Positron emission tomography (PET) scan of the brain (cerebellum level) of an unknown type of dementia. The cerebellum is at left. The colour- coded scan through this area shows brain activity: from low (blue) to high (yellow). PET scanning relies on an injected radioactive tracer to reveal variations in metabolic activity in the brain. In this unknown form of dementia, due to cerebellar dysfunction, speech comprehension and social abilities were seriously impaired. Disease or damage to the cerebellum can cause jerky, uncoord- inated movements and slurred speech. Alcohol abuse may be a cause, although dementia is frequently a progressive brain disease of the elderly.