A low laugh has two meanings one refers to a personality trait and is not necessarily a precursor to Alzheimer’s disease. The other is a disease condition such as severe dementia which can be characterized by crying and laughing. Pre-dementia stage is mainly memory loss, dementia stage is characterized by a variety of ability to lose, and severe can be characterized by crying and laughing. 1. Pre-dementia stage: It is divided into pre-mild cognitive dysfunction and mild cognitive dysfunction stage. The former has no clinical manifestations or only very mild memory loss. The latter is characterized by mild memory loss and impaired ability to learn new knowledge. However, it basically does not affect daily life. 2. Stage of dementia: In the mild stage, memory loss is manifested, starting with near-term memory loss and followed by distant memory loss. In moderate cases, memory impairment worsens and behavioral and mental abnormalities occur. In severe cases, there can be crying and laughing, personality changes, inability to accomplish simple daily life events, and can be complicated by systemic systemic diseases and eventually death due to complications. Excluding the character itself cause of the low laugh, the sudden appearance of personality changes should be taken seriously, it is recommended to go to the hospital in time for a professional examination, a clear diagnosis, and early treatment.