Neocortical Development in Brain of Young Children-A Stereological Study

The early postnatal development of neuron and glia numbers is poorly documented in human brain. Therefore we estimated using design-based stereological methods the regional volumes of neocortex and the numbers of neocortical neurons and glial cells for 10 children (4 girls and 6 boys), ranging from neonate to 3 years of age. The 10 infants had a mean of 20.7 × 109 neocortical neurons (range 18.0–24.8 × 109) estimated with a coefficient of variation (CV) = 0.11; this range is similar to adult neuron numbers. The glia populations were 10.5 × 109 oligodendrocytes (range 5.0–16.0 × 109; CV = 0.40); 5.3 × 109 astrocytes (range 2.7–8.3 × 109, CV = 0.39); and 0.32 × 109 microglia (range 0.15–0.43 × 109, CV = 0.31). Thus, the estimated mean composite number of neocortical neuron and glial cells was 36.8 × 109 (range 26.8–48.3 × 109, CV = 0.21), of which approximately one-half were glial cells. There was a significant linear increase in oligodendrocyte and astrocyte numbers during the first 3 years of life, but no change in the total number of neurons. This is in line with our expectation that the total number of neocortical neurons is already determined in mid-fetal life.