Fig. 3. Migration of GFP⁺ neurons observed in flat-mount preparation of the neocortex. (A,B) A is an image from E13 mouse dorsal cortex and B is the same cortex taken 50 minutes later. (C) Merged view of images in A,B. The images were taken from the leading edge of migratory streams. Most cells stay almost in the same position (yellow). Although they show some motility, migration toward a specific direction was not observed. Occasionally, some cells near the leading edge showed medially directed migration (arrows). *A neuron moving laterally. The white rectangle in the inset illustrates approximate position of the image. (D) The same as A but from an E13.5 mouse dorsal cortex. (E) An image captured 50 minutes later (red) was merged with D (green) as in C. The white rectangle in the inset illustrates approximate position of the image. (F) The movement of 85 arbitrarily selected cells in D, taken during a 20 minutes interval, was plotted. Yellow dots indicate stationary cells and green dots with arrows indicate migrating cells and their direction of migration. X symbols and double circles indicate where cells disappeared or appeared, respectively. Medial is upwards, lateral is downwards and anterior is towards the left. For an animated version of the complete time-lapse sequence, see Movies 3 and 4 at http://dev.biologists.org/supplemental/. Scale bar: 50 µm.