The cerebral cortex assembles itself on a schedule. Stem cells first copy themselves, then briefly switch to making neurons, and only after the neurons are finished do the support cells, called glia, appear. The phases run in sequence, not at once, and when that sequence is disrupted by a genetic mutation, the result can be a brain that ends up far too small or far too large.
Researchers at the Institute of Science and Technology Austria have now grown cortex-like tissue from mouse stem cells and observed it producing the same cell types that the real thing produces. What it did not do was produce them on the same clock, and the clones its stem cells generated were less varied than those a living mouse produces.
