Pii: S0197-4580(00)00250-5

In the course of normal aging from about age 20 to 100, the population density of neocortical synapses declines toward, but not reaching, the level found in Alzheimer disease. A deficiency of synapses at birth or due to inadequate childhood education would theoretically cause the synaptic slope to reach the Alzheimer level early. The normal slope would cross into that dementia range at about age 130, resulting in true primary senile dementia without regard to the presence of plaques and tangles. © 2001 Elsevier Science Inc. All rights reserved.