The term 'bipolar' has become common, not least because of celebrities like Stephen Fry and Catherine Zeta Jones being open about the fact that they have been diagnosed with it. But a decade ago, most people had never even heard of it. So what does bipolar actually mean? As part of BBC Radio Scotland's Mental Health season, Pennie Latin investigates the truth behind bipolar, how it manifests itself for people who have it and how scientists are working to try and understand the brains of people with the condition.