Cellular Composition in the Aging Cerebral Cortex of Humans

The numbers/densities of neurons and gliocytes and the neuron-to-glia ratios were calculated in different layers of the cerebral cortex of three subjects in a post mortem study. The subjects were 60 to 70 years old (which was qualified as a relatively early period of aging) and had no history of neurodegeneration diseases. The brains embalmed in 10% formalin-fixative solution were processed, and coronal 4-μm-thick slices of tissues of the frontal, parietal, temporal, and occipital lobes were prepared and stained with hematoxylin-eosin. Clear cortical lamination was observed in all lobes. In the frontal lobe, the mean neuron density (number of neurons within visual fields at a 400× magnification) was significantly higher, while that of gliocytes was significantly lower compared to the respective values in other lobes (P < 0.05). A significant association between the number of neurons and glia was found in the frontal lobe (r² = 0.40, P = 0.0029) and in all superficial cortical layers (r² = 0.72, P = 0.0025), but not in the deeper layers (r² = 0.18, P = 0.14). The mean neuron-to-glia ratio in different lobes and layers varied from 1.0 : 0.81 to 1.0 : 3.54. It is concluded that, in early-aging subjects with no cerebral pathology, the quantitative characteristics of cortical neurons and glial cells do not differ significantly from those in the brains of younger adult healthy subjects.