Alzheimer's disease brain tissue, light micrograph. Two characteristic features of Alzheimer's disease are seen here; neurofibrillary tangles (dark teardrop shapes) and amyloid plaques (rounded brown agglomerations). Alzheimer's disease is a degenerative disease of the brain, and is the most common cause of dementia. It causes progressive memory loss, impaired intellect, loss of co-ordination and an inexorable decline in the ability to perform daily tasks. The cause of the condition is not known and there is no cure, although some drugs can alleviate some of the symptoms.