Figure 2.

(A) The cortical surface undergoes a large amount of growth and folding during the first 5 weeks of life. Surface model representations of the cortex were generated from the segmentation volumes using CARET software (Van Essen et al. 2001). Surface meshes consist of 10 000–30 000 points and 20 000–60 000 triangular faces. A sphere of radius 1 mm is plotted for scale. (B1): The surface area of the isocortex (IC) and allocortex (AC) are shown as a function of age. A model selection algorithm identified a transition in the rate of the isocortical surface area at P12.7 days. The rate of expansion increases from 17.2 mm²/day per hemisphere to 36.7 mm²/day per hemisphere after P12.7 days. The surface area of the allocortex increases at a much lower rate (3.8 mm²/day per hemisphere) than the isocortex during development. (B2) The average of normalized mean curvature (${\overline{K}}^{*}$) increases rapidly from P10 to P17, while it increases slightly both before P10 and after P17. (B3) The average of normalized sulcal depth (${\overline{\Delta }}^{*}$) increases steadily at a high rate until P21 and increases at a lower rate after P21. Note that both ${\overline{K}}^{*}$ and ${\overline{\Delta }}^{*}$ have no units.