The density of neurons in the human hippocampus.

The aim of this study was to determine the density and pattern of distribution of the neurons in the human hippocampus, and twenty-nine brains of healthy individuals were examined. The cells counted in each unit area were the pyramidal cells in the H-fields and the granule cells. Difference in density was found between all H-fields. The neuronal density was highest in the H2-fields. The density decreased through the transitional area H1-2 and H1, with the lowest density in H3. The neuronal density increased in all H-fields in the antero-posterior direction, while the granule cells decreased in density. In the individual brain there was a positive correlation found respectively between high and low cell density in the different H-fields. The pyramidal cell density decreased in persons more than 68 years old. No difference was found between neruonal cell density in the two sides of the brain. Sex did not influence the neuronal cell density.