Age-related variations in the neuron content of the cerebral cortex in senile dementia of Alzheimer type.

The cell content of the cerebral cortex in senile dementia of Alzheimer type has been examined using a stereological method which combines gross cortical measurements and microscopical observations to give volumetric data on cells and neuropil. In the neocortex only the large (greater than 12 micron diameter) neuron fraction was found to be abnormal; the volume of these cells was reduced in most patients aged less than 80 years, but was not usually abnormal for age in older cases. Smaller neurons and glial cells showed no consistent change from normal values. Neuropil was diminished in both age groups, so that patients over 80 years of age tended to show cerebral atrophy without neocortical neuron loss. By contrast to the neocortex, the subiculum of the hippocampus consistently showed pathological neuron loss in both age groups.