Quantitative Structural Changes in the Ageing Brain

An estimate of the total number of neurons in neocortex was obtained by multiplying an estimate of neocortical volume by the numerical density obtained with optical dissectors. Normal human brains were found to contain 20–25 × 109 neurons in neocortex. The overall numerical density of neurons in the neocortex was about 45–50 × 106/cm3 and did not show major variation with age or sex. Females have fewer neocortical neurons and correspondingly smaller cortices than males of the same age.