Schizophrenia. Positron emission tomography (PET) scan of the brain (temporal lobe) of an hallucina- ting patient suffering from schizophrenia. This colour-coded cerebral layer scan shows brain activity: from low (blue) to high (yellow). PET scanning relies on an injected radioactive tracer to show metabolic activity in the brain. Normal brain metabolic activity produces a roughly symmetrical pattern in the yellow areas of left and right cerebral hemispheres (see P332/148). PET scanning shows abnormalities of function in the brains of schizophrenics. Schizophrenia is characterised by delusions, hallucination and depression.