The onset of dementia is mostly slow and insidious. Memory loss is the main core symptom. Early on, near memory impairment occurs, the ability to learn new things is significantly diminished, and in severe cases, the person cannot even find his way home. As the disease progresses further, distant memory is also impaired. Thinking is slow and impoverished, comprehension and judgment of general things become increasingly poor, attention is increasingly impaired, time, place and person orientation disorders may occur, and sometimes the inability to write and identify people occurs. Another early symptom of dementia is a decreased ability to learn new knowledge and acquire new skills. The ability to think abstractly, generalize, synthesize, analyze and judge is progressively diminished. Impairment of memory and judgment can appear as a definite impairment, and patients lose the ability to recognize time, place, people and even themselves. Therefore, the patient is often indistinguishable between day and night, and does not know the way back or wanders aimlessly. Emotionally, patients may experience emotional instability in the early stages and gradually become indifferent and sluggish as the disease evolves. Sometimes emotions lose control and become shallow and changeable. Patients may become anxious, depressed, or indifferent, or angry, cry and laugh easily, and cannot control themselves. Some patients may first experience personality changes. They usually show reduced interest, poor initiative, and social withdrawal, but may also show disinhibited behaviors, such as impulsivity and childish behavior. Patients have impaired social functioning and are unable to perform tasks that they are familiar with. In the late stage, the patient is unable to take care of himself/herself and gradually loses motor functions, even needs assistance in dressing, bathing, eating and urinating and defecating. Mania and hallucinations may even occur.