Appliance of Science: Why do we talk to ourselves inside our heads?

Our inner voice is important for language development and our sense of self, writes Dr Naomi Lavelle

It can be a comfort, a companion, or even a mild irritation, but we are all familiar with that little voice inside our head that chatters away throughout our day. The voice may take different forms for different people, but why is it there at all and does it serve any purpose?