Expansion of the human embryonic brain during rapid growth: area analysis.

This report focuses on growth of the brain of the early human embryo, Carnegie stages 12-23. Areas of median sections from 50 to 58 embryos were measured to determine the best mathematical model to describe growth of the three primary brain vesicles and to determine the change in the ratio of tissue to cavity areas (T/C). An exponential model best describes growth of the brain and head during this time period. The head expands 248-fold compared with a 171-fold growth of the brain. The whole brain, forebrain, and midbrain all exhibit larger cavities than tissue initially followed by a reversal of such at a critical time (stages 21-24). The presumptive cerebellar tissue which was twice the cavity initially grows to become more than six times the cavity. Boxplots of the T/C ratios for the head and brain plus its components reveal that initially the tissue is less than the cavity (10-20% and 40-60%, respectively) but eventually becomes larger (60-200%).