Basic symptoms of psychosis-from historical foundations to current evidence.
PURPOSE Psychoses are among the most debilitating mental disorders, making early detection a major public health priority. In extension of the ultra-high-risk (UHR) approach, which was developed to identify an imminent risk of psychosis, the basic symptom (BS) approach aims for the earliest possible detection of the developing disorder; it is increasingly used worldwide. Basic symptoms are subtle, self-perceived disturbances affecting various domains, such as cognition, perception, affect, and drive, that precede and scaffold the development of attenuated and frank psychotic symptoms. METHODS AND RESULTS This narrative review outlines historical foundations, phenomenology, and assessment instruments for BSs. It summarizes empirical findings on their predictive value for subsequent psychosis and their specificity for psychotic disorders across all age groups. Furthermore, developmental aspects and neurobiological findings are highlighted that support one of the core assumptions of the BS concept, namely, that BSs represent the most immediate phenomenological manifestation of the cerebral alterations underlying the development of psychosis. Finally, evidence for the broader clinical significance of BSs beyond psychosis prediction is discussed, indicating that BSs as a whole are useful for both multi- and differential-diagnostic purposes. CONCLUSION Overall, the reviewed findings underline the value of BSs for advancing neurobiological research on the etiopathology of psychoses and for developing individualized prediction models and targeted early interventions.