Book excerpt: Schizophrenia is a chronic, severe, and disabling psychosis, which is an impairment of thinking in which the interpretation of reality is abnormal. Psychosis is a symptom of a disordered brain. Approximately One percent of the population worldwide develops schizophrenia during their lifetime. Although schizophrenia affects men and women with equal frequency, the disorder often appears earlier in men, usually in the late teens or early twenties, than in women, who are generally affected in the twenties to early thirties. People with schizophrenia often suffer symptoms such as hearing internal voices not heard by others, or believing that other people are reading their minds, controlling their thoughts, or plotting to harm them. The current evidence concerning the causes of schizophrenia are many. It is quite clear that multiple factors are involved. These include changes in the chemistry of the brain, changes in the structure of the brain, and genetic factors. Viral infections and head injuries may also play a role. New molecular tools and modern statistical analyses allow focusing in on particular genes that might make people more susceptible to schizophrenia by affecting, for example, brain development or neurotransmitter systems governing brain functioning. State-of-the-art imaging techniques are being used to study the living brain. They have recently revealed specific, subtle abnormalities in the structure and function of the brains of patients with schizophrenia. In other imaging studies, early biochemical changes that may precede the onset of disease symptoms have been noted, prompting examination of the neural circuits that are most likely to be involved in producing those symptoms. This book presents new and important research in the field.