Non-Organic Psychosis

The goal of this clinical trial is to learn if a group therapy called the Positive Emotions Program for Schizophrenia (PEPS) can reduce apathy in adults aged 18 to 60 who have schizophrenia or a related psychotic disorder. Apathy means having little motivation or drive and getting less pleasure from daily life. The trial will also look at how the brain responds to this therapy. The main questions it aims to answer are: Do people who take part in PEPS have less apathy after the therapy than people who continue with their usual care? Does PEPS increase activity in a brain areas important for motivation? Are changes in brain activity linked to changes in apathy? Researchers will compare PEPS with usual care (regular visits with the treating psychiatrist and nurse, without PEPS) to see if PEPS reduces apathy. They will also compare brain scans of people with schizophrenia to those of healthy volunteers, to see whether brain activity after PEPS becomes more similar to that of people without the illness. Participants with schizophrenia will: * Be placed by chance into one of two groups: PEPS or usual care * Have an interview and questionnaires about their symptoms * Have an MRI brain scan while doing computer tasks * In the PEPS group, attend 8 weekly group sessions of 1 hour led by a psychologist. They will learn skills to notice, enjoy and look forward to pleasant moments, to question discouraging thoughts, and to share positive feelings with others. They will also do short exercises at home. * In the usual-care group, continue their usual care for 8 weeks. They will be offered PEPS after the study ends. * Repeat the interview and the brain scan within 2 weeks after the 8-week period