Dementia is a brain condition that affects memory, thinking and daily function. There are different types of dementia including: Alzheimer's disease, and Vascular, Lewy body and Fronto-temporal dementia. These have differing features, but mostly the similarities are more important than the differences.

Dementia is characterised by progressive loss of memory plus changes in at least one other area of cognitive function, including aphasia, agnosia, apraxia or executive function. This leads to impairments in judgement, thinking, planning, reasoning and the processing of information.