The cytoarchitectonic distribution of senile plaques in three aged monkeys.

The density of senile plaques (SP) was determined in 55 cytoarchitectonic areas of the cerebral cortex in three aged (27+ years) macaque monkeys. In silver-stained sections the SP distributions pattern was variable, with a predilection for frontal areas and the primary somatosensory cortex. In one monkey, SP density in motor and premotor areas reached a level comparable to that found in Alzheimer's disease (AD). Lower SP densities were found in the amygdala and insula, and in cingulate, limbic temporal, and temporal, occipital, and parietal association cortices. Then lowest densities were in the hippocampus and in the primary auditory and primary visual cortices. SP stained with Congo red, to identify the older amyloid-containing plaques, showed a similar distribution but were fewer in number. There was at times a marked shift in SP density between adjacent cytoarchitectonic fields, suggesting that cytoarchitectonics or connectivity may play a role in determining SP distribution. The distribution of the SP in the normal aged human brain according to cytoarchitectonic areas is not known. Their pattern of distribution in these three primates appears to differ from that found in AD, which emphasizes the hippocampus, amygdala, entorhinal cortex, and temporal and parietal lobe.