Hallucinations can occur in two ways: first, functional mental disorders; second, organic mental disorders. Functional mental disorders can occur when the patient is under strong stimulation, such as fear or excitement, or has a hereditary mental illness, such as schizophrenia, and will be prone to hallucinations and delusions, and will have visual hallucinations and auditory hallucinations. In case of organic mental disorder, its caused by organic diseases of the brain, such as viral encephalitis, traumatic brain injury to the frontal and temporal lobes or advanced stages of Alzheimer’s or Parkinson’s disease, will lead to abnormalities in the higher centers in charge of cognitive functions and emotions, and hallucinations and delusions will occur, generally visual hallucinations are more common. The improvement of cranial MRI and EEG can help to identify functional and organic psychiatric disorders.