Why do dementia patients become unable to lead a daily life with decreasing cognitive function?

In order to understand the words and deeds of dementia patients that we find very hard to explain or understand, we have paid attention to the self-awareness ability of dementia patients, the intellectual subject that integrates their own intellectual functions, and created 'a model for interpreting puzzling words and deeds of dementia patients from the viewpoint of self-awareness'. The purpose of this study is to explain the reasons why dementia patients become unable to successfully perform activities of daily living (ADL) with advancement of dementia, using our model to present viewpoints understandable to caregivers. We classified dementia inpatients of a geriatric health services facility into four stages, using the model of self-awareness ability (consisting of 'theory of mind', 'self-evaluation' and 'self-consciousness') that was constructed by combining 'theory of mind' and Lewis's developmental model of cognition and emotion. Furthermore, we observed and documented scenes from daily life, and we interpreted the reasons why patients become unable to seek assistance from others for ADL, based on the model. We came to understand why the patients could not seek assistance from others, because the patients who failed in the task of 'theory of mind' were unable to self-assess their own mind and the minds of others, and those having failed in the task of 'self-evaluation' could not evaluate their own situation.