Watch Horizon Season 50 Episode 16 Online

Michael Mosley explores the latest science about how our personalities are created - and whether they can be changed. Despite appearances, Mosley is a pessimist who constantly frets about the future. He wants to worry less and become more of an optimist. He tries out two techniques to change this aspect of his personality - with surprising results. And he travels to the frontiers of genetics and neuroscience to find out about the forces that shape all our personalities.