redouté J, Dreher J-C. The Architecture of Reward Value Coding in the Human Orbitofrontal Cortex. J Neurosci. 2010 Sep 29;30(39):13095–104.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/abnormal-activity-in-reward-system-in-parkinsons-disease-patients-with-rapid-eye-movement-sleep-behavior-disorder/