REM sleep behaviour disorder and visuoperceptive dysfunction: a disorder of the ventral visual stream?

In idiopathic rapid eye movement sleep behaviour disorder (RBD), an association with visuoperceptive disorders has been described. However, such an association has not been clearly established in RBD secondary to Parkinson's disease (PD). We compared visuoperceptive function in four groups of non-demented patients (parkinsonian patients with or without RBD, patients with idiopathic RBD and control participants) via a procedure enabling the analysis of the various components of visual information processing and in order to answer the following question: is RBD associated with visuoperceptive and/or attentional disorders in PD and, if so, where is the dysfunction located along the visual pathway? Sensorial aspects of visual information were evaluated using a contrast sensitivity test, perceptual aspects were assessed using a contour-based object identification test and visual attention was measured in an attentional capture paradigm. The diagnosis of RBD was confirmed by polysomnography. We observed a higher object identification threshold (OIT) (1) in PD patients with RBD compared with PD patients without RBD and with controls and (2) in idiopathic RBD patients compared with controls. There were no significant OIT differences between PD patients with RBD and idiopathic RBD patients or between PD patients without RBD and controls. We did not find any significant inter-group differences in any of the other visuoperceptive tests. RBD, idiopathic or secondary to PD, is associated with perceptual closure dysfunction. Our results suggest that this perceptual dysfunction is specifically associated with RBD and may be related to a non-dopaminergic impairment.