Neurons numbers and dendritic extent in normal aging and Alzheimer's disease.

Evidence is reviewed regarding neuron numbers and dendritic extent in normal aging in rodent, monkey and human brain and in Alzheimer's disease (AD) in man. Neuron loss and change in dendritic extent appear to be regionally specific but not identical in rodents and primates. In AD there is excess neuron loss and dendritic regression in some but not all brain regions. Overlap between AD and control groups, however, is known to occur. Methods to assess dynamic morphology of the living brain may be superior to analysis of static, post-mortem brain structure in explaining functional deficits in AD and normal aging.