Schizophrenia is formally characterized by three symptom clusters: positive, negative, and cognitive (van Os and Kapur, 2009). The positive-symptom dimension includes psychosis (i.e., paranoid delusions and auditory hallucinations); the negative-symptom dimension includes social withdrawal, lack of motivation, and difficulties in social interaction; and, the cognitive-symptom dimension refer to problems in attention, thought, perception, learning, and memory. Within the cluster of these symptoms-based diagnostic categories, which include other psychotic disorders, the term schizophrenia is used to define a syndrome characterized by prolonged periods of psychosis with bizarre delusions, negative symptoms and few affective (mania or depression) symptoms. The age at onset is typically in adolescence or early adulthood. Current medications provide relief only from positive symptoms without effective improvements in negative and cognitive symptoms (Leucht et al., 2009).
