Early psychosis is a concept that includes first episode psychosis (FEP) and high-risk status for developing psychosis, i. e., at-risk mental state (ARMS). FEP refers to the first experience of sustained positive psychotic symptoms (1 week or more) due to conditions such as schizophrenia, schizophreniform disorder, schizoaffective disorder, or mood disorders with psychotic symptoms. Reduction of the duration of untreated psychosis (DUP) by early detection of FEP and adequate treatment during the 'critical period' (first 2-5 years of psychosis) are thought to be important to improve the long-term clinical outcome. ARMS, which is defined using major rating systems such as the Comprehensive Assessment of At Risk Mental State (CAARMS) and the Structured Interview for Prodromal Symptoms (SIPS/SOPS), is a clinical condition characterized by the possible development of a psychotic disorder. Individuals with ARMS have a higher risk of developing psychosis, such as schizophrenia (approximately 60% of the individuals who developed psychosis), within a relatively short period of time (approximately 30% at 2 years). As both FEP and ARMS are diagnosed based on clinical symptoms, the main purpose of brain imaging and neurophysiological tests for these patients in the clinical setting is the diagnosis of organic brain disorders. On the other hand, increasing evidence from brain magnetic resonance imaging and electroencephalograms, especially event-related potential studies, has suggested the possible clinical applicability of biomarkers, particularly for the diagnosis of schizophrenia, i. e., differentiation from healthy controls, and prediction of future psychosis in high-risk subjects.
 <Author's abstract>