What part of the brain is affected if visual and auditory hallucinations and delusions appear in an elderly person?

If part of psychosis: That is a symptom of dementia due to alzheimer's disease or many small brain infarctions (multi-infarct dementia), there exists death of brain cells in many areas of the brain, but areas where cells are replaced by 'amyloid plaques and tangles' are usually concentrated in an area of the brain called the hippocampus. Once judgment, behavior, psychosis, hallucinations occur, it has spread to cortex.