Impaired event-related potential (ERP) indices reflecting performance monitoring systems have been consistently reported in patients with schizophrenia. However, whether these impairments exist from the beginning of the early phase of psychosis, such as in first-episode psychosis (FEP) patients and individuals at clinical high risk (CHR) for psychosis, has not yet been clearly ascertained.
Thirty-seven FEP patients, 22 CHR subjects, and 22 healthy controls (HCs) performed a visual go/no-go task so that three ERP components associated with performance monitoring-error-related negativity (ERN), correct response negativity (CRN) and error positivity (Pe) -could be assessed. Repeated measures analysis of variance (ANOVA) with age and sex as covariates was used to compare ERN, CRN and Pe across the groups.
Repeated measures ANOVA with age and sex as covariates revealed that compared with HCs, FEP patients and CHR subjects showed significantly smaller ERN amplitudes at the Fz (F = 4.980, p = 0.009) and FCz (F = 3.453, p = 0.037) electrode sites. Neither CRN nor Pe amplitudes showed significant differences across the FEP, CHR and HC groups.
These findings suggest that performance monitoring is already compromised during the early course of psychotic disorders, evident in FEP patients and CHR subjects, as reflected in the reduced ERN amplitude. Considering these findings, ERN could serve as a potential indicator of early-stage psychosis. This article is protected by copyright. All rights reserved.

This article is protected by copyright. All rights reserved.