We report on a new framework to investigate the rapid brain development of newborns. It is based on the analysis of depth maps of the cortical surface through the study of a displacement field estimated by surfacic optical flow methods. This displacement field shows local evolution of sulci directly on the cortical surface. Detection of its critical points is performed with the Helmholtz decomposition which allows us to identify sources of the developmental process. They can be viewed as growth seeds or in other terms points around which the sulcal growth organizes itself. We show the reproducibility of such growth seeds across 4 neonates and make a link of this new concept to the "sulcal roots" one proposed to explain the variability of human brain anatomy.