However, scientists have not been able to show any correlation between the number of plaques in the brain and the loss of neurons or with the degree of dementia. Normal elderly people can also have plaques without showing loss of memory. So the role of the beta-amyloid peptide in the disease is unclear. Whether the aggregation of the beta-amyloid peptide is the cause or a secondary event in Alzheimer's disease is an area of active study. The other characteristic feature of an Alzheimer's brain is the presence of tangles.
Tangles are abnormal twisted fibers that accumulate within neurons.
Tangles are made up of a protein called tau, which normally helps to stabilize the neurons' structure or cytoskeleton. In Alzheimer 's disease tau is chemically modified which causes it to twist around other filaments and form tangles in the brain. The tangles can interfere with normal nutrition and with communication and eventually lead to cell death. The cause of the chemical modification is not clear. The relationship between plaques and tangles and their association with the disease state is still a mystery and is being studied in many labs.