Half of all money spent on advertising is wasted. But we just don't know which half. In recent years, marketing professionals have been trying to use neuroscience to locate the "buy button" in our brain, which if pressed would make us buy their stuff. It's the holy grail: a way of knowing, in advance, which ads are going to work and are worth spending money on, and which ones would flop. The promise, from both marketers and some neuroscientists, is that our brains can, effectively, be hacked. But does it work? Presenter/producer: Jolyon Jenkins