Limbic hypoconnectivity in idiopathic REM sleep behaviour disorder with impulse control disorders

Introduction Current neuroimaging research has revealed several brain alterations in idiopathic REM sleep behaviour disorder (iRBD) that mirror and precede those reported in PD. However, none have specifically addressed the presence of changes across the reward system, and their role in the emergence of impulse control disorders (ICDs). We aimed to compare the volumetric and functional connectivity characteristics of the reward system in relation to the psychobehavioral profile of patients with iRBD versus healthy controls and PD patients. Methods Twenty patients with polysomnography confirmed iRBD along with 17 PD patients and 14 healthy controls (HC) underwent structural and functional resting-state brain MRI analysis. Participants completed the questionnaire for impulsive-compulsive disorders in PD (QUIP), the short UPPS-P impulsive behaviour scale, as well as neuropsychological testing of cognitive function. Results A higher percentage of iRBD patients reported hypersexuality, compared to HC and PD (p = 0.008). Whole-brain and striatal voxel-based morphometry analyses showed no significant clusters of reduced grey matter volume between groups. However, iRBD compared to HC demonstrated functional hypoconnectivity between the limbic striatum and temporo-occipital regions. Furthermore, the presence of ICDs correlated with hypoconnectivity between the limbic striatum and clusters located in cuneus, lingual and fusiform gyrus. Conclusion Altered functional connectivity between the limbic striatum and posterior cortical regions was associated with increased hypersexuality in iRBD. It is possible that this change may ultimately predispose individuals to the emergence of ICDs when they receive dopaminergic medications, after transitioning to PD.

Automated summary

Research compared brain alterations in the reward system between idiopathic REM sleep behavior disorder (iRBD) patients, healthy controls, and PD patients, finding differences in volumetric and functional connectivity characteristics, particularly in relation to hypersexuality. The presence of impulse control disorders (ICDs) correlated with altered functional connectivity within the reward system.