At the very earliest stages of life, how do stem cells know how to turn into the right cells at the right time and go to the right places. Just a few cells create the billions of brain cells we have. In this episode, we talk to Professor Helen Cooper, Deputy Director of Research at the Queensland Brain Institute. She studies the complex world of the signalling pathways that stem cells use to turn into neurons - and what happens when this goes wrong. Listen to From stem cells, billions of brain cells grow.