I have read that scientists have been able to discover adult stem cells in human brains in the grey matter. Is it possible to activate and control the differentiation of these stem cells into different neuron types within the human brain itself instead of a culture? If not, why not? what would one need to investigate to try to do this? What is there in the brain that produces adult stem cells? Also maybe this is a silly question but if you increase your cranium size artificially , would the brain expand to fill this enlarged cranium? Will it do this regardless of age?