You know the old saw about half our advertising being wasted but we don’t know which half? Well, now we do, thanks to Martin Lindstrom, a Danish brand consultant and the author of the book Buyology, who took a brave leap into neuroscience to figure out why we buy — or don’t. Using functional MRI and other brain-scanning techniques, he went beyond the flimflam of the Mad Men and measured the minds of more than 2,000 consumers, all observed under the influence of marketing.