Approximate doubling of numbers of neurons in postnatal human cerebral cortex and in 35 specific cytoarchitectural areas from birth to 72 months

From 1939 to 1967, J.L. Conel quantitatively studied the microscopic featur es of the developing human cerebral cortex and published the findings in ei ght volumes. We have constructed a database using his neuroanatomical measu rements (neuronal packing density, myelinated large fiber density, large pr oximal dendrite density, somal breadth and height, and total cortical and c ortical layer thickness) at the eight age periods (0 [term birth], 1, 3, 6, 15, 24, 48, and 72 postnatal months) he studied. In this report, we examin e changes in neuron numbers over the eight age-points for 35 von Economo ar eas for which Conel gave appropriate data. From birth to 3 months postnatal age, total cortical neuron number increases 23-30%, then falls to within 3 .5% of the birth value at 24 months, supporting our previous work showing t hat the observed decrease in the number of neurons per column of cortex und er a 1-mm(2) cortical surface from birth to 15 months is almost entirely du e to cortical surface expansion. The present study also shows a 60-78% incr ease in total cortical neuron number above the birth value from postnatal a ges 24 to 72 months. The generalization, to humans at least, of the finding of no postnatal neurogenesis in rhesus macaques, a species belonging to a super family that diverged from that of Homo sapiens more than 25 million y ears ago, is not warranted until explicitly proven for humans. The data of the present study support the existence of substantial postnatal neurogenes is in humans for the 35 cortical areas studied.