https://yourbrainmatters.org.au/about-dementia/what-is-dementia
Dementia describes a collection of symptoms that are caused by disorders affecting the brain. It is not one specific disease. Dementia affects thinking, behaviour and the ability to perform every day tasks. Brain function is affected enough to interfere with the person’s normal social or working life. The hallmark of dementia is the inability to carry out everyday activities as a consequence of diminished cognitive (thinking) ability.
Doctors diagnose dementia if two or more cognitive functions are significantly impaired. The cognitive functions that may be affected include:
memory
language skills
understanding of information
spatial skills
judgement
attention
People with dementia may have difficulty solving problems and controlling their emotions. They may experience personality changes, agitation, delusions or hallucinations.
Dementia is usually progressive. This means that the disease gradually spreads through the brain and the person’s symptoms get worse over time.