Mental illness is a term used for a group of disorders that cause severe disturbances in thinking, feelings, and relationships. The result is a substantially reduced ability to cope with the ordinary demands of life. (Mental Illness Defined) There are a few different perspectives on the causes of mental illness. Perspectives include biological, psychodynamic, humanistic and existential, behavioral, cognitive, and sociocultural. Advances in brain imaging techniques have helped scientists study the role of brain structure in mental illnesses. Some studies have demonstrated brain abnormalities in some mental illnesses. Some people with schizophrenia have enlarged brain ventricles. Additionally, a variety of medical conditions can cause mental illness. Brain damage and stroke can cause memory loss, impaired concentration and speech, and unusual changes in behavior. Other factors include brain tumors, hormonal imbalance, nutritional deficiencies and viral infections. Freud believes that mental illness is caused by unconscious, unresolved conflicts in the mind. Both the humanistic and existential perspectives view abnormal behavior as resulting from a person's inability to find meaning in life and realize their potential. The behavioral perspective explains mental illness, as well as all human behavior, as a learned response to stimuli. Despite all these different theories, most modern psychologists agree that mental illness is caused by a combination of these factors. (Mental illness) Schizophrenia does not result from a single cause, but from a variety of factors. Most scientists believe that it is a biological disease caused by genetic factors, an imbalance of chemicals in the brain, structural abnormalities of the brain, or abnormalities in the prenatal environment. Additionally, stressful life events can contribute to the development of schizophrenia in those predisposed to the disease. About 1% of people develop schizophrenia at some time in their lives. An estimated 1.8 million people in the United States alone suffer from schizophrenia. (Schizophrenia) The prevalence of schizophrenia is the same regardless of gender, race and culture. For many schizophrenic patients, symptoms gradually become less severe as they age. About 25% of people with schizophrenia disappear from their symptoms later in life. Schizophrenia is characterized by a variety of symptoms. The most prominent include symptoms of psychosis, such as delusions and hallucinations, as well as bizarre behavior, strange movements, and disorganized thinking and speech. (Brain disorders: schizophrenia) Many people with schizophrenia do not recognize that their mental functioning is disturbed. Usually a family member points it out.