Schizophrenia is a complex and puzzling disease because it is characterized by a multiplicity of symptoms affecting most aspects of human cognition, emotion, and behaviour. Patients may experience abnormal perceptions such as auditory hallucinations, subjectively feel that their thoughts and emotions have been taken from them, or believe that their ideas, feelings, and movements are under the influence or possession of some malevolent outside force. They may experience intense emotions such as anger, display shallow silly emotions, or seem completely impoverished of emotion. Their speech may be normal and logical, disorganized and confused, or empty and laconic. In motoric activity they may be agitated and restless, manifest stereotypes or repetitive behaviour, or sit inactively or even in a stupor. Their personal relationships may be marred by intense jealousy and suspicion and fear, or disinterest and apathy. Finding an integrative explanation for this diversity of signs and symptoms is the fundamental question that has perplexed investigators and clinicians since the time of Kraepelin.