Brain aging and Alzheimer's disease.

The most common cause of senile dementia appears to be a pathological process indistinguishable from that found in presenile dementia of the Alzheimer type. Consideration of the neuropathological changes suggest that this disease may involve in interaction of at least three processes: a viral-like infection, a disorder in the immune system and the neurotoxic effect of an environmental agent. The evidence in support of this hypothesis is reviewed.