Visual object processing in rapid-eye-movement sleep behavior disorder: An event-related potential study

Idiopathic rapid-eye-movement sleep behavior disorder (iRBD) is becoming widely considered a prodromal symptom of Parkinson's disease (PD). Visuoperceptual deficits have been described in iRBD with still conflicting results. Since this cognitive domain is often impaired in PD, it appears of great interest to better describe visuoperceptual deficits in iRBD patients. Secondly, defining the neurophysiological correlates of these deficits would bring important data on the pathophysiology of iRBD. This study aimed to study the visual object processing in iRBD patients. High-density electroencephalograms were used to record event-related potential in fourteen iRBD patients and fourteen matched healthy volunteers during a fragmented images categorization task. The task consisted in categorizing “recognizable” images as real objects, and “unrecognizable” images as non-objects. The Ncl component (negativity associated with closure) was recorded and used as a marker of incomplete objects recognition processing. Behavioral results revealed no significant differences between the 2 groups in number of correct categorization and response time. The ERPs in the control group had significantly smaller amplitude for “recognizable” compared to “unrecognizable” images from 240 to 640 ms in the left posterior scalp regions. This relative negativity (Ncl) was absent in the iRBD patients group. This study provides neurophysiological data suggesting changes in the fragmented images processing in iRBD patients.