Dementia is a syndrome characterised by progressive deterioration in mental functions, especially memory and cognition. It affects up to 5-10% of the elderly population in the west. Alzheimer's disease is the commonest form of dementia. In the past, dementia has been divided into presenile and senile dementia but the distinction is not necessary. Most of them are Alzheimer's disease. However, Alzheimer's disease occurring in the younger population is more likely to be familial and dementia in the younger group can be due to diseases other than Alzheimer's disease.

In this brain, the gross appearance of the brain reveals marked atrophy. The brain weighs lighter and there is atrophy of the gyral convolutions with widening of the sulcal spaces.