Objectives Idiopathic rapid eye movement sleep behavior disorder (IRBD) patients are prone to cognitive deficits, which include attention, executive, and visuospatial dysfunctions. Even patients with normal cognition may exhibit subclinical electrophysiological dysfunction. This study aimed to evaluate visuospatial attention processing in IRBD patients with normal cognition and to compare their findings with those of age- and sex-matched healthy controls. Methods We recorded event-related potentials (ERPs) and performance measures during a variant of the Posner task in 14 IRBD patients and 14 control subjects. Behavioral data and the mean P300 amplitude were compared between groups. Results No group difference was found for reaction time or accuracy, but a significant group effect was observed for the P300 amplitude. IRBD patients had reduced P300 amplitude (μV) than controls in both valid (IRBD: 0.53 ± 1.05 vs Controls: 1.61 ± 0.95; p = 0.008) and invalid (IRBD: 0.74 ± 0.99 vs Controls: 1.73 ± 0.86; p = 0.009) conditions. The P300 amplitude was correlated with Montreal cognitive assessment (MOCA) scores (r = 0.424, p = 0.024). Conclusion Reduced P300 amplitude during the Posner task provides electrophysiological evidence for subclinical visuospatial attention deficits in cognitively normal IRBD patients. The results of this study imply that cortical dysfunction is already present in patients with IRBD in their early disease stage.
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