You are asking what might be the most important question in the world that 1000's of scientists are researching and trying to find out each day. Nobody yet knows. It seems like when you pack enough neurons together something magical happens and they become conscience, whatever that really means. Having an extremely high amount of ordered information in a small space (like our brain with trillions of neuron connections) seems to lead to it. It will revolutionize the world if and when we can answer this question and maybe allow us to create living things from scratch, such as a robot that is conscience just like us.